Trouble Shooting – “When Ordering Trusses”
S -Truss Span:
This is the measurement from the outside of one bearing wall to the outside of the other bearing wall or from heel to heel.
o/h – Overhangs:
These are requested in addition to the Truss span.
i.e. “I need a 24’ truss (outside-bearing to outside-bearing) with 1’ overhangs.” not “I need a 26’ truss.”
P – Pitch:
A 4/12 pitch means the pitch rises 4” high for every 12” of length.
- 4/12 pitch is the average agricultural pitch.
- It is not recommended to use a pitch lower than 2/12 for shingle roofs.
OC – On Center Spacing:
This is the spacing between each truss.
Common spacing’s are:
- 16” OC or 2’ OC, for residential applications (shingle roofs and drywall ceilings)
- 4’ OC for agricultural applications (metal roof and metal ceilings)
B – Bearing Thickness:
This is the thickness of the bearing wall. i.e. 2×4 wall, 2×6 wall, 8.5” pole barn wall… This information is especially important to know when designing scissor trusses.
cn – Cantilever:
This is when the bottom-cord of the truss extends beyond the bearing wall. The truss designer will need to know the full truss span (from heel to heel), as well as the span between the outside of each bearing.
vl –Scissor/Vaulted Trusses:
Most often the pitch of the vault is half that of the roof pitch. i.e. 6/12 over 3/12.
NOTE: When ordering a scissor/vaulted truss it is important for the designer to know the thickness of each bearing wall, to insure a proper seat cut.