Looking at purchasing a 1600 square foot building. It was built in the late fifties to serve as a store front and home. The house has block walls to ceiling with some interior walls all block as well. The building is square, 40 x 40, and has a very good central fireplace with insert. The brickwork and clay flues are solid. Now the question.. I am looking to put down leveling cement to bring entire floor to level and then glue down 4" solid blue board foam with laminate on top. Will this suffice for moisture problems and give good insulation value. I was thinking of radiant also but may not be able to do this. what do you think?

Where are you located (zip code, if USA), for climate & subsoil temp references?

Blue board is XPS (extruded expanded polystyrene), which has zero capillary draw (it won't wick moisture) and fairly good vapor retardency. At R5/inch you're looking at R20 for the slab, which may be overkill, especially if the money would be better spent on insulating the walls & attic, etc. In much of the US 2" would be sufficient under a radiant floor.

EPS (bead board) also has no capillary draw and is often cheaper per R value (but thicker, since it's only ~ R4/inch), and would be just fine under a radiant floor from a loading point of view, despite having somewhat lower compressive strength compared to blue-board.

With any type of finish flooring (laminate included) you'll still need to install some sort of sub-flooring, but it need not be as heavy as the subflooring designed for joisted floors, since it's fully supported by the foam & slab. (Tongue & groove half-inch OSB sheathing would be able to take the load.)

Cement block walls leak air & water vapor, and have very little insulation value. It's possible to get decent measurable improvement on the air-leakage & R value front by filling the hollow cores with a non-expanding injection foam. In a full-gut bare/wall situation it's also possible to insulate with spray foam, rigid foam board etc on the interior as well, but there a many particulars that need attending to with approach (some of which are climate or construction specific.)

Thank you for the reply.

Southern Ontario on coast of Lake Erie due north of St. Williams. I'll let you practice your Google maps. LOL.

I have been looking into InSoFast to lay down on floor. I was thinking about laying the dimpled plastic used on foundations(dimple side down) and then screwing the insulation down. Maybe some OSB on top of this. I am not looking at the expense of the radiant heat, just conventional (wood cookstove).

Researching, I came across QuadLock R-Etro panels which I would install externally on the walls (R26) to take advantage of the thermal mass of the block. Ceiling of course VERY well insulated.

Your thoughts on this idea.

Regards.

First focus on insulating the walls and add wings of foam that extend outwards from the exterior wall. Dry ground insulates reasonably well if there is enough distance to the cold.

You can add radiant - I'd use heat transfer plates (over floor foam of course).

The Erie shore weather & subsoil temps are pretty much the same as US climate zone 6, and going to at least R10 center slab XPS (2" blue-board) or R12 with EPS (3" bead-board) is cost effective in the long term using reasonable discount rate and energy inflation assumptions. Extending it a meter beyond the slab edge (as jonr suggests) protects it from frost heaving as well.

Beyond those levels, R15-R20 would only make sense if the slab was a radiant floor or you were using reclaimed/recycled goods at 1/3 the cost of virgin stock or less.

The dimpled plastic would not be necessary under InsoFast on the floor (which is EPS). If code requires a vapor barrier, 6mil poly is much cheaper. EPS will not absorb ground water, so it's not really a problem to lay it directly on the slab. Any subflooring that is above it is warmer & drier than the slab, and thus protected from groundwater moisture as well- it's moisture content is driven by the room's RH & temp, since the now cooler slab has a much lower water vapor pressure.

The R-Etro system works, but a do-it-yourself solution would be somewhat cheaper, if you have the time to figure it all out. (using reclaimed foam it would be MUCH cheaper, if you can find a local supplier, or have it shipped from somebody like InsulationDepot.com.) R26 walls would be appropriate for an R10 slab. An R55-60 roof would also be appropriate, if it fits. With any foam-overcoat solution it's probably worth first applying a foundation-waterproofer type sealant over the outside of the block as a primary air-barrier. Using recycled/reclaimed polyiso on the walls R40-R50 walls (6-8" of insulation, similar to an R26 InsoFast thickness) would not be out of the question- cheaper than virgin-stock EPS of the same dimensions, but with 50% more R.

Thank you both for taking time for the further replies.

jonr, the foundation goes four feet down. Should I take the vertical down four feet and then wing out three feet? Would two feet down and then three feet on a 45 degree angle be sufficient?

Thank you for the link to Insulation Depot Dana1. What would be the best process of attaching the foam, as there is no connecting system as the R-Etro, to the exterior. Will be using vinyl siding as exterior finish. Also, would it be best to put house wrap before or after the foam?

Once again, thank you for your insights.

Regards.

Shallow wings of foam with a slight slope away from the building involve minimal digging. Or if you are going to insulate the floor and the walls completely on the inside, then you can skip all exterior insulation.

Posted By onecansay on 12 Jul 2011 03:12 PM
Thank you both for taking time for the further replies.

jonr, the foundation goes four feet down. Should I take the vertical down four feet and then wing out three feet? Would two feet down and then three feet on a 45 degree angle be sufficient?

Thank you for the link to Insulation Depot Dana1. What would be the best process of attaching the foam, as there is no connecting system as the R-Etro, to the exterior. Will be using vinyl siding as exterior finish. Also, would it be best to put house wrap before or after the foam?

Once again, thank you for your insights.

Regards.

Use exterior furring through-screwed to the cement block to mount the foam and provide something on which to attach the siding:

http://www.greenbuildingadvisor.com...athed-wall

You'll have to use different fasteners & spacing for mounting to a block wall rather than timber-framed. I haven't seen a block wall foam-overcoat retrofit yet, but I'm sure there are a few ways to go at it.  For mounting thinner foam on interior walls I've used TapCons + furring, but SFAIK the longest 1/4" shaft Tapcons are the TCF146  (6"), which would be good for 4" of foam + 1x furring.  You can probably do 6" of foam into block using 5/8 x8" Titens, but that's an awfully fat screw.  Try to find a suitable concrete anchor screw with a 1/4" shaft if you can, 3/8" at most.  With vinyl siding it's not as if it needs a fatter (and more thermally-bridging) screw to handle the loading.

Housewrap location within the stackup depends on how you intend to mount & flash the windows:

http://www.greenbuildingadvisor.com...ie-windows

WOW. Information conduit or what!!

Thank you VERY MUCH.

Some call me frank