A Builder’s Checklist for Ordering Roof Trusses

Most truss problems start on paper, where a missed dimension or a late change can force a redesign and cost real money.

Freeze the roof geometry first

Truss designers need final plans with locked dimensions to engineer each triangulated frame for its exact position in the roof. That means span, pitch, overhangs, and heel height are fixed before quoting. Don’t guess at this stage.

Wall layout matters just as much. The designer has to know where each truss bears and whether supports are timber frames or steel beams. Girder trusses that pick up hips or valleys need clear support details on the plan. If there’s a cathedral entry or a lowered bulkhead, that has to be on the drawings too.

A missing beam seat or a shifted wall can throw out three or four trusses at once. Ceiling type drives depth from the start, so flat ceilings and raked ceilings call for different chord setups and different heel details. When the fabricator has exact spans, heel heights, bearing locations, and ceiling profiles, the engineering run moves faster and approval drawings come back with fewer queries and fewer redraws.

Send sections that show ceiling lines and roof planes together. For alterations, confirm existing wall heights with a site measure instead of relying on old drawings alone. It’s far cheaper to redraw a line than to remake steel-plated timber.

Renovation work needs extra care. Measure existing plate heights and wall thicknesses twice, because old frames rarely match the original drawings. Note any out-of-square walls on the sketch so the designer can allow trim tolerance at hips and abutments.

Define loads and wind rating up front

Every truss is sized for load, so incorrect load inputs mean incorrect engineering.

Start with cladding and ceilings. Tiles weigh far more than metal sheet, and that difference changes member sizes and plate sizes. Add ceiling lining weight plus extra layers for sound control or fire control. There’s no standard house load, so each job needs its own numbers on the order.

In Western Australia that check usually refers to AS/NZS 1170.2 for wind actions. Sites near the coast or in exposed areas carry higher design pressures than sheltered suburban blocks. The fabricator needs the wind classification for the specific address, not a guess based on the last job. That rating sets tie-down size and truss thickness, and it drives connection checks at heels and girders.

Solar arrays, hot water units, air-conditioning plant, and battery cabinets all add point loads that stress individual members. A raised top chord or parallel chord truss can be detailed to carry services, but only when the designer knows weights and positions early. Raising those details after delivery can mean new calculations and new plates rather than a minor adjustment.

Put those numbers in writing on the order. List cladding type, ceiling weight, wind class, and service loads on one sheet so details aren’t lost between the estimator and site lead.

Coastal jobs often need heavier tie-downs and closer batten screws, so confirm those extras at quote time rather than face late surprises during frame inspection. A clear load sheet keeps variations down and gives the certifier the information needed.

Set spacing and ceiling details together

Spacing looks like a small choice. It affects the whole roof. Most homes use 600 mm or 900 mm centers, and that decision carries through to the rest of the build.

The wider spacing cuts truss numbers but calls for larger members plus heavier battens to span between trusses. Closer spacing uses more trusses but can keep timber sizes down and spread loads across more bearings. Price both options when spans or loads are high, because the cheapest truss quote doesn’t always give the cheapest roof build.

Match spacing to the ceiling plan from day one. Parallel-chord trusses hold the same depth from end to end and suit flat ceilings where duct runs stay below the frame. Raised top chord trusses lift the top chord at the heel to leave room for insulation plus a clear path for wiring and ducts.

That gap stops trades cutting or notching webs to force services through, and cut webs lose strength fast. Talk through bathrooms, kitchens, laundries, and plant decks early, since exhaust fans and duct drops all compete for the same ceiling space. A little extra heel height or a planned service zone beats patching hacked timber later, and it keeps electrical and plumbing runs tidy.

Walk the plan with electricians and plumbers before the order goes out. Mark where large ducts cross corridors and where downlights cluster, then size the service cavity to clear them. This coordination before ordering helps avoid chopped chords later.

Check the layout plan before steel meets timber

Builders can skip the layout review when programs get tight, but it needs time in the schedule. The truss layout plan shows each truss in position with marks, spans, fixing notes, and tie-down notes.

Read it with the architectural and structural drawings side by side. Look for truss numbers, direction arrows, bearing widths, and bracing call-outs, since those four details catch most errors. Check bearing widths on site before you sign, because a short bearing can crush wall plates or split bottom chords.

Check that girder positions line up with hips and that bearer drops match the frame below. Ask for signed design drawings and compliance certificates at the same time, with timber sizes, plate locations, load notes, and connection notes for each truss.

A pencil change costs nothing while a rebuilt truss costs days.

Many Perth builders reduce that risk by ordering through a local shop that designs Roof Trusses Perth to site wind ratings and builds each frame under the Pryda connector system with full certification.

Hip ends deserve a second pass. Check jack spacing, creeper lengths, valley positions, and saddle details against the roof plane drawing. A flipped jack or a missing saddle truss shows up fast on site and stalls the whole run.

Tie bracing and hold-down into the order

A single truss is strong upright, yet a row of loose trusses is not.

Engineered roof trusses rely on permanent roof bracing to act as one stiff plane. That bracing includes bottom chord ties plus diagonal straps in the roof plane that carry wind loads back to walls and barge ends. Without that link, trusses can bow or roll under load. Bracing is an essential part of the roof structure.

Tie-down matters just as much. Each heel joint needs a defined connection to the top plate or beam, and girder ends need heavier anchors where uplift peaks. The national framing rules in AS 1684 set out tie-down and connection checks while AS 4440 covers handling and erection practice. Use both documents when establishing who supplies straps, screws, brackets, and plates.

Battens fix to top chords and top chords fix to frames. Those frames then fix to slabs or footings, so one weak link breaks the chain.

Temporary erection bracing is separate from permanent bracing. Props and diagonal ties hold trusses plumb during the lift, then permanent straps and ties lock the final shape. Don’t pull temporary props until the permanent system is fixed and checked.

Plan lifting, delivery and storage early

Long trusses need transport and lifting arrangements suited to their size. Plan them like a crane job. Tell the fabricator about site limits before the truck is booked.

Note tight streets, overhead wires, soft verges, and crane set-down points for the driver and the crane crew. Long-span and deep profiles may need a crane or a second truck with rear steer. If the crew plans a hand lift, keep spans short and weights within safe limits.

Set storage ground rules too. Have the supplier provide storage, restraint and lifting instructions for the actual truss pack. The trained erection team should plan bearers, restraints, lifting points and the safe sequence for removing transport bands before delivery. Keep storage areas clear of mud, ponded water and other trades.

A cracked joint or a bent plate often traces back to a bad lift. The first three trusses take time to plumb and brace, so leave room in the program for a slow set.

Follow AS 4440 practice for handling and erection safety. Never stand on unbraced chords and never stack materials on an unbraced roof. Keep the crew clear of the lift zone until ties are on.

Confirm timber spec and allow real lead time

The paperwork needs attention too. Ask for stress grade marks on each stick. Most truss plants run MGP10 or MGP12 pine, and the grade sets what each chord and web can carry. Keep a copy of the grade information on site for the frame inspection.

The marks should be clear on delivery and match the engineering sheets. If the spec calls for certified supply, ask for PEFC or FSC chain-of-custody papers with the pack. Many clients now ask for that proof to meet green loans or rating tools. File it with the compliance certificates so handover doesn’t stall.

Ask the fabricator about current production capacity and how far ahead a delivery slot needs to be reserved. Plant workloads can change during busy construction periods. Allow time for design checks, engineer sign-off, plate pressing, and transport, since those four stages can’t be rushed without mistakes.

Order after design freeze. Late moves of walls or roof planes force a redraw and push the delivery date. A two-week buffer helps avoid leaving a site without roof cover, and it gives the supplier room to sequence cutting, pressing, assembly, and delivery without overtime errors.

Good roofs are ordered twice: once on paper and once on site. Builders who freeze geometry, confirm loads, check drawings, and stage lifts give the fabricator a clean run and get a frame that fits.