With about 76% of Bow Island homes built before 1991, the band where the floor meets the foundation is the single most reliable retrofit in this town. On older houses it is also rarely the tidy rim joist the textbooks draw, and the first thing we do is find out what is actually there.
What you actually find at this level on an old house
Sometimes it is a conventional rim board between the joist ends. Often it is a plank or shiplap sheathing run past the floor level with nothing behind it. On the older houses it can be a short cripple wall standing on the foundation, or joists bearing directly on a mudsill with a beam pocket cut into the concrete. Each of those is a different shape to seal and a different amount of work to reach, and a quote written before anybody has looked at it is a guess.
Dry air has opened the joint between wood and concrete
This is the detail that makes the job pay here. Foundations in this era were poured and the mudsill bolted straight down onto them, with no gasket and nothing sealing the interface. Decades of genuinely arid air have taken moisture out of that timber and it has shrunk. What is left is a thin, continuous, slightly irregular gap running the entire perimeter of the house between the bottom of the wood and the top of the concrete. It cannot be stuffed, it cannot be taped onto a dusty concrete face, and it is open to the outside along its whole length.
Why foam is the only honest answer to that shape
Closed-cell foam is applied as a liquid and expands into the joint before it sets, bonding to the concrete on one side and the timber on the other. It spans an irregular gap, it does not need a flat surface to adhere to, and at roughly R-6 to R-7 per inch it becomes the air seal, the vapour control and the insulation in a single pass. Two to three inches across the rim and down over the sill is the usual specification. Nothing else available does all of that in a space you have to reach between joists.
What the batt that is in there now is doing
Many of these bays already have a piece of fibreglass pushed into them, sometimes with a paper facing turned the wrong way. It is doing almost nothing, because air passes through fibreglass freely and the gap at the sill is upstream of it. Worse, it holds the warm humid air of the house against a cold rim board, which is why the batt in a bay like that is often damp or black at the outer face when we pull it out. Taking it out and spraying the bay changes the behaviour, not just the number.
Why we recommend this one first
It needs no demolition, nothing has to come off the outside of the house, nobody moves out, and it is reachable from an unfinished basement in a day on most houses in this town. It also closes the band that drives stack effect, which is the mechanism behind cold floors on the main level and draughts that seem to come from nowhere. On a pre-1991 house we would rather do this properly than do a wall badly.
Bow Island houses where it is harder
A finished basement with drywall right up to the joists means access has to be cut, which changes the job from an afternoon into a project. Houses on crawl spaces have the same detail but a tighter working space. In both cases we would rather tell you that up front than discover it on the day.
Who quotes it and who sprays it
Rim joist spray foam insulation Bow Island is quoted, scheduled and sprayed by us. Our own installers are on the job, and the number you are given is the number we stand behind.
Rim Joist Spray Foam Insulation Bow Island: Common Questions
What exactly is the rim joist? The band of framing at the top of the foundation wall that the floor sits on. It is outdoors on one side and inside the house on the other, and on old houses it is usually the worst-sealed part of the envelope.
Why is there a gap under the mudsill? Because there was no gasket when it was built and the wood has shrunk since. Dry air does that progressively, so the gap on a sixty-year-old house is wider than it was.
Should the existing fibreglass stay? No. It lets air through and it holds moisture against cold wood. We remove it and spray the bay.
How much does rim joist spray foam insulation cost in Bow Island? It prices by the length of perimeter and the thickness sprayed, so a straightforward open basement is the cheapest useful spray foam job on the house. Cutting access through finished walls is what adds to it.
How do I choose a rim joist spray foam contractor in Bow Island? Ask them what they expect to find at the sill on a house of this age. If they have not thought about the mudsill joint they are quoting the bays and missing the leak.
Size it with the R-value calculator, then get a free Bow Island quote. More on Rim Joist Spray Foam Insulation Alberta province-wide.