I saw a house yesterday with a foamed roof deck.  While talking to the HO and his wife, she got the invoice and the recommendation out.  It recommended taking the old insulation out and the spraying 4 inches of foam.

If you take the old out, why foam the roof deck?  Why not foam the attic side of the ceiling?

Why only 4 inches?


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Sorry, I can't help you out on the first part, nor why they want it removed

A Hot Roof - as you know I do like those (Closed Cell - not Open), but you first need to make sure the sheathing is in good condition, venting has to be eliminated, etc... which maybe out of the budget range

4" is a favorite in this area also (6" as soon as you start hitting up north) - some will argue that because the air sealing is so good that you don't need the full amount to get the recommended R-Value. Others will argue that this is what they use for walk in coolers, some will argue that the payoff starts dropping past this point, etc... Personally I have gone with a 4" CC Foam for one project I wrote about & it far exceeds any other product used, including attic insulation in the 50+ range

On the other side of the equation Martin Holliday wrote about this on GBA - of course that was with Icenyne with a whole lot lower R-Value than the Closed Cell
Do you know how to tell the difference between closed and open cell foam?

I am still at a loss as to why the attic floor is so clean and they moved the attic into the envelope by spraying the roof deck. Why not spray the attic floor?

Open Cell Spray Foams generally remain soft and pliable like a sponge.  Closed Cell Spray Foams are hard,

 

Scott Cummings

Dow Building Solutions

 



John Nicholas said:
Do you know how to tell the difference between closed and open cell foam?

I am still at a loss as to why the attic floor is so clean and they moved the attic into the envelope by spraying the roof deck. Why not spray the attic floor?

Actually the easiest way is by pressing on it - If it is hard & dense it is Closed Cell, if it easily is pushed on and does not spring back it is open cell

Now I am not sure about the vapor &/or flame barrier they spray on it, if that would make it appear to be as hard as Closed Cell or not - I have a feeling that would vary by manufacturer

As for why you don't spray the floor - why would you want to? Any wiring located in the foam would be almost impossible to ever get to - you could not use junction boxes & plenty of houses have the ducts running in the attics - which would perform better in the conditioned zones

The only reason I can see doing that, is to save money on the SF of foam that needs to be applied - but as listed above if they have wires or plumbing there, that makes it a no-go right there
John,
One reason not to foam the attic floor may be to leave open the possibility of future use of the attic as conditioned space. (Not sure, but I'm assuming the attic floor was where the old FG batts were?) This would, of course, depend on the size of the attic floor joists - whether they are properly sized to support live loads or not.

@Sean makes a good point about where the duct work is located. Duct work inside the thermal boundary would not require additional insulation.

There are several good reasons to insulate the attic floor, as you suggest. One would be to maintain and not increase the total cubic footage of conditioned space, thereby not increasing the energy requirements. Wiring, etc. does get encapsulated inside wall cavities when foam is used there, but if you wanted to be certain about future access, you could insert wiring conduits and plumbing chases.

I have to say, I am an un-ventilated "hot roof" advocate myself in most instances, particularly for habitable space that includes kneewalls, but it does depend on a variety of factors.

There is no single definitive answer as to where the new thermal boundary should be. It depends, as always, on intended use (storage or habitable), location of mechanical systems, feasibility of access, etc.

As always, you have to do you "homework" to determine the best solution for each individual case.
I had the underside of the roof deck of my 1952 tract house in Walnut Creek insulated with 6 inches of open cell foam. We had the disgusting old 4 inches of cellulose vacuumed out and now we can see all the old electrical and be able to work on it and actually see where it goes and be able to improve it. The ducts are now in enclosed space and the house is far more confortable.

The cellulose had excretia rodentia, rat poison, 57 years of dust, asbestos and who knows what else in it. Now it is clean. I can install can lights w/o worrying about losing heat. I can put a hole in the ceiling w/o dust falling all over. Now I can actually work up there. I'm very happy.

We also had the perimeter concrete foundation insulated with closed cell polyurethane foam. I sealed off the vents and now the floor is not so cold. I have installed repurposed pool insulation on the dirt floor and plan to install the thicker membrane made for that purpose on top of it to finish the job.

What I've been trying to figure out is how to get max insulation in the uninsulated stud walls. I would like to use PU closed cell.
George -

Foam CAN be used in a closed wall cavity, but you have to be very careful and it can be time consuming. Manufacturers suggest drilling many small holes so you can monitor the foams "progress" in the wall. For my money, especially since you know your walls are uninsulated, I would recommend dense packing will cellulose. Far cheaper, faster, less dangerous and very effective when installed properly with close attention to filling ALL cavities.

I know of a company that did a foam wall fill in the Schenectady, NY area, but I could not find any published info on it.

Here's a link to one manufacturer’s recommendations on how to use foam in a closed cavity:

http://www.foampower.com/howto/insulate_wall_cav.html

Here's the demo video: http://www.foampower.com/howto/how_to_movies/sr_met_tubing_wht.mpg

I've never used this product, so this is just a suggestion, not a recommendation


George M. Matthews said:
house in Walnut Creek insulated with 6 inches of open cell foam. We had the disgusting old 4 inches of cellulose vacuumed out and now we can see


What size vacuum did you use? Truck mounted? Shop vac? I have a client with a similar vintage home and 1.5 inches of Rockwool.
SDI insulation on the Peninsulat did the work. They had a giant vac mounted on a truck. Two men operated it. They got the vast majority of the old stuff. It still needs a little precision vacuuming with a HEPA vac. It is beautiful up there now - a yellow cave that is comfortable summer afternoons.

I wanted to mention that my setup has the 6 inches of PU on the underside of the roof joists so that the entire attic is in enclosed space.

I'm looking forward to adding a HRV in the crawlspace and retrofitting the heating system to use my polaris condensing 95% efficient water heater to run a hydronic air handler. One of my aims is to make the crawl space clean and bright and get some warm air down there so that the floor will be relatively warm. The floor is better than it was but still not as comfy as I want. (My lovely wife gets cold feet).



John Nicholas said:


George M. Matthews said:
house in Walnut Creek insulated with 6 inches of open cell foam. We had the disgusting old 4 inches of cellulose vacuumed out and now we can see


What size vacuum did you use? Truck mounted? Shop vac? I have a client with a similar vintage home and 1.5 inches of Rockwool.
I actually had a conversation with Allison Bailes about this topic last week. Instead of regurgitating it, I will send him a note and have him comment himself. He is a former physics professor and is now a HERS and BPI provider with years of experience. If you aren't familiar with him, I strongly suggest checking him out.
I would be interested in hearing more about this topic as I have a client now with an uninsulated attic with 2 furnaces and ducts up there. The roof is of very high quality and I don't expect it ever to leak. The bedroom ceilings all leak air into this attic. There is old knob and tube as well as more modern romex wiring and lots of communication wiring. There is also a "secret" doorway to a little area up there that gets used. It is easy to walk through here to fix or change services to the rooms, a functional attic space.

I'm told that the space is as hot as a furnace in the summer. It is quite pleasant this week.

It seems to me that if one were to install cellulose it would make the area hard to get around, it would obscure the wiring one might want to change and it would leave the ducts in uninsulated space losing heat to the atmosphere.
BTW, this is in Berkeley, a 10,000 sf house.

Aside from the cost, is there a downside to making this attic a "conditioned space" by blowing polyurethane foam (open cell) into the ceiling joists and sealing off the attic from the outside?
George Matthews
Wish they were all that easy, but that would be a perfect candidate for spray foam. One of the questions I ask homeowners when it comes to attics is how do they plan on using the space. If they aren't using it for a least storage, then it's difficult to justify the extra cost of spray foam. As soon as they say "well we would like to use it as storage space", I discuss spray foaming as an option, especially if there is HVAC equipment present.


George M. Matthews said:
I would be interested in hearing more about this topic as I have a client now with an uninsulated attic with 2 furnaces and ducts up there. The roof is of very high quality and I don't expect it ever to leak. The bedroom ceilings all leak air into this attic. There is old knob and tube as well as more modern romex wiring and lots of communication wiring. There is also a "secret" doorway to a little area up there that gets used. It is easy to walk through here to fix or change services to the rooms, a functional attic space.

I'm told that the space is as hot as a furnace in the summer. It is quite pleasant this week.

It seems to me that if one were to install cellulose it would make the area hard to get around, it would obscure the wiring one might want to change and it would leave the ducts in uninsulated space losing heat to the atmosphere.
BTW, this is in Berkeley, a 10,000 sf house.

Aside from the cost, is there a downside to making this attic a "conditioned space" by blowing polyurethane foam (open cell) into the ceiling joists and sealing off the attic from the outside?
George Matthews

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