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

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Neil Moore wrote:


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
I did not think about the roof ventilation issue as this is a flat (1/4" per foot) slope. What I found out after questioning the use of a flat roof in a snow region is that Pinyon Crest is at about 2000-feet which is generally below the snow line. I've built in this area and never had a snow load imposed by the local building official. The plan check is done by county and the designer went to the county for the snow information, however, the county covers a large area and much higher elevations. As you suggested, I asked if anyone had gone to the local building official to get a snow load based on the location of the home and he was not sure.

I wrote to Daryl Richardson that I think there are other issues in play here if only because the unsupported span on the Trus-Joist products is 25-feet and the allowable deflection is still pretty high for a taped joint on gypsum ceiling. These deflections are code minimums, but I would not have allowed more than 1-inch or 3/4-inch when the ceiling is applied directly to the bottom of a  roof rafter.

As I also mentioned, I have a similar problem in my own home from a poor drywall job, and before painting, I solved the ones I caught (others occurred a few years later)  using a fabric tape.

To be honest, I have to review the calculations and verify the snow load, if any, with the building official. However, if there is no snow load and snow does occur, I don't see that this is the problem of the engineer or builder when a storm exceeds the codes 50-year limit. We have a responsibility to satisfy only the minimum life safety issues in the code and according to the new comments added to the 97 UBC - prevent major structural damage. Cracks in ceiling is far from a life safety issue and I don't see that the owner has a complaint - especially when he was so happy to save a few dollars in design and materials.

Damned if you do and Damned if you don't!

Thanks Neil,


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


760.564.0884 (office - fax)

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