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Attic Insulation Quickie

One of the most frequent questions we get on attic insulation is: where should it go?  On the floor of the attic or on the underside of the roof (celiling) of the attic?  The next most frequent question we are asked is: what material should you use to insulate your attic?  Foam, cellulose, fiberglass, something else?
In two of our whiteboard sessions, I have tried to answer these questions.
The answer goes something like this:

  1. Decide what is inside or outside your building.  Is the attic space inside the building envelope or is it outside?
    1. It would be outside the building if there is nothing up in the attic and no one spends any time up there.
    2. It would be inside the building envelope if there is something up in the attic, like living space, storage or more likely heating and cooling equipment, like ductwork, heat pumps, air handlers or other HVAC equipment.
  2. If the attic is outside the building area then the insulation should go on the floor of the attic.  In this case you would want to use a product like blown cellulose or fiberglass or batts of cellulose or fiberglass.
  3. If the attic is inside the building area then the insulation should go on the underside of the roof (ceiling) of the attic.  In which case you would want to use foam insulation.
Once you understand where your building envelope begins and ends things are pretty straightforward.

For those with a more academic approach to the world, here is a great paper from the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. ( Published in ASHRAE Journal (Vol. 48, April 2006), entitled Understanding Attic Ventilation by Joseph Lstiburek, Ph.D., P.Eng., Fellow ASHRAE.  

Check out the whiteboard videos for one minute explanations!

Harold Simansky



I knew nothing about this! Thank you, 360Chestnut. I've never even been in my attic.
Posted @ Tuesday, April 17, 2012 11:27 AM by Katherine
I didn't mention it but iis worth considering, while it is standard to use foam on the underside of the roof. It is also possible to use cellulose. This install is a little trickier as it involves putting up netting on the studs and filling the cavity with cellulose. Then you would dry wall normally. Such an install may be more cost effective than foam.
Posted @ Tuesday, April 17, 2012 12:08 PM by Harold Simansky
This is great info Harold. Thanks for sharing!
Posted @ Tuesday, April 17, 2012 2:13 PM by Lauren
This is sweet...can I do this by myself or do I need a contractor??? Why don't contractors know this? I like doing projects by myself- should I use a mask? Is this baby safe?
Posted @ Tuesday, April 17, 2012 2:53 PM by Sean
Yes, you can do this by yourself without a contractor. Now the question is what degree of difficulty do you want to undertake.  
Anyone can roll down fiberglass batts or spread cellulose on an attic floor. Easy.  
Spray foaming is a lot harder but still a DIY project if you are so inclined. There is a site called where you can purchase everything.  
To answer the question do you need to wear a mask. Yes. Should it be a respirator, as opposed to a dust mask. Yes.  
With regard to baby safe. Cellulose is not a problem, fiberglass is a marginal problem (don't have the baby roll around in it), foam requires you to move out for a couple of days. 
Personally, I wouldn't do the fiberglass myself. When I was 18, I did a fiberglass job and I am still scratching from it. It is very uncomfortable. 
Let us know what you end up doing. 
- Harold
Posted @ Tuesday, April 17, 2012 3:08 PM by Harold Simansky
Thanks! Will take note and not roll around in the fiberglass.
Posted @ Tuesday, April 17, 2012 3:15 PM by Sean
I removed the old porous insulation myself the day before a vacation, then had professionals (an energy contractor and spray foam company) install new non-porous insulation (foam and high density cellulose). The attic removal was easy (fiberglass batts) but the crawlspace under my office (blown cellulose on top of cardboard ceiling) was challenging. The initial reward was finding a 3 x 8 inch hole in the sill (top of the foundation) from the crawl space directly into the subfloor of my office. No wonder my feet were always cold and the heating pipes in that zone froze when the furnace was off for two hours one winter for a blower door test!  
What a difference now! The icynene foam blocks cold drafts and is thicker than the old insulation, thus better insulating. No surprise, our bills went down immediately and significantly; comfort improved immensely.
Posted @ Tuesday, April 24, 2012 11:16 AM by David L
Finding a person or company who does good attic insulations is very hard. Plus there are harmful chemicals you have to look out for. Who do you recommend?
Posted @ Thursday, July 19, 2012 3:13 PM by karl
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Posted @ Thursday, July 26, 2012 2:59 PM by Tra
Thanks for one's marvelous posting! I certainly enjoyed reading it, you can be a great author.I will be sure to bookmark your blog and will eventually  
come back down the road. I want to encourage yourself to continue your great work, have a nice evening! 
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Attic Cleaning  
Attic Clean Up  
Attic Insulation Removal
Posted @ Tuesday, December 04, 2012 10:09 PM by Attic Insulation Installation
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Posted @ Wednesday, September 04, 2013 2:55 AM by Liquid EPDM
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