# Spray Foam insulation under roof decking



## Windows on Wash (Aug 30, 2011)

Open or closed does not really matter. Open will allow the water to pass through at some point whereas closed will not but that is really only helpful if you are trying to locate the leak (something that most good roofers can do from the top side).

Closed cell has a higher R-Value per inch so if you can afford the offset in cost, that is the better option.

No need for a vapor barrier in this region and the foam will that in this case anyway. Painted drywall is more than enough vapor retarder in this region.

Make sure you foamer knows what he is doing and don't go for the cheapest as a default...you will regret it. There is a bunch of suspect foamers out there that are making stuff in their garage that is untested, unproven, and crappy quality. 

Make sure you are using the right stuff.


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## federer (Aug 20, 2010)

thanks for the input. well foam is pretty expensive so i think we are going with open cell. are you a general contractor in the area?


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## shazapple (Jun 30, 2011)

Spray foam to the underside of the roof deck is not recommended. Blocking off your roofs ventilation will lead to overheating the shingles and lower shingle life span. Also, it typically voids or limits your shingle manufacturer warranty.


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## Windows on Wash (Aug 30, 2011)

shazapple said:


> Spray foam to the underside of the roof deck is not recommended. Blocking off your roofs ventilation will lead to overheating the shingles and lower shingle life span. Also, it typically voids or limits your shingle manufacturer warranty.


shazapple,

This is completely incorrect. You have been reading too many pdfs from the roofing suppliers.

Ventilation is for moisture control and has nothing to do with shingle temperature or life. Shingle manufacturers have been trying to prove this myth unsuccessfully for years.

Shingle data in Las Vegas (read...desert and extremely high radiant heat amounts) shows only about a 2 degree increase between a completely vented assembly and a closed up/unventilated assembly.

Don't quote me on the percentages but something like 98% of shingle cooling happens to the outside surface.


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## Windows on Wash (Aug 30, 2011)

federer said:


> thanks for the input. well foam is pretty expensive so i think we are going with open cell. are you a general contractor in the area?


Yes I am. Feel free to email me directly for any other questions. I can point you in the right direction.


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## Msradell (Sep 1, 2011)

shazapple said:


> Spray foam to the underside of the roof deck is not recommended. Blocking off your roofs ventilation will lead to overheating the shingles and lower shingle life span. Also, it typically voids or limits your shingle manufacturer warranty.


I definitely agree with Shingles that this is completely untrue! All recent documentation supports this position, in addition I can speak directly from experience. Part of my home has a very low pitch roof and the rest a very high pitch. The low pitch has closed cell foam sprayed directly on the roof deck and the other section has 18" of blown in fiberglass (the two areas are completely independent). The shingles in both sections look exactly the same and neither has deteriorated different from the other.

Another advantage of the foam on the roof deck is that it's much easier to work in your attic because the temperature control is better and you're not constantly getting insulation on yourself.


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## AGWhitehouse (Jul 1, 2011)

shazapple said:


> Spray foam to the underside of the roof deck is not recommended. Blocking off your roofs ventilation will lead to overheating the shingles and lower shingle life span. Also, it typically voids or limits your shingle manufacturer warranty.


Me three...ventilation is for heat & moisture control, though mainly moisture...not shingle life. If "rubberized" material needed ventilation for longevity then flat roofs would require it too and not just sit right on the insulation boads.


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## federer (Aug 20, 2010)

thanks for the input guys. it is also my understanding that the insulation against roof deck would be ok for the shingles. in fact my roof is flat on one side and sloped on the other half. also, the attic itself is actually the upstairs space, so we have closed off all the soffit vents to prevent any ventilation with the closed roof system (i forget what it's called). essentially the entire house becomes part of the conditioned space, including the attic space, thus not requiring any ventilation.


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## federer (Aug 20, 2010)

so here is the proposal from the contractor: what do you guys think?

Attic
Icynene foam 5.5" 

Gable Wall
Icynene foam 3.5" 
Flameseal thermal barrier


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## Windows on Wash (Aug 30, 2011)

How much per sq/ft is he asking for?

I would prefer to have more on the roof deck where I can get it but if you have 2x6 construction, that is as much spray foam as you can get up there.

Maybe a layer of rigid foam to break up the thermal bridging of the studs.


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## Msradell (Sep 1, 2011)

My first question is what type of Icynene foam is he going to use? They vary from R-3.7 to >R-6.0 and obviously that would make a considerable difference in your project.


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## HomeSealed (Jan 3, 2008)

I'm late to the party, but I'd also agree with the "shingle-life" argument being bunk... In fact, the larger shingle manufacturers seem to be backing off a bit on that.


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## federer (Aug 20, 2010)

Msradell said:


> My first question is what type of Icynene foam is he going to use? They vary from R-3.7 to >R-6.0 and obviously that would make a considerable difference in your project.


you know i am not sure they specified. i assumed icynene is just open cell. i didint know there were different R values for icynene. i will try and find out! thanks


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## Windows on Wash (Aug 30, 2011)

Anything near R-6 is going to be closed cell.


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## shazapple (Jun 30, 2011)

I would like to see the Las Vegas shingle study you mentioned. Moving air is very poor at holding heat, where insulation is very good, so I can't see how the shingle temperature difference is minimal. 

Have any of you ever seen a ventilated flat roof? They last forever; Up to 50 years where you would be lucky to get 30 out of most insulated build up roofs. They don't have the expansion and contraction problems due to heat (because they're ventilated!). Trying to compare a built up roof to a shingle roof is ridiculous. I have also seen plenty of insulated sloped decks with no ventilation under the shingles. They don't last year as long as they should. 

Whatever science you choose to ignore, you can't ignore the manufacturers warranties that specifically state that a lack of ventilation will limit or void your warranty. Certainteed is the only exception (as long as you use their fiberglass shingles)


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## AGWhitehouse (Jul 1, 2011)

shazapple said:


> Have any of you ever seen a ventilated flat roof? They last forever; Up to 50 years where you would be lucky to get 30 out of most insulated build up roofs. They don't have the expansion and contraction problems due to heat (because they're ventilated!).


Been in the Architectural field for 11 years and have never seen a ventilated flat roof. Could you provide me with an example of one? Also, 50 years out a membrane roof sounds like a fairy tale, ventilated or not. The real failure of membranes isn't due to the heat, but rather the UV degredation. Hence the common practice of reflective coatings.



shazapple said:


> Whatever science you choose to ignore, you can't ignore the manufacturers warranties that specifically state that a lack of ventilation will limit or void your warranty. Certainteed is the only exception (as long as you use their fiberglass shingles)


It's not that we are ignoring anything, but I have no documentation that says it affects warranty. Could you provide me with a warranty document that says so? I was in contact with a roofing manufacturer not but a month ago and asked if they had a "hot roof" requirements or concerns. They said they had none.


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## shazapple (Jun 30, 2011)

AGWhitehouse said:


> Been in the Architectural field for 11 years and have never seen a ventilated flat roof. Could you provide me with an example of one? Also, 50 years out a membrane roof sounds like a fairy tale, ventilated or not. The real failure of membranes isn't due to the heat, but rather the UV degredation. Hence the common practice of reflective coatings.


I can, I'll find a couple drawings and photos later. The 50 year claim does seem ridiculous but a lot of large buildings jn my area (schools, offices) in the 50's and 60's were built with this attic space. 




> It's not that we are ignoring anything, but I have no documentation that says it affects warranty. Could you provide me with a warranty document that says so? I was in contact with a roofing manufacturer not but a month ago and asked if they had a "hot roof" requirements or concerns. They said they had none.


http://www.iko.com/warranties/
12. Any damage or distortion caused by inadequate ventilation either at the eaves or on the rooftop of the building. This includes failure of ventilation caused by blocked, non operative or defective vents or any other condition that renders the ventilation system ineffective. Roof system ventilation should meet local building code standards for total vent area. Ventilation must also be distributed evenly between the rooftop and the eaves of the building;

http://www.bpcan.com/documentation-and-tutorials.aspx
(b) the roof and each part of it must be designed and built in accordance with the applicable local and National Building Codes. All roof structures must be provided with thorough ventilation and the deck over which the shingles are installed must meet minimum building code requirements. Where local building codes have specific requirements which differ from National Building Codes, the more stringent requirement must be followed.

http://www.certainteed.com/resource/roofing/warranties
This is the only warranty that says you can use fiberglass shingles without ventilation. Using asphalt shingles gives you a reduced warranty period.

http://www.powerhrg.com/_files/files/Roof_Warranty.pdf GAF-ELK
Goes into less detail than the rest, but says warranty does not apply if there is "inadequate attic ventilation"


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## federer (Aug 20, 2010)

so they are using open cell at about 3.5R per inch. we decided since we need about R38 in our region we are bumping it up to 8inches of foam. it's open cell so no need to go over in separate layers. what do you guys think?


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## Msradell (Sep 1, 2011)

You are still only going to get R-28. It's going to take 11 inches of open cell to achieve R-38!


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## shazapple (Jun 30, 2011)

Heres an example. This building was built in 1952, and the original membrane was replaced with modbit in 1993. No insulation between the membrane and deck (or in the attic space for that matter). 

Lots of slope to the drain, and very little deterioration in the membrane considering it is 18 years old 








Roof hatch opens up into the attic space, and then into the conditioned space.








There was another we retrofitted to a BUR this year, because someone previously had stuffed insulation into the attic space and blocked the ventilation. Also, the vapour barrier was in very poor condition so they were having water problems from condensation. We removed the insulation (installing a new VB would have been impossible), blocked off and insulated the vents, and insulated on top of the roof.


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## federer (Aug 20, 2010)

so this roof had no insulation but was ventilated?


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## federer (Aug 20, 2010)

Msradell said:


> You are still only going to get R-28. It's going to take 11 inches of open cell to achieve R-38!


well i guess thats what we have to settle for =/


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## shazapple (Jun 30, 2011)

federer said:


> so this roof had no insulation but was ventilated?


Yes, goes to show what was actually important! Insulation was not as big of a deal back then as it is today. Many large buildings I deal with don't have any insulation. Most flat roofs are lucky to have 2".


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## AGWhitehouse (Jul 1, 2011)

So you found a random roof that has no insulation at all. Do you know of any flat roofs that have insulation and are ventilated? I've been asking colleagues and builders and no one has heard of what you claim. The best I heard was a BUR that lasted almost 40 years, but was repaired yearly for the last 10 years of it's life. So I would consider that a 30 year roof...20 years shy...

I'll retire from the topic...good day


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## federer (Aug 20, 2010)

AGWhitehouse said:


> So you found a random roof that has no insulation at all. Do you know of any flat roofs that have insulation and are ventilated? I've been asking colleagues and builders and no one has heard of what you claim. The best I heard was a BUR that lasted almost 40 years, but was repaired yearly for the last 10 years of it's life. So I would consider that a 30 year roof...20 years shy...
> 
> I'll retire from the topic...good day


i have to say when we re did the flat roof we decided to make it un ventilated. now we are putting in insulation in. so i agree with your point here.


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## federer (Aug 20, 2010)

well so it's finally done!!! been very very crazy last couple weeks trying to get everything ready for the foam guys. the demo process was brutal. i will try to post some pics tonight for those curious how it looks


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## Mike in Arkansas (Dec 29, 2008)

waiting......


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## federer (Aug 20, 2010)

heres a couple


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## federer (Aug 20, 2010)




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## federer (Aug 20, 2010)




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