Attic Insulation via Foam

[Doug19]

So my parents are in the process of getting quotes to have there attic of there home spray foamed. The house was build in the mid 70's and has insulation batts in the ceiling joists. I've read about closed vs open cell foam and am good with that part. The part i'm confused on is if they should be removing the current insulation and spraying in the ceiling joists or spraying the foam on the roof deck.

For more information the house is in the Pittsburgh Pa region and we experience pretty much everything from hot to cold, humid, and snow. The attic has rafters vs. trusses and has vented soffits and ridge vent. Also the attic isn't tall enough to do anything livable and nothing will ever be stored in it. There also isn't any HVAC equipment in it.


Any advice?

 

[Doug19]

What would make the most sense to me would be to remove the current insulation and spray the ceiling joists and leave the soffits open to vent through the ridge vent.

The one guy that came out wanted to spray the roof deck. He was going to remove the current insulation and spray the roof deck leaving the ceiling joist open. I assume he would foam over the soffit vents and the ridge vent. Would they also have to foam the two gable ends? This would essentially make it part of the HVAC envelope correct? So they would essentially be heating and cooling this space also?

 

[yeldogt]

When you foam -- you do the whole roof deck side walls -- close off any venting. The attic becomes conditioned space.

Retrofitting and the need to remove the old ceiling insulation depends -- I'm assuming no HVAC in attic.

No knee walls

 

[Doug19]

When you foam -- you do the whole roof deck side walls -- close off any venting. The attic becomes conditioned space.

Retrofitting and the need to remove the old ceiling insulation depends -- I'm assuming no HVAC in attic.

No knee walls

Correct no knee walls and no HVAC. I'm assuming if it is done this way they can't seal the ceiling joists at all like around can lights. So could the HVAC be overworked or undersized due to this new room it has to cool and heat.

The only advantage I can see in this is the joists are still open so it would be easy to route new wires if ever needed and I would be doing it in a climate controlled environment.

 

[K'ledgeBldr]

Making the attic conditioned space (foaming roof deck, gable walls, etc.) increases the demand on the current HVAC system that is designed for the existing square footage. The biggest con to spraying roof decking is leaks. You won't know if you have a roof leak(s) for months- and imagine the damage that can be done to structural framing in that amount of time(?).

I would just add blown f/glass to the existing and bring it up to current code- R-38+.

 

[rjacobs]

The biggest con to spraying roof decking is leaks. You won't know if you have a roof leak(s) for months- and imagine the damage that can be done to structural framing in that amount of time(?).

Thats why you spray open cell...

Water can penetrate it if you have a leak and you can get it fixed.

Closed cell on a roof deck would be an issue.

If spray foam on a roof deck was such a bad idea it wouldnt be done in millions of homes...


To the OP: the attic doesnt suddenly become "conditioned space"...it becomes part of the conditioned "envelope". There is a difference. It is true the temp does stay within 5-10 degrees of the house(supposed to anyway) vs. the 130-140 degrees it likely gets now, but its not like you are suddenly plumbing AC venting into that space that it might overwhelm your parents HVAC system. USUALLY in a house with spray foam you get by with a SMALLER overall HVAC setup because you arent fighting that 140 degree air in the attic.

 

[rok_hunter]

My (new construction) house matches what rjacobs mentioned - foam is sprayed against the inside roof surface and completely seals the area. There are no ridge vents and the soffets are sealed. The HVAC doesn't condition the air in that attic space but it does stay significantly cooler than a traditional attic space, and since there is so much less ambient temp loss from the HVAC ducting in that area it lets your system run more efficiently. My house has a barrier put up between the attic above the living space and the useable attic space above the garage where I actually store everything, and the garage side isn't foamed.

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[dcg9381]

Making the attic conditioned space (foaming roof deck, gable walls, etc.) increases the demand on the current HVAC system that is designed for the existing square footage.

I don't agree with this at all. I get where it's coming from, IE - you just added more sqft to your home, but that's really not the case. You're not actually cooling (actively) any of this space, it's just that the space is now "semi-conditioned" passively by leaking and nature of the vents going through that space.

Think of it as increasing the R value of your home, substantially decreasing the thermal losses of the duct work and you just took your HVAC out of desert conditions, so it's more efficient.. You're not really adding another room.

I'm up for an alternate opinion - but my understanding is that HVAC tonnage for foam insulated versus traditional insulated is less. The BIG advantage is that you don't have a cooling system sitting in a super hot attic anymore..

You do need to seal the eves, etc. If you can seal it up, I don't see any reason why the existing insulation over the ceiling can't stay.

 

[K'ledgeBldr]

Thats why you spray open cell...

Water can penetrate it if you have a leak and you can get it fixed.

Closed cell on a roof deck would be an issue.

If spray foam on a roof deck was such a bad idea it wouldnt be done in millions of homes...

Open cell foam is "moisture permeable"- water isn't going to just run right through it. Spray foam, either open or closed cell clings to lumber wet creating a seal- try cleaning it off.

Your last statement just confirms the sales ability of people who prey on those that are not savvy to the insulating industry.

 

[MrSurly]

"clings to lumber wet creating a seal- try cleaning it off."

I'm not sure I understand your message, but I HAVE cleaned foam from lumber and metal siding. I found it a very easy thing to do.

Your last statement just confirms the sales ability of people who prey on those that are not savvy to the insulating industry.

Are folks who have spray foam installed... "preyed upon"?

 

[rjacobs]

LOL...

He's like the ONE person on this site that would recommend against spray foam for insulation...

Why dont you(kledgebldr) educate us on all of these fine points that we are all obviously wrong and mistaken about... Then I will continue to LOL about it...

 

[yeldogt]

First -- there is nothing wrong with closed cell on the roof.

Have never understood this roof leak problem. Where are this mystery leaks that I always catch with a house not having spray foam? Actually -- it can save you a lot of damage in a disaster. The roof will not leak.

IMO closed is a superior product -- open will work .. but it must be thick enough to minimize vapor transfer in a cold climate.

You are not heating or cooling the attic space -- it becomes like a bedroom with the door closed.

What people don't understand is vented attics and crawl spaces don't just vent that space .. they vent conditioned air that leaking from the house into those spaces. To the OP question about lights ,,, they are leaking into the attic now. Yes .. they do cap them.

 

[Doug19]

First -- there is nothing wrong with closed cell on the roof.

Have never understood this roof leak problem. Where are this mystery leaks that I always catch with a house not having spray foam? Actually -- it can save you a lot of damage in a disaster. The roof will not leak.

IMO closed is a superior product -- open will work .. but it must be thick enough to minimize vapor transfer in a cold climate.

You are not heating or cooling the attic space -- it becomes like a bedroom with the door closed.

What people don't understand is vented attics and crawl spaces don't just vent that space .. they vent conditioned air that leaking from the house into those spaces. To the OP question about lights ,,, they are leaking into the attic now. Yes .. they do cap them.

So I should make sure they cap the recessed lighting if they do the roof. I know right. Now there is just insulation surrounding the light and air is leaking through there.

 

[wade_660]

I have open cell in my house. I had a leak with a faulty boot when I was building. The water leaked at the boot, and came through the insulation and dripped on the floor in the same spot. There was no running on top of the insulation, the water went right through it. Not that this was a question, but it may clear up the issue for some.


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[Leaflessshadetree]

Spray foam is good for sealing and for R per inch where space is limited. This is one situation where I wouldn't add spray foam.
They already have fiberglass. I'd add another layer of bats perpendicular to the existing ones or blow in insulation on top. They will get more insulation per dollar.
.
BTW: I had my garage walls spray foamed then installed batts (only 7" of space to fill). In the ceiling there isn't that space constraint. I could layer fiberglass or blow in insulation several ft thick (If I wanted it). I'll still be able to access any part of the ceiling if I need to (wiring, HVAC ducts. ceiling repairs). Just move the insulation and put it back when I'm done.

 

[banjopete]

I'm with leafless this is a situation where batts will be effective and much less expensive. I'm a big fan of foam and sprayed our basement reno, love the stuff in tight places, and for its vapour control. In an attic you have tons of room, easy access partial insulation already and aasuming the existing insulation isn't suffering from critters or leaks adding R-s to it is simple and cheap for pros. Could just be a hour or two to lay out the batts, easy peasy.

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[dcg9381]

Foam has been used extensively on both commercial and residential construction. Pole barns, metal buildings, residential stick and brick. My last 2 homes and current barn all use foam. Almost every building at our rural airport (most are barndominiums) use foam. If don't like it, I get it, but it's a well proven solution.

Closed cell on a roof deck may make or may not make it difficult to find the source of a water penetration.

R-value is one thing, but to me, the BIG advantage of foam is that it creates an "envelope" that is a far better air seal than most traditional insulation. I'll continue to use it exclusively.