Minimum roof dead load per IBC/CBC

[awa5114]

I often need to evaluate roof framing members for existing buildings for which available as-builts are sometimes incomplete. This prevents me from generating accurate roof dead load takeoff estimates. For these cases, I use a minimum design load of 15 psf as instructed by my supervisor. However I was wondering if there was some sort of minimum value that the CBC or IBC imposes for cases where the roof dead load is not available? Thanks for your help.

 

[BadgerPE]

I think I would be more apt to determine what the actual dead load is, rather than relying on what the CDs say. However, to answer your question, I am unaware of any minimum dead loads published for a roof system.

 

[msquared48]

As far as I know, there is no minimum. That is left up to the structural engineer to determine.

If there are any penetrations, you may be able to determine the dead load on site, or even with drawings (if you are lucky).

Mike McCann, PE, SE (WA)

 

[jayrod12]

Personally I don't go lower than 15 psf for any roof unless I have accurate information regarding the existing roof construction, and I need to sharpen my pencil to get an existing condition to work.

 

[Guastavino]

Not that I know of for a roof system, however, ASCE 7 makes mention of "minimum" roof dead loads based on the actual components. I think the logic behind this is to provide a consistent assumption database for engineers to use. This to likely keep the conscientious engineers and the "stamp anything" engineers from having to argue as much.

 

[wannabeSE]

You might get a better response if a description of the roof is provided. Do you mostly work with wood roofs with composition shingles? Last week, I was adding up the dead loads for am existing roof with 4" precast planks, 4 1/2" concrete topping plus 2"-4" lightweight insulating concrete. Needless to say, 15 psf doesn't come close.