We are renovating an old concrete block home. We just have furring strips on the exterior wall, so regular insulation won't work. We are looking for the cheapest option and the insulation boards are quite expensive. Does anyone know of a good DIY spray foam? Thanks

If you think insulation boards are expensive, give up the dream on spray foam. Based of estimates I have received in my area, the cheapest you could get closed cell is about $1.50 a ft^2 for 2" thick, and open cell about $1.00 ft^2 for 4" thick, but this would end up very bumpy. The DIY spray foam kits are actually more expensive than getting a professional on the job for a project of any size at all. The cheapest option is probably used board foam. The foam boards I got for my last double stud project were EPS boards 2 3/8" thick, 3.5' by 7' for $2 each. They were compressed in places because they had been used shipping laminate flooring rolls from overseas. This didn't matter for me because it was going between the studs, but if you are looking for something more "perfect" do a few internet searches for reclaimed or factory second foam boards.

aardvarcus is right about the DIY spray foam - it works out cheaper to have a pro do it for you.

You may want to consider putting rigid insulation on the outside of the concrete block (on the exterior of the home), but I know this may not be an option depending on the external finish of your house.

Recycled or factory-seconds rigid board insulation is less than half- price. If you can find a manufacturer near you, call & ask.

Otherwise the recycled stuff comes in good/better/best condition, and if you need a lot of it, can be well worth shipping. If you can't find anything else, Insulation Depot (see http://www.insulationdepot.com ) has several locations, and will ship if the quantity is significant.

EPS is usually your best R/$ value, but you end up with a thicker wall structure. (Iso gives you the best R/inch of thickness.) Be careful about vapor permeability & condensation issues when using any insulation, particularly rigid-board stuff with foil or poly facers, but also XPS or closed cell spray foam in thicknesses over 2".

Brushfire: Without knowing bebe72's climate zone we can't make any flat delcarations as to whether/where to apply a vapor retarder!

The answers are different in AL than in AK (or in the northern glacial plain of the Badger state.)

Where possible, it's usually preferable to place the insulation on the exterior of the cement block to take advantage of thermal mass of the block itself. (This is true independent of climate zone, but the amount that buys you will differ with climate & season.)

But insulating basement walls at least from the frost line up is essential in any heating climate. In N.WI you can lose a lot of heat through the basement slab, too, given your average sub-soil temps. (In FL, not so much. :-) )

Wow, flamed on 1st message!  However I suppose there's a slight chance that bebe (or anybody else for that matter)  would like to have water seeping into their blocks in order to find its way to the basement.  But why waste a few bucks on a water/vapor barrier when you can save it for a rainy day to pay big bucks for future mold remediation and water damage? 

P.S. you may be able to refill your flat "delcaration" at the local spell checker station...

Brushfire
I don't think you were flamed, I think a logical correction was posted to complimnet your answer! Considering you already have a contractor, why are you trying to provide answers to people's queries with what appears to be limited understanding?

This is not a flame, its a suggestion that what you're having done may not be appropriate for someone else in a different climate(especially the 5 gallon Black Jack Pail approach)

I just bought reclaimed 2" XPS at a third of box store prices. http://pittsburgh.craigslist.org/mat/1463257379.html

As a caution, about a dozen boards of the 280 I purchased were wet enough that I am not inclined to use them. While XPS is very water resistant, it is subject to vapor penetration in challenging installations. (around a freezer; in a bathroom ceiling.) The seller said let em dry out, but you'd probably need a kiln to get this molecular-level work done in a reasonable time frame. Heft some new boards so you know how much they should weigh, and handle reclaimed boards one at a time. I am going to sort mine again using a postage scale.

Thanks for the replies. We are going to go ahead and use the boards, they are $34 each. They are being used on a old cement block home. It has tar paper under the furring strips. The tar paper is ripped in many sections. We do not want to remove theold furring strips. Any suggestion on how this board should be installed? Do we just cut it to size and stick it in? Do we need to add some sort of new moisture barrier or will the foam board be sufficient? The board has a silver liner on each side. Thanks

If pointing out that...

 "It is essential to put the poly over the cement block as a vapor barrier prior to installing the foam."

...isn't a universal truth, but climate-specific, is taken as a flame, methinks somebody is taking it WAY too personally. 

How that becomes personal is beyond me, (as is obsessive grammar & spell-checking)...


















...but I s'pose it was really meant to complement, rather than complimnet brushfire's post, eh? 

I make no conjecture as to brushfire's understanding of water vapor issues based on a single post though.

You don't say what your climate is- got a zip code?

The silver liner is aluminum foil, and extremely vapor retardent. If the interior finished side has a vapor retarder this could become an issue. (Foil/vinyl wallpaper? Poly under the gypsum board?)

Assuming there isn't an interior vapor retarder, it's "safe" to put this stuff on the exterior.  You can leave the ripped felt (it's semi-permeable anyway).  Depending on climate zone you may/may-not want a full poly vapor retarder over the old stuff, including the old furring (which puts them inside of the pressure & vapor envelope of the structure.)

Don't cut the to fit between the furring, but rather use construction adhesive & screws to attach the foam board, and either foam seal/caulk/FSK-tape every seam to make it air and vapor-tight.  Tape or foam any cuts/dings in the foil facing as you go too.  Any housewrap/felt etc can then go over the whole shebang. (Housewrap is highly vapor-permeable, somewhat water resistant, but air-impermeable. It may/may-not be necessary depending on how you do the siding.)

Seal the air gap between both the top & bottom of the insulation and the wall completely with spray foam, making it air-tight from the exterior.

Then, attach new exterior furring long-screwed through the foam & old furring anchoring it to the structural wall. (The required screw spacing will depend on the weight of the intended siding and the thickness of the foam.) Attach the siding to the new furring, leaving the air gap as a drain-plane for any rain penetration and ventilation for high vapor-drive conditions (like sunshine on rain-wetted siding.)

Then you'll end up with:

outside| siding/furring& gap | air & vapor tight foil-clad foam board | old furring & felt | concrete block | interior finish wall

This should work in any climate zone, but it's important that the block wall be able to dry toward the interior when you have foil-clad foam on the exterior.  Any slab-edge (if slab-on-grade) or foundation wall is best  insulated on the exterior, but not with foil clad stuff.  XPS (blue or pink) or EPS (bead-board) will work.  In very wet environments XPS is preferable.  If it's a full basement or crawl space it's possible to insulate it from the interior (again, with EPS or XPS), but know that the concrete block forms a thermal short-circuit in the thermal envelope if it's insulated on one side below grade, and the other side above grade. (The significance of this varies with climate.)

Bebe, dunno where you are, but if there is more than one box store nearby, stop by the contractor's desk in each and ask for a price based on a volume purchase. The national chains routinely knock off 10 percent on purchases that top a grand or two. My fallback, before finding reclaimed foam, was a Lowes quote of $28 on a purchase of 70 2" boards.
To find used, google all the variations of blueboard, extruded, xps, insulation, foam board, reclaimed and toss in "craigslist." I found it in a dozen cities.
You should consider buying a flatbed trailer if you want to take advantage of all the stuff out there laying on the ground. Based on my finds, there are tons of companies making "inventory adjustments" at the moment. Could be yearend cash management. Could be the bottom.