Spray foam on wet rubble walls - yea or nay?
December 31, 2020 12:38 PM   Subscribe

So, we bought a century home (circa 1895) six months ago here in Ontario and are slowly discovering all the quirks of owning this old gal. As you might expect, temperature control is proving tricky: the first floor is quite chilly all year round, while the second floor is hot in summer and cold in winter. We're planning to upgrade the attic insulation, but the other question that has come up is how to insulate the basement - more details inside.

The basement is unfinished, with rubble walls and a dirt/limestone floor, both of which get fairly wet with heavy rains. We've accepted that we'll never have a finished basement but we're getting conflicting opinions about what to do about moisture/insulation.

The spray foam people say, of course, "just spray foam the walls" which will ostensibly keep moisture and cold out. Others I've spoken to have said not to use spray foam with hundred year old rubble walls since they're leaky by design and blocking the passage of moisture into the basement could cause problems downstream. They've suggested installing perimeter drains leading to a sump pit, putting a dimpled membrane on the walls, laying concrete, and then framing out the basement with insulation.

As a science-minded person, what bugs me is that I can't find any actual hard evidence about the pros and cons of various approaches.

Has anyone else gone through this kind of process and gotten solid advice about what to do?
posted by greatgefilte to Home & Garden (15 answers total) 2 users marked this as a favorite
Theres a lot of advice for houses of this age on the Peter Ward youtube channel.
posted by Lanark at 12:50 PM on December 31, 2020

Best answer: I had a century home in Ontario with fieldstone walls. My basement wasn’t as leaky as yours (it was definitely useable) but the advice I got from multiple professionals was to NOT insulate the walls. The plan to install perimeter drains and then basically build a basement within the basement sounds about right.
posted by saucysault at 12:56 PM on December 31, 2020 [6 favorites]

Best answer: I also have a century farmhouse in Ontario, it's a small world. My basement doesn't have any water issues but temperature control was very tricky until I fixed two things:

1. Replaced the board-and-batten siding and put proper insulation under it, and found sections of brick that had no insulation on the interior side (a few closets) where I insulated over the ancient lath and plaster. The windows were already new-ish so this was enough to fix the first floor.

2. Ductless split head heat pump with 3 heads on the second floor. This was game changing, the upstairs had no ducts so running the lines up the exterior of the house made it possible to fix both heating and cooling all at once.
posted by allegedly at 1:12 PM on December 31, 2020 [2 favorites]

Best answer: I wouldn't. All the sprayfoams I've seen will absorb water to at least some degree. Your best bet is to dig a french drain to dry things out, then sprayfoam for insulation (if you still think it the best route) only after you are sure your water problems are dealt with.

My boss had what amounted to a creek running around a large boulder that was part of his foundation wall in his old house's basement. One of the previous owners had dug a channel into the floor to direct the water outside, but any time there was heavy rain it would spray everywhere due to the water pressure. After putting in a french drain, it stayed dry as a bone no matter the weather. It took a lot of digging, but it was doable.
posted by wierdo at 2:49 PM on December 31, 2020 [3 favorites]

Another approach that I've seen is to insulate the basement ceiling/house floor to insulate the living space of the home from cold of the basement. But, using highly rated roll-in batting is preferable to spraying foam as you'll want to be able to get to any piping or wiring that may be in that space for repair, etc.
posted by quince at 3:59 PM on December 31, 2020 [1 favorite]

Response by poster: allegedly, I was thinking of a heat pump as well. Do you find that they're helpful in the winter? We used to have one in our old house but only tried using the heat up til October/November.

Also, what did you put over the lath and plaster? I suspect there's not much if any insulation behind our first floor walls, which are most L&P. And there's non-structural brick on most of the exterior so sadly I don't think we can work things from that angle.
posted by greatgefilte at 4:47 PM on December 31, 2020

We had four heat pumps installed in an 1800s house in Philadelphia (not nearly as cold as Ontario, but still a data point!). Our experience with them has been exceptional. I would strongly recommend the models that work in very cold weather - we have Mitsubishi Hyperheat. They provide effective heating and cooling for a very reasonable operating cost. (For us, in the coldest months, it's costing just over half to heat the place compared to our [admittedly old and oversized] gas steam boiler. They are now the primary heat source in the house, and are used all year round. However, keep in mind that heat pumps work most efficiently in moderate temperatures and get less efficient the more extreme the outside temperature, so in a real cold snap, they will be less efficient to run than in 30sF weather. Even so, as I said, they cost about half what the gas boiler cost to run in the coldest months, and the cost to run in the shoulder season months is very little).

I think in your application they would work great. They're really good at zone heating, and I think as something to supplement the main heat source and even out the temperature, they'd be superb. Using the minisplits to cool has also been much cheaper than window units. They also dehumidify in the summer, which is nice. We've had the oldest two installed for coming up on four years, and they've needed almost no maintenance, are basically idiotproof, and are super quiet while running. We got something like a free 15-year warranty on them because they were installed by a Mitsubishi diamond dealer. They're very pricey to install - the main downside - but they've been worth it to us.
posted by ClaireBear at 5:50 PM on December 31, 2020 [1 favorite]

I might look into five things, re. insulation:

1) Insulating the attic (as you said).

2) The basement perimeter drains idea with insulation beyond them (as you said).

3) Insulating between the basement's ceiling joists (i.e. insulating between the basement and the living space above). You'll want to look into where your pipes are, what heat there is in the basement to prevent them from freezing (furnace/boiler?), etc.

4) You could potentially build stud walls over the lath and plaster and put insulation between the studs (i.e. essentially make modern new-build walls inside your house). This would be tremendous effort, would create complications with plumbing and electric running in your walls, and would also create issues with window sill depth etc. But an option to consider.

5) Replacing the windows. I know it's sacrilegious in certain circles to consider replacing historic windows, but I know from experience it can make an enormous difference, especially if you live in a windy climate. If you have windows from the 1920s or earlier, you likely have open channels on either side of your windows for the movable weights to raise and lower the window, and the wind just whips inside through those. If you replace your windows, you can get new full-frame windows (not "replacement windows) that involve removing those channels and enlarging the windows (or, if you're unwilling to do that, filling those windows with spray insulation). Also, modern windows are so much tighter and more energy efficient than old windows - low e glass, double paned, etc.
posted by ClaireBear at 5:59 PM on December 31, 2020

Response by poster: ClaireBear , thanks, that's helpful. On the plus side, all the windows in the house are relatively new so I think less of an issue. Though there are still plenty of air leaks around the doors that I need to tackle.

I also just happened to notice that there's very chilly air coming out of the furnace return on the main floor (it looks to be a remnant from an old gravity furnace system). And lo and behold, it's basically open on one side to the foundation wall and looks pretty leaky elsewhere, so likely another source of misery.
posted by greatgefilte at 6:13 PM on December 31, 2020

Oh, one more idea. We had an energy engineer in to size our minisplits. (Definitely do not let the minisplit companies size them - we had several companies in, and their sizing was all over the place relative to each other! The minisplits are designed to work at partial capacity by modulating, so it's not a bad thing to oversize somewhat, but if the average load is below the minimum modulation, you'll get significantly decreased efficiency and comfort. The sizing is key, as is the placement.) The $500 we spent on the energy engineer was well worth it, especially given that's only about 10% of the cost of one minisplit. He did a blower test to measure air leakage, and determined how many BTU we needed on each floor, as well as optimal placement of minisplits for air flow etc. For another $500 (which we haven't done yet, but will likely do at some point), I think he was going to do more advanced energy analysis, including coming back with an infrared camera to see precise areas of air leakage, which can then be sealed with foam insulation or whatever. For that matter, you could probably buy an infrared camera and have a go yourself.
posted by ClaireBear at 6:29 PM on December 31, 2020 [1 favorite]

I got an "enhanced capacity" heat pump which works down to -25C / -13F. I'm far south enough that we don't have a lot of nights colder than that, on average, and the house also has a furnace for the first floor. It's hard to get much lower without going into bivalent heat pumps that literally put a gas burner in front of the intake. I've never seen one but I'm told they exist in northern Canada.

Over the lath and plaster - studs, spray foam, drywall. All of the closets luckily had space to bring in the outer wall that much.

+1 to insulating between the basement's ceiling joists, I had that done as well with the other spray foam.
posted by allegedly at 7:19 PM on December 31, 2020

The short version is that if it were up to me and I had a do-over, I'd not try to turn an older basement into living space. It can still be made very useful with a tiled bathroom, a sauna, laundry room, workshop and storage shelving.

I had a 1911 Toronto home with very roughly poured concrete walls and large stones impinging on the interior. I stayed away from spray foam mostly because it was really expensive in the early 00s, but also because people had said that it provides perfect cover for termites.

As part of an underpinning job, I'd had perimeter drains installed on the inside with another drain and a dimpled membrane on the exterior. Ideally, it would have been good to install rigid foam under the exterior membrane, but the foundations was too irregular (with your rubble wall, I doubt it would be safe to excavate for this). To finish the basement, I installed a stud wall several inches away from the concrete with a vapour barrier behind it and pink insulation between the studs. It sort of worked but it's nearly impossible (and maybe not advisable) to retrofit a seamless vapour barrier on an older home that wasn’t designed for it. On really hot summer days, you had to keep the basement doors shut to keep the humidity from getting into the wall cavity and creating a musty smell. It really wasn’t worth the trouble or expense.
posted by bonobothegreat at 8:44 PM on December 31, 2020

https://www.buildingscience.com/ Is a good resource for this kind of thing, I think the guy may live in Ontario even.
posted by sepviva at 9:25 PM on December 31, 2020 [1 favorite]

Just a note -- if your house is double brick construction, and many of that era are, you want to be very careful about how much you insulate the walls. The bricks and mortar of the time are accustomed to being heated by the body of the house to prevent ice formation in the body of the bricks, which leads to spalling (shards falling off) and eventual crumbling. Insulate the living space too much, and the bricks will begin to fail due to cold weather action.

In a single brick (bricks over a wood frame) house this isn't as big a deal because the bricks aren't totally load bearing, but a double brick house the integrity of the structure depends on the bricks completely.

You will need to balance the extra expense of heating the house (and the bricks) with poor wall insulation, or having your house start to crumble and needing regular work from a mason.

The alternative is insulating the exterior of the house, which can be done for sure, but certainly changes the character of the whole building and leads one to wonder why one bought a century home in the first place.

They're beautiful houses but not cheap to keep no matter what you do. (Ours was built in 1927 and it was lovely, truly lovely, but paying $600 a month in the winter for an efficient gas boiler to just keep the house at 19/15C is kind of bullshit.)

I advise consulting a mason or an engineer who specializes in old houses specifically about your brickwork before you begin any major insulating project.
posted by seanmpuckett at 7:31 AM on January 1, 2021 [2 favorites]

Response by poster: I advise consulting a mason or an engineer who specializes in old houses specifically about your brickwork before you begin any major insulating project.

Thanks! I'm pretty sure it's just a brick veneer rather than double brick but will definitely keep that in mind.
posted by greatgefilte at 7:37 AM on January 1, 2021

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