Second Layer Reroof Less than 3 psf Procedure 1

[waytsh]

I have a client that would like to perform a metal over metal reroof on an existing commercial steel building. The second layer of roof is less than 3 psf. IEBC grants an exception when the second layer of reroof is less than 3 psf, but what exactly does this mean? Does this mean that they don't need to involve a structural engineer and can just proceed with the reroof ? Does it mean that a full scale investigation of the building is not required to ensure that it complies with the current code but an engineer should still do a visual inspection of the building to make sure everything looks sound? Curious how you all are handling these situations.

Thanks!

 

[gte447f]

but an engineer should still do a visual inspection of the building to make sure everything looks sound

Well it certainly doesn't mean this. Although you could certainly do this if you want, but expect it to potentially expand the scope of the problem far beyond determining whether the reroof exceeds 3 psf.

I would say that what is actually required will depend on the local building authority having jurisdiction (AHJ). They may have an exception for reroofing that allows the contractor to proceed without a permit. They may require an engineer to evaluate the capacity of the existing roof for the addition of the new load. They may accept an engineer's evaluation of the proposed additional load (less than 3 psf) and a statement that it conforms with the exception in the IEBC. They may accept a similar statement that the proposed additional load is still less than the original design loads (if you know what the original design loads were). It really depends on what the AHJ requires and will accept. Often times they will accept almost anything with an engineer's stamp on it. Knowing this, I would be very careful in defining your scope of work in your contract with your client.

 

[XR250]

How much does the roof actually weigh? 3 PSF seems high for a metal roof.

 

[waytsh]

thank you for the replies.

(if you know what the original design loads were)

Unfortunately at this point we don't know the original design loads. Not sure we are going to get them either. I agree that this is going to depend on the local authority. I have instructed the client to reach out to them to see what they say.

How much does the roof actually weigh? 3 PSF seems high for a metal roof.

They are still working on getting the weight of the new roof but it is expected to be much less than 3 psf.

 

[lexpatrie]

I'll just point out the distinction between "the code doesn't require it" and "this is safe". They aren't the same thing, but one would suppose the 3 psf in the code wouldn't be there over the strenuous objections of the engineering community (or, perhaps, it would), but there are situations where 3 psf wouldn't be safe, probably involving flat roofs that are deficient for slope to start with (courtesy of old codes that allowed "sloped to drain" rather than a specific slope, i.e. my kitchen table, while flat, is "sloped to drain" as when I pour a gallon of water on the table, besides a lot of yelling from my family, most of the water ends up on the floor so it's "sloped to drain", right? That's how it seemed to be interpreted. "perfectly flat" and increasing the dead load increases the chances of a ponding hazard or collapse and the definition of "susceptible bay" in the IBC isn't all that well connected to any charging language.

Steep sloped roofs you'd likely not encounter this situation. To me the 3 psf has an origin from shingles, and most shingle manufacturers don't (explicitly) allow slapping their shingles on old shingles now, anyway.

I do a lot of construction defect work, so ...... I tend to look at these things more holistically. And with a "what's the intent/origin of the provision" perspective. The NRCA does a fine job of fussing over covering secondary roof drains, or the need to add them, but the slope/ponding interaction, that seems to be a bit of a blind spot for them, as well as working on code slope requirements without noticing that the manufacturer's installation instructions also have slope requirements (as a backup).

 

[gte447f]

I'll just point out the distinction between "the code doesn't require it" and "this is safe". They aren't the same thing, but one would suppose the 3 psf in the code wouldn't be there over the strenuous objections of the engineering community (or, perhaps, it would), but there are situations where 3 psf wouldn't be safe, probably involving flat roofs that are deficient for slope to start with (courtesy of old codes that allowed "sloped to drain" rather than a specific slope, i.e. my kitchen table, while flat, is "sloped to drain" as when I pour a gallon of water on the table, besides a lot of yelling from my family, most of the water ends up on the floor so it's "sloped to drain", right? That's how it seemed to be interpreted. "perfectly flat" and increasing the dead load increases the chances of a ponding hazard or collapse and the definition of "susceptible bay" in the IBC isn't all that well connected to any charging language.

Steep sloped roofs you'd likely not encounter this situation. To me the 3 psf has an origin from shingles, and most shingle manufacturers don't (explicitly) allow slapping their shingles on old shingles now, anyway.

I do a lot of construction defect work, so ...... I tend to look at these things more holistically. And with a "what's the intent/origin of the provision" perspective. The NRCA does a fine job of fussing over covering secondary roof drains, or the need to add them, but the slope/ponding interaction, that seems to be a bit of a blind spot for them, as well as working on code slope requirements without noticing that the manufacturer's installation instructions also have slope requirements (as a backup).

@lexpatrie What in the world are you getting at with this? It just seems like much ado about nothing to me. Maybe it's just me.