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

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        Your assessment that there was more snow than the code allows for seems reasonable and may well be correct.  There are, however, other possible reasons for having excessive snow loads than your suggestion that the snowfall this year in much more than the statistically expected design snow load.
        Some possibilities include the following.
1.)    Influence of the mountains.  Snowfall in mountainous regions is difficult to predict.  It's possible that buildings on the specific site should be designed for higher loads than those specified in the code.  This may mean either that the code loads need to be increased or that an experienced engineer should have recognized this and allowed for more snow load than the minimum specified by code.  There were postings on the list (in which I was a participant) dealing with this subject a couple of years ago some of which I saved on my old computer.  I found one private correspondence and forwarded it to the list; you should be able to find more in the archives.
2.)    You didn't mention anything about large nearby buildings (with higher roofs), signboards, parapets, penthouses, or other structures that could influence snow drift patterns,  It is not uncommon for these obstacles to double (or more) the snow load.  These effects usually apply to small localized portions of the roof, not to the whole roof (you didn't say how extensively the observed overload effects were distributed).  One possibility: a higher building could have been built after the subject building and it should become the second building owner's responsibility to reinforce the roof of the older building.
        I hope this is of some help.
H. Daryl Richardson
----- Original Message -----
Sent: Friday, March 04, 2005 4:06 PM
Subject: Ceiling deflection damage caused by excessive snow - who is responsible

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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