# Foam insulation blown on bottom of roof sheathing



## Teetorbilt (Feb 12, 2004)

Grumpy, 3 of the roofers that I have talked to are pushing a radiant barrier film directly under the shingles. At what temp. do shingles melt? To my way of thinking this will concentrate all of the thermal energy in the shingles.
Obviously heat is our major concern here, I have yet to see an ice dam. I know of people who have added the barrier under the trusses/rafters but now the fox is already in the henhouse. Comments?


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## Grumpy (Oct 8, 2003)

LOL melting nothing!

I think we can both agree asphalt will dry out as the oils in the asphalt evaporate. Prolongued exposure to heat will cause the oils to dry out quicker.

Non-ventilation of attic space super heats shingles because hot air builds in the attic space. Super heated shgingles will last half as long as intended. Let us ask ourselves, will insulating the underside of the roof deck block that heat from reaching the shingles? Or will insulating the underside of the roof deck block air from cooling the shingles?

Teetor what is a radiant barrier film? That's a new term to me. I know you may not see ice damns down by you, but it's a major concern up by me. 

Yes Ice shield helps block ice damns from getting in the house, but I'd rather an ice damn not occur in the first palce. That's like saying a bullet proof vest will block bullets from entering your body but personally I'd prefer not to be shot!


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## Teetorbilt (Feb 12, 2004)

Radiant barriers reflect heat in the same manner as a mirror reflects light.
You know the pans that go under a conventional element on a cooktop, commonly refered to as 'drip pans'? In the industry they are called reflector pans. The idea is to reflect the energy released from the bottom of the coil back up thus increasing efficiency. 
Radiant barriers work in the same manner, to reflect the heat back where it came from. Thus the question about the melting point of shingles. Most radiant barriers claim to reflect 90+% of the heat. If that barrier happens to be directly under the shingles, they are taking a thermal whuppin'.


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## AaronB. (Oct 6, 2004)

What is this thermal reflector made of? If it is one of those shiny things, they reflect light, not heat. These shiny things cut down on heat because they reflect the light that is turned into heat when light is absorbed into anything. 

The shingles would have already absorbed this light and the light-to-heat physical reaction would have already taken place when the light hit the shingles. The ventilation would come into play in this scenario because this heat would be radiated to the attic air and taken away by the ventliation system. Now we are getting somewhere. What's next?

So, you might, could, possibly end up baking the shingles more quickly because of the lack of air flow to carry radiantly transferred heat from the underside of the roof deck. So the heat builds up within the roof assembly on top of the foam insulation....in winter, the melt MUST occur from the topside and not refreeze over the unheated eave since the entire roof would be the same temperature, eliminating ice damming, as Tom Beck said in another post.

Condensation on the underside of the roof deck would not be a problem, as the foam is impregnible to water if installed correctly, and sure stiffens a house from movement forces. 

I suddenly think you would not want to spray the foam over the building envelope so as not to risk moisture build up on the inside of said envelope. Heavy duty interior ventilation would be needed or have HVAC running all the time to remove it. 

Maybe, then we should have open ceilings, no attics, and a direct climate ventilation system at the ridge...................Im going way out now, LOL


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## Teetorbilt (Feb 12, 2004)

Aaron, back to physics class. Heat is energy that is radiated, cold is a lack of energy that absorbs heat. Those 'shiny things' reflect heat wavelengths not lightwaves which is a very short spectrum.
As for the rest, did we score some good crippie tonight?


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## AaronB. (Oct 6, 2004)

Ahhh, but even in the cold, there is still heat. Absolute zero (the lack of all movement) is way below zero F. 

I get to thinking now and then.....


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## AaronB. (Oct 6, 2004)

isn't it like -273F? 0 K?


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## Teetorbilt (Feb 12, 2004)

Absolute zero is -460 F. And that's F'in cold.


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## AaronB. (Oct 6, 2004)

wow thats cold.


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## AaronB. (Oct 6, 2004)

so what is -273? Anything related to what were talking about?


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## PipeGuy (Oct 8, 2004)

So beer served at 494 F above 0 Kelvin is OK then?


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## AaronB. (Oct 6, 2004)

That is the perfect beer serving temperature.


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## Teetorbilt (Feb 12, 2004)

Absolute 0 is also -273.15 deg. C


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## PipeGuy (Oct 8, 2004)

Teetorbilt said:


> Absolute 0 is also -273.15 deg. C


Is Kelvin a scale or just a molecular state? If zero Kelvin = absolute zero, is there a 100 Kelvin? If so, what is its celsius equivalent?


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## metalroofer (Mar 2, 2005)

Had just this same talk with a customer who INSISTED that he get his insulation sprayed on. That was 6 weeks ago. The local inspector is looking at this with a fish eye and obviously doesn't like it one bit. We would have to agree as the answers from the people selling this seem to have a lot of smelly fine print to sort thru. So the fight continues as inspector asks for engineering report after report.


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## jmorgan (Jan 31, 2004)

I stumbled on a strange job the other day. A home built with composite foam panels. (7/16 OSB, 8-10"EPS,another 7/16) See the photo. They are going to use it as a roof deck too. I reminded the builder that the insulation board mfr's changed the "old" nail-base board to include shims between the iso board and the OSB for venting because they were sued because of voided warranties from the shingle mfr's. Right?
Jim


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## Teetorbilt (Feb 12, 2004)

I somehow dropped this post. 
Pipe, Kelvin is the same gradient as Celcius, just different starting points. You can figure it out.

Board panels are much different than sprayed foam and foam is in two varieties, open cell and closed cell. Panels allow moisture to get trapped between them. Open cell foam allows the transmission of moisture. Closed cell foam seals everything.
Shingle manufactures are working hard to get up to speed with the new housing but are, generally, not the lead dogs. Everything still smells pretty much the same to them.


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## TomHay (Nov 21, 2003)

:no:Seems a lot on this thread were mistaken:no:

http://www.certainteed.com/NR/rdonlyres/D74FFBDA-10FF-4635-9969-78885E93B0F6/0/TBR201b.pdf

Elk, which is GAF is the same

Tom Hay
http://soythane.com/


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## Sportbilly (Oct 4, 2006)

I'm with Teetor. Visible light, infra-red radiation (heat) and UV are all part of the same spectrum, and are all reflected by a shiny surface. Same reason toasters and pots and pans are usually shiny, keeps the heat in.

So yes, the shingles will absorb the radiation of all wavelengths, then re-radiate a portion of them them both from the bottom (towards the attic), and from the top (back into the outside air). A radiant barrier would reflect that energy that was headed downwards back up into the shingles, giving them another dose of heat.

I always thought that an air gap was recommended for such radiant barriers, in order to evacuate as much of that energy as possible before it hits the outside surface again. If so, the radiant barrier would prevent radiant heat infiltration, and the air gap would let it escape to the outside without degrading the shingles, or siding, depending on application.

One degree is exactly equal to one Kelvin. Kelvin scale starts at absolute zero, Celsius starts at the freezing point of water, thus 0 K = -273C, 273 K = 0 C


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## TomHay (Nov 21, 2003)

:no:What it boild down to is @ 90 Degrees with sun shining the attic will be 200 Degrees, with the foam it will be 85 degrees.

Tom
http://soythane.com/


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## MEL (Apr 7, 2007)

*It's becoming more common but I don't like it*

I recently did a roof job and the customer said she was getting estimates for insulation.

She said they all wanted to spray foam on the underside of the roof deck and they wanted to make the attic air tight.

That doesn’t make sense to me because ventilation lets excess humidity out of the home.

Also the air inside the attic is going to get hot and radiate heat into the home. You would be better off insulating the ceiling instead of the roof.


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## dlcj (Oct 1, 2007)

The first time i saw the foam being sprayed on the bottom of the roof decking i thought, thats kind of dumb, now you have to heat and cool the attic too! I just dismissed it as that particular installers idea and hoped not everybody done it that way. I guess they do. On larger homes with high pitch roofs the cubic feet of attic air space can be as much or more than the house interior! How can it be more effiecent to heat and cool that too. The owner of A house we built last year wanted to have his sprayed but the hvac guy talked him out of it saying it would be an additional $6k for the fresh air exchanger needed in such a tight house. He claimed a lot of people were getting sick from too tight of house.


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## Ed the Roofer (Dec 12, 2006)

There is a lot of Buiding Science headed in that direction.

Google "Unventilated Roof Assemblies" or check out http://www.buildingscienceconsulting.com/index.html

It may be a good "Niche Marketing" add on to consider implementing.

Ed


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## neolitic (Apr 20, 2006)

Ed the Roofer said:


> There is a lot of Buiding Science headed in that direction.
> 
> Google "Unventilated Roof Assemblies" or check out www.BuildingScience.org
> 
> Ed


Ed, The link is just advertising.
Do you know where Building Science went?



dlcj said:


> The owner of A house we built last year wanted to have his sprayed but the hvac guy talked him out of it saying it would be an additional $6k for the fresh air exchanger needed in such a tight house. He claimed a lot of people were getting sick from too tight of house.


I agree with your guy!
It has to be the whole "system", insulation
ventilation, air to air exchangers....
Just spraying foam can only lead to trouble.:whistling


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## Ed the Roofer (Dec 12, 2006)

I typed it in from the top of my head. I thought it was a Dot Org address.

Sorry for the error.

Try this instead:

http://www.buildingscienceconsulting.com/index.html

Here is the Unventilated Link:

http://www.buildingscience.com/documents/digests/bsd-115-wood-pitched-roof-construction/

Other links on this page:

http://www.google.com/search?hl=en&...nventilated+Roof+Assemblies,+building+science

Another source for good reading material:

http://www.nachi.org/forum/showthread.php?t=14367

Thermal degradion of framing mebers article:

http://scitation.aip.org/getabs/ser...00008000004000203000001&idtype=cvips&gifs=yes


Ed


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## neolitic (Apr 20, 2006)

Thanks Ed.:notworthy


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## dhall (Nov 7, 2007)

It is obvious why houses are hard to heat economically, leak air like a sieve and in general are built the same way they have been build for years. Because people (builders and customers) don't take the time to learn how to do it right. Combined with manufacturers and inspectors who are more concerned about covering their butts with new theories and products. As far as shingles go, stop and think about why you ventilate the attic. Is it to keep the plywood cool under the shingles or is it to vent hot air out from above the living space? I would contend, and studies and mfg thinking (see the above post concerning Certainteed) is that it is to vent hot air to help house cooling. As far as venting the attic in the winter, I can not tell you how many energy audits we have done only to find some problem with the seal between the attic house and the attic, either gaps allowing conditioned air directly into the attic, ductwork in unconditioned space without proper insulation or my favorite, ductwork that was stepped on or somehow left open to the attic space and blowing conditioned air into the attic.

Somewhere builders in this country have got to stop and understand exactly how the building envelope works and how to properly build a house that does'nt break the bank to heat and cool.

Having said all of that what is my opinion on the question posted. Foam the bottom of the roof and make sure you do it right and hit everthing that has to be done. Then make sure that you have properly sealed all of the penetrations from the house to the attic. Once you have sealed up the house install an air exchanger and watch your customer's joy at the first heat bill.

Don't forget that once people realize that the price of gas is nothing compared to what the price of heating their house this winter. The nice thing is that the average house, with an energy audit and some simple projects by the homeowner can save 20-30% of the energy bill.

I would suggest that every builder and remodeler hook up with someone who can do energy audits for them and either learn what it takes to build or retrofit an energy efficient house or addition or find someone they trust to guide them. And then when it comes time, make an intelligent decision and take a gamble.

I spent quite a bit of time studying the building envelope and when we decided to foam our projects I took a gamble and went ahead and did it even though the manufacturer couldn't decide if it was right or not. And when we started using SIPs panels and we were faced with the same question on the shingles we went ahead and put them on. What we also did however was go back and look at them every now and then and we find no indication of anything other than normal wear and tear. And our customers have had the benefit of energy efficient homes and low utility bills.

So in the end, while it is nice to shove all the risk of product use off on someone else such as the mfg sometimes it pays to learn what you can about a product or process and then take a gamble on what you learn.

Especially now with housing in the tank, there is going to be a huge market for builders and remodelers that are well versed in how to build a energy efficient, reasonably priced structure.

So to answer the original post, ask questions, take time to learn how the envelope works and then take a gamble and do it the way that makes the most sense. Just understand why you are doing it. Not because that is the way it has always been done.


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## orson (Nov 23, 2007)

*If you didn't like science class skip this post...*

Just a little clarification about heat:

There are three mechanisms for the flow of heat- conduction, convection, and radiation.

Conduction- transfer of heat through connected materials from hotter to cooler

Convection- transfer of heat by moving particles (think air or water)

Radiation- transfer of energy via electromagnetic waves (think sunlight or campfire) 

Additional facts: 
Radiant heat does not pass through solid objects, it only moves through air and vacuums. 
R-Values account for all 3 types of heat transfer(but only in a specific standardized test). 
Radiant barriers reduce the amount of heat that moves across an air space that is adjacent to the radiant barrier.

Radiant Barriers:

Materials have an emissivity rating and reflectivity rating. 

These values are between 0 and 1, and add up to 1

A material that has a reflectivity value of .95 (and emissivity of .05) is said to be 95% reflective.

A material must have a reflectivity of .90/90% or more and an emissivity of .10/10% or less to be considered "refelective" (and must face an open air space to perform properly).

Again, radiant barriers must be adjacent to an air space to work.


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## scottsanders250 (Jan 6, 2008)

I'm sorry to revive this post from a month ago, but there are a number of things in it that I think need clarification in case someone else happens to come across it in a search.

Unvented attic assemblies/conditioned attics/hot roofs are allowed by the 2006 IRC and detailed in the 2007 Supplement to the IRC provided that they are constructed in a specific way.

CertainTeed and ELK/GAF allow unvented attic assemblies under their shingles provided they are properly constructed. Other roofing manufacturers are simply behind the 8-ball in terms of keeping up with research and building science.

Unvented attics do not have significantly higher shingle or sheathing temperatures than vented attic assemblies and shingle color makes more of a difference than venting or not. Other posters have referenced the Building Science site and other case studies can be found on Google (Google "FSEC-CR-1496-05", 1st link).

The main purpose of attic ventilation is not to dissipate heat but to dissipate any moisture that gets into the attic and prevent it from condensing on the underside of the roof deck or the rafters. I am not saying that ventilation doesn't dissipate heat, it does to some extent, but the main purpose is to control moisture. 

Other posters are correct that a house insulated with spray foam needs mechanical ventilation because it is so tight and air infiltration is so low. Other posters have also pointed out that you are bringing the attic into the conditioned space of the house, which is a good thing if you have HVAC equipment or ducts in the attic area. If you do not, then conditioning the attic may be less beneficial.

Unvented attics need to be part of a whole house strategy and should not be done without thinking how it will affect the rest of the building envelope and its occupants. On top of that, there are considerations for closed cell versus open cell foam, vapor retarders, and effective r-values that need to be accounted for. So if your insulator or roofer is trying to persuade you to use spray foam without asking about your HVAC system, occupant load, shingle manufacturer, etc, you should probably be careful.


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## rodeo (Jan 4, 2008)

del


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## monticellohomes (Mar 19, 2008)

I had gotten work from CertainTeed as well that they were standing behind their warranty with sprayfoam.

What is the rate conditioned air needs to make it to the attic when it is part of the building envelope? I know for a conditioned crawlspace it is 1 CFm/50sft.

I am getting ready to start an energystar home with foam and want to cover my bases.


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## neolitic (Apr 20, 2006)

monticellohomes said:


> I had gotten work from CertainTeed as well that they were standing behind their warranty with sprayfoam.
> 
> What is the rate conditioned air needs to make it to the attic when it is part of the building envelope? I know for a conditioned crawlspace it is 1 CFm/50sft.
> 
> I am getting ready to start an energystar home with foam and want to cover my bases.


I know it's painful to hear, but
you need to do your home work!
There are plenty of links above
to get you started.
You *can't* just pick and choose 
which parts you want to do, it's
a system.
The *house* becomes a system.
It is not a no brainer.
Reread the thread. :thumbsup:


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## monticellohomes (Mar 19, 2008)

Im not sure what homework you're referring to.


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## monticellohomes (Mar 19, 2008)

Dhall - Have any suggested reading on the housing envelope?


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## neolitic (Apr 20, 2006)

monticellohomes said:


> Dhall - Have any suggested reading on the housing envelope?





Ed the Roofer said:


> I typed it in from the top of my head. I thought it was a Dot Org address.
> 
> Sorry for the error.
> 
> ...


You might start here.


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## monticellohomes (Mar 19, 2008)

Thanks. Ill take a look.

Neolitic: You said you can't pick or choose....How did it sound like I'm "picking and choosing" what parts I'm doing or not?


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## neolitic (Apr 20, 2006)

monticellohomes said:


> Thanks. Ill take a look.
> 
> Neolitic: You said you can't pick or choose....How did it sound like I'm "picking and choosing" what parts I'm doing or not?





monticellohomes said:


> I had gotten work from CertainTeed as well that they were standing behind their warranty with sprayfoam.
> 
> What is the rate conditioned air needs to make it to the attic when it is part of the building envelope? I know for a conditioned crawlspace it is 1 CFm/50sft.
> 
> I am getting ready to start an energystar home with foam and want to cover my bases.


That part sounded like a short cut version.
Sorry if it wasn't, I'm kind of running 
a short fuse today.
Lot's of guys try it without the whole house 
ventilation system, tying in range hoods, 
bath fans, etc.
Which leads you to an air-to-air heat exchanger......
Getting it right is complicated, and expensive.
Which is why, if done right, the savings 
turn out to be pretty long term.


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## monticellohomes (Mar 19, 2008)

So with the whole house ventilation system all those items are tied together? I guess I'm not following.

My question earlier was about the introduction of conditioned air into this ventless attic space. I have seen some systems about conditioned crawlspaces and part of the system you have to introduce conditioned air at that rate and either provide a source of return or an exhaust out of the home if I remember correctly. I was wondering how this is in the attic? Am I to introduce conditioned air to the attic? There should be few opportunities for leakage from the living area because of drywall taping and mudding.


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## neolitic (Apr 20, 2006)

monticellohomes said:


> So with the whole house ventilation system all those items are tied together? I guess I'm not following.
> 
> My question earlier was about the introduction of conditioned air into this ventless attic space. I have seen some systems about conditioned crawlspaces and part of the system you have to introduce conditioned air at that rate and either provide a source of return or an exhaust out of the home if I remember correctly. I was wondering how this is in the attic? Am I to introduce conditioned air to the attic? There should be few opportunities for leakage from the living area because of drywall taping and mudding.


It isn't that simple.
You really need to study this
in depth.
There is very real potential
to create a nightmare.
This deal can be great, or
it can make the whole deal with the
mold/mildew lawsuits look like
a weekend in the park.
It really requires a studied approach
to the whole house.


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## monticellohomes (Mar 19, 2008)

Neolitic, you're confusing me. What isn't that simple? I am trying to look at the whole house.


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## neolitic (Apr 20, 2006)

okay


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## tersh (Jul 19, 2004)

*how valuable is the warranty on roof shingles?*

Interesting thread.
I've been wishing that the foam solution would/could work. When you guys keep saying "voids the warranty", are you saying that manufacturers have replaced significant installations for you or anyone you know?. In other words, even if the manufacturers have to "cover their ass" by voiding the warranty, if their shingles have always performed fine, maybe that's all we get , anyway?
I think that when paint manufactureres guarantee their paint for years and years, the warranty is pretty worthless, since the main cost of the job is the labor to apply ; is this true for roofing , too?
BTW one of my customers says many houses around her that were painted after I did hers ( 8 years ago) have peeled- are all these people going to the paint companies and demanding new paint job ? I don't think so- the prep is the important thing ( slow penetrating oil primer)
thanks
Tersh


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## apehangeralfy (Oct 26, 2008)

We did one for an HVAC contractor that we worked around for many years and on many projects. 9/12 2 story cut up on the river in South Daytona. 5/8 plywood that was sprayed with foam as well as the trusses, walls ceilings and everywhere else they could find a place to spray the stuff. We used a fully adhered underlayment and an Elk 50 yr arch shingle. Only penetrations were plumbing. All .032 aluminum flashing set in MB. Shingles were all 6 nailed with 1.25" stainless and the hip and ridge was double nailed with 1.75" stainless. It will take a sever hurricane to take this roof off but I can assure you that I do not want to be the one tearing it off when it comes time, that will be 85 square of misery... but the customer loves it, it's been five years now and it still looks brand new... 

We also have done quite a few with fully adhered underlayment and tile without any issues, the foam adds to uplift. It is the way of the future, I am seeing it more and more on the very high end jobs to the point the it is almost common now....


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## OverUnity (Jun 15, 2009)

*Some thoughts on the physics...*

The primary reason for ventilating under a roof is to prevent warm attic air from melting snow and creating ice dams and icicles, not to protect shingles from excessive heat. Being directly exposed to incident sunlight is the main heat source for shingles, not secondary accumulated heat beneath them, which is why shingle color is a far more important factor for how hot the shingles will get. And to the extent that accumulated attic heat is a problem for shingles, insulating beneath them is also a cure. Foaming directly under the roof sheathing both prevents heat from migrating from the shingles into the attic or living space, and also prevents heat from in the attic or living space from escaping to the roof. 

Furthermore, by having spray foam in the rafter cavity, the dew point is inside of the closed-cell foam, where moisture cannot possibly be a problem since closed-cell foam is air-tight. This prevents condensation on any surface inside or outside. Condensation is another major problem in attics, and it is completely solved by foaming the roof. 

And one additional benefit is that any HVAC equipment or ducts inside the attic are now inside the envelope and thus are not subject to excessive heat and leaks are less of a problem between the attic and the living space below. Consider that there are generally far more openings between the living space and the attic than through the roof. Even though there is now more conditioned space to worry about heating and cooling, the massive efficiencies gained through a tighter envelope mean that the total system size can be decreased rather than increased to account for it. 

On the topic of radiant barriers under the sheathing... when they are attached to the sheathing and insulation is directly attached below, they serve no purpose at all. Radiant barriers are very conductive, so when they touch surfaces on both sides, they merely conduct the heat readily. They only work when one side or both are exposed to air. When they are attached to the sheathing with air space under them, they don't reflect energy but rather keep it from being emitted into the space below. When the air space is between the roof and radiant barrier, they reflect heat back up through the roof. Being a relatively thin, flat surface, the roof easily cools itself to the exterior, so there is no "build-up" of heat from this.

When the roof is foamed and the attic becomes a part of the envelope, then it does need to be ventilated to the living space in order to prevent excessive moisture from building up. Even though the surfaces will not be below the dew point, excessive humidity will promote mold growth otherwise.


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## MEL (Apr 7, 2007)

What happens to an insulated roof deck it when to comes time to replace the shingles and bad wood is found? 

The insulation will be damaged when the decking is removed.

If there are any gaps in the insulation moisture will migrate into that area and rot the wood.

Most of the people promoting this are dealing in theory not reality.

I inspected one of these insulation jobs on a bungalow style roof. It was not air tight at the point where the slanted ceiling starts directly above the kneewall. This will allow humidity into the unvented area.

The whole thing is a bad idea.

After my consultation the person I did the inspection came to the conclusion that the entire deck and insulation should be removed.


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## perperp (Aug 11, 2009)

OverUnity said:


> Furthermore, by having spray foam in the rafter cavity, the dew point is inside of the closed-cell foam, where moisture cannot possibly be a problem since closed-cell foam is air-tight. This prevents condensation on any surface inside or outside. Condensation is another major problem in attics, and it is completely solved by foaming the roof.


This is not my area of expertise but there seems to be a glaring problem with this scenario. Kind of restating what MEL said above - let's say a tree branch / raccoons / mice / caulk or flashing failure/ (name your favorite issue here) damages the exterior roof envelope. If you have closed cell foam directly under the decking, how long before the average homeowner would detect a problem and where does the exterior moisture flow in the interim?

I realize there isn't a consensus on this but this is the first recommendation I've seen for using closed cell foam in a rafter space.


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## SLSTech (Sep 13, 2008)

perperp said:


> This is not my area of expertise but there seems to be a glaring problem with this scenario. Kind of restating what MEL said above - let's say a tree branch / raccoons / mice / caulk or flashing failure/ (name your favorite issue here) damages the exterior roof envelope. If you have closed cell foam directly under the decking, how long before the average homeowner would detect a problem and where does the exterior moisture flow in the interim?
> 
> I realize there isn't a consensus on this but this is the first recommendation I've seen for using closed cell foam in a rafter space.


I didn't bother reading the whole thread seeing it is a 2005 post - but I will start with your last paragraph first, Closed Cell sprayed on the bottom of the sheathing has been code tested & approved by some manufacturers - I prefer Demilic

This is not new & has been done countless times. I have one that is over a year & half old now - shingles look just like they did when they were installed, no excess humidity, no mold, no other issues. (Yes the place has an ERV & the bath fans to help with the humidity & stale air issues.

Onto the first paragraph - Icenyne will love you (that is there favorite argument) for why you should install their Open Cell product which they don't even bother getting tested because #1 marketing sells & #2 it would never pass the test w/o modifications. (i.e. a vapor barrier spray would have to be installed which would eliminate one of their favorite selling points)

Non Issue personally - #1 water flows downhill
#2 if the sheathing needs to be replaced - you get the insulation fixed
#3 how many roofs that needed sheathing replacement did the owner actually now about when it happened, 1/2 the time the roofer has to show them after it is stripped or when they are walking on it
#4 assuming the owner knew he needed sheathing replaced as soon as it happened - that means he is probably getting his drywall & regular insulation replaced to as it was catostrophic


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## roomrenovators (Sep 20, 2007)

You know I hear both sides of this argument and they sound good....The insulation wont cause heat transfer blah blah blah and the Shingles will be toast because of the lack of ventilation .........I say someone with a Lab test this out and accelerate it by 20 years to really see what happens then we have scientific proof........


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## SLSTech (Sep 13, 2008)

roomrenovators said:


> You know I hear both sides of this argument and they sound good....The insulation wont cause heat transfer blah blah blah and the Shingles will be toast because of the lack of ventilation .........I say someone with a Lab test this out and accelerate it by 20 years to really see what happens then we have scientific proof........


They have - one said 2 weeks loss of life, 1 went for 10% - reality is probably somewhere in between & I would lean more towards the lesser number in most climates, especially if there is a lot of clouds, trees, etc...

Here's the one with the 10% 
http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

If your really worried about it - go with a concrete tile roof, best of all worlds


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## roomrenovators (Sep 20, 2007)

god no! concrete tile here in the south?? no way these people barely wanna pay for 25 yr 3 tabs.........they do love metal roofing though and will put it on anything even if it looks like crap!!!


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## AaronB. (Oct 6, 2004)

Ok, after all of this, I can still install spray foam in your attic, or as the most viable stand alone, longest lasting, and seamless roofing system available.


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## OverUnity (Jun 15, 2009)

perperp said:


> let's say a tree branch / raccoons / mice / caulk or flashing failure/ (name your favorite issue here) damages the exterior roof envelope. If you have closed cell foam directly under the decking, how long before the average homeowner would detect a problem and where does the exterior moisture flow in the interim?


I've never seen mice or racoons eat through asphalt. But if they did, or any other scenario that you list, then the closed-cell foam is waterproof, so it's like an extra layer of flashing underneath. Perhaps in 10 years, you might have a rotted patch of sheathing, however the closed-cell foam is structurally supportive, so the entire wood layer could completely rot out or be eaten by termites and your roof would still be sound. This is the same material that amusement parks use to create fake boulders for their water rides. The shingles are almost superfluous.

Also, if this question is supposed to elicit doubt about using this insulation method, then what would be the result if a different method were used? If you had fiberglass, then a hole in the roof means ruined insulation and drywall and a majorly expensive repair. If you put an air gap and then spray foam, then it's not really much different of a scenario than with spray foam all the way to the deck. The sheathing will still get water damage and the homeowner still would be no more aware of the issue. But in that case, the roof deck may actually lose structural integrity and fall in since it doesn't have that waterproof support below.


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## perperp (Aug 11, 2009)

OverUnity said:


> I've never seen mice or racoons eat through asphalt. But if they did, or any other scenario that you list, then the closed-cell foam is waterproof, so it's like an extra layer of flashing underneath. Perhaps in 10 years, you might have a rotted patch of sheathing, however the closed-cell foam is structurally supportive, so the entire wood layer could completely rot out or be eaten by termites and your roof would still be sound. This is the same material that amusement parks use to create fake boulders for their water rides. The shingles are almost superfluous.
> 
> Also, if this question is supposed to elicit doubt about using this insulation method, then what would be the result if a different method were used? If you had fiberglass, then a hole in the roof means ruined insulation and drywall and a majorly expensive repair. If you put an air gap and then spray foam, then it's not really much different of a scenario than with spray foam all the way to the deck. The sheathing will still get water damage and the homeowner still would be no more aware of the issue. But in that case, the roof deck may actually lose structural integrity and fall in since it doesn't have that waterproof support below.


I think we are going to need to agree to disagree. Reading between the lines here -- I suspect you've never installed a roof or repaired damage caused by a leaking one.

If this system works for you, I say great. The last thing I want in my life is long term undetected damage to my exterior roof membrane and no place for the water to go except direct contact with the now exposed wood underlayment and the adjoining framing members.


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## echase (Dec 18, 2009)

What happens if the roof gets a leak? 

Doesn't this spray foam make a watertight seal? Wouldn't any moisture from a leak (or driven rain) be trapped in an envelope between the shingles and the insulation, leaving decking and rafters to rot without any spots appearing in the ceiling to alert the homeowner of the problem?


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## SLSTech (Sep 13, 2008)

I love these arguments - isn't it better to create 1000's to tens of thousands of dollars of damage inside a house so the homeowner knows he has a leak? How many times have roofers been left shaking their heads wondering where the water is coming in at on a regular roof? How many supposed roof leaks are actually condensation issues caused by HVAC lines run in the attic? How many vented assemblies have at least one if not more sheets of damaged sheathing that needs to be fixed when the roof gets replaced?

Sure a leak can cause rot in the area where the leak is but it is blocked from flowing downhill into the actual structure by the foam. If the homeowners follow normal maintenance methods, the leak should be detected before it can cause any structrual damage. 

As for the "water has no place to go" - the bulk of it will flow down the roof with the rest of the water minus the small amount that the intrusion area can hold. If you over fill a cup - it doesn't start coming out the bottom does it or magically start expanding? The water is limited to the space it can fill & the absorption rate of the material surrounding it.


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## echase (Dec 18, 2009)

My concern was exactly that, that since the water has no place to go that it (the "small amount") might just sit in purgatory between the shingles and the foam, and with no way to evaporate it could lead to fungus problems, and potentially structural damage.

I know in most areas of construction it's a big no-no to have vapor barriers on BOTH sides of any component for the risk of trapping moisture... I'm surprised it's different here. 

I'm certainly no expert on this type of insulation, just curious why this isn't considered a problem.


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## AaronB. (Oct 6, 2004)

Some people fail to realize that closed cell foam is 100% waterproof. It would, in theory, aid in keeping water out ofthe structure.

Maintain the roof like it should be and you would find these issues early on, before said damage could occur to the extent you are talking about.


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## echase (Dec 18, 2009)

AaronB. said:


> Some people fail to realize that closed cell foam is 100% waterproof. It would, in theory, aid in keeping water out ofthe structure.
> 
> Maintain the roof like it should be and you would find these issues early on, before said damage could occur to the extent you are talking about.


Pardon my ignorance... Besides a visual inspection for obvious impact/wind damage, nail pops, blistering, etc how would one detect a leak hidden above the waterproof foam? 

I really love the promise of this product, but am always skeptical of new tech.


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## SLSTech (Sep 13, 2008)

First it's not a new product & products that have been around for a while like Demilic have been tested extensively. Besides what you listed, if it was a major leak , that section would feel a tad spongy instead of solid as a rock. 

On the flip side, how many homeowners go into their attics to look for leaks - they don't until it starts leaving water marks inside. By that time how much damage has occurred? As for the sudden damage others like to point to - if a tree falls on your roof, it should be checked out, right? 

If water gets in to a structure it will cause damage - pretty simple, I don't care what roofing system you have. All things being equal, you stand to have more issues with a vented structure due to dew point, humidity, condensation, water blowing in through the vents, water not limited to a small area, etc....


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## echase (Dec 18, 2009)

SLSTech said:


> First it's not a new product & products that have been around for a while like Demilic have been tested extensively.


Thanks for clarifying... how long is a long time? 

I'd love to hear from any roofers who have done tear-off on homes with this treatment.


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