Spray foam vs. other kinds of insulation in a house

[Zachary Hoyt]

I am hoping to get some advice from the collective brain here about insulation. A couple of local people have spoken to me recently about the value and benefits of closed cell spray foam for the 100 year old 900 square foot house I am working on. There is a local guy who has a spray foam business who came out to measure and make a quote on Friday. It would be $11,660 to do the whole house, including the walls, the kitchen roof, the main house attic, the sill/rim joist area and the basement walls down to frost line. The alternative is to put loose fill in the attic floor, rockwool in the walls and kitchen roof, and not worry about the basement for now. I have not run the numbers at current prices but I would guess I'd be looking at $2-4,000 or so if I do that myself. Primary heat will be a wood stove, with a mini split for backup/shoulder seasons. The climate is quite cold, a solid Zone 4 agriculturally.

One thing that surprised me was that he recommended spraying the underside of the roof and the gable ends in the attic, so it would not be insulated off from the rest of the space. He said it would be more efficient because it would keep the heat and cold further away from the actual living space. I am planning to put a floor in the attic and use it for storage.

I forgot to add: the quote is itemized so I can get some things spray foamed and do other things myself if I want to do it that way.

If anyone has any advice about what to do I would be grateful to hear it. I don't have to decide right now, but will need to in the next 2-3 weeks to keep things on schedule. Spray foam is a lot of money, but some people seem to think it is really a lot more efficient and effective and I can afford to do it if it is really that much better.

[Lee Schierer]

Spray foam is probably the better R value for existing walls. It also will reduce air infiltration from the wind. The main disadvantages are cost and it makes retrofitting electrical work more difficult.

[Jim Becker]

Closed cell spray foam has a lot of benefits, despite the cost, including increasing structural rigidity and sealing for infiltration and vapor as a natural property of the product. It can also go into all those spaces that just don't get handled well, if at all, by products like fiberglass and cellulose. Doing the attic as you describe and making that conditioned space is a somewhat normal technique with spray foam. It can go right on the bottom of the deck as it eliminates the need to have ventilation to cool the space and can result in a much more efficient heating and cooling situation in the house because that attic space is not receiving the heat or cold from outside. The whole house becomes a conditioned envelope.

When we built the 2200 sq ft addition to our previous home, we opted for closed cell spray foam and it was an envelope as described. In out case, it being new construction, some of the spray foam cost was balanced by the ability to use 2x4 construction for most walls rather than the 2x6 that would be required to obtain a minimum of R19 in the cavities.

BTW, you do have the option of only doing an inch of spray foam in the walls to provide that sealed envelope and then using fiberglass or rockwool to fill out the spaces. It may or may not be less expensive but does involve more labor on your part.

[Lisa Starr]

We had our almost 200 year old home sprayed with closed cell foam when we renovated it. Though expensive, we were able to get much better r-values than we could have with other materials. Additionally, the sealing of all the little cracks greatly reduces air infiltration. We're solidly in Zone 5. We had the underside of our roof sprayed, as it is a cape style home with only 4" x 4" rough sawn timbers on roughly 36" centers for roof rafters. Heating the house is very inexpensive with a natural gas boiler and radiant floor heat.

[Kevin Jenness]

I believe the spray foam contractors charge by depth of coating so you may get the best value by sealing the outside of stud bays with an inch or two of foam and supplementing it with less costly rock wool or cellulose. That would give you more flexibility with mechanicals in the outside walls. You should really research the specific foam to be used as they are not all the same and make sure of the contractor's track record. You also want to be sure that the foam is thick enough that the inside surface (the vapor barrier) is warmer than the dew point in cold weather, otherwise you may get condensation in the walls.

You can do some types of insulation yourself, but oftentimes a contractor can do the job for little more than a homeowner would pay for the materials.

[Jim Becker]

Closed cell spray foam is about R7-7.5 per inch. And yes, they do charge based on materials used which is relative to thickness. So 2" in the walls gives about an R15 (plus the extra better sealing) 3" is R21 and that still fits in a 4" bay.

[Maurice Mcmurry]

(In case you have asphalt shingles). Spraying the underside of the roof deck is not recommended by many asphalt shingle manufacturers, and will void the warranty with some brands and products. Sometimes creating an un-ventilated "hot" roof is unavoidable. The shingles do suffer. We put DIY Foam-It-Green on the roof deck of a project. It was an unpleasant undertaking. As mentioned, Old houses tend to suffer from air infiltration. Foam works amazingly well and usually leads to a need for combustion air intakes for the water heater, and woodstove,

[Jim Becker]

OTOH, I've seen a roof deck rot out under really good shingles because of condensation if ventilation in the bay is compromised after an inspector insisted that there be an air gap between the foam and the deck, against the advise of the spray foam installer and manufacturer. It cost me ten grand to remediate...

[roger wiegand]

If you are concerned about venting your roof (I wouldn't be), when you re-roof you can put sleepers on top of the existing roof, an additional layer of decking and then ventilate that space with ridge and soffit vents. This is a near ideal system. The insulation directly applied to the underside of the roof almost always eliminates ice dam problems, a real benefit.

Suggest you visit the GreenBuildingAdvisor site for lots of great information on this topic.

If you want to save money focus first on air sealing the structure as thoroughly as possible and then insulating the roof. Rim joists are almost always very leaky and would probably get foamed as part of air sealing (you can get DIY kits to do the rims for a few hundred bucks-- it's fun!) Walls give you the least improvement per dollar spent, but foaming all of the cavities around windows will be an important aspect of air sealing.

We did a mix of things on our house, in the 1950 part we stripped the exterior siding and wrapped the building in rigid foam, blew dense pack cellulose into the wall cavities, spray foamed the underside of the roof (essential IMO if you have HVAC ducting or equipment in the attic), foamed the rims, and put rigid foam on the basement walls. In the new addition we used spray foam throughout but also wrapped the exterior with 1" rigid foam to block thermal bridging. This was a fairly over the top effort, but will eventually pay back in both energy savings and resale value in our part of the country. Our heat bills are about a third that of neighbors with similar houses-- and we don't have ice dams any more.

[Maurice Mcmurry]

Zachary Hoyt. Is your project open to the studs or is it a retro-fit job? The house we used foam on was open to the studs. We used a bare minimum of foam followed by "net and fill" cellulose.

[Zachary Hoyt]

Thank you all for your help. You've given me lots to think about. This house is completely open, I tore it all out last fall after I bought it. The house was abandoned for 6 years, and initially the owner allowed the oil tank to run dry and the pipes to freeze, and then the town water line filled the basement with water. Then the owner used the house to hold ( I am told) 6 dogs and 24 cats. I have removed all the plumbing and heating and electrical equipment as well as the lath and the weird brown drywall-ish stuff and will be putting everything in new. The wood stove will get an outside air kit and the water heater will be electric on demand since I don't like propane for several reasons.

The outside has pretty good aluminum siding on it, so I will leave that other than a few repairs and maybe painting it. Rigid foam on the outside seems like a good idea if the outside is getting worked on anyway, but not ideal in my case. The walls are 2x4 balloon frame and the foam guy said that he would put in 3" in the walls for R21 except he would fill the gap at the second floor level to act as a fire block. I need to ask him about the fire resistance of the foam he uses and whether it would need to be covered in the attic or on the cellar walls. He said it will burn but the ignition point is 1000 degrees.

The roof is metal on the outside, and still in good shape after 20 years or so. I can see the edges of wood shingles under the metal. I think the roof should be fine unventilated. It's 2x4 rafters, which would never be approved now, but I guess they have worked all these years. Not having ice dams would be great, and resale value does seem like it would probably be better up there too with spray foam, though I don't know for sure. Roof deck remediation does not sound like fun. The foam guy said the inspector in my town is very reasonable (that has been my impression too) and willing to accommodate spray foam and how it is best used. I will check out greenbuildingadvisor, that sounds great. Thank you all very much.

[Mitch schiffer]

I actually own a spray foam rig and there are a ton of benefits to go to spray foam the biggest is air sealing. R values are a huge misleading factor. The typical r value rating does not account for air leakage. I would suggest you watch some of the YouTube videos on the channel sprayjones he is very knowledgeable and does a good job explaining the benefits. With a wood stove you have to be somewhat cautious about the size even a small wood stove in a fully foamed 900 square foot area will run you out of there pretty easy. If you decide to go with traditional insulation don't neglect the air sealing. Use a fully adhered house wrap or zip system sheeting. Another thing to consider if you do go with foam is to look into installing a HRV to avoid the problem of stale air that you can get with a tight envelope.