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2ofUs 05-26-2011 07:25 AM

Does this estimate sound reasonable?
This isn't exactly DIY, but we got our first estimate for spray foam insulation in our attic, and are looking to compare the price. For a townhouse attic, 20x20x2, 6 inch cellulose foam of the underside of the roof and the two walls shared with neighbors, we had an estimate of $2,200. Does that seem reasonable? Company gets good reviews on Angie's List and we got personal recommendation from trusted source. Will try to get couple more estimates. Thanks!

oh'mike 05-26-2011 07:30 AM

Sorry,but I'm a bit confused---The underside of a roof is not typically insulated,except in a vaulted ceiling situation.

Why are you doing that?

2ofUs 05-26-2011 10:10 AM

Thank you, oh,mike. I don't think it's unusual for people to get spray foam on the ceiling of their attic. If you would like to offer constructive suggestions for attic insulation to improve the thermal break of a house, keep cool air in, and lower utility bills, I am totally open to hearing them.

oh'mike 05-26-2011 12:11 PM

The living space gets the insulation---the ceiling is the most important.

the attic space and roof system need plenty of ventilation to keep the open attic as close to the outside air temperature as possible.

That means open soffit vents and a ridge vent or mushroom vents at the top.

That is the way to keep the utility bills down and offer a most comfortable home.

Insulating the roof sheeting is not a common practice as the ventilation take care of most of the heat generated by the roofing.

I'm always open to new things---explain the benefit and I'll listen.---Mike---

sixeightten 05-26-2011 12:16 PM


I have heard of houses that used closed cell foam that require zero ventilation. I haven't actually worked on one, but they do exist. I think trying to do it on an existing house would be a lot of trouble though.

2ofUs 05-26-2011 01:01 PM

We have existing blown-in insulation on the floor of the attic, between the living space and attic. Our thought was to leave that and do spray foam on the attic ceiling. My understanding from the estimate was that the ridge vent and soffits would not be covered. In fact, our reading recommends spray foam should not be done DIY, because the average DIYer usually unwittingly sprays over important and necessary vents.

But later today I talked to another contractor who said although he was talking himself out of money, he would not recommend the spray foam. He would recommend adding to the blown-in insulation to up the R factor. For that he gave an estimate of $800 over the phone. This second contractor does not like the mix of blown-in on the floor of the attic and spray on the ceiling. He says to do spray foam at all he would want to remove all the blown-in and spray the entire area.

Obviously a little more research is required.


oh'mike 05-26-2011 01:04 PM

That's a new one to me. I do mostly interiors now --last addition I built was 12 years ago.

Last house almost 20.----I still don't see the benefit over the cost---Might be Gary or one of the other members will offer a link to something that will explain the benefits.---Mike---

HomeInsulation 06-04-2011 09:10 AM

Hot Roof

Insulating the underside of a roof deck with spray foam insulation is known as a --- Hot Roof.

It's a new insulation technique that does have it's merits IF you have a lot of heating and cooling equipment, like your furnace, air conditioner and ductwork located in your attic.

IF NOT, it's usually a waste of money, although it does work well. Your roof deck is probably 1/ 1/2 times the square footage of your attic floor. Spray foam insulation is expensive and will take many years to recoup your investment.

Spray foam contractors are absolutely convinced that this is the best approach to lowering energy bills. Of course, cellulose insulation contractors are absolutely convinced cellulose is the best insulation.

I'm always looking for the least expensive way to save the most money on my energy bills. So I look for a quick return on my investment.

AIR SEALING your attic floor is the most cost effective way to save money on your heating and cooling bills. Best of's CHEAP! (less than $100 for DIY) And it's definitely a DIY project you can do in a weekend.

Air sealing can save you 20-30% on your energy bills. It helps you keep the conditioned air you've paid to heat or cool inside of your home.

Allison1888 06-06-2011 09:37 PM

Are there industry standards on this, as it sounds like there are two very diverse views here. We didn't do the underside of our roof--just the walls and floor of the attic, but now I'm confused....

vsheetz 06-06-2011 10:11 PM

Where are you located?
What is the R value now on the attic floor?
What is the R value now in the walls?
How long are you going to stay in the house?

I reviewed the various options when I did a whole house remodel year before last and again recently for a coming addition this summer, to include a hot roof.

Best for the remodel effectiveness and ROI was to add blown in insulation to the attic floor - R40 or better is typically the goal. For the addition I am looking to do 2" of foam plus fiberglass batts (2x6 walls) and R40 in the ceiling.

Ensure the big holes in your walls (aka windows) are dual pane, low E, etc.

Got air leaks around doors, windows, etc? Plug'em.

Gary in WA 06-07-2011 02:35 PM

I agree with HomeInsulation in post #8 above. Air-sealing is more important than insulation.

You can load the attic with insulation but to no or little avail (especially f.g.) if you didn’t air seal first:

In fact, that is why this new roof came about, because you can’t effectively air seal an attic with HVAC in it. BSC info:

Some problem with Hot Roofs in a cold climate:

Pages 3-5:

I might add it depends on location and meeting minimum code, spending money on other places rather than overkill in one area that may not be cost-effective beyond a certain point:



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