Rim joist spray foam insulation in Claresholm is the single best-value item on most houses in town, and on a stock where about 72% of homes were built before 1991 it is also the one that was built with no air sealing at all. The rim joist is the band where the floor framing sits on top of the foundation wall — a few inches of wood, a sill plate, and in a lot of these houses a gap you can see daylight through.
The cold strip along the skirting
The way this shows up to a homeowner is a line of cold along the floor at the outside wall, usually worst in a finished basement and worst again at the corners. People put it down to the flooring or to the basement being a basement. It is the rim.
The reason it reads as a strip rather than a general chill is that the leak is a line, not a point. It runs the entire perimeter of the house at one height, and the air coming in at that line is at outdoor temperature. It spills along the floor because cold air is denser, which is why you feel it at ankle height two feet in from the wall and not standing up.
In a chinook climate the strip also moves. Each time the outdoor temperature swings, the pressure difference driving air through that line changes with it, so the cold band appears, fades and comes back rather than staying constant. That inconsistency is why it so often gets reported as something other than a draught.
Why nothing cut to size seals it
The standard treatment was a piece of batt pushed into each joist bay. It does not seal, for three reasons: the batt is air-permeable, so air moves straight through it; the bay is not a clean rectangle, because there are joists, bridging, pipes, wires and often a gas line crossing it; and the critical joint is the horizontal one between the sill plate and the top of the foundation, which no batt touches.
Closed-cell foam sprayed into the bay adheres to the rim board, the sill, the top of the concrete and the sides of the joists in one continuous piece. At R-6 to R-7 an inch it gets real R-value into a shallow depth, and at roughly two inches it becomes its own vapour barrier, which matters on a cold wood surface sitting on cold concrete.
The joist space that is doing a duct's job
Here is a detail specific to houses of this vintage and worth checking before anything is sealed. In many of them the return air for the forced-air system was not ducted — a joist space was panned off at the bottom and used as a return. That means the furnace is drawing air from a cavity that is open, at its far end, to the rim.
Where that is the case, the furnace is actively pulling outdoor air through the rim joist every time it runs, which is both a comfort problem and a flue-safety consideration. It is also an easy fix once it is understood, and it is the kind of thing that is invisible unless somebody lifts a ceiling tile and looks.
Look before sealing, and do the top of the house too
Two cautions. Before we spray, we want to know whether there is knob-and-tube wiring, an abandoned chimney chase, or signs of water entry at the sill — foam is permanent and those get dealt with first. And sealing only the bottom of the house changes the pressure in it: the air leaving at the top of the house is what pulls air in at the bottom, so the attic penetrations are the natural companion job rather than a separate one.
Rim Joist Spray Foam Insulation Claresholm: Common Questions
Why is there a cold line along the floor at the wall? Because the leak is a line. The rim runs the whole perimeter at one height, and the cold air that enters there spreads along the floor rather than mixing.
Why does it come and go? The pressure driving air through the rim changes with the temperature difference, and in the chinook belt that difference moves constantly.
We have batt in the joist bays already. Is that not enough? No. Batt does not stop air, and it never reaches the joint between the sill plate and the top of the foundation, which is the actual gap.
How much does rim joist spray foam insulation cost in Claresholm? Priced per board foot of sprayed area, and the rim is a small area, which is why it is the best-value item on most of these houses. Clearing finished ceilings to reach it is the variable.
How do I choose a rim joist spray foam contractor in Claresholm? Ask whether they will check what the joist spaces are being used for first. On this stock some of them are carrying return air, and that changes the job.
Size the assembly with the R-value calculator, then get a free Claresholm quote. More on Rim Joist Spray Foam Insulation Alberta province-wide.