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RE: Weights for design

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Somewhat of a side issue but rather interesting: Back in the ‘80s, the Building Department of Santa Cruz CA required the use of wet weight for batt insulation in the ceilings of commercial structures.




From: Jordan Truesdell, PE [mailto:seaint(--nospam--at)]
Sent: Tuesday, March 08, 2005 12:42 PM
To: seaint(--nospam--at)
Subject: RE: Weights for design


If the roof can be covered with asphalt shingles, always count two layers for gravity loads (2.5 to 3.0 psf is typical).  Sprinklers usually gets lumped into a 4 to 5 psf "MEP" catchall unless it "looks" heavy (lots of lighting or lots of piping...both usually require special circumsstances in the buildings).

R30 is usually batts or rigid. A lot of churches tend to be built like big houses, and FG batts are common around me. Batts are light, but I can't find a number right now (0.1 to 0.2 psf per inch?), and are usually R3 to R4.5 per inch depending on the density. EPS rigid is 0.2psf/in and about R3.5 per inch, Urethane/Icynene is 0.5psf/in and R7 per inch. Either way, 2psf for insulation should do it.

I think the "Fiberous Glass" number is from the ASCE-7 dead load tables (C3-1), and is really meant for rigid fiberglass panels. That type is commonly used to insulate ductwork and to create sound-attenuating panels, and not for building insulation.


At 12:49 PM 3/8/2005 -0700, you wrote:

Per ASCE 7:
Fiberous Glass Insulation is 1.1 psf per inch of thickness.
For sprinklers, I break down what is being used for pipe, how often it is being used, the volume of the pipe and the additional weight due to the water.  Tack on a little bit of fudge factor for fittings, spread this load out over the entire roof area, if I see it is possible, badda-bing badda-boom, I have a dead load.
For industrial buildings been known to have upwards of 10 to 12 psf for dead load, but that includes roof sheeting, purlins, and what have you.  I do, however, take a quantitative look at things, and come up with a good, and even conservative, additional dead load onto the structure.
Dave Maynard, PE
Gillette, Wyoming

-----Original Message-----

From: David Smith [mailto:smith1129(--nospam--at)]

Sent: Tuesday, March 08, 2005 12:22 PM

To: seaint(--nospam--at)

Cc: smithassociates(--nospam--at)

Subject: Weights for design

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

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