I need help making a decision on how to insulate the interior of our 90-year-old stone foundation basement. We want to finish this area and make it livable.

We've got an all-brick semi-detached (shares one party wall) in Toronto, built 1917 on a stone foundation. Because of the proximity to neighbors, finished porches and other issues, we've basically ruled out digging and insulating the outside.

I've read several of the threads here on basement insulation and I've read the BSC info [link]http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation/[/link]

My head is just spinning with all the information.

The existing concrete floor is very uneven and we are definitely tearing it out, so under-pad insulation and weeping tile are in the plans.
I'm just plain and simply unable to determine what to do to the walls. The walls aren't straight enough for a solution like InSoFast.

We got a quote for using delta-wrap stretching down under the pad to the weepers. We were going to frame in from that and blow in something like icynene , but the whole delta-wrap inside is starting to sound like a bad idea.

The sill plate is about 2 feet above grade, brick above, stone below. Walls are 77 inches from concrete pad to the bottom of the joists. Joists are 2x10 roughcuts (i.e., the real thing from 1917). So that leaves me about 87 inches from pad to the ground-level subfloor .

Total wall square footage is approximately 580.

Questions: 1) What is the best solution for high R-value interior retrofit insulation in a stone-wall basement? (Given our Toronto climate)

2) Seems like delta-wrap protects us from one-off large-leak events (big rains, plugged downspouts), but may prevent drying and/or aggravate condensation and rot. Seems like semi-permeable XPS sheets or blown-in Icynene allow drying, but could get soaked if a leak develops. What to do?

3) If we went instead with rigid insulation, what do we do about air leakage up around the joists? We had an energy audit today (blower test) and the place is a sieve.

4) Also, with the rigid insulation, how do we seal and/or provide additional insulation. 2" is only R10, but if we blow in more insulation, this will limit the permeability.

Any comments greatly appreciated.

Sounds like you have an occasional (?) water problem, so you'll need to dig a trench near the base of the walls and direct the water to a sump pump. When you insulate under the slab, use at least 4" of XPS. The ideal insulation for stone walls is closed cell spray foam because it will adhere to the stone and does not absorb water, but I'm unclear how this will affect the drainage. My guess is that the water will drain through the rock wall down to the drains. The Delta Wrap would provide a positive path for the water and I assume you could apply closed cell spray foam on top of this which would follow the contours of the stone and provide excellent insulation. One potential danger is that moisture could be directed upwars towards your sill and exterior walls, so stop the Delta Wrap slightly above grade level and foam directly to the rock above that. Extend the foam up to the subfloor, covering the sills and joist ends. The spray foam on your rock walls and sill area will go a long way towards helping your infiltration problems.

Hi Bob,
Unfortunately, we've only had the house for a few months, so we don't really know the history of water infiltration. Our best guess is that it's pretty minimal. There are two pieces of evidence that support this: 1) The narrow area between the houses is concrete and graded properly away from the house and 2) there was a very poorly "finished" basement that looked to be about 15 years old and didn't have any signs of mold.
We broke into the floor in a couple of spots already and the soil is very dry. The contractor thought we maybe didn't even need weeping tile.
The issue that we're butting up against is the idea of "interior drying" that seems to be cropping up. Plus the problem of condensation on the interior side of the delta-wrap. I'm not seen evidence that even a closed-cell spray foam can protect against the hot warm interior air permeating the foam and condensing on the cool delta-wrap.
Neither of the two methods listed on the http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation/ mention a delta-wrap on the inside.

I'd be tempted to eliminate the Delta Wrap, but I may be overruled by others more familiar with your climate. As to the weeping tile, you may not need it - now. BUT if you have the one storm where you do need it, it'll be a PITA to do it then. Do it while the floor's open. It may be an unnecessary expense, but on the other hand its good insurance.

Toronto climate is fairly similar to this project in central MA, where they went with 3-5" of the 2lb Icynene product on a stone foundation, sprayed with BlazeLok IB for an ignition barrier, in a wet-basement situation:

https://www.powerofaction.com/media/pdf/DER_CaseStudy.pdf

Pay special attention to how they did the slab insulation, including detialing the short vertical edging of XPS around the slab perimeter, and the sub-slab vapor barrier. The 2lb Icynene product is more vapor-permeable than 2lb polyurethane, so the foundation can still dry toward the interior at ~ R30, whereas you'd have to stop at ~ R12 (2") with most polyurethane. If you intend to finish the interior, you can put up a studwall and 12-13mm gypsum wall-board inside the uneven spray foam to form the ignition barrier rather than going with a sprayed-on product. Do NOT use a poly vapor barrier on the walls- 3" of2lb Icynene (R15) will be enough vapor retardency, and you could install as much as 6" (R30-ish) before you run into foundation-drying trouble.

You can save a bit of money by going with low density Type-I or Type-II EPS rather than XPS under the slab, but would have to add ~25% to the thickness to acheive the same R. On the walls you could also stop at 3" with the 2lb Icynene, and add up to another R13-15 as blown rock wool (blown-only, not batts, due to the unevenness) to deliver ~R30. You'd probably have to make the argument with the inspectors about NOT using an interior vapor retarder, as is still required by Canadian code, even below-grade (despite good science that it is more likely to create than avoid moisture problems when used in basements.) With Icycnene on the wall at 50% of the total R, there IS no condensation problem from the interior air at the foam/fiber interface with Toronto's -6.3C average January temps, and an interior vapor barrier would only trap ground moisture slowlyydiffusing through the foam in the studwall, creating a rot/mold problem.

Open cell foam (like half-pound Icycnene) isn't a good idea here if there is an indication of high ground moisture, or the outer few cm of the foam will saturate. If going with closed cell polyurethane 2" (R12) would be an absolute limit, and 1.5" (R9) would be better if the ground moisture issues are iffy, which is why the higher-perm rating of closed-cell Icycnene works better here- you can go thicker with lower risk of driving ground moisture up to the foundation-sill.

Hi Bob,

Yes, the weepers are a fairly minimal expense now, so probably we'll go with them.
We're having a hard time deciding about the delta-wrap. The contractor is quite insistent that it really protects against moisture intrusion.

Does anyone know if we're just setting ourselves up for an eventual condensation problem on the interior side of the delta-wrap using this method?

Thanks

Hi Dana1,

Thanks for your detailed info. I posted to Bob before seeing your your post today.

After looking over the Case Study, and reading your analysis on insulation, it seems as though you would recommend against the delta-wrap and instead use at least some xps on the wall to create a drain path?

Posted By damon on 08 Nov 2010 01:15 AM
Hi Dana1,

Thanks for your detailed info. I posted to Bob before seeing your your post today.

After looking over the Case Study, and reading your analysis on insulation, it seems as though you would recommend against the delta-wrap and instead use at least some xps on the wall to create a drain path?

Delta Wrap is highly vapor-IMpermeable, which if applied to the foundation wall would increase the moisture content of the foundation sill, and potentially induce efflorescence & spalling on the exterior the above-grade portion of the foundation mortar.

If you look at the cutaway diagram of the installation (see lower left, p3: https://www.powerofaction.com/media...eStudy.pdf ) You'll see that the XPS isn't so much a drain path, but a stub of less-permeable foam around the edge of the slab that gets completely surrounded by semi-permeable MD-R-200. You COULD use Delta-Wrap under the slab and on the perimeter wherever they use XPS (blue, in the diagram) without increasing rot issues at the foundation sill.  The 2lb Icycene is rated 1.3perms at 3", whereas 1.5lb XPS is rated less than 1.0 perms at 2", so the combined permeance of the XPS + Icynene stackup on that section will be ~0.5perms, give or take, allowing SOME drying capacity, but at a reduced rate compared to higher on the foundation wall.  Delta Wrap is more than an order of magnitude lower still, offering essentially ZERO drying capacity.  Under the slab and the lowest portion of the foundation that will be just fine, but the the higher you go on the wall with it, the higher the moisture content of the foundation & sill, raising the risk of problems with the above-grade mortar & wood.

Thanks for the detailed explanation. It seems reasonable then to at least consider the delta-wrap up to grade (or near grade) to protect against a possible one-off water event. We have about 24~26" above grade foundation before the sill.

Ideally, it sounds like an XPS layer under the slab and at least part-way up the wall would work well, then the Icynene.

Is there a non-trademark generic term for Icynene? That is, is any 2lb. open-cell polyurethane foam basically the equivalent?

Thanks,
Damon

Posted By damon on 08 Nov 2010 10:50 AM
Thanks for the detailed explanation. It seems reasonable then to at least consider the delta-wrap up to grade (or near grade) to protect against a possible one-off water event. We have about 24~26" above grade foundation before the sill.

Ideally, it sounds like an XPS layer under the slab and at least part-way up the wall would work well, then the Icynene.

Is there a non-trademark generic term for Icynene? That is, is any 2lb. open-cell polyurethane foam basically the equivalent?

Thanks,
Damon

2lb polyurethane is FAR more vapor retardent than 2lb Icynene. 

If you use generic 2lb polyurethane DO NOT GO OVER TWO INCHES (~R12).

There may be 1.5lb polyurethane products with similar perm ratings though, but DO look at the specs before signing the contract.

All 2lb SPF is under 1 perm @ 2", whereas the Icynene MD-R-200 is 1.3 perms at three inches.

With a perm rating  that high it's reasonable to go 5-6" with it, and you'd be still over 0.5 perms at R25-R30.   Some brands of SPF is already below 0.5 perms at 2", which is something of an absolute lower limit for this sort of application.

The 2.lb Icynene has a 17% lower R for any given thickness than generic 2lb SPF, and it's higher perm rating isn't ideal for every application, but for basement walls it hits the sweet-spot on R vs. permeance.

OK. Excellent. I'll be sure to look at the perm rating. I'm assuming then that the permeability of any drywall will be negligible.