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Re: Ceiling deflection damage caused by excessive snow - who is responsible

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There seems to be some sort of a disconnect here concerning the proper snow loads criteria.   What was the snow load criteria, which is usually provided by the local building official in keeping with section 1614 of the CBC?   Further, did your friend review and approve and complete the design of the trusses as required by the CBC and the ANSI/TPI design standards?    The snow loads for this year might have been high, but I don't know if this area had 12" of snow or 20 feet of snow to try to come up with some sort of good response to your questions.   Engineers in our area have had problems with joists designed by the truss companies here.  Last year I decided to try to provide to my one client where I'm using trusses to have a specialty truss engineer provide the design.

In El Dorado County, the building department has a web site where one can enter the APN (area parcel number) and the maximum ground snow load were be provided for the specific parcel.

Another problem could be improper ventilation which will cause the trusses to move and also detailing of the trusses where they pass over non-bearing walls.  Most of these issues have been discussed in the past on this list and these issues are also addressed by the gypsum board association. 

Neil Moore, S.E.
neil moore and associates

At 03:06 PM 3/4/2005, Dennis S. Wish, PE wrote:
I have a friend who designed a commercial building in Pinion Crest - an area in the mountains near Palm Springs California. The roof was designed to state and municipal code using top chord sloped Trus-Joist products. My friend is actually the designer, he hired the engineer and the joists were verified by design from Trus-Joist.
The joists span a maximum of 25 feet and I have no other information at this point on the type and spacing of the sloped joists. However, I think this is secondary to the issue.
The joints at the Gypsum Ceilings began to split. The TJI calc's verified that the joists were within the allowable deflection range (although allowable deflection for 25 feet may still be too much to prevent gypsum damage if paper tape is used). The owner is demanding that my friend (who was also the General Contractor) on the project repair the damage and upgrade the roof at his cost.

Although I have not confirmed it, I believe that the snow load for this year probably exceeded the code limits. The owners expert claims that the Gypsum Association states that the deflection criteria for a gypsum ceiling (total load) shall not be greater than L/240. I have asked to have the calculations faxed to me but I can no imagine Trus-Joist being less than conservative on their design and would like to verify this.

Assuming that Trus Joist is accurate and the joist calc out, then the only answer is that the roof live load was exceeded by the amount of snow load exceeded the code allowable. In my opinion, this is an Act of Nature and the owners insurance should cover - it is not the responsibility of the EOR, Trus-Joist or the Designer/Contractor.

Any thoughts on this matter before I decide to step in and represent my friends position? Am I missing anything? I am hesitant at this time to go into much more detail until I see the calculations produced by Trus-Joist, but I would be interested in your comments.

Dennis S. Wish, PE
California Professional Engineer
Structural Engineering Consultant


760.564.0884 (office - fax)

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