Question on Existing Roof in Delaware 1

[CUENGR]

Looking to see if anyone is familiar with this roof system (photo file attached). I need to estimate the dead load of this system for a rehabilitation project. The 2" of "rigid material" is what I am most unfamiliar with as far as weight goes. Per SJI the joists are either "J series" or "H series" so back calculating the dead load in this case gives varying answers depending on which joist is assumed. I think it can be assumed light weight concrete conservatively but any theory/proof of reducing this number would be very helpful.

Another question is whether additional steps should be taken when cutting new duct openings in this system other than angle framing typical with metal deck?

Location: Christiana, DE
Material (top to bottom): TPO membrane, 3" insulation, 3/4" plywood, 2" rigid material similar to lightweight concrete, 1" insulated base layer.

 

[JedClampett]

It might be a poured gypsum material. Take a look at the document attached.

 

[phamENG]

It probably is gypsum, but I'm not so sure about poured. Looks like it has interlocking tabs? There have been gypsum panel roofing products. What year was it built? I've seen a couple of Tectum roofs in Delaware - I think I was around Dover? It's been a few years. But Tectum usually looks white.

 

[CUENGR]

It was built between 1970-1982. I scraped and cleaned a small surface and it was pure white.

I attached another photo that shows some type of reinforcing (likely WWF). It seems like this could be a poured gypsum roof due to the WWF, possible bulb-T subpurlins underneath, and 2" formboards as specified in the document. The subpulins looked similar to drop ceiling grids but supported the formboard/insulation. I was unable to find a demoed area that would verify bulb-T or not. There were also expansion joints every 5 bays or so which seems to align with the requirements on page 4 of the document for expansion/contraction.

 

[Ron]

That's poured in place gypsum with bulb tees and WWF reinforcing. The formboard on the bottom is gypsum as well and fits inside the bottom flanges of the bulb tees. This was a common deck in that time period.

It also looks like the existing roof membrane was installed above an older built up roof system with a heavy flood coat of either coal tar or asphalt. There is more insulation above that. The existing membrane looks like a fully adhered EPDM membrane. The insulation above the original membrane looks like a foam insulation. In all, there's a lot of thickness there and correspondingly a lot of weight.

Lightweight insulating concrete and poured in place gypsum are two different animals. The LWIC is lighter than gypsum. Poured in place gypsum weighs about 5-7 psf per inch of thickness and LWIC weighs about 2-1/2 to 3 psf per inch of thickness.

Thanks to JedClampett for providing correct information on this type of system.

 

[phamENG]

Nice. I see the form board now. Good info.