Why this, not that

Where on the lot does the house go, and which way does it lie?

Decided by setbacks · the slope and where water runs · trees and ground worth keeping · sun and view · the length of the drive and the service lines

1. Near the front, long side along the contoursThis house

   The house sits close to the front setback, its long walls running across the slope, parallel to the contours.

   Choose it when the lot is deeper than it needs to be and its back is steeper or wooded; the drive, water, sewer and power should run short: every foot from the street costs; the house should span the least change in height, so the least cut and fill.

   The catch less privacy from the street; a smaller front yard, and the back yard is the uphill side, cut and swaled.

2. Long side down the slope

   The house is turned so that its long walls run downhill, across the contours.

   Choose it when the lot is too narrow to turn the house the other way; a split level or a long walkout is wanted, stepping with the ground.

   The catch the fall across the house grows with its length: on this lot 36 ft instead of 24 ft of slope, half as much again of cut and fill for a level pad; water coming down the lot meets a long wall end-on and must be split round it.

3. Up the lot, toward the back

   The house is pushed back from the street, up the slope.

   Choose it when the view or the quiet is at the back; the front is low, wet or in a flood zone; a long front garden or a deep setback is wanted.

   The catch a longer, steeper drive; longer and deeper service trenches: the sewer must still fall a quarter inch per foot to the street; more of the lot disturbed and more trees lost.

Here Its ridge runs across the lot, along the contours, 30 ft back from the street: the 24 ft depth of the house spans only about 2 ft of fall, and the oak at the back is left alone.

What does the house stand on?

Decided by frost depth · groundwater · what the soil bears and how it moves · slope · use of the space below · flood and radon · cost

1. Full basementThis house

   A storey of concrete walls below grade on footings 8 ft down, with a slab floor inside.

   Choose it when frost is deep, so footings go 3 to 5 ft down anyway and the rest of the dig buys a storey; the water table stays well below the floor all year; you want room for storage, the furnace and water heater, or a future finished room; the lot slopes enough for a walkout on its low side.

   The catch the most excavation, concrete and time of any; needs dampproofing, a footing drain and often a sump; a wet site floods it, and a high water table can float the slab; radon gathers in it unless the slab is sealed and vented.

   Digging, walling and draining it No. 11 →
2. Crawl space

   Short foundation walls on footings below frost, holding the floor frame 1½ to 2 ft over the ground.

   Choose it when frost is moderate and a basement's space isn't worth its cost; pipes and ducts should stay reachable under the floor; the ground is uneven or gently sloping; a slab would sit on wet or termite-prone ground.

   The catch a cramped, damp space unless sealed and conditioned; vented ones let humid air in to condense in summer and freeze pipes in winter; still needs footings below frost and a drain where the floor is below grade.

   A crawl-space footing, sized No. 12 →
3. Slab on grade

   A concrete floor poured on stone at the ground, thickened at its edge to carry the walls.

   Choose it when frost is shallow, a foot or less; the site is flat or graded level; the water table is high: nothing is dug below the surface; cost and speed matter most: one form, one pour.

   The catch in deep frost its edge heaves unless it gets a frost wall or insulation; pipes cast under it are hard to reach or change; on expansive clay it needs a post-tensioned or ribbed slab; no space below for ducts and services.

4. Frost-protected shallow

   A slab with a 16 in edge whose face, and in colder places a wing beside it, is wrapped in rigid foam, so the house's heat keeps the ground under it from freezing.

   Choose it when frost is deep but a basement isn't wanted; the building is heated all winter; excavation is expensive: ledge, a high water table, a tight site.

   The catch only works under heated space; an unheated garage needs a different design; the foam must be protected from damage, sun and burrowing insects; less familiar to some builders and inspectors.

5. Piers and beam

   Concrete piers on pads below frost, with beams across them and the floor framed above open ground.

   Choose it when the site slopes or the ground must not be disturbed; a flood zone requires the floor to stand above the flood; the house is small, light or in a mild climate; piers can be drilled past expansive clay to firm ground.

   The catch the floor is outdoors underneath: insulate it and keep pipes from freezing; less stiff against wind and earthquake: it needs bracing or anchored piers; an open underside invites animals unless skirted.

6. Piles and grade beam

   Steel helical, driven or drilled piles carried down through weak ground to a firm layer, joined at the top by a concrete grade beam.

   Choose it when the top of the ground is soft fill, peat or loose sand; expansive clay is deep and active; a steep slope or tight access keeps machines out; loads must reach a firm layer far below.

   The catch two to three times the cost of a footing where firm ground is near the surface; needs a geotechnical report and an engineer's design; specialist rigs and crews.

Here The lot's frost line is 42 in down, so the footings had to go 3½ ft deep anyway; going on to 8 ft buys an 864 sq ft storey. The water table, 14 ft down, stays below the slab, and the stiff clay bears 2,000 psf under a 20 in footing.

Where does the waste go?

Decided by a sewer in the street, and how deep · lot size and setbacks · how fast the soil drains · groundwater and bedrock · cost of connection against cost of a system

1. Public sewerThis house

   A building sewer from the house to the city's main, which carries the waste to a treatment plant.

   Choose it when a main runs in the street, deep enough to take the lowest drain by gravity; the lot is small: a septic field and its setbacks need a quarter of an acre or more; the city requires it, as most do within reach of a main.

   The catch a connection and impact fee, often several thousand dollars, then a monthly charge for ever; a main shallower than the basement means an ejector pump for everything below it; the stretch from the house to the main is the owner's to maintain.

   The building sewer No. 21 →
2. Septic tank and drain field

   A buried tank where solids settle and digest, and perforated pipes in gravel trenches that let the clarified water soak into the soil.

   Choose it when there is no sewer within reach; the soil drains at a moderate rate: a percolation test of roughly 5 to 60 minutes per inch; the lot has room for the field and a reserve field, 10 ft from the house, 100 ft from any well.

   The catch useless in tight clay, over shallow rock or a high water table: the effluent surfaces or reaches groundwater untreated; the tank must be pumped every three to five years, and a field ruined by grease or roots is costly to replace; a basement drain below the tank's inlet needs a pump.

3. Mound or engineered system

   A septic tank whose effluent is pumped up into a bed of sand built above the natural ground, or through a treatment unit first.

   Choose it when there is no sewer and the soil is too tight, too shallow or too wet for a trench field; the site is otherwise buildable and the county permits it.

   The catch two to three times the cost of a conventional field; a pump, an alarm and power: it stops in an outage and needs servicing; the mound is a visible hill in the yard.

Here An 8 in sewer runs 9 ft under the street, deep enough for the basement to drain by gravity. A septic field on an 80 × 130 ft lot, behind its setbacks, would barely fit, and the stiff clay under it drains too slowly to take it.

How does the house meet a sloping lot?

Decided by how steep the lot is · what the lower level is for · the soil and how deep frost goes · the cost of moving and hauling earth · where the water goes

1. Level pad, cut and fillThis house

   The ground round the house is cut down uphill and filled downhill to one level, and the house is built as if the land were flat.

   Choose it when the lot falls less than about 1 in 10 across the house; a full basement is wanted anyway, and its spoil can raise the low side; the soil makes good fill: it can be compacted and drains.

   The catch earth that leaves the site is paid for twice, to dig and to haul, about one truck for every 10 cu yd; fill must go down in thin, compacted lifts or the yard and anything on it settles; the uphill cut slopes toward the house: a swale must turn the water round it.

   Digging the basement No. 11 →
2. Stepped footings

   The floor stays level while the footings step down the slope in level runs, each still below frost, with a crawl space behind short walls.

   Choose it when the ground falls more than 1 in 10 under the footings, where the code requires them to step; no basement is needed; most of the ground can be left as it is.

   The catch every step is another form, riser and cold joint: more labour per foot of footing; the downhill walls grow tall and must resist the soil and the wind; the crawl space still has to be kept dry, sealed or vented.

   How a footing is sized No. 12 →
3. Walkout basement

   The basement is buried on the uphill side and opens at grade on the downhill side, with a door and full windows.

   Choose it when the lot falls about a storey, 8 ft or more, across the house: a slope near 1 in 3; the lower level is to be lived in, with light, air and a door to the yard; the downhill side faces the sun or the view.

   The catch on a gentle slope it means cutting a yard down to the basement floor, or raising the house; the uphill wall holds back a full storey of soil and must be drained and reinforced; the framed downhill wall needs its footing below frost and clear of splashing ground.

   The basement and its alternatives No. 10 →
4. Retaining wall and terrace

   A wall holds the higher ground back so that a level terrace can run out from the house instead of a long cut slope.

   Choose it when the lot is too tight for slopes at 3:1; level yard is wanted on the uphill side; the ground behind the wall drains, or can be made to.

   The catch a wall holding back more than 4 ft (1.2 m) must be engineered; without drainage behind it, water pressure can double the load: stone, a pipe and weep holes are not optional; the most expensive way to deal with a foot of slope, and a wall is forever.

5. Piers or posts

   The house stands on concrete piers or posts that reach below frost, and the ground underneath keeps its slope.

   Choose it when the slope is steep, or the ground must not be disturbed: tree roots, wet ground, a flood zone; good soil lies deeper than it is worth digging a basement to; there is little money for earthwork.

   The catch no basement, and a floor open to the cold underneath: insulate it and skirt it; posts alone rack: the frame needs bracing or shear walls down to the piers; pipes and ducts must run in insulated chases from the ground to the floor.

   Piers among the foundations No. 10 →

Here The lot falls 8 %, about 2 ft across the house, and the house wants a full basement: a level pad is the plain answer. The basement's spoil is more than the grading can use, so most of it is trucked away; set the house 3 ft higher and the yard would take nearly all of it instead, at the price of a house standing taller on its lot and fill slopes running down to the street.

How do the sides of the dig stay up?

Decided by soil type · depth · room on the lot · groundwater · cost

1. Slope the sidesThis house

   The banks are laid back at the angle the soil can hold: ¾:1 in hard clay, 1:1 in medium soils, 1½:1 in sand or anything wet.

   Choose it when there is room on the lot: a 10 ft deep dig in Type B soil runs about 9 ft past the over-dig on every side, 14 ft in Type C; the soil is dry and stands on its own; the dig is under 20 ft deep; deeper than that, an engineer must design the protection.

   The catch the most soil to dig and to put back: going from 1:1 to 1½:1 adds half again to the banks; spoil piles, machines and trucks have to stay at least 2 ft back from a wider edge; rain softens the banks, so they are checked after every storm and before every shift.

   The banks, by soil type No. 11 →
2. Bench the sides

   The banks are cut as steps no more than 4 ft high, set back so their edges stay on the safe slope.

   Choose it when the soil is cohesive, OSHA Type A or B, and stands vertically for a few feet; the dig is deep enough that a straight slope would run a long way back; workers and small machines need somewhere to stand partway down.

   The catch not allowed at all in Type C soil: granular or wet ground runs out of the risers; each riser is a short vertical cut that can still slough when it gets wet; it saves only part of the digging a slope takes, and takes more care to cut.

   Benches in clay No. 11 →
3. Shore the sides

   The sides are cut straight down and held: steel soldier piles with timber lagging, interlocking sheet piles, or a trench box.

   Choose it when the lot is tight: a neighbour's foundation, a street or a lot line lies within the width a slope would need; the soil cannot stand on its own: Type C sand, or ground below the water table; the dig is deep enough that the banks would take up the whole yard.

   The catch an engineer designs it, and a rig drives or drills the piles before the dig begins; it costs several times as much as laying banks back on an open lot; the lagging is usually left in the ground, and pulling the piles can loosen the backfill.

   Soldier piles and lagging No. 11 →

Here An 80 ft lot with 22 ft side yards has room to lay stiff silty clay, Type B, back at 1:1: about 9 ft of bank beyond the over-dig at the deepest corner. It is the cheapest safe hole, and the spoil stays on site for backfill.

What are the basement walls made of?

Decided by crews and suppliers nearby · height of soil against the wall · water · insulation · season · cost

1. Poured concreteThis house

   8 in of concrete cast in rented forms on the footing, bars at the corners and openings, keyed into the footing.

   Choose it when a ready-mix plant and a forming crew are within reach: the walls are formed in a day or two and poured in an hour; the wall holds back a lot of soil, or water: one solid piece has no mortar joints to leak or crack along; the basement will be finished: the walls come out straight, plumb and flat.

   The catch forms, pump and concrete trucks must arrive together, and freezing weather needs heaters and blankets; it needs about a week before it is strong enough to backfill against; insulation has to be added afterward, inside or out.

   Forming and pouring the wall No. 11 →
2. Concrete block

   8 × 8 × 16 in hollow units laid in mortar on the footing, the cells with bars grouted solid, parged and dampproofed outside.

   Choose it when no ready-mix within reach, or a small crew working a course at a time; an addition or an awkward plan where forms would be wasted; masons are easier to find than forming crews.

   The catch hundreds of mortar joints: more ways in for water, and a stair-stepped crack where soil pushes too hard; slower: about 1,000 blocks for this house, laid by hand; weak in bending unless reinforced and grouted, which adds labour.

   The block wall No. 11 →
3. Insulated concrete forms

   Hollow foam blocks stacked dry, braced and filled with concrete; the foam stays on both faces as insulation.

   Choose it when the basement will be lived in and must be warm: about R-22 comes with the wall; a small crew without forming gear builds the walls itself; a cold climate, where heat lost through a basement wall adds up.

   The catch the foam outside must be covered above grade, and watched for termites in warm regions; a form bursting during the pour is messy: pour rate and bracing matter; usually costs more than a poured wall with insulation added.

   Foam forms, filled No. 11 →
4. Permanent wood foundation

   Pressure-treated 2× studs and plywood standing on a gravel footing, the whole basement drained through gravel to a sump.

   Choose it when concrete is scarce or dear, or the season is too cold to pour; a framing crew can build the basement too, in any weather, fast; a finished basement: the stud bays take insulation and drywall like any upper wall.

   The catch everything depends on the right preservative treatment and on stainless or hot-dip galvanized fasteners; drainage is everything: gravel under the whole floor and a working sump; less familiar to inspectors, lenders and buyers in many places.

   The wood foundation No. 11 →

Here Ready-mix and forming crews are everywhere in the region, 7 ft of clay presses on the back wall, and one solid piece of concrete resists both water and bending best for the money.

Should a crawl space breathe outside air, or be sealed into the house?

Decided by climate and summer humidity · groundwater · pipes and ducts below the floor · radon · cost of conditioning

1. Vented

   Openings in the walls let outside air through; the floor above is insulated and the ground covered with a thin liner.

   Choose it when the climate is dry; no pipes or ducts run below the floor; local code still asks for it and no one will maintain a sealed space.

   The catch humid summer air condenses on the cool floor framing and grows mould; pipes and ducts sit outdoors in winter; floor insulation sags and falls out over time.

2. Sealed and conditioned

   No vents: foam on the walls, a heavy liner sealed to them over the ground, and a little conditioned air or a dehumidifier.

   Choose it when summers are humid or the site is wet; ducts, pipes or the furnace live under the floor; radon has to be kept out.

   The catch costs more to build, and the liner must stay intact; foam needs a fire covering or an ignition barrier; it becomes part of the heated house: it must be kept dry and conditioned.

How is water kept out of the basement?

Decided by how high groundwater rises · how fast the soil drains · how the basement will be used · the grading around the house

1. Dampproofing and a footing drainThis house

   A sprayed or rolled bituminous coat on the wall below grade, with a perforated drain in washed stone beside the footing.

   Choose it when groundwater stays well below the basement floor all year; the ground is graded to shed surface water away, so little reaches the wall; the basement is for storage and machines, or will be finished with care inside.

   The catch it stops moisture wicking into the concrete, not water pressing on it, and it does not bridge cracks; it fails if the drain clogs or the ground settles toward the house.

   Dampproofing No. 11 →
2. Membrane and drainage board

   A rubberized sheet or thick fluid membrane bonded to the wall, and a dimpled board over it that lets water fall freely to the drain.

   Choose it when groundwater can rise to the floor in a wet season; the basement will be finished living space, where a damp wall ruins the finishes; clay backfill holds water against the wall for days after rain.

   The catch three to five times the cost of dampproofing; it needs a clean, dry wall and careful laps and edges to work; a stone in the backfill can puncture it: backfill against it with care.

   Membrane and board No. 11 →
3. Interior drain and sump

   A perforated pipe along the inside of the footing, under the slab, collecting water that comes through or under the wall and leading it to a pumped sump.

   Choose it when an existing basement leaks and digging outside is impractical; a high water table, as a second line behind an exterior system; soil gas or radon also needs a sealed sump and a vent.

   The catch water still reaches the wall and the underside of the floor before it is taken away; it depends on a pump, and on power: a backup pump or battery is wise; added later, the edge of the slab has to be broken out to lay it.

   The sump No. 11 →

Here The water table is 14 ft down, below the 10 ft dig even in a wet spring, and the ground is graded to fall away with a swale uphill. Dampproofing and a footing drain led to a sump pit are enough.

What carries the floor down the middle?

Decided by the span from wall to wall · how many posts the basement can have · headroom under it · what the crew can lift

1. Built-up lumber

   Three or four 2×10s or 2×12s nailed side by side, their joints staggered over posts.

   Choose it when posts can stand every 7 to 9 ft; the crew wants to carry and nail it in pieces; the cheapest girder will do.

   The catch many posts in the basement; it shrinks like any sawn lumber; joints between plies must land on posts.

2. GlulamThis house

   Kiln-dried laminations glued under pressure into one deep, straight beam.

   Choose it when spans of 12 to 20 ft between posts; the beam will be seen; it must stay straight and barely shrink.

   The catch made to order in set widths; heavier to place than built-up plies.

   The girder in the house No. 03 →
3. LVL

   Laminated veneer lumber: thin veneers glued with all their grain one way, sold in plies 1¾ in thick.

   Choose it when a strong, stiff beam is needed in the same depth as the joists; the plies must be carried in by hand and nailed together in place.

   The catch costlier than lumber; must be kept dry on site; plies nailed or bolted to the maker's schedule.

4. Steel W-beam

   A wide-flange rolled steel beam, often with a wood plate bolted on top for the joists to nail to.

   Choose it when the longest spans or the fewest posts; the least depth for the load, for headroom.

   The catch a crane or a crew to set it; a different trade to fabricate it; a cold line to insulate where it meets the outside wall.

5. Bearing wall

   A stud wall on a strip footing in the basement, carrying the joists along its top plate.

   Choose it when the basement will be divided anyway; no beam is wanted at all.

   The catch a wall where an open basement might have been; a footing along its whole length.

Here A 5⅛ × 12 in glulam spans 12 ft between two steel columns, so the 36 ft basement has just two posts, and its top is flush with the sill so the joists bear on it level.

What are the floors framed with?

Decided by the span · the depth the floor can have · what must run through it · stiffness underfoot · budget and lead time

1. Sawn joistsThis house

   Solid 2×8 to 2×12 joists, cut to length on site and set 16 in apart.

   Choose it when spans of up to about 15 ft for a 2×10, which a centre girder makes easy; the crew wants to cut, notch and block on site; ducts and pipes can run along the joists rather than across them.

   The catch it shrinks as it dries, about ¼ in per floor with the plates; long, deep, straight joists are scarce and dear; floors near their limit bounce.

   The house's joists No. 03 →
2. Wood I-joists

   Engineered joists: an OSB web glued between two flanges of solid wood or LVL, 9½ to 16 in deep.

   Choose it when clear spans of 16 to 24 ft with no girder; flat, stiff, quiet floors that do not shrink; long lengths that one person can carry.

   The catch their thin webs burn through quickly, so codes ask for board under them in many floors; holes only where the maker's chart allows, never a notch; blocks and web stiffeners at every bearing.

3. Open-web floor trusses

   2×4 chords laid flat with webs between them, joined by toothed plates, made to order 12 to 24 in deep.

   Choose it when long clear spans to 24 ft and more; ducts, drains and wires must cross the joists through the open webs; a wide flange to glue the subfloor to.

   The catch designed and built before framing, so the plan is fixed early; never cut on site; a deeper floor raises the whole house.

Here The girder cuts the 24 ft depth into two 12 ft spans, well inside what a 2×10 at 16 in carries, so plain lumber is the cheapest floor. The heating branches run between the joists toward the outside walls, along them, so nothing has to cross them.

Platform or balloon framing?

Decided by lumber lengths · how the crew works · fire spread in the walls · movement under brick or stucco

1. Platform framingThis house

   Each storey's walls stand on their own floor deck, one storey high.

   Choose it when almost any light wood frame built today; short studs, and a safe deck to build each storey on; plates that stop fire at every floor by themselves.

   The catch it stacks flat-lying wood at every floor, so it settles about ¼ in per storey as it dries; brick veneer and stucco must be detailed to let it move.

   The house, framed this way No. 03 →
2. Balloon framing

   Studs run unbroken from sill to roof, and the upper floor hangs on a ribbon let into them.

   Choose it when repairing a house framed this way; tall walls in a stairwell or gable where a joint at the floor would hinge the wall; under masonry or stucco, where little shrinkage matters.

   The catch long, straight studs are scarce; every cavity is a flue unless firestopped at each floor; no deck to work from while raising it.

3. Post and beam

   Heavy timber posts and beams carry the loads; the walls between them only enclose.

   Choose it when open plans and exposed structure; few, large members with wide bays between them.

   The catch large timbers and joinery cost more; the walls between need their own bracing and insulation.

Here Like nearly every house built now: precut studs, a deck to stand on at each storey, and lap siding that does not mind the frame settling a little.

What are the outside walls built of?

Decided by the insulation the climate and energy code ask for · wall height and load · labour and speed · fire, insects and wind · budget

1. 2×4 at 16 in

   The classic stud wall, 3½ in (89) deep: room for R-13 to R-15 batts.

   Choose it when mild climates where R-13 meets the code; interior partitions anywhere; the cheapest, most familiar wall.

   The catch too shallow for cold climates without foam outside; studs, plates and headers, about a quarter of the wall, carry heat straight through.

2. 2×6 at 16 inThis house

   5½ in (140) deep, holding R-19 to R-21 batts.

   Choose it when cold and mixed climates; taller walls; room for pipes, boxes and deeper insulation.

   The catch about half as much lumber again as 2×4; the studs still bridge the insulation, so newer codes add foam outside as well; deeper jambs at every window and door.

   The house's 2×6 wall No. 18 →
3. Advanced framing

   2×6 at 24 in, in line with the joists and trusses above, two-stud corners, headers only where loads need them.

   Choose it when more insulation and less wood: the framing falls from about 25 to 15 percent of the wall; trusses at 24 in already set the module; the plan is drawn to that module from the start.

   The catch it must be planned, not improvised; sheathing and board have to span 24 in; crews used to 16 in resist it.

4. Double-stud wall

   Two rows of 2×4 studs set apart, 10 to 12 in overall, filled with dense-packed cellulose.

   Choose it when very cold climates or very low energy targets: R-35 to R-40 walls; breaking the thermal bridge without foam.

   The catch thick walls take floor area; the outer sheathing runs cold and must be able to dry; airtightness is essential.

5. Structural insulated panels

   Foam 4 to 8 in thick glued between two OSB skins, cut in a factory and set by crane.

   Choose it when a fast, airtight, well-insulated shell; simple shapes known early.

   The catch changes after ordering are hard; wires run only in factory-cut chases; leaky joints let damp air rot the skins.

6. Insulating concrete forms

   Hollow foam blocks stacked and filled with reinforced concrete; the foam stays on as insulation.

   Choose it when hurricane and tornado regions; quiet, massive walls; one system from the footing to the roof.

   The catch costs more than wood framing; poured in lifts, with bracing and inspections; openings are hard to change later.

7. Light-gauge steel

   Cold-formed galvanized C-studs screwed together, in the same sizes as wood.

   Choose it when termite country; straight walls that never shrink or twist; noncombustible construction.

   The catch steel carries heat about 400 times better than wood, so a cavity of batts loses about half its value without foam outside; a different trade and fasteners.

Here Climate zone 5 asks a wood wall for about R-20, or R-13 with R-5 of foam outside: 5½ in holds R-21 batts where 3½ in holds only R-15. Studs at 16 in suit the crew; with trusses at 24 in the house could move to advanced framing for a little more insulation and less wood.

What keeps the walls from racking?

Decided by wind speed and earthquake risk · how much solid wall there is between openings · the sheathing the wall gets anyway · inspection and labour

1. Structural sheathingThis house

   OSB or plywood nailed on every edge to studs, plates and rims, over the whole wall: every wall a shear wall.

   Choose it when almost always: it is the strongest and stiffest light-frame method; it also ties each storey to the next and gives the siding something to nail to; taped, it doubles as the air barrier.

   The catch the nailing schedule must be kept, 6 in at edges and 12 in in the field; every panel edge must land on framing or blocking.

   Sheathing on the frame No. 14 →
2. Let-in braces

   A 1×4 set into notches cut across the studs, diagonally from top plate to sole plate.

   Choose it when low wind and low earthquake risk; walls sheathed with foam or fibreboard that cannot brace.

   The catch far weaker than sheathing; needs clear wall at each end of every wall line; cannot cross an opening.

3. Steel strap braces

   Flat galvanized straps nailed diagonally across the studs, in crossed pairs.

   Choose it when steel stud walls; sheathing that is not structural; a quick brace.

   The catch a strap only pulls, so they go in pairs; they slacken if not tensioned; nailed at every stud they cross.

4. Portal frames

   A narrow wall panel beside a big opening, its header strapped and its base held down so it acts as a small rigid frame.

   Choose it when garage fronts and window walls with little solid wall; panels as narrow as 16 in (405).

   The catch engineered nailing, straps and hold-downs; costs more per foot of wall; a careful inspection item.

Here Every outside wall is sheathed in 7⁄16 in OSB anyway, so nailing it to a schedule makes the whole skin bracing. The panels lap the rims, tying each storey to the one below.

How does a frame resist a sideways push?

Decided by where the openings must be · how stiff the building must be · the material of the frame · wind and earthquake forces

1. Braced frame

   Diagonals of steel rod, strap or timber turn each rectangle into two triangles.

   Choose it when steel and timber frames where some bays can be crossed; the stiffest resistance for the least material.

   The catch a crossed bay cannot hold a door or a window; rods only pull, so they come in pairs; the joints carry large forces.

2. Shear wallThis house

   A wall stiff in its own plane: sheathing nailed to a frame, or a wall of masonry or concrete.

   Choose it when the walls are needed anyway, as in every house; concrete and masonry buildings; stiffness at little extra cost.

   The catch enough solid length between openings; hold-downs at the ends so the wall cannot tip over; open plans and walls of glass leave too little.

   Shear walls in the house No. 04 →
3. Moment frame

   Columns and beams joined so rigidly that the corners cannot turn: the frame resists by bending.

   Choose it when openings must stay open: shopfronts, garage doors, glass walls; steel and concrete buildings of several storeys.

   The catch it sways more than a braced bay with the same members; heavy members and costly joints.

Here The house's sheathed walls are its shear walls: the cheapest stiffness there is, in walls that need sheathing anyway.

What shape is the stair?

Decided by the floor area it may take · the length of opening the floor above can give it · safety and ease of climbing · carrying furniture up

1. Straight runThis house

   One flight from floor to floor along a wall.

   Choose it when a long wall and a long opening above are available; the simplest framing and the easiest stair to carry things up.

   The catch the longest opening: about 11 ft for 15 risers; a fall has nowhere to stop.

   The stair in the house No. 03 →
2. L with a landing

   Two flights at right angles, turning at a landing.

   Choose it when the stair must fit a corner; a resting place halfway, and a shorter fall.

   The catch the landing takes floor area; a post or wall to carry the landing.

3. U, or switchback

   Two flights side by side, turning back on themselves at a landing.

   Choose it when a compact stairwell that stacks floor over floor; multi-storey houses and most other buildings.

   The catch a wider opening; the landing must be at least as deep as the stair is wide.

4. Winders

   Wedge-shaped treads turn the corner instead of a landing.

   Choose it when a turn in the least space, in a house.

   The catch the narrow ends are hard to step on, so codes set a minimum tread at the walkline and at the narrow end; not allowed on most non-residential stairs.

5. Spiral

   Pie-shaped treads around a central post, often in a 5 ft (1525) circle.

   Choose it when the smallest footprint, to a loft or a second exit.

   The catch steep and narrow: the code allows taller risers and shallower treads only on spirals; furniture cannot be carried up it.

Here The 36 ft house has room for an 11 ft opening along its bearing wall, and a straight flight is the cheapest to frame and the easiest to move a bed up.

What holds up the roof?

Decided by the span and shape of the roof · whether the attic is to be used · schedule and crane access · budget

1. TrussesThis house

   Prefabricated frames of 2×4s joined by toothed steel plates, designed by the maker and set 24 in apart.

   Choose it when simple roofs spanning wall to wall, to 40 ft and more, with no bearing walls inside; a roof set and sheathed in a day or two; the lowest cost per square foot.

   The catch webs fill the attic: no rooms or storage unless attic trusses are ordered; designed before they are made, and never cut on site; bracing to the maker's drawings, and a crane.

   The house's trusses No. 03 →
2. Stick-framed rafters

   Rafters cut on site from 2×8 to 2×12, bearing on the wall plates and a ridge, tied by ceiling joists.

   Choose it when roofs with hips, valleys and dormers; a usable attic or a vaulted ceiling; small jobs and additions.

   The catch skilled cutting and slower framing; spans limited by the lumber; the outward thrust must be tied, or the ridge made a beam.

   Rafters cut and raised No. 15 →
3. SIP roof panels

   Insulated panels running from a structural ridge beam to the eave: foam and two OSB skins in one piece.

   Choose it when rooms vaulted to the roof, with no attic; a fast, airtight, insulated roof.

   The catch a ridge beam and engineering; joints that must be sealed perfectly or the skins rot; a higher price.

4. Timber frame

   Heavy rafters or purlins on principal trusses, exposed inside, with plank decking, insulation and roofing above.

   Choose it when the structure is the architecture; long spans with few members.

   The catch costly timber and joinery; insulation goes above the deck, thickening the roof edge.

Here A simple gable 24 ft deep, no bearing wall wanted upstairs, and an attic that only holds insulation: trusses are the cheapest and fastest roof. The 14 in of blown insulation lies over their bottom chords.

Which truss for this roof?

Decided by the ceiling you want under it · span and load · room in the roof · cost per truss

1. FinkThis house

   The W-shaped house truss: four short webs, all 2×4.

   Choose it when flat ceilings under a pitched roof, 20 to 40 ft; the cheapest truss for the span.

   The catch webs fill the attic.

   Finks on the house No. 03 →
2. Howe

   Verticals and diagonals in regular panels.

   Choose it when longer spans and heavier roofs such as tile; girder trusses that carry other trusses at their panel points.

   The catch more members and plates than a Fink at house spans.

3. King post

   A single post from the peak to the bottom chord.

   Choose it when short spans: porches, sheds, garages; the fewest pieces.

   The catch long panels need heavier chords; limited span.

4. Scissors

   The bottom chords rise toward the middle, giving a sloped ceiling inside.

   Choose it when a vaulted ceiling without a ridge beam.

   The catch they spread at the walls under load, so the bearings must allow for it; less depth for insulation near the peak.

5. Attic

   A room framed into the truss: floor, kneewalls and ceiling within the triangle.

   Choose it when a room or storage in the roof, built with the roof.

   The catch steeper pitch, deeper chords, stiffer joints; the costliest truss, and the room is narrow.

Here A flat ceiling under a 6 in 12 roof across 24 ft is exactly what the Fink is for, and nothing cheaper does it.

What shape is the roof?

Decided by the plan of the house · wind and snow · attic space · complexity and cost

1. GableThis house

   Two slopes meeting at a ridge, with a triangular wall at each end.

   Choose it when a rectangular plan; the simplest framing and roofing; attic space and ventilation are easy.

   The catch the gable walls catch the wind and must be braced; the gable ends stand exposed to the weather.

   A gable end, trussed No. 17 →
2. Hip

   Slopes on all four sides, meeting along hips.

   Choose it when high-wind and hurricane regions: lower uplift and no gable wall to blow in; eaves all round, shading every wall.

   The catch more cutting and more roof; less attic space; harder to ventilate at a short ridge.

3. Hip and valley

   Two hipped wings meeting in an L, with a valley where they cross.

   Choose it when an L or T plan roofed as one.

   The catch the valley gathers water and must be flashed with care: most leaks start there; the most labour.

Here A plain rectangle in a region of moderate wind: the gable is the cheapest roof to frame and to shingle, and its ends are braced by the gable trusses and their outlookers.

What goes on the roof?

Decided by roof pitch · wind, snow, hail and fire · the weight the frame can carry · life span against first cost · the look of the region

1. Asphalt shinglesThis house

   Glass-fibre mats soaked in asphalt and faced with mineral granules, laminated for depth, nailed over underlayment.

   Choose it when pitches of 4 in 12 and steeper, or down to 2 in 12 with doubled underlayment; the lowest first cost; any roofer can lay and repair it.

   The catch 20 to 30 years of life; storms lift shingles that are not wind-rated; never on a low slope.

   Shingles on the house No. 03 →
2. Standing-seam metal

   Steel or aluminium panels running eave to ridge, joined by raised seams over hidden clips.

   Choose it when heavy snow, which slides off; wildfire country: it does not burn; a 40 to 70 year roof; slopes down to 3 in 12, or lower with sealed seams.

   The catch two to three times the cost of shingles; clips must let long panels move with heat; specialist installers.

3. Concrete or clay tile

   Heavy interlocking tiles hung on battens over underlayment.

   Choose it when hot, sunny or fire-prone climates; a 50 to 100 year roof; the regional look.

   The catch three to four times the weight of shingles: the frame must be designed for it; breaks when walked on; 4 in 12 or steeper.

4. Slate

   Split natural stone, each slate hung on copper nails and lapped over two below.

   Choose it when a roof to last a century or more; steep pitches and historic work.

   The catch the heaviest and costliest roof; skilled slaters only; brittle.

5. Wood shakes

   Split or sawn cedar laid in overlapping courses.

   Choose it when the look, in dry or well-ventilated places away from wildfire.

   The catch combustible unless treated, and banned where wildfire is a risk; moss and rot in damp shade; 20 to 40 years with care.

Here A 6 in 12 roof sheds water well under shingles, snow on this site is moderate, and laminated asphalt costs about a third as much as standing-seam metal.

What keeps water and air out behind the siding?

Decided by rain exposure · the cladding over it · whether it must also be the air barrier · the crew's skill with laps and tapes

1. HousewrapThis house

   A spun-bonded polyolefin sheet fastened over the sheathing, lapped like shingles and taped.

   Choose it when most wood-frame walls; vapour must pass so the wall dries outward; taped and sealed, it is the air barrier too.

   The catch tears in wind before the siding is on; every lap at every window must face down; under stucco it needs a second layer or a drainage wrap.

   Wrap on the house No. 03 →
2. Felt or building paper

   Asphalt-saturated felt or kraft paper lapped in courses.

   Choose it when under stucco and stone, where two layers make a drainage plane; a forgiving, traditional layer.

   The catch tears easily; no air barrier; more courses and more labour.

3. Fluid-applied membrane

   A liquid sprayed or rolled onto the sheathing that cures into one seamless sheet.

   Choose it when complex walls with many penetrations; a seamless air and water barrier; over concrete or masonry.

   The catch costs more; its thickness depends on the applicator; weather limits when it can go on.

4. Taped sheathing

   OSB with a factory-bonded water-resistive face; the joints are taped instead of wrapping the house.

   Choose it when one trade does bracing, water and air barrier at once; a quick, tear-free dry-in.

   The catch the tape is the system: every seam must be right; one maker's products for repairs; less open to vapour than housewrap.

Here Cheap, open to vapour so the wall dries outward, and taped at its seams it is the house's air barrier as well. The windows are flashed into it in a set order, so every lap faces down.

What carries the water to the fixtures?

Decided by cost of pipe and labour · the water's chemistry · freezing risk · how much wall and floor it must pass · local code and the plumber's habits

1. PEXThis house

   Cross-linked polyethylene tubing, flexible enough to bend round corners, joined with crimped or expanded fittings; often run home-run from a manifold.

   Choose it when speed matters: one line pulled from the manifold to each fixture, with no joints hidden in walls; the house is in a cold climate: PEX swells rather than splits when it freezes; the water is acidic or aggressive, which pits copper.

   The catch sunlight degrades it in weeks: it must stay covered, inside; it cannot connect straight to a water heater, and rodents can chew it; home runs use more pipe, and every line has a slower wait for hot water.

   The manifold No. 21 →
2. Copper

   Rigid type L or M copper tube, cut and soldered (or press-fitted) into a trunk with branches teed off it.

   Choose it when durability is the priority: copper lasts 50 years and more in neutral water; pipe will be exposed to sunlight, heat or in a fire-rated assembly; the house has a recirculating hot-water loop, where copper's rigidity and stability help.

   The catch the most expensive pipe, and the slowest to install: every joint soldered by hand; acidic or very soft water pits it into pinhole leaks; it splits when water in it freezes.

   Trunk and branches No. 21 →
3. CPVC

   Rigid chlorinated PVC, rated for hot water, solvent-welded into a trunk and branches like copper.

   Choose it when the budget is tight and the plumber is used to solvent welding; the water would corrode copper.

   The catch brittle with age and in the cold: a knock or a freeze cracks it; solvent joints need cure time before the pressure test; it expands with heat more than copper, so long runs need room to move.

   Trunk and branches No. 21 →

Here PEX from a manifold beside the heater: ten unbroken lines, no fitting hidden in a wall or floor, a shutoff for every fixture in one place, and pipe that survives a hard frost. It installs in about half the time of copper.

What heats the water?

Decided by fuel at the site and its price · how much hot water at once · space and venting · efficiency over the heater's 10 to 15 years · first cost

1. Gas storage tankThis house

   A 40 to 50 gal (150 to 190 L) insulated tank heated by a burner under it, vented outdoors; power-vented models push the flue gas out through a side wall.

   Choose it when the house has gas already; first cost matters most; the family draws a lot of hot water at once: it recovers about 40 gal an hour.

   The catch needs a vent and combustion air; loses heat through its jacket around the clock: a uniform energy factor of about 0.6 to 0.7; burns fossil fuel indoors.

   The water heater No. 21 →
2. Electric tank

   The same tank heated by two resistance elements, with no flame and no vent.

   Choose it when there is no gas; the heater must go where a vent cannot; the lowest installed cost is the goal.

   The catch slow to recover, about 20 gal an hour; resistance heat is the dearest way to heat water nearly everywhere; needs a 30 A, 240 V circuit.

3. Heat pump

   An electric tank with a small heat pump on top that pulls heat from the air around it into the water, with elements as backup.

   Choose it when operating cost matters: it uses a third to a half of the electricity of an electric tank, a uniform energy factor of 3 and more; it can stand in a basement or garage of 700 ft³ or more that stays above about 40 °F (4 °C); cooling and drying the basement is welcome.

   The catch costs two to three times as much as a plain tank; taller, a little noisy, and needs a condensate drain; cools the room it is in, which costs heat in winter.

4. Tankless

   A wall-hung unit that fires a large burner (or element) only while water flows, heating it on the way through.

   Choose it when space is tight; the household uses hot water in short, separate draws; endless hot water for long showers is wanted.

   The catch a gas unit needs a large gas line and its own vent; an electric one may need 120 A or more; limited flow: two showers at once in winter can outrun it; needs descaling in hard water, and costs much more than a tank.

Here The house has gas for its furnace and a basement with room for a tank: a 50 gal power-vented heater is the cheapest to install and keeps up with a bath and the kitchen at once. A heat-pump tank would halve its running cost, and is the better long-run choice where electricity is clean or cheap.

How is the house heated and cooled?

Decided by the winter design temperature · the fuels on the street and their price · whether the house needs cooling too · room for ducts · first cost against running cost · carbon

1. Gas furnace and air conditionerThis house

   A condensing furnace blows heated air through ducts; an outdoor condenser and a coil on the furnace cool the same air in summer.

   Choose it when gas is on the street and cheap against electricity; winters are long and very cold, where a furnace's output never falls with the weather; the house needs cooling too and has room for ducts in the basement and the walls.

   The catch two machines, two fuels and two service lines; it burns fossil fuel on site: a flue, a gas line and carbon monoxide to guard against; ducts lose heat and leak unless sealed and kept inside the insulated house.

   The furnace in the basement No. 20 →
2. Ducted heat pump

   An outdoor unit moves heat into the house in winter and out of it in summer, through the same ducts a furnace would use, with electric strips for the coldest hours.

   Choose it when there is no gas, or the owner wants none; winters reach about −15 °F (−26 °C) or warmer, within reach of a cold-climate unit; one machine should both heat and cool; the house is tight and well insulated, so a modest unit carries it.

   The catch capacity and efficiency fall as it gets colder: below the balance point the backup strips run, at a third of the efficiency; cooler supply air, about 95 °F (35 °C), feels less warm at the register and needs more airflow, so larger ducts; the outdoor unit needs a stand above the snow and room for its defrost water.

   The heat pump outside No. 20 →
3. Radiant floors and a boiler

   A boiler heats water that runs through PEX tubing under or in the floors; the floors warm the room and everything in it, with no moving air.

   Choose it when comfort comes first: warm floors, no drafts, no blowing dust, silence; floors are tile, stone or concrete that store and spread the heat; the house needs little or no cooling, or will get a separate system for it.

   The catch no cooling at all: summer needs a second system; slow to respond: a cold room takes hours to warm, so setbacks hardly pay; the highest first cost, and carpet or thick wood floors smother it.

   The boiler and manifold No. 20 →
4. Ductless mini-splits

   Small heat pumps whose outdoor units feed wall-mounted heads in the rooms through thin refrigerant lines, with no ducts at all.

   Choose it when there is nowhere to run ducts: an addition, an old house, an open plan; the house is very tight and needs little heat, so a few heads carry it; rooms want their own control, and the owner accepts a unit on the wall.

   The catch a head heats only the room it is in: closed bedrooms without one run several degrees cooler; no filtration or fresh air for the whole house: ventilation needs its own ducts; each head has a filter to clean, a condensate drain, and a box on the wall.

   A head and its line set No. 20 →

Here A condensing gas furnace with an air conditioner: gas is in the street, Chicago-like winters reach −4 °F (−20 °C), and the basement gives the ducts an easy home. The same ducts would take a cold-climate heat pump later, which is why they are sized generously.

How does power reach the house?

Decided by the utility's rules for the street · storms and ice · trenching cost and rock · the look of the street · how far the house is from the line

1. Underground lateralThis house

   The utility's cable runs from a pad-mounted transformer in conduit 2 ft (610) or more down, and turns up the wall into the meter base.

   Choose it when the subdivision's lines are already underground, as most new ones are; ice storms and falling trees take overhead lines down; nothing should cross the yard overhead: trees, a crane, a view.

   The catch a trench to dig and restore, and rock or a long run make it costly; a fault is harder to find and slower to repair; anyone digging must call first: the warning tape is the last line of defence.

   The lateral in its trench No. 22 →
2. Overhead drop

   Triplex cable hangs from the utility's pole to a bracket on the house, then down a mast from a weatherhead to the meter.

   Choose it when the street's lines are on poles and the utility serves from them; the run is long, or the ground is rock, so trenching would cost far more; an old house is being rewired and its drop is already there.

   The catch storms, ice and falling branches bring it down; it must clear the yard by 12 ft (3.7 m), and a mast through the roof needs flashing; it is in sight, and it limits where trees and cranes can go.

   The pole and the drop No. 22 →

Here Underground: the subdivision's power is already buried along the street, with a pad-mounted transformer at the corner of the lot, and the run to the meter is short.

What carries the circuits through the walls?

Decided by the local code · how protected the wire must be · labour · future changes

1. NM cableThis house

   Insulated conductors and a bare ground in a plastic sheath, run through bored holes and stapled to the framing.

   Choose it when the walls are wood-framed and will be covered; the code allows it, as it does for houses in most of the United States; speed and cost matter.

   The catch a nail or screw can reach it, hence the steel plates near the faces; not allowed exposed where it can be damaged, nor in some cities at all.

   Cable to a box No. 22 →
2. Armoured cable

   The same conductors inside a spiral steel sheath: MC or AC cable.

   Choose it when the cable is exposed in a basement or garage; a stronger sheath is wanted without the labour of conduit; metal studs or commercial-style framing.

   The catch slower to cut and terminate; costs more per foot than NM cable.

3. Metal conduit

   Thin-wall steel tube (EMT) run box to box, the wires pulled through it afterwards.

   Choose it when the local code demands it, as Chicago's does for houses; wires may need replacing or adding later without opening walls; the work is exposed and must survive knocks.

   The catch much more labour: every bend made on site; the highest cost, and bulky in a 2×4 wall.

Here NM cable, as the model code allows for a wood-framed house, with nail plates wherever a hole comes near a face. Built inside Chicago itself, the same house would be wired in conduit.

What insulates the walls?

Decided by the R-value the climate asks for · the depth of the cavity · air sealing · where the wall must dry · cost and installer skill

1. Fibreglass battsThis house

   Blankets of glass fibre cut to fit between the studs.

   Choose it when open cavities of standard spacing; the lowest cost; a crew that cuts neatly around every box and pipe.

   The catch gaps and squashed batts lose a third of their value; no air barrier on their own.

   Insulation in the house No. 03 →
2. Cellulose

   Shredded recycled paper treated with borates, blown loose into attics or packed dense into walls behind netting.

   Choose it when attics, where loose fill is deep and cheap; filling odd-shaped or existing cavities completely; quieter walls.

   The catch dense-pack needs a skilled installer; it soaks up water, though it dries again; loose fill settles.

3. Open-cell spray foam

   Polyurethane sprayed into the cavity, expanding about a hundredfold; soft and open to vapour.

   Choose it when sealing air and insulating in one step; irregular spaces and roofs insulated at the rafters.

   The catch only about R-3.6 per inch; two to three times the cost of batts; needs a vapour retarder in cold climates.

4. Closed-cell spray foam

   Dense polyurethane, R-6 to R-7 per inch, an air barrier and vapour retarder at once.

   Choose it when rim joists, crawl spaces, basements; thin spaces needing a high R-value.

   The catch the most expensive; blowing agents with a climate cost, though newer ones are far lower; hard to remodel through.

5. Mineral wool

   Stone wool spun into dense batts or boards that cut cleanly and keep their shape.

   Choose it when fire separations and sound control; places that may get damp; boards outside the sheathing.

   The catch costs more than glass fibre; heavier to handle.

6. Continuous exterior foam

   Rigid boards over the sheathing, unbroken by the studs.

   Choose it when cold climates and the latest energy codes, which add R-5 to R-10 outside; warming the sheathing so it cannot condense; stopping heat through the studs.

   The catch thicker walls: windows and trim are detailed again; siding fastened through it on long screws or furring; the water barrier must be detailed with the foam.

Here R-21 batts fill the 2×6 cavities, rigid foam is cut in against the rim joists and sealed, and 14 in of loose fill is blown over the ceiling: the cheapest way to meet climate zone 5, provided the air sealing comes first and the batts are cut neatly.

What is the house clad in?

Decided by rain and sun · fire exposure · upkeep · first cost against life · the look of the street

1. Fibre-cement lapThis house

   Boards of cement, sand and cellulose fibre, primed in the factory and nailed 7 in to the weather.

   Choose it when the look of painted wood without rot, insects or fire: it does not burn; paint that lasts 10 to 15 years.

   The catch heavy and brittle: two people to carry a board; silica dust when cut, so it is sheared or cut wet; kept clear of roofs and soil.

   Siding on the house No. 03 →
2. Vinyl

   Extruded PVC panels hung loosely on nails so they can slide as they warm and cool.

   Choose it when the lowest first cost; no painting, ever.

   The catch burns and melts in fire; brittle in cold, warps near heat; hangs loose, so the water barrier behind does more of the work.

3. Wood

   Cedar or pine clapboards or shingles.

   Choose it when the traditional look; easy to repair and renew.

   The catch paint or stain every 5 to 8 years; rots if it stays wet; burns.

4. Brick veneer

   One wythe of brick an inch off the sheathing, tied to the frame and standing on the foundation.

   Choose it when a century without painting; fire resistance; the regional look.

   The catch a foundation ledge to stand on; weeps and flashing at every base and opening; the frame shrinks and the brick does not.

   Ties that hold a veneer No. 13 →
5. Stucco

   Portland cement plaster in three coats on metal lath.

   Choose it when dry, sunny climates; a seamless, hard skin.

   The catch over wood in a wet climate it traps water unless a drainage gap is behind it; it cracks; skilled plasterers.

6. Metal panels

   Steel or aluminium in lap, board-and-batten or flat profiles.

   Choose it when wildfire country; a long life with little upkeep; a modern look.

   The catch dents; moves with heat; costs more.

Here It looks like the painted clapboard on the rest of the street, will not rot or burn, and over the house's life costs less than wood once repainting is counted.

Which web pattern for a long truss?

Decided by what the members are made of · the shape the roof or floor needs · how the load is applied · the span

1. Pratt

   Verticals and diagonals sloping down toward the middle: under weight, the long diagonals pull and the short verticals push.

   Choose it when steel trusses carrying gravity, where slender members can take the tension; parallel-chord roofs and bridges.

   The catch wind uplift reverses every force, so the diagonals must also be able to push.

2. Howe

   Diagonals slope the other way: they push, and the verticals pull.

   Choose it when timber trusses with steel rods for the pulling verticals; heavy, short timber struts.

   The catch long diagonals in compression must be stocky to avoid buckling.

3. Warren

   Diagonals alone, in alternating directions, making equilateral triangles.

   Choose it when even loads on parallel chords; open-web steel joists, with the fewest pieces.

   The catch the pushing diagonals are long; a load between panel points bends the chord.

4. Fink

   Short webs in a W under a pitched top chord.

   Choose it when pitched roofs over a flat ceiling; spans where short webs keep every member light.

   The catch it suits a pitched shape only.

5. Bowstring

   A curved top chord that follows the bending of the span, with light webs.

   Choose it when long halls, hangars and bridges; an even load, which the curve carries almost without the webs.

   The catch the curved chord is costly to make; uneven loads such as drifted snow load the webs hard.

Which bond for a brick wall?

Decided by whether the wall is one wythe or two · how the wythes are tied · the look wanted · labour

1. Running bond

   All stretchers, each course half a brick over the one below.

   Choose it when veneers and cavity walls, the usual case today; the wythes are tied with metal ties instead of headers.

   The catch no headers: two wythes need ties or joint reinforcement.

2. Common bond

   Five or six courses of stretchers, then a course of headers.

   Choose it when solid two-wythe walls at the least cost; headers that tie the wythes in brick.

   The catch header courses must line up through the wall.

3. Flemish bond

   Header and stretcher alternate in every course.

   Choose it when solid walls with a fine, even face; historic work.

   The catch more cutting and more care; many headers are half-bats in a veneer.

4. English bond

   Whole courses of headers alternate with whole courses of stretchers.

   Choose it when the strongest bond for a solid wall; bridges, piers and retaining walls.

   The catch more bricks and labour than common bond.

5. Stack bond

   Bricks set directly over each other, every joint continuous.

   Choose it when a modern pattern in a veneer.

   The catch no bond at all: steel in the bed joints every 16 in; only as a veneer.