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Open Cell Foam insulation In Attic? Rafters or Floor?

Open Cell Foam insulation In Attic? Rafters or Floor?


  #1  
Old 09-26-14, 12:01 PM
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Open Cell Foam insulation In Attic? Rafters or Floor?

Alright just had the local spray foam insulation rep stopped by.
I have a vaulted living room with 50 year old( sagging) insulation 8 inch rafters which I intended to have it spray OC foamed. Which would be a drastic improvement.! Not a real hard decision. It would give me R31.Alt fiberglass maybe R15

The thing I am questioning was the reps suggestion that I continue thru the rest of my ranch style home into attic crawl space but strictly on the roof rafters.
In a way theoretically sealing the house.

I was anticipating of doing the attic Floor side above all the living areas Ceiling.
Laying down some fiberglass, or letting him give me a quote .
So I would like to know who has done this with open cell. I know the closed cell would be far superior but more costly. Just want to know if folks who might of done this are satisfied with the results. Feed back on pros and cons
Thank you
 
  #2  
Old 09-26-14, 12:21 PM
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Is the attic (not the living room) conditioned space or is there ductwork or HVAC equipment up there?

Should the answer be no, then I would not be looking into creating a hot roof, which is what was proposed to you. Foam on the floor of the attic is both insulating and air sealing so I would be on board with that.
 
  #3  
Old 09-26-14, 01:06 PM
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The choice between open cell and closed cell for a cathedral ceiling is more than the cost. Beyond simple r-value you need to prevent any moisture from inside the home from permeating through the building material to the bottom of the cold roof sheathing or being carried directly there through an air path. Since open cell foam has a high permeance the details of a moisture/air barrier MUST be obtained within layers preceding the foam (inside to out).

I'll give you some reading, since I can't keep up with all of mine How to Build an Insulated Cathedral Ceiling | GreenBuildingAdvisor.com

Note the other links they reference.

As for how much is needed, check your local code requirements. Some areas require renovations to come up to full insulation levels and open cell might not make it in 7.5".

One of my concerns is how quickly this industry shifts direction. Insulating as you have describes is relatively new, yet we are already encountering failures. Following a more traditional approach, even though it would require more depth, is time tested and will still be working 50 years from now.

Bud
 
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Old 09-27-14, 06:15 AM
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Is the attic (not the living room) conditioned space or is there ductwork or HVAC equipment up there?
Answer NO HVAC. just a fan and some elec wiring

He did propose a 2 inch layer of closed cell then fill with open cell 5 inches. I thought this was a good idea but will do some reading up.
thanks for the responses!
 
  #5  
Old 09-27-14, 06:29 AM
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In Southern climates where they frequently stick the ac unit and all the ducts up there a "hot roof" approach where they insulate the rafters and close off all ventilation is necessary. Otherwise, air sealing the ceiling (attic floor) and adding lots of insulation in a traditional manner is the time tested method.

There are many negatives to foaming the bottom of the roof deck and all can be avoided by insulating the attic floor.

Bud
 
 

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