Rim joist (solive de rive): what it is, how serious, what it costs

The rim joist closes off the ends of the floor joists, all around the house. It sits on the sill plate, the wooden piece laid on top of the foundation. In an unfinished basement, it is the band of wood you see between the top of the concrete wall and the main floor, in each space between two joists.

It is a cold spot: only that piece of wood and the siding stand between inside and outside. A French report says « solive de rive », often « isolant absent ou endommagé » (insulation missing or damaged), « pare-vapeur absent » (no vapour barrier) or « non visible » (not visible).

When poorly insulated, the rim joist lets cold and air through. Without a vapour barrier, the warm, humid air of the house reaches it in winter and the moisture condenses there: over the years, the wood can grow mould or rot. The same risk exists when outside water reaches it, through poorly done siding or flashing.

I place it by what the report says: “Can wait” for insulation to redo, “To check” when finishes hide it, higher when the inspector sees damp, rotten or weather-exposed wood.

Insulating the rim joists: $300 to $700 for one section, $1,000 to $2,200 all around the basement. Adding the missing vapour barrier around the whole perimeter: $600 to $1,200. Replacing a rotten section of rim joist: $800 to $2,000.

These are ballpark figures for Quebec, to be confirmed with quotes.

1. Are the rim joists insulated, with what, and is there a vapour barrier?
2. Did you see damp, darkened or soft wood, or signs of mould?
3. How much of the rim joists could you see?

Does your report mention the rim joist? Upload it: in five minutes, I tell you what comes first, what to have checked and what to ask the seller.

Often with spray polyurethane foam, which insulates and stops air and vapour in a single layer. Another option is rigid foam board, well sealed, or batt insulation with a vapour barrier sealed all around.