Gable Roof Truss Calculator

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Use of manufactured roof trusses can dramatically cut labor costs when framing a gable roof compared to building rafters.

Trusses can be constructed with smaller sized lumber than rafters and often their cost is not significantly higher than normal rafters.

Since they can be fastened directly in place much less labor is required compared to bird mouth, plumb, and tail cuts on individual rafters.

Our roof truss calculator can be used to aid you in the purchase of your trusses by determining the quantity of trusses and lineal feet required.

Truss Terminology

roof truss calculation points
A) Roof Length in feet B) On Center (inches between trusses) C) Width of bottom cord in feet
ft inches ft

For Top Chord Length -> Rafter Length Calculator

How to Enter Sizes
24 Feet24
24 Feet 6 inches24 6
24 Feet 6 & 1/2 inches24 6 1/2

Meaning of 25-5-0-5

25 psf Top Chord Live Load (snow)
5 psf Top Chord Dead Load (materials)
0 psf Bottom Chord Live Load
5 psf Bottom Chord Dead Load

4' oc 25-5-0-5 psf Truss Member Sizing
(No ceiling)
Dimensional Lumber Required 2x4 Flat oc Image
Span Top Chord Bottom Chord Webbing Lateral Purlin  
20' 2x4 #2 2x4 #2 2x4 #2 72" 24" 20' span gable truss drawing
24' 2x4 #2 2x4 #2 2x4 #2 72" 24" 24' span gable truss drawing
30' 2x6 #2 2x4 2400f-1.8E 2x4 #2 72" 24" 30' span gable truss drawing
36' 2x6 #1 2x6 #1 2x4 #2 72" 24" 36' span gable truss drawing
40' 2x6 #1 2x4 2100f-1.8E 2x4 #2 72" 24" 40' span gable truss drawing

Connector plates are generally 16 gauge to 20 gauge depending on truss design requirements.

The information provided here is not intended to replace truss drawings.

Engineered truss drawings should be obtained for specific site locations incorporating specific snow load, wind speed, eave wall height, building length and importance factor (use of building).

mechanically graded lumber design values


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