Something Blue

I just noticed at the Toronto National Home Show this weekend that BASF now has a ‘eco’ version of their Walltite, called Walltite-Eco, which is made partially with recycled products and has the same performance as regular Walltite. It is a purple colour (only for visual differentiation purposes). It is similar to other eco spray foams on the market now.

Any reason you didn’t use this one?

Indeed, you are correct… I would have preferred that we used it, but the only reason we didn’t was cost. Well, that and I wasn’t aware of it until we were just about to spray, and it was too late to stop and evaluate if the numbers would work.

By filling the entire roof cavity with the walltite foam, will that remove any potential condensation issues since you won’t have a ventilated gap space?

Yep, that’s the plan… We have to fill the entire void, and then simply apply vapour barrier (which the building inspector demanded.) This actually seems odd to me, what with the sprayfoam acting as a vapour barrier itself… but I digress, they demanded it so they’ll get it.

We’re also considering filling the rest of the void with batt insulation (so there isn’t any gap between the spray and the plastic). I suppose it may be overkill, but it’s a possibility as well.

The building inspector is wrong, as you now end up with a double vapour barrier. This means that you now have the potential too have moisture trapped in between the two vapour barriers. I would try to convince him (show him the data sheets for the product, let him talk to the manufacturer, etc) or go above his head (which, of course, could result in him being even stricter with other things). He doesn’t understand the product, but no surprise there. Maybe he doesn’t understand the difference between the low density and high density (ie 2 lb) spray foam. Try to find out if there is some written directive from the building department or a building code regulation stating that you still have to have a vapour barrier with the high density, because, if not, then it’s a discretionary item.

One of the installation mistakes almost everyone makes with high density spray foam is that they forget it is only a vapour barrier between the studs (ie where it is applied). As such, it is not a continuous vapour barrier. You still have the potential for tiny gaps between studs where they are sandwiched (or ‘sistered’) against eachother. You also have tiny gaps where studs meet headers, etc. Yes they are small, but that’s all you need for air and moisture to get through. And, those tiny gaps are all over the place (25% of the exterior face area of a house is comprised of framing members, not insulation). It is important that these tiny gaps be caulked. I have yet to encounter a single spray foam installation company that mentions this issue, yet it is a real issue.

I am surmising that inspectors don’t accept high-density spray foam as a vapour barrier because of the fact that no one is caulking these joints.

I’d recommend filling the rest of those ceiling voids. You’ll get some extra R-value in the roof, but more importantly you’ll cut down on sound transmission.

Because Walltite is rigid, when it rains, you’ll hear it much louder and more clearly than a batt or blown insulation. A few inches of Roxul should make it bearable!

I think Scott has a point. Did some digging and found a reference for unvented roof assemblies under the International Residential Code, 2007 Supplement, section R806.4 “Unvented Attic Spaces”.

Have a read through the following page:

http://www.inspectorsjournal.c.....ic_id=6120

At the bottom of the page, there’s a link that actually opens up a pdf of the IRC 2007 supplement. On page 73 of the supplement it states the following (paying close attention to point #2):

R806.4 Unvented attic assemblies. Unvented attic assemblies (spaces between the ceiling joists of the top story
and the roof rafters) shall be permitted if all the following conditions are met:

1. The unvented attic space is completely contained within the building thermal envelope.
2. No interior vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly.
3. Where wood shingles or shakes are used, a minimum 1⁄4 inch (6 mm) vented air space separates the
shingles or shakes and the roofing underlayment above the structural sheathing.
4. In climate zones 5, 6, 7 and 8, any air-impermeable insulation shall be a vapor retarder, or shall have a
vapor retarder coating or covering in direct contact with the underside of the insulation.
5. Either Items a, b or c shall be met, depending on the air permeability of the insulation directly under the

structural roof sheathing.
a. Air-impermeable insulation only. Insulation shall be applied in direct contact to the underside of the
structural roof sheathing.
b. Air-permeable insulation only. In addition to the air-permeable installed directly below the structural
sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing
as specified in Table R806.4 for condensation control.
c. Air-impermeable and air-permeable insulation. The air-impermeable insulation shall be applied in direct
contact to the underside of the structural roof sheathing as specified in Table R806.4 for condensation
control. The air-permeable insulation shall be installed directly under the air-impermeable insulation.

I know this is based on US based International code, but it would probably be worthwhile to bring up with your building inspector if there should be a vapour barrier on the ceiling side. The worry is that any moisture that did get in between the closed cell foam and the vapour barrier would have no place to escape, whereas without the vapour barrier then moisture could then escape to the interior side.

It also sounds like your setup falls under 5.c. air impermeable + air permeable insulation.

sorry for the long message!

Hi Jeremy –

I think the house is looking great. Thank you for sharing all of this info for us to learn from. Can you give a rough estimate of what it costs to spray insulate?

Thanks – DAN

It’s based on square footage (with probably a premium for small jobs). Interesting to see what he paid, as when I was at the Toronto National Home Show last weekend, I asked one of the companies offering high-density spray foam insulation (both regular and ‘eco’ versions) and it was in the order of $1+ per square foot per inch of depth + tax, depending on which particular brand is used. With 3 inches (in order to get about R20) usually used on exterior walls that’s $3+ per square foot of wall area. but, nothing beats it.

$1 per inch per square foot is what I paid for BASF Walltite.

Did they calculate it per gross sq ft of wall area or did they make an allowance for studs, headers, protrusions and the like (which comprise about 25% of the total external envelope of a house?). I assume they must take the sq ft of window and door openings out of the equation.

For me, they deducted the openings. They didn’t make allowances for studs, etc. ... but I’d be hard pressed to say they account for 25% of the wall area.

A 1.5” stud every 16” is only 9%. Headers, jack studs, etc., will increase that, of course … but surely not three-fold. Maybe you’re overframing your walls!

Oh, and it was suggested to me to use acoustic seal in all the gaps between double joists, where headers meet studs, etc., then cover them with tuck tape.

You could also add 1/2” or 1” of rigid insulation on the exterior, and tuck tape the joints, to provide a full thermal break … but that’s going to cost a chunk more!

I got that 25% from both Holmes on Homes and Ask Jon Eaves and other publications too.

But, I thought, why not calculate it? The following calculation is for a 12” wide width of wall in a 2-store home with 10’ and 9’ ceilings, where the headers are 12” high and there are double 1.5” thick floor and ceilings plates on each floor. This is pretty typical construction. In fact, maybe a bit conservative in terms of framing as headers are often higher than 12”. I am excluding the basement as it is a concrete or block wall.

The height of the wall will be 10’ floor height + 1’ header + 9’ floor height + 1’ header. For a 12” width of wall, the total of the 2×12” headers and the 4×1.5” double floor and ceiling plates is 30”, so the square footage of wood in this 12” width is 12” x 30” = 360 sq in.

With studs at 16”, for each 16” width of wall you have 1.5” of stud so therefore for each 12” width you have 12/16×1.5” = 1.125” of stud. For the 9’ and 10’ wall heights the total height of the studs, accounting for the floor and ceiling plates is 10’ + 9’ = 19’ the 6” for the 4 plates so that’s 18’6”. 18’6” x 1.25” = 222” of height. 222” of height x 1.125” taken up by studs = 249.75 sq inches. 249.75 sq in + 360 sq in = 609.75”. 12’ width of 21’ high wall is 12 x (21×12) = 3,024 sq in. Of this, 609.75” is taken up by wood. So 609.75/3,024 = 20.2% of wall area.

And, that’s not even including any corners, sistered or packed studs, jack studs, cripple studs, protrusions or the effect of window or door openings. So the % could easily be 25% or higher.

So it looks like the 25% figure is quite accurate. Let me know where my arithmetic is wrong if you find an error in my calculations.

I guess in the end, it really depends on where the guy decides to take measurements from in terms of how much he adjusts, if at all. But if he used the entire exterior frame dimensions, the 25% figure is pretty accurate plus or minus any roof contribution.

thanks for all the info.

I’ll be writing a detailed post about the price of insulation once all of the costs are all finalized, but your $1 per square foot is pretty accurate. For R-20, it was about $3.50 per inch, per square foot. The cost was also affected by the amount of preparation required. For instance, the two exterior overhangs needed to be completely enclosed to ensure the overspray didn’t land on anything.