Spray foam insulation

I have found a Water Furnace dealer who really is interested in doing the job right. He wants to size my replacement unit according to house plans, window size and types, etc. He checked the temp of the ground water line, and it shows 80 degrees. Sounds like it may be good enough to support the 4 ton Envision.
But he described to me the benefits of spraying foam into the spaces between rafters and including the attic in the envelope. By doing this, he says it would be possible to remove all the attic insulation that is there now. Soffit vents could also be blocked off.
Does anybody have any useful observations about this stuff?
Butch

 

The jobs that we do that employ the top tier on the insulation choices, are ridiculously low on load compared to simmilar square footage homes with traditional batts or whatever.
Eric

It has also been said that the most bang for your buck is spent on your envelope not your tonnage.

 

Eric,
Thanks. I am beginning to understand the concept. Just a month ago I had 8 inches of additional cellulose blown into my attic to bring it up to R38. I hate to see that go to waste, but I believe the foam will be the better investment for the long run.
Butch

 

If your project is anything like my personal projects, it is allways two steps forward and one step back to turn to the right to make any meaningfull proggress. lol
Eric

 

Yes, that's very true for mine, as well.
Butch

 

Soffits

They can be extended so as to not be blocked. Don't block them

 

By extending the soffit vents, I would be allowing outside air into the envelope. I think there is probably enough coming through the walls without doing that.
Butch

 

I got 3 or 4 quotes for spray foam when we were building our house. All wanted to insulate the underside of the roof. I was thick headed and asked to have the ceiling insulated. My thought was "less space to condition". 2 summers later I wish I had done the underside of the roof.

I have 2 pull down stairs I had to insulate. 1 high return ducted in the attic w/insulated flex, slight condensation problem. Melted candles in storage boxes.

Insulation should fill space over the top plates of the walls.

Go for it, I wish I did.

ChrisJ

 

Hi Chris,
I'm excited about the prospect, but I have not received the estimate yet. I may change my mind when I find out what it will cost. How much more were your estimates compared to insulating the joist spaces?
Butch

 

Sorry Butch, I had them quote the ceiling everytime, never got the roof quoted.
Shouldn't be too much more, only a little more sq. ft., unless high pitched roof.

ChrisJ

 

We foam underside of sheathing and seal up attics on all new construction and major retrofits. Effect on tonnage is dramatic - last 3 examples:

1) 7 tons reduced to 4
2) 7 tons reduced to 5
3) 5 tons reduced to 2

Foam didn't allow for all those tonnage drops, but it was the single biggest contributor. In no case did we change windows or add wall insulation to achieve those drops. Foam helps reduce infiltration and summer humidity.

All that said, foam comes with one big caveat: Foam is both an excellent insulator AND and excellent air seal. Some insulators don't seem to realize this. They are inattentive to details necessary to achieve a proper air seal.

Case in point - recent new construction house around 4000 SF blower door tested at 4100CFM50 post foam despite foam boss insisting they'd done an excellent job in the eaves. We used a theatrical smoke machine and handheld smoke stick to find and seal hundreds of little misses. House tested at 1300 when we turned it over to the drywall crew.

 

Curt,
That is very impressive. I think foaming the sheathing may be the coming thing and a partial solution to energy waste, but it's going to be hard to get out of the mindset of ventilating attics to disperse heat and moisture.
Butch

 

I have another question for you, Curt. When you foam the sheathing, do you leave the ceiling joist spaces empty?
Butch

 

If retrofitting foam, we leave existing insulation in place. However, that is NOT advisable in climates where attic temperatures drop below indoor air dewpoint. That is a distinct possibility outside the deep south.

In new construction we do not install insulation on attic floor / ceiling joists.

 

I probably won't use foam insulation, because I have large porches on the front and back of the house that would be isolated and cut off from ventilation.It sure sounds like the best way to insulate a house that is designed to use it.
Butch