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Construction glossary · Wood framing

What is a roof trussin construction?

A truss is a pre-engineered, factory-built roof or floor frame made of dimensional lumber webs and chords connected by metal plates, delivered ready to set. In roof framing it replaces stick-built rafters and ceiling joists with a single component spanning wall to wall. Standard roof truss spacing is 24 in OC, so the count is the building length divided by 2 ft plus one, before the gable-end and girder trusses the layout calls out.

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Updated August 2026 · Reviewed by the Ruh construction team

Spacing 24 in. o.c.Count rule (length ft / 2) + 1Engineered Shop-fabricatedLead time 3-6 weeks typical
The definition

Truss, explained.

A roof truss carries the roof load across a clear span using a triangulated arrangement of top chords, bottom chords, and internal webs, joined at the panel points with stamped metal connector plates. The truss manufacturer engineers each profile to the span, pitch, loads, and bearing conditions, then ships a sealed layout and placement plan. For the estimator, trusses are a supplied component: you are not buying loose 2x lumber, you are buying a count of engineered units plus girder trusses, hangers, and bracing. Common spacing is 24 in OC, which lets the roof sheathing and ceiling drywall span without extra framing. Trusses go up fast, give predictable material, and remove most cutting from the roof, but they limit attic use and lock the roof geometry once the package is engineered. The takeoff is a count along the building length plus special members at hips, valleys, and openings.

How it is measured

Trusses are counted as each, off the truss placement plan or, in early budgeting, off the roof framing plan. Read the building length along the ridge line, the on-center spacing (almost always 24 in OC), and any gable-end and girder trusses called out separately. The count is the run length divided by the spacing, plus one for the starting truss, plus the gable ends. Add girder trusses at load points, hip and valley sets, and any doubled trusses under point loads. Bracing lumber, metal connector hardware, and hangers are taken off the engineering package. Confirm the bearing length and overhang from the truss profile, not the wall plan.

What is standard roof truss spacing?

Standard roof truss spacing is 24 in OC, and on a truss job that is a budgeting number rather than a given. Standard truss spacing holds only until the sealed placement plan lands, because the on-center dimension the order has to run on is the one printed on that sheet. Work at 24 in OC to budget, then take the spacing off the layout before the count is priced.

The spacing for trusses drives the count directly, because the count is a division. On the 60 ft run in the worked example below, 24 in OC gives 31 field trusses. If a layout comes back at 16 in OC instead, the same run is 720 in divided by 16 = 45 spaces, plus 1 = 46 field trusses, 15 more units on the same building before the gable ends are added.

Roof truss layout: gable-end and girder positions

A truss layout, the placement plan the manufacturer ships with the engineering, is a plan view of the run: it puts every unit in a position along the building rather than in a quantity column. Read in position order it separates into three groups. The field trusses repeat at the on-center dimension across the open length, one gable-end truss closes each end of that run, and the girder trusses land at the interior bearings the layout marks.

Position is what changes the order, not just the total. A gable end sits at the end of the run and is bought on its own line, so it never falls out of the length divided by spacing arithmetic. A girder sits where the structure puts a bearing, and it is added to the count rather than swapped into it, which is why the worked example below picks up an extra leaf at the girder rather than reusing a field truss. A multi-ply condition or a doubled truss under a point load works the same way: one position on the layout, more than one unit at the plant.

Hip roof truss layout

A hip roof changes what the layout calls out at each end, and with it the count. A hipped end is called out as a hip set with its valley members and taken off as its own group, the same way a gable end or a girder is taken off separately.

That is why a hip roof count cannot be closed off the roof framing plan. The gable building in the worked example below finishes with two end trusses, one per end, and a hipped end is not that unit. Read the members at each end off the sealed placement plan, and carry the hip and valley sets and any girder under them on their own lines.

Worked example

Roof truss spacing and count: 60 ft building at 24 in OC

Worked example

A 60 ft long building, common trusses at 24 in OC (2 ft). Field trusses = 60 ft / 2 ft = 30 spaces, which gives 30 + 1 = 31 trusses to cover the run. Then add the two gable-end trusses: 31 + 2 = 33 total trusses on the roof. Say the layout also calls for 1 girder truss at an interior bearing and a 2-ply condition there, adding 1 more leaf: 33 + 1 = 34 truss units to order. At an illustrative supplied price of 165 dollars per common truss, the 33 units run 33 x 165 = 5,445 dollars before the girder, hardware, and freight, which are priced from the truss vendor quote.

How Ruh handles it

How Ruh handles truss.

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Truss: frequently asked questions

How many trusses do I need for a 60 ft building at 24 in OC?+

60 ft divided by 2 ft spacing is 30 spaces, so 31 common trusses cover the run. Add the two gable ends for 33, then any girder or doubled trusses the layout calls out.

Do I count gable-end trusses in the spacing?+

No. Run the field trusses by length divided by spacing plus one, then add the gable ends as separate units. They are built differently, often with vertical studs for siding, and are priced on their own line.

Can I take off trusses before I have the engineered package?+

You can budget a count off the roof framing plan using length and spacing. The final order must follow the sealed truss placement plan, since girders, hips, and doubled members change the count and price.

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Related terms

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Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.

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