Spray foam on flat roof to give it some slope
Last Post 02 Oct 2015 07:48 AM by Will17109. 10 Replies.
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yetanotherjohnUser is Offline
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21 Mar 2012 10:42 PM
Our church has been having some roof leaks and the current membrane over the flat roof has it's warranty expire in July. So we are looking at different alternatives. The preferred solution is to build up a sloped roof and put on a metal roof. But this is also the most expensive solution. One alternative is to put down a spray foam over the existing flat roof in such a way as to give the roof some slope. We would then put a membrane roof on top of the spray foam. I believe the proposed spray foam is a 3lb closed cell foam. 1) Does any one have recommendations about the spray foam/membrane on top of a flat roof based on your experience? 2) How effective is the slope part of the spray foam? Does it start to sag and create pools after a while?
Ray P. SIPLOCK SystemsUser is Offline
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21 Mar 2012 11:24 PM
Spray foam is not smooth enough for membrane to be applied over it . The preferred way would be to slope the roof with a tapered EPS or ISO system then apply membrane depending on the existing roof --foam and coating may be applied . coating vary from acrylic to butyl rubber or urethane. most of these are fairly expensive .. prefer taper and TPO at least 60 mill tpo
R Parkison
www.siplocksystems.com
RGatesUser is Offline
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27 Aug 2015 08:20 AM
With the spray foam system you do not need a membrane roof on top of it. The spray foam is sprayed with a silicone based top coat material and stone granules are added to the top coat while it is wet. The top coat and stone serve to protect the foam from the sun.
chrsUser is Offline
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22 Sep 2015 06:06 PM
EPS can be ordered in special shapes like wedges as needed to do what you want. And it's a much "greener" material, avoiding the major global warming impact of the gasses used to blow bubbles in spray foam.
smartwallUser is Offline
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28 Sep 2015 08:09 AM
Eps is made from pentane, hardly green
smartwallUser is Offline
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28 Sep 2015 08:09 AM
Check out SD Carruthers, they've been doing spray foam roofs for 30 plus years. No metal needed. I drive by one of their spray foam roofs every day. I think it's 20 years old or more.
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29 Sep 2015 11:36 AM
Posted By smartwall on 28 Sep 2015 08:09 AM
Eps is made from pentane, hardly green

EPS is blown with pentane, not made from pentane.  EPS made of polystyrene created from feedstocks of ethlylene and benzene. and the density of roofing EPS is typically 1.5lb per cubic foot, and runs about R4.2/inch.

Pentane has a 100 year global warming potential about 7x that of CO2.

Sprayed polyurethane foam roofing is typically 3lb per cubic foot closed cell polyurethane created from feedstocks of polyols & isocyanates, blown with HFC245fa, and runs about R6.5/inch.

The HFC245fa blowing agent (almost universally used in North America) has a 100  year global warming potential about 1400x that of CO2.

The 3lb spray foam uses 27% more polymer per R and a blowing agent that is 2000% more damaging, so there's no question that EPS is a far greener type of insulation (and far cheaper ) type of insulation than 3lb polyurethane.

But is any foam green?

In situations like this it's not easy to design all foam out of the stackup, but opting for the lesser of evils is still a worthwhile consideration.

Polyisocyanurate is also blown with pentane, and is made from the same feedstocks as polyurethane.  Typical roofing polyiso is 2lb density, and R5.5/inch, but has performance issues at very cold temps.
Will17109User is Offline
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30 Sep 2015 08:34 PM
I thought polyiso lost R value at low temperatures because the pentane liquifies. If EPS is also blown with pentane why doesn't it also lose effectiveness in the cold?
cmkavalaUser is Offline
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30 Sep 2015 09:25 PM
Posted By Will17109 on 30 Sep 2015 08:34 PM
I thought polyiso lost R value at low temperatures because the pentane liquifies. If EPS is also blown with pentane why doesn't it also lose effectiveness in the cold?



the pentane used for EPS offgasses very quickly and is not present after a day or two
EPS actually increases in R value the colder it gets,
and does not lose value as it ages
Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br />
Dana1User is Offline
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01 Oct 2015 12:09 PM
Different isomers of pentane condense anywhere from +50F to +98F at one atmosphere of pressure, and is not the explanation for the low temp performance hit with polyiso. (Normal pentane condenses at 98F.) It's a fairly small molecule compared to HFCs and CFHCs, and leaves fairly quickly. While foil faced polyiso retains some pentane for the first year or three, it's not a big factor in it's long term R-rating. There are other gases & materials in the soup with polyiso that affect performance, including the fire retardents used, an the exact mix of stuff is tightly held proprietary information by the manufacturers.

The performance hit with temperature varies between manufacturers, but none of the current material has the long term performance stability of the stuff blown with CFHCs prior to the Montreal Protocol. The retention of the old-school now-contraband CFHCs is very long term (longer than the HFC134a in XPS or the HFC245fa in closed cell polyurethane), and a significant performance booster. CFHC blown polyiso does not have the low-temp performance issues of current polyiso.

Chris is correct that the pentane leaves EPS pretty quickly. it's more like a month or two for thicker blocks, maybe a week or two for thin board stock. Large block EPS used as runway or roadway frost heave protection is sometimes a fire-hazard on job sites, due to the continued outgassing pentane several weeks after manufacture. You have to be a bit careful how you handle and store freshly blown EPS & polyiso. But in sheets of a few inches it's almost all gone before it hits the distributors loading dock. EPS is tested & labeled at the fully depleted R-value.
Will17109User is Offline
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02 Oct 2015 07:48 AM
Thanks for explaining that. I should have known I was oversimplifying.
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