Existing framing

[erikuofo]

I'm looking at putting some light solar above the framing attached. The framing is 1 x 4 laid flat top and bottom chords with a 40' span. The depth of the trusses are at about 24" min to 44" max. The top chord is lightly sloped supporting a "flat" roof above. I've looked for tags to pull information from the trusses, but cant find any. The trusses are stamped with a "Simpson" logo and the "kiln dried" stamp as well. Is anyone familiar with what type of truss this is? I'm trying to find the capacity of the trusses.

Thanks,

 

[JAE]

This is a similar product - not Simpson -

Redbuilt link

 

[MiketheEngineer]

Trus-Joist (Ijoist.com) used to and still makes these. However - they may be custom for loads and spans.

I have fludn that many light wiegh solar panels are in the 2-3 psf range and shouldn't normally be a problem. Anchoring can be a bit of a problem - leaks, etc.

 

[asixth]

How much load consititues as light? If it is under 5psf say I don't think it would require engineering design.

Trusses are designed by truss engineers who generally speaking are little more than a cad technicians. When I was designing trusses I would allow for an additional 10psf dead load allowance for services and other hanging items and a 5psf minimum live load for roof which are not accessible or used for floor type activities.

Most cases wind governs or snow for the cooler cliamtes.

 

[woodman88]

Trusses are designed by Professional Engineers from input given to them by the truss manufacturer. The truss manufacturer may be hiring people off the street with little design experience to input, check workability with the program, and send the information to the Professional Engineer. But the truss designs are carefully reviewed to insure the code requirements are met for the truss design, per that input, by the engineering staff and engineer before sealing. Whether the truss manufacturer inputs the correct information for the project for the truss design or not is the responsibility of the Building Designer/EOR to verify.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[BigInch]

1x4 on a 40 foot span looks VERY light weight. I wouldn't expect to see 1x4s on anything longer than a 25-30 foot span.

What would you be doing, if you knew that you could not fail? Ans. Bonds and derivative brokering.

 

[erikuofo]

Sorry, I meant 2 x 4 flat chords. I understand that the trusses are to be designed per the loads given to them by the original engineer, I just dont know what the initial data was that was given to the original joist designer to design for.
During my site investigation, it looks like the joists are supporting
ACTUAL ROOF DEAD LOADS (DL):
(Estimated from visual site review)
Built-up roofing 2.5 psf
Insulation 1.5 psf
1/2" plywood 1.5 psf
Joists at 2'-0" o.c. 3.0 psf
Suspended Acoustical Ceiling 1.5 psf
Mech, Plumbing, Elec. 1.0 psf
Fireproofing 1.5 psf
Sprinklers 1.5 psf
Miscellaneous 1.0 psf
15.0 psf

EXISTING ROOF LIVE LOADS (LL): (Reducible) 20.0 psf

TOTAL: 35.0 psf

 

[erikuofo]

Whoops, I meant 2 x 4 chords. After looking at the existing loading on the structure, here are the loads i've generated that are being supported by the joists:
ACTUAL ROOF DEAD LOADS (DL):
(Estimated from visual site review)
Built-up roofing 2.5 psf
Insulation 1.5 psf
1/2" plywood 1.5 psf
Joists at 2'-0" o.c. 3.0 psf
Suspended Acoustical Ceiling 1.5 psf
Mech, Plumbing, Elec. 1.0 psf
Fireproofing 1.5 psf
Sprinklers 1.5 psf
Miscellaneous 1.0 psf
15.0 psf

EXISTING ROOF LIVE LOADS (LL): (Reducible) 20.0 psf

TOTAL: 35.0 psf

So it looks like a 15 psf dead is currently being supported by the joists, but I'm just not sure what they were designed for. The additional load on these joists will be around 5 psf, so I'm optimistic that the framing will be able to support the joists, but still want to try to find some capacity of the existing joists. Some jurisdictions are allowing roofs supporting solar panels to have a reduced live load down to almost zero where panels are covering the roof and no live load could be applied to the areas. The project is in Phoenix, so Snow loads are nil to minimal that they wouldn't add anything or much to the panel loading. Therefore, the roof seems to be ok if it was designed for 20 psf live load, but I just dont know if it was because of its 20 year age (its in good shape though).