Spray foam diy

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I would think there would be less cuts though and a snugger fit with 15" pieces.
 
Other issues aside, will I get a higher r value with 9" r 30 pink insulation?

Most people in the country use fiberglass batt for what you are doing. Sure foam is superior but FG is just fine. You can do a great job with FG in that standard size joist bay. Shop the insulation selection and I bet you can find something that is 10" thick or even 12" thick. It is okay to compress FG, you will only get the compressed thickness R-value. So if you compressed a 9" R-30 batt down to 3.5 inches you would only get R-13 or R-15 out of it. I would rather insulate at R-30 with FG than R-10 with foam.

There is also this mineral wool product called roxul that people like to install as well.

Why pay the premium for XPS? If you insist on foam, the white EPS is usually about half the cost and just as good.
 
If you were close to Maine I would suggest giving Tom In Maine a PM, he sells seconds of insulating foam board for really great pricing.
 
Most people in the country use fiberglass batt for what you are doing. Sure foam is superior but FG is just fine. You can do a great job with FG in that standard size joist bay. Shop the insulation selection and I bet you can find something that is 10" thick or even 12" thick. It is okay to compress FG, you will only get the compressed thickness R-value. So if you compressed a 9" R-30 batt down to 3.5 inches you would only get R-13 or R-15 out of it. I would rather insulate at R-30 with FG than R-10 with foam.

There is also this mineral wool product called roxul that people like to install as well.

Why pay the premium for XPS? If you insist on foam, the white EPS is usually about half the cost and just as good.
You say SF is superior; but then question why anyone would use it. Can you please explain.
 
You say SF is superior; but then question why anyone would use it. Can you please explain.

There are certainly places where foam is superior and is the right choice. Under slabs, thin wall cavities, pipe insulation, etc. but when you can accomplish the same job with other products it is generally MUCH cheaper.

For example, how often do you see open attics insulated with spray foam? Almost never. It is very cheap, effective, and easy to blow in R-50 of cellulose. In that attic floor, foam would have been superior due to air sealing and thickness required but it is super expensive.

In summary. It's about the extra cost for the same R-value when both foam and another product could be used.
 
Fiberglass settles which is great for an attic or even a sealed wall cavity. Not good for a exposed ceiling or floor once it settles you have a gap and its R value is non existent.
 
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Fiberglass settles which is great for an attic or even a sealed wall cavity. Not good for a exposed ceiling or floor once it settles you have a gap and its R value is non existent.

I don't believe either of those claims to be a real issue.
 
I don't believe either of those claims to be a real issue.

I can only speak from having a crawl space with insulation hanging it was sagging air was free to move behind the insulation. In our bonus room the R-30 between a floor and drywall of our garage the insulation settled there was about 1 inch gap. Air would be free to move throughout the cavity insulation was dirty indicating air movement in the cavity. When I pulled off the insulation in the rim joists the insulation was filthy again indicating air movement.
 
I have some cantilevered areas of our house where loose fiberglass was blown (packed?) in. An energy survey later showed that the floors above those cantilevers were cold.
I opened it up and found the FG had settled leaving a significant air gap under the floor.
I yanked all the FG (fun job) and installed foam under the floors and then filled the space under the foam with packed cellulose.
If I used batt insulation now it is Roxul or another rock based product.
 
If you are looking for used foam board of any kind, look on craigslist. I have found 8x4 sheets of 2.5" foil on both sides EPS for $12-20/sheet. I'm sure they are wheelers and dealers as well..come with cash.
 
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