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Truss diagram questions
- Thread starter fifth
- Start date
chaosracing
Well-known member
Weight load is under Loading on the left hand side.
TCLL = Top Chord Live Load (Yours 20 pounds per sq ft, or psf)
TCDL = Top Chord Dead Load (Yours 14 psf)
BCLL - Bottom Chord Live Load ( Yours 0 psf
BCDL = Bottom Chord Dead Load (Yours 10 psf)
The bracing being asked for is as follows, on the roof side (Top Chord) they want either plywood/OSB or 2x purlins spaced at a min of 3' on center. On the bottom chord, they want 2x put on top of the bottom chord to stabilize and prevent the truss from moving. They are also asking for additional bracing during install, typically nailed on the underside of the top chord or nailed on the webs.
TCLL = Top Chord Live Load (Yours 20 pounds per sq ft, or psf)
TCDL = Top Chord Dead Load (Yours 14 psf)
BCLL - Bottom Chord Live Load ( Yours 0 psf
BCDL = Bottom Chord Dead Load (Yours 10 psf)
The bracing being asked for is as follows, on the roof side (Top Chord) they want either plywood/OSB or 2x purlins spaced at a min of 3' on center. On the bottom chord, they want 2x put on top of the bottom chord to stabilize and prevent the truss from moving. They are also asking for additional bracing during install, typically nailed on the underside of the top chord or nailed on the webs.
matt_i
Well-known member
Could you explain a little more on this: "On the bottom chord, they want 2x put on top of the bottom chord to stabilize and prevent the truss from moving."
Its either that or a rigid ceiling, of which I believe drywall will suffice.
Every 10 feet on center, across the 32' span, you should have a run of 2x4s going down the length of the building, perpendicular to the bottom chords. Imo that's a waste of timber if you are going to actually put up the ceiling.
They also note a 20psf rating where a certain size of box will fit in between the bottom and top chord. This seems to apply only to the center section.
Its either that or a rigid ceiling, of which I believe drywall will suffice.
Every 10 feet on center, across the 32' span, you should have a run of 2x4s going down the length of the building, perpendicular to the bottom chords. Imo that's a waste of timber if you are going to actually put up the ceiling.
They also note a 20psf rating where a certain size of box will fit in between the bottom and top chord. This seems to apply only to the center section.
That space between the top and bottom chord is designed for AC unit.
Question:
TCLL = Top Chord Live Load (Yours 20 pounds per sq ft, or psf)
Using the above, my sq footage of my roof is 1,550... so 20 psf x 1,550 = 31,000 pounds. Does this mean my roof will support 31,000 pounds?
matt_i
Well-known member
Using the above, my sq footage of my roof is 1,550... so 20 psf x 1,550 = 31,000 pounds. Does this mean my roof will support 31,000 pounds?
Yes, but distributed at a rate of 20 pounds per square foot. Its not able to support that load, hung from a single concentrated point. But that's part of the total load (also walls, footings, slab, etc) that the building is placing on the earth.
moneypit_k5
Well-known member
Man, that really puts things into perspective doesnt it. 18,000 lbs of roof tiles! Good thing youll never get snow!
The 2x on top is commonly referred to as a rat run. You might check that it is in lieu of a ceiling. Kind f doubt it. The rat run will keep the trusses from moving. The span is generally wnough that without structural support, the bottom cord might move even with drywall, giving you nail pops forever. Whoever is hanging the ceiling will really appreciate having that brace there as well. Keeps it all straight.
The 2x on top is commonly referred to as a rat run. You might check that it is in lieu of a ceiling. Kind f doubt it. The rat run will keep the trusses from moving. The span is generally wnough that without structural support, the bottom cord might move even with drywall, giving you nail pops forever. Whoever is hanging the ceiling will really appreciate having that brace there as well. Keeps it all straight.
RocketScott
Well-known member
Man, that really puts things into perspective doesnt it. 18,000 lbs of roof tiles! Good thing youll never get snow!
The 2x on top is commonly referred to as a rat run. You might check that it is in lieu of a ceiling. Kind f doubt it. The rat run will keep the trusses from moving. The span is generally wnough that without structural support, the bottom cord might move even with drywall, giving you nail pops forever. Whoever is hanging the ceiling will really appreciate having that brace there as well. Keeps it all straight.
Quoting from the truss spec:
Rigid ceiling directly applied or 10-0-0 oc bracing
ETA: Chaos and Matt pretty much nailed it, not much more to add.
Last edited:
moneypit_k5
Well-known member
Sorry, i couldnt get the photo to open large enough to read the text.
ard
Well-known member
Thanks, got worried when I was informed the total weight of the roof tile... 18,000 pounds.
Make sure whatever licensed roofer who is installing the roof tile gets a copy of that trust design as part of the contract/bidding process.....
Along with 18k lbs of tile, there should be other parts too...