10-12 pitch attic trusses on 24' x 24' garage. Load?

[crxguru]

I am going to raise the roof of my garage for the purpose of adding an office in the upstairs space. The existing roof is a 4-12 pitch so I want to replace the trusses with attic type that are 10-12 pitch and use the center space created as the office. The garage is concrete block construction on slab. My local truss Co. told me that the attic trusses have a 2x10 bottom beam to support the weight of an upstairs room. My question is, in the 24' span will I need a center beam to help with the load or is the 2"x10" bottom beam sufficiant on its own? Also, should I consider running them at 16" on center instead of 24"? Would this help eliminate the need for a center load bearing beam? If a beam is needed, what dimensions and type should be used.
Thanks. In southern Maryland if it matters.

 

[baritone6foot4]

All the information you need will be on the certified truss design drawings which your truss supplier should be more than happy to provide.

Make sure the truss design itself complies with code and you should be OK. Check the certified truss design drawings for design loads. If this is a private home office, 40 psf live loading in the "center room" portion of the truss should be adequate, but if this is to be your business office look for 50 psf live loading.

Additionally, since Maryland is currently using the 2000 International Codes, check the drawings for references to ASCE 7-98 for wind and unbalanced snow considerations.

If your supplier can't or won't give you the drawings, buy your trusses elsewhere.

Brian K. Willis, PE

http://www.pfscorporation.com

 

[baritone6foot4]

Of course this all assumes your masonry walls and foundation will be able to carry the additional gravitational and wind resistance loadings.

Brian K. Willis, PE

http://www.pfscorporation.com

 

[boo1]

The floor loading is dependent on the usage. Bedroom live loads ~ 30 psf, others residential ~40psf, comm 50 and up.
The span of Souther Yellow Pine can be found at:

http://www.southernpine.com/tables/1.htm

http://www.southernpine.com/tables/2.htm

Typically for that long of a span we buy trusses or hand frame with I beam floor joists and SYP rafters. As Baritone6foot4 indicated the tusses are usually certified designs.

 

[bylar]

What you are describing is an attic truss and if that is the case the live load for an attic is a lot less than for an office. Make sure the truss manufacture used the correct loadings, live, dead, snow and wind.
From what you reported I doubt they did.