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On chosing spray foam installation for the attic

Which type of spray foam is recommended, open or closed-cell?

I'm about to remove my blown-in insulation out of the attic, and I was trying to figure out which product is recommended -- the open or the closed-cell?

Posted Jul 22, 2014 7:50 PM ET
Edited Jul 23, 2014 5:41 AM ET


3 Answers

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If you plan to install the new insulation on the attic floor, spray foam isn't the best product (because it is expensive for the R-value you get). The best insulation for attic floors is cellulose insulation.

If you decide to take this advice and install cellulose, it's important to perform air-sealing work before the attic is installed. This article discusses the necessary steps: Air Sealing an Attic.

If you want to install the insulation between your rafters (along the sloping roof line), then spray foam makes sense. In most climates, closed-cell spray foam has proven to be less problematic than open-cell spray foam in this location, although open-cell spray foam can work if the details are right.

Open-cell spray foam has a lower R-value per inch than closed-cell spray foam, and is more vapor-permeable.

For more information on these issues, see:

GBA Encyclopedia: Spray Foam Insulation

Creating a Conditioned Attic

Open-Cell Spray Foam and Damp Roof Sheathing

Answered by Martin Holladay
Posted Jul 23, 2014 6:01 AM ET


In addition to what Martin has advised you, do your homework on your insulation installer. If you elect to use spray foam you MUST verify their insurance policy, workman's compensation, error's and omissions and/or Contractors Pollution Liability. "IF" your SPFI installer does not install the spray foam correctly causing voids, odors and/or off-ratio foam (open and closed cell foam) the typical contractors general liability insurance plans and your homeowner policy will not cover these issues and they certainly will not correct the problem. Ask a lot of questions. Place yourself in the worse possible scenario you can think up and start writing the list. Think about how your going to fix your home when no one can help if something does goes wrong.

There are plenty of articles written on blogs about these issues including here on GreenBuildingAdvisor.com ....as the headline and the comment section. You may have to sniff out the insulation guy's who make attempts to sway readers to believe nothing ever goes wrong. It's simply not true.

Your work does not end with insulation selection. Now you have mechanical devices to investigate and you need them properly sized for your new energy retrofit. (Furnace, air exchanger / HRV-ERV, air conditioning...2 ton or 3 ton, added ventilation so your wood stove functions properly, etc)

My advice to you, save yourself a lot of time and aggravation and hire one of the many building scientist Mr. Holladay may share with you from his Rolodex. It may be the best money you have not wasted in years.

This new modern building practice of "build tight - ventilate right" can be the most costly mistake any homeowner could possibly do when insulation and mechanicals are not installed and/or sized correctly. I personally would not trust the plumber to do the insulation and no more than I would trust the insulation company to design my ventilation system. This is all fairly new to most contractors from what my research has shown. That's my opinion for what it's worth. Happy building!! :)

Answered by Richard Beyer
Posted Jul 23, 2014 7:41 PM ET


A couple of added links to help you understand the process behind (what industry claims is) correctly installed SPFI...

http://vimeo.com/50807638 and


What possibly could go wrong? As you will see it's a he said, she said episode of a poorly written Seinfeld flick with catastrophic financial consequences for both sides of the feud. One side wants their health back and home fixed, while the other side is spending more money in lawyers and political lobbying to protect the reputation to satisfy their share and/or stake holders.

(This is not intended to support this legal firm. It's intended to show the argument of both sides.)

Again, That's my opinion for what it's worth. Happy building!! :)

Answered by Richard Beyer
Posted Jul 23, 2014 8:12 PM ET

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