Q&A: A Forum for Green Building Experts and Beginners

I was talking with a urethane spray foam installer this morning who stated numerous concerns about all other spray foam products but his - more notably open cell products. He says they do not perform in areas such as rim joists, etc. They don't belong anywhere but in stud cavities on sidewalls. Go figure. He is currently spraying my neighbors' exterior above grade block wall foundation(in addition to 4-6" below grade) wall with a closed cell spray foam. He said there was a study that indicated this is as efficient as spraying the main floor 8' exterior walls.

I was at a house recently. It was a 2-story built around 1920, so it probably had 2 x 4 rafters. In speaking with the owner he said that he open-cell foam sprayed on the under side of the roof deck. I asked if I could see it.

What I found was that the open-cell foam was left uncovered, with no fire barrier. I do not know how thick it was, but doubt it was much over 4.inches. I am in Nebraska to give you an idea of the climate.

He was told open-cell was used as it will allow any roof leaks to show up.

I'm working on the roof structure details for our passive solar home. We plan to use the "Perfect Wall" concepts from Building Science Corp. for our frame walls (advanced framing, exterior rigid foam) and would like to make that continuous with our roof structure. However, I need help putting the layers together. Here are some details:

-Standing seam steel exterior
-Rigid foam exterior insulation (polyiso or EPS)
-Dense pack cellulose fill between framing members
-T&G decking for interior finish material

I'm building a new building that will have radiant floor heat from a boiler. Using a type of foam insulated cement wall -- foam is just on the outside. I'm using s shallow frost-protected foundation and wonder about using XPS foam under the footings to stop the thermal bridge that is there.

Any thoughts anyone?