extruded polystyrene insulation--is this a deal worth pursuing

[MikeT]

i am always looking for a good deal on things, especially nowadays.  A local yard is selling 4x8 sheets of the pink extruded polystyrene for $4 per sheet, R 7.5.  I am trying to decide if this is a good enough deal to leap at to get stuff for my  (as yet) uninsulated house,  I would want to cut it and put it in the stud bays (doubled up) and then possibly for crawspaces, or ?

What do you think?  Jump or let is pass?

mt

[rwanders]

Sounds like a deal to me but how would it compare to per square inch for fiberglass? Achieving a good tight ft in stud bays with rigid foam is pretty time consuming and air leakage is actually a greater heat loss source for most homes. But the price sounds really good and for crawlspaces it could be a very good choice.

[tc-vt]

Mike,

Another good place to insulate with the foam board, if you have a second floor or a wood framed first floor and crawl space, is the rim joist between the studs.  Use caulk or spray foam insulation to seal around the edges.

Tom

[MountainDon]

Having fitted rigid foam sheet into a couple stud bays I totally second the comment about it being difficult to fit to close clearances. A tight fit is necessary, there's no point in going to all the trouble without it being a tight fit.

I believe you would be time and money ahead if you used the sheet foam on the exterior.

[n74tg]

How about squirting in some GreatStuff expanding foam along the hard to seal edges of the foamboard.  If it doesn't eat the foamboard it should seal it well. 

[MountainDon]

Great Stuff works, itis compatible with the pink foam I used. It's also messy, not cheap and more bother than I would want. I used the pink foam in some header areas. I would not want to do the entire cabins worth of walls with it. That's just my opinion though.

[rwanders]

I agree about the great stuff----excess expansion is hard to avoid and even harder to remove.

[MikeT]

thanks, folks.

I decided to be more casual about the rigid stuff.  I will not put it in my walls, but if there is enough available next time I am there, I will get enough for some crawl spaces, etc.

mt

[poppy]

I would jump all over that deal.  I plan to use rigid foam for my primary insulation in full 4x8 sheets, so that would be a great money saver for me.

You might consider using that pink board on the outside of your studs.  It is a solid enough base to nail through to support your sheathing or siding.

[MikeT]

If I had come across the material earlier in the project, I might have jumped and put it on the exterior.  But I already have started my siding, so I am trying to figure if this is useful for interior applications.  I am thinking of using it as a crawl space and underneath the floor joists between the main floor and by basement.

mt

[jb52761]

I used those 4x8 extruded sheets on interior walls of my little cabin. I agree with the tight fit BETWEEN the studs, but I nailed them directly on top of the studs, butting the edges tight together right in the middle of each stud. Since the line was there, I knew right where to nail on the t&g carsiding, 16" o/c. I did the front and back gables the same way.....jb