Lightweight Insulation Roof Fill note

[StrucCyclist]

Hello,

I have a question about a detail I came across in a set of Record Drawings for a structure built in 1972. The detail is attached. The detail references "LT. WT. INSUL. ROOF FILL". The roof fill is reinforced with 2" hexagonal woven mesh, which seems to essentially be chicken wire. Does anyone have a good idea of what this material may be, and approximately what it may weigh, in PSF?

Thanks.

 

[milkshakelake]

115 to 125 psf lightweight concrete.

 

[StrucCyclist]

The roof is supported by 18 gage decking with an allowable total load of 48 PSF based on the panel data I found. The purlin spacing is 12.5'-13.33', depending on the location. If it was lightweight concrete at 115 to 125 PSF, the decking would not have survived.

 

[LittleInch]

Rock wool?, fibre glass?

Is it speed to be structural?

What keeps it waterproof?

A small snap shot of one drawing won't tell anyone much....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[milkshakelake]

Sorry, that was a typo with the units. I meant 115 to 125 pcf lightweight concrete, not psf. You can find modern Vulcraft manuals for 3" roof deck + 3" lightweight conc fill. With modern notes, this gets you right around 43-44 psf self-weight only for 110 psf LW concrete. Meaning you'd still need about 10 psf superimposed dead load on top of that, and an additional 30 psf or so snow drift or live load on top of that. That hexagonal mesh to me is some kind of welded wire fabric for shrinkage.

 

[StrucCyclist]

Unfortunately, there's not much to see. The material in question is sandwiched between the metal deck below and a built up roof above. May have to request a core of the roof to get something conclusive.

I caught what you were saying though. The self-weight of 43-44 psf is still way too high for the specified decking, which leads me to believe it's a more lightwieght material. Something not concrete, but then I can't explain the wire reinforcement.

 

[Deker]

Check out this article: Link. For new construction you can specify a max weight, but for existing you may need to core some samples since the weight can range considerably. I've seen the weight limit specified to be anywhere from 30 pcf to 60 pcf.

 

[LittleInch]

Could be foamglas or PUF or perlite concrete?

https://www.perlite.org/wp-content/uploads/2018/03/perlite-concrete.pdf

That stuff has been used for decades for insulating tank bases and swimming polls and roofs

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[StrucCyclist]

Interesting read. Thanks for the link.

Seems like this is most likely what it may be. I'm going to push the client to get a sample or confirm the actual material.

 

[StrucCyclist]

All,

The client cut out a sample of the material so we could definitively measure and weigh the material. The final analysis is a unit weight of around 31.4 PCF for the lightweight fill material. Just in case anyone was wondering. I didn't get to see the actual sample, but it was described as a concrete foam.

 

[JAE]

I think one brand name used "back then" was Zonolite. Usually came in around 40-50 pcf.

 

[IRstuff]

So, roughly 8 psf, based on the 3" thickness, not counting the fill in the corrugations shown in your drawing.

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[LittleInch]

That's about 500 kg/m3 so lighter than some aerated concrete, but at the lower end for "foamed concrete".

https://en.wikipedia.org/wiki/Foam_concrete

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GC_Hopi]

Gypsum concrete was big back in the 70s and the lightweight stuff was around 35 pcf. It was typically reinforced with wire mesh. Usually it was on formboard but metal deck was used if attachment points were needed...