Rim joist spray foam insulation in St. Paul is the best value item on almost any older house in this town, and it has a local wrinkle. Because so much of the stock has been added to over the decades, a single house often has more than one rim joist: the original one around the old foundation, another around the addition, and sometimes a third where a porch or a back entry was built on a different footing. They are different ages, different depths and different levels of bad.
What the rim joist is and why it leaks
It is the band of wood at the top of the foundation that the floor joists land on, and it sits exactly where the foundation stops and the house begins. It is a horizontal joint, it is interrupted by every joist end, and in houses of this era it was rarely sealed at all. Warm air leaves there in winter and cold air comes back in lower down. People feel it as cold floors near outside walls, and it is usually a bigger single loss than any wall in the house.
Three rim joists, three different problems
The original is typically the deepest and the roughest, often sitting on a stepped or uneven top of foundation with gaps you can see daylight through. The addition's rim is newer and better built, but the joint where the addition's floor system meets the original wall is open unless somebody closed it on purpose, and that joint is interior so nobody has ever looked at it. The third, under a porch or an entry, is frequently over a crawl space or open to outside air underneath, which makes it the coldest of them even though it is the smallest.
Why batt does not solve this
The usual treatment is a chunk of batt pushed into each joist bay, sometimes with a scrap of poly. It fails for a specific reason: batt does not stop air, so the warm moist air still reaches the cold rim board behind it. Then it condenses there, out of sight, against wood. In northeastern Alberta the cold is sustained for months with no reliable thaw to dry anything out, so that moisture stays in the wood all winter. The batt also traps it. Rotted rim boards and stained joist ends in older houses here are usually the result of that detail rather than of any exterior leak.
How foam is applied here
Closed-cell foam is sprayed directly onto the rim board and carried onto the sides of each joist and down onto the top of the foundation, so the whole joint becomes one continuous sealed surface. At roughly R-6 to R-7 per inch it reaches a useful value in a couple of inches, and at about two inches it is its own vapour barrier, so the rim board stays warm enough that nothing condenses on it. Each bay is a separate little cavity, which is why this is slow, fiddly work and also why it is so effective.
What it takes to do and what gets in the way
The bays have to be accessible, which means clearing stored material away from the perimeter and, in a finished basement, cutting access where the ceiling is closed in. Wires, pipes and ducts running through the bays get sprayed around rather than moved. Anything with a gas appliance nearby needs its combustion air and venting confirmed, because sealing the rim tightens the house. A quote should state which rim joists are included: on an extended house, one of them is often not reachable without opening something, and that should be decided before the crew arrives rather than during.
Who quotes it and who sprays it
You are dealing with the contractor directly on rim joist spray foam insulation St. Paul. We quote the job, we schedule it, and our own installers do the work.
Rim Joist Spray Foam Insulation St. Paul: Common Questions
Why start with the rim joist? It is the leakiest accessible part of an older house, it is a small quantity of material, and it does not require renovating any living space.
We have batt in those bays already. Is that enough? No. Batt does not stop air, so moisture still reaches the cold rim board and condenses behind it where nobody can see.
Our house has an addition. Are there two of them? Usually, and sometimes three. The joint where the addition's floor meets the original wall is the one that gets missed.
How much does rim joist spray foam insulation cost in St. Paul? It is priced by sprayed area and thickness, so it follows the perimeter length and the bay depth. Clearing access and any cutting into a finished ceiling should be separate lines.
How do I choose a rim joist spray foam contractor in St. Paul? Ask how many rim joists your house has. On an extended house in this town the right answer is more than one, and a contractor who says one has only walked around the original basement.
Size the assembly with the R-value calculator, then get a free St. Paul quote. More on Rim Joist Spray Foam Insulation Alberta province-wide.