Specs, loads and standards
The reference numbers estimators and plan reviewers ask for, in one place. These are planning figures. The sealed truss design drawings for your job govern.
Load cases we design to
Truss loads are given as four components. Getting them right at quote time is the difference between a price that holds and a change order.
| Component | Abbreviation | Typical value | What it covers |
|---|---|---|---|
| Top chord live load | TCLL | 20–40 psf | Snow or roof construction live load, whichever governs |
| Top chord dead load | TCDL | 7–15 psf | Sheathing, underlayment, roofing material |
| Bottom chord live load | BCLL | 0–20 psf | Attic storage or habitable floor load, where applicable |
| Bottom chord dead load | BCDL | 5–10 psf | Ceiling finish, insulation, ducts, fixtures |
Heavy roofing changes TCDL substantially: asphalt shingles run about 3 psf, standing-seam metal about 2 psf, concrete tile 9–12 psf and clay tile up to 15 psf. Tell us the roof covering, not just “shingles”.
Deflection limits
Deflection governs comfort rather than safety, and it is where a floor feels cheap or solid. The limit is a fraction of the span: L/360 on a 24-foot span is 0.8 inch.
| Application | Live load | Total load | Note |
|---|---|---|---|
| Roof, no ceiling | L/180 | L/120 | Code minimum |
| Roof with gypsum ceiling | L/360 | L/240 | Protects the ceiling finish |
| Floor, standard | L/360 | L/240 | Code minimum for floors |
| Floor, preferred | L/480 | L/360 | What we recommend; noticeably stiffer |
| Floor with tile or stone | L/720 | L/480 | Required to stop grout cracking |
Pitch, rise and transport
Pitch sets truss height, and truss height sets how the load travels. Past roughly 13 feet of overall height a truss usually has to ship as a piggyback assembly.
| Pitch | Rise per 12" | Angle | Peak height, 30 ft span |
|---|---|---|---|
| 2/12 | 2" | 9.5° | 2 ft 6 in |
| 4/12 | 4" | 18.4° | 5 ft 0 in |
| 5/12 | 5" | 22.6° | 6 ft 3 in |
| 6/12 | 6" | 26.6° | 7 ft 6 in |
| 8/12 | 8" | 33.7° | 10 ft 0 in |
| 10/12 | 10" | 39.8° | 12 ft 6 in |
| 12/12 | 12" | 45.0° | 15 ft 0 in |
Peak heights are measured from the bottom chord and exclude heel height. Add the heel to get overall truss height.
What we build to
Practical questions about ordering, lead times and field changes are on the FAQ page.
- ANSI/TPI 1National Design Standard for Metal Plate Connected Wood Truss Construction. The governing design standard, referenced directly by the International Building Code and the International Residential Code.
- BCSIBuilding Component Safety Information. Joint SBCA and TPI guidance on handling, installing and bracing trusses. A BCSI summary sheet ships with every load.
- SBCA QCStructural Building Components Association quality control. In-plant inspection of plate placement, lumber grade and truss dimensional tolerance.
- ASCE 7Minimum Design Loads for Buildings. Source of the wind and snow criteria we apply for your site.
- NDSNational Design Specification for Wood Construction. Governs allowable stresses for the lumber in the truss.
- CodeWe design to the building code edition adopted in your jurisdiction. Confirm the edition with your plan reviewer, because adoption lags publication by years and it changes the loads.
What ships with your order
- Sealed truss design drawings, one per truss type
- Truss placement diagram, numbered to the delivery bundles
- Hanger and connection schedule at girders and bearings
- Permanent bracing requirements
- BCSI handling and installation summary sheet
- Lumber grade and plate specification for the job
Need a span table for your job?
Published span tables only go so far — they assume loads that may not be yours. Send the plan and the site criteria and we will run the actual numbers, which costs you nothing and takes less time than reading a table.
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