Code Question
Code Question
(OP)
I've been asked to evaluate an existing flat roof structure (reinforced concrete) of a building built in the 1970's for the installation of replacement skylights. The new skylights that the owner wants are double glazed and between that, the new flashing needed, and a canopy shading mechanism, the load on the structure in the vicinity of the lights will increase by around 20 psf. The area of the lights is around 2,900 sf which is less than 10% of the total roof area. The question has been raised as to whether the current IBC or ACSE-7 (snow load) loading requirements need to be considered in the analysis. The original design allowed for a 30psf live load and in fact the structure has a little more capacity than that. Under the code requirements that were in effect at the time (BOCA) the roof structure will be ok for the new loads with even a little to spare. It's possible that it might pass even with the higher snow loads of ASCE-7-02, and then again it may not, but before I launch into the new code analysis, I first want to determine if it's even necessary. What do you think? If I do check it against the current code and it fails, then that would mean no new skylights for the owner I suppose and I wouldn't want to say that if it were not really necessary. Your views would be appreciated.






RE: Code Question
The existing roof *should* be adequate to handle the new loads, right? It's not to make sure, then. A flat roof snow load analysis using ASCE 7-02 shouldn't take more than an hour. Plus, the loads might not necessarily be higher. Did the ground snow load change?
Things to consider: do the new skylights project above the flat roof? If so, by how much? Will they cause drifts? What about impacts to drainage, rain-on-snow-surcharge (5 psf), etc., etc., all the good structural engineering snow load things we worry about...
Run the analysis and charge accordingly. Be safe rather than sorry, and all the other stuff we like to safe about ourselves practicing due dilligence and such.
RE: Code Question
RE: Code Question
I believe that the interpretation by most governing agencies (such as city building departments that are responsible for ensuring code compliance) is that only the current code is to be used for new designs and design checks.
So if a building was designed based upon a 1970's era code, and you now want to do something different to it, you should check it against the current applicable code for that area, probably an IBC code that references out to the ASCE 7 document.
RE: Code Question
RE: Code Question
My understanding (in my local area) is that if you are making a change to a building that was built in the 70's, if that change (using the original code from the 70's) does not require that the structure be reinforced then it is OK, however, if the structure needs to be reinforced then the reinforcement and affected structure needs to meet the current governing code.
RE: Code Question
akastud
RE: Code Question