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Re: Weights for design

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Rigid insulation is on average close to 1 psf per inch, but there is no way roll insulation is anywhere close to 11 psf.  Typical roll insulation is .1 to .3 psf per inch depending on type (rock wool, glass wool, or similar).  A typical R30 roof with roll insulation would be maybe 1.0 psf additional load.
 
Sprinkler loads are typically 1.0 to 1.5 psf.  The big issue with sprinklers is the location of the main risers / feeds, where two trusses could end up carrying a 4 or 6 inch line.
----- Original Message -----
Sent: Tuesday, March 08, 2005 12:15 PM
Subject: Re: Weights for design

David Smith wrote:
I am reviewing the loads for wooden trusses on a church roof.  The architect specified R30 insulation and automatic sprinklers.
 
It looks like the weights for each of these can vary all over the map.  I would appreciate seeing some typical design weights used by the rest of you.
 
Dave Smith
For R30, an average value is R=3 per inch.  This comes out to about 10", although batt insulation vendors list 9" thickness for R30.  Using ASCE-7 loads, fibrous insulation is 1.1 psf/inch.  The insulation DL comes to about 11 psf. 

For the spinklers, assume something like 2" STD pipe at 10' spacing. The pipe when filled with water is 5.10 plf or .51 psf.

 The total dead load is 11.5 psf but doesn't include the sprinkler mains.  You would have to adjust the sprinkler DL based on what the mechanical engineers are coming up with..