Thread: Spray foam under wood shingle on lath

Has anyone seen any horror shows with this application. Builder said that a barrier was stapled into the rafter bays to keep the foam from expanding through the gaps between shingles but not sure if there is a preferred method. It would seen to me that no matter what, moisture will be penetrating to the top of the foam.

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Thats a mess in the works. Did you get the phone # of the contractor the put that up.


Best

Ron

Yes I did, and it's not in the works. It's done. 1.5 years done.

You're most likely right Wayne
moisture will be penetrating to the top of the foam, and
water damage could be concealed for a considerable
amount of time.

Wayne, I know it's late with the information, and the report is history, but here is some info for the future. (Building Science Digest 149)

Note the installation instructions for wood shingles or shakes on pg. 6. I am not sure if this is what the contractor described?

One way to identify open cell from closed cell is the resistance to denting with slight pressure of the thumb. Open cell is very easy to dent.

Leaks in the roofing, seep through the open cell foam and make locating the source easier to find. Closed cell is a different story!


www.buildingscience.com/.../bsd-149-unvented-roof-assemblies-for-all-climates/2007-07-

Yes, Vern, Open cell foam at this location. Did all the homework. The leak detection is much better and the foam will dry. No r factor till dry but will dry. I told them to call you if they had any. HAHA

Vern

Your link is not fully complete. Can't find the info.

Thanks,

operable link

BSD-149: Unvented Roof Assemblies for All Climates —

Thanks Jerry.

Also I found this statement interesting:

Rainwater migration is severely limited due to the low water transmission and high adhesion (“waterproofing”) characteristics of the foam and damage is limited to the area immediately adjacent the hole in the primary rainwater control membrane. This tends to contain the damage, making it easier to identify the source and preventing it from spreading throughout the assembly and to interior finishes which can be costly to repair.

That's great, but if its leaking and the damage is contained, you still aren't going to find out about the leak for possibly quite some time.

Putting foam on the back of wood shingles is not going to allow them to breath, likely cutting the life expectancy in half or more in my opinion. The whole purpose of the lathing is to permit ventilation, the foam would seem to defeat the lathing. Personally speaking its not something I would do on a wood shingle roof.

Originally Posted by Raymond Wand

Putting foam on the back of wood shingles is not going to allow them to breath, likely cutting the life expectancy in half or more in my opinion.

Did you read the part about putting it under wood shingles?

If wood shingles or shakes are used a layer of drainage mat (e.g. minimum_in or 6 mm vented airspace) should be installed between the roofing and the underlayment.

6 millimeter = 0.236 220 472 44 inch or 1/4" (between 7/32" and 1/4")

I know ... but what about when the foam is applied after the wood shingles and shakes are already there?

In this case a breathable barrier was installed to prevent the foam from adhereing to the shingles and allow water to pass through if leaks occur.
Heard it from the horse.

Originally Posted by Jerry Peck

I know ... but what about when the foam is applied after the wood shingles and shakes are already there?

There is going to be a lot of wet wood.

Wayne - for what this is worth...

I have had very little experience with the new "green" ventless roofs here in Virginia. I have done lots of reading (Building Science and so forth) and am generally skeptical about all the "green" stuff being thrown around, and I mean all of it. To me, green means mo' money and mo' gubment control, but that is me.

However, I had a gentleman call me the other day with condensation problems throughout his house. He proudly informed me that he had a ventless roof - three years now. Looking inside the attic looks very much like your photo. Until this thread, in my readings, I had not come across the closed cell and open cell foam criteria, so I don't know what he had. But he did have molds everywhere and did not know the cause. My gut diagnosis then, prior to my readings, was the lack of ventilation throughout the roof.

In my readings I understand that in humid climates the foam should not be used, in favor of a cellulose instead. One of my building science links states that when humidity gets above 40% it presents problems with moisture being held inside the wood (framing, sheathing and, in your case, shakes) as there is no where for it to go. This reminds me of undrained EIFS and recently the problems associated with the faux stone sidings.

Theorectically I know wood will not rot without one of three things - air, food and water. How foaming a roof prevents moisture, via humidity, from getting into and then not conveniently out of wood is beyond my current understanding. When I said this to my client with the mold problem he poo-pooed me saying that soon all houses will be built this is the new wave,"way of the future," and I need to get with it! Okay then! So, smart guy, why is your whole house molding?

Wayne, you say this is 1.5 years old - any molds? Untoward condensation? Moisture retention? As an inspector, I am very interested in this "new wave." Lemmino!!

Originally Posted by Jay Markanich

To me, green means mo' money and mo' gubment control, but that is me.

This is what "green building" means to me:

- cheaper materials (uses fewer trees)

- fewer materials (uses even fewer trees)

- less labor (fewer man hours needed with fewer trees needed)

- less energy used in construction (during manufacture of the materials and the installation of the materials)

- workers make less, so they must faster on more jobs to make the same money, which makes for low quality work

- nice big signs which state "This is a Green Building."

- much chest beating by builders

- big smiles by clients who think 'That is a good thing.'

- yet, for some unknown reason, all that "saved" money does not lower the cost of the house, in fact, the cost just went up "Sure, it costs more" says the builder "but it is better for the environment. That is a good thing for all of us."

- they buyer thinks "Okay, that IS a good thing."

- builder smiles and walks away, with pocketfuls of extra money, thinking "Well, it does help me. Now I can go buy that ... I've always wanted. AND THAT helps everyone else."

Like I said, mo' money, mo' gubment control.

But what about the moisture? That is my real interest here...

Just because the guy has a foamed roof it does not mean that is the source of his condensation issues.
There have been many moisture related issues with vented attics as well.
Was the moisture prevalent in the attic or other areas of the home?

There were no moisture issues. Just wanted some input. got alot of that.
Now the post has turned into a sales pitch for that Green stuff.
Not "That" green stuff Barry

Originally Posted by Ron Bibler

Thats a mess in the works. Did you get the phone # of the contractor the put that up.


Best

Ron

Looks fine to me... Ron... mess? I just did a spray no vent roof. The home has no problems and uses far less fuel to heat.

adkjac

others... mold.. look for water source and cold air leaks. Cooks that don't use pot covers and fans, showering without fans, lots of plants watered daily, cellar, crawspace lacking vapor barrier. humidifier running way to much.

One of the things that happens when you have a conditioned attic is the HVAC unit has to be down sized to compensate for the additional "tightness" of the structure. If the HVAC contractor just figured in the space that he was cooling and sized it to that then the HVAC unit would not cycle long enough to take out the humidity. That's why you down size! The unit must run longer to remove the humidity from the structure.

Sounds like the guy with the mold problem might have too much AC.....amongst other things mentioned.

Originally Posted by Wayne Carlisle

One of the things that happens when you have a conditioned attic is the HVAC unit has to be down sized to compensate for the additional "tightness" of the structure. If the HVAC contractor just figured in the space that he was cooling and sized it to that then the HVAC unit would not cycle long enough to take out the humidity. That's why you down size!

Not necessarily.

You are are effectively adding the entire attic to the area (cubic feet of space) which much now be 'conditioned'.

One cannot say that the AC must be downsized because of the greater tightness anymore than one can say that the AC must be upsized because of the greater cubic feet of air being handled.

In both cases (insulation on the ceiling and insulation on the underside of the roof sheathing) all top plates *are supposed to be* draftstopped/firestopped - which means "sealed" (with the appropriate materials and methods).

Agree on some disagree with other comments. The entire attic is not conditioned like your normal living area. If it was then you would have to upsize the unit. That would be like going from heating and cooling a 2000 sq. ft. building to a 4 to 5000 sq. ft. building. What would the savings be there? They are promoting the conditioned attic space to save money on utilities.

Also with all the new energy codes there is a much more "tightness" to the homes constructed today. That was all that I was trying to imply was that they are sealing homes more that what needs to be in my opinion. Houses have to breath.

Originally Posted by Jerry Peck

Not necessarily.

You are are effectively adding the entire attic to the area (cubic feet of space) which much now be 'conditioned'.

One cannot say that the AC must be downsized because of the greater tightness anymore than one can say that the AC must be upsized because of the greater cubic feet of air being handled.

You are redefining the thermal boundary more than anything with a foamed attic instead of making the attic a solar collector like it is in a standard vented attic.
You are stopping the heat before it makes it to that space with a foamed attic.
It is not technically conditioned as no one is living there, a little airflow to it and all is well.

Also if the infiltration rates on a building are reduced it will result in a downsizing of the equipment, less load due to unconditioned air not seeping into the building envelope.

Originally Posted by DavidR

You are redefining the thermal boundary more than anything with a foamed attic instead of making the attic a solar collector like it is in a standard vented attic.
You are stopping the heat before it makes it to that space with a foamed attic.
It is not technically conditioned as no one is living there, a little airflow to it and all is well.

I've always read, and been told, that it is considered 'semi-conditioned space' as it is not "conditioned" (and you can have "conditioned space" in which no one lives) in the sense that you have supply and return to it (in some cases you may, though), yet it is not at the same temperature and humidity as the conditioned space is, either.

There is a thermal transfer and moisture transfer through the gypsum board ceiling (there is no thermal break there, the insulation is no longer at that plane), however, the attic will also not be at the temperature of the exterior either, because the thermal envelope is enveloping the attic space.

I can tell you from all the houses built that which I've been in, the attic certainly was 'not a cool' as the interior, but it was not 'hot' either, maybe 'slightly warmer' would be a good description of it. You could certainly tell when you got out of the attic and back into the interior, maybe like going 85 degree attic (don't remember what their temperatures measured) to 73 - 75 inside, but nothing like 130 degrees in a normal attic.

I've seen the same thing Jerry, it's nice going into an attic space that is constructed like that isn't it?

Houses "need to breathe" is incorrect. We can now accurately control the amount of ventilation with several fresh/whole house ventilators following ASHRAE guidelines. The building science mantra has been Build Tight, Ventilate Right, for years. If you want your house to breathe, open a window. A leaky house only costs more money to operate--all things being equal.