The rim joist is the band of framing that sits on top of the foundation wall and carries the floor. In a town where about 70% of the housing was built before 1991, it is the single most reliable job we do, and the reason is simple: it is the leakiest accessible part of these houses, it is the easiest surface to reach, and it is a small scope with a result people notice within a day.
It is outside the ground, in the wind
A foundation wall below grade is protected by soil, which is a poor insulator but a perfect windbreak. The rim joist is the part of the same wall that sticks up above the ground, so it has nothing against it but outdoor air. On a lot with open field upwind, that band is being pressurised by wind all winter, and the gaps in it are the ones that matter most: between the sill plate and the concrete, between the sill and the rim board, and at the end of every joist bay.
Why cold floors happen along the outside walls
Walk an older house here in January and the floor is noticeably colder within a couple of feet of the exterior walls. That is the rim joist. Cold air entering at the sill moves into the floor cavity, chills the subfloor from below, and in a finished basement it does the same thing behind the ceiling where nobody can see it. The complaint that arrives as "cold floors" is almost always this.
What was there before, and why it failed
The original treatment, if there was one, is a piece of batt stuffed into each joist bay, sometimes with a plastic bag around it. Batt does not seal, so the air keeps moving. Worse, warm humid basement air gets into that batt, reaches the cold rim board behind it, and condenses there. Pull an old batt off a rim joist in an older house in this town and the wood behind it is frequently stained and occasionally soft.
The assembly that works
Closed-cell foam sprayed directly into each joist bay, against the rim board and up onto the underside of the subfloor, with the sill plate joint and the top of the concrete included. It adheres, so there is no gap for air to move in. It is a vapour barrier at about two inches, so moist basement air never reaches the cold wood. And at roughly R-6 to R-7 per inch it reaches a worthwhile R-value in a cavity only a few inches deep.
Cantilevers and bay windows get missed
Where a floor projects past the foundation, for a bay window or a cantilevered section, the cavity underneath is open to outdoor air on three sides and is usually either empty or stuffed. Those are the coldest spots in the house and they are routinely left out of a rim joist quote. Ask about them specifically.
The crew on your job
Rim joist spray foam insulation Stettler 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 Stettler: Common Questions
Why is the floor cold only near the outside walls? Because cold air is entering at the rim joist and moving into the floor cavity. The middle of the floor is over a warmer basement.
Is batt in the joist bays good enough? No. It does not stop the air, and it lets warm moist air reach the cold rim board behind it, which is how the wood gets damp.
Is this worth doing on its own? It is usually the best single-item job in an older house here. Small scope, accessible, and it addresses the biggest accessible leak.
How much does rim joist spray foam insulation cost in Stettler? It is priced per board foot over the sprayed area, so the perimeter length of the house drives it rather than the floor area. Clearing stored items away from the walls and removing any existing batt are the usual preparation items.
How do I choose a rim joist spray foam contractor in Stettler? Ask whether the sill plate joint and any cantilevered sections are included. Those are the two places a rim joist quote most often stops short.
Size the job with the R-value calculator, then get a free Stettler quote. More on Rim Joist Spray Foam Insulation Alberta province-wide.