Double Rim Joists between Foundation and Log Walls

Log home construction often uses logs or timbers as rim or band joists. We used engineered lumber, Weyerhaeuser LSLs.

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The rim joists are laminated strand material. The log walls will sit atop this structure, so we used double rim joists.

Henryk, double rim joist pieces and floor ijoists all in position for cutting.

Laminated strand lumber is prone to breakage in handling the long, flexible pieces. Watching these expensive, special-order boards flop up and down made me nervous, but we got them in place without breaking any.

Once in place, LSLs support the bearing load as well as a log, and provide more R value. Along the short dimension it took 2 rim joists with about a 3 inch space between them. The space is filled with insulation.

Double rim joists will support the log walls

Along the long dimension, perpendicular to the floor joists, the outside rim joist is one continuous piece (an advantage of man-made lumber) and the inside rim joist is made up of blocks between the floor joists. Again, the space is filled with insulation. 

Curt stuffs insulation into cavities along the blocked rim joists

The floor joists are nailed through the rim joist into the top and bottom flanges of the i-beam joists, just like a typical sawn-lumber structure. The floor joists are toe-nailed down to the mud sill through the bottom flange. The blocks are nailed or toe-nailed to the joists.

The web of the i-joists allows air and moisture to escape from the small cavities between joists. (It also creates critter hiding spaces, which is another good reason to leave no ingress to the crawlspace for crawly things, like bugs and rodents.) On the short dimension, but penetrations for wiring will allow convection there.

On the walls where the patio concrete slab extends above the stem wall, we attached ledgers.

Mike installs a ledger on a slab. Tar paper will go between the untreated wood and the concrete.

On advice of somebody, I tried top flange joist hangers instead of a ledger along one side of the slab. It did not go well. Yes, the mud sill gave me a place to nail the flange, but I didn't consider the details.

The first problem with top flange joist hangers was that the slab and house have the same finished floor level. The hangers are too high and I had to hand-cut subflooring around them. I'll have to do the same with the finished flooring. The baseboard will hide the galvanized steel.

The second problem was a door. There's no mud sill across the door threshold, thus noplace to nail the flange. Not only did I have to install a ledger after all; I had not wet-set the bolts, so they had to be hammer-drilled into the concrete. Hitting one rebar takes as long as drilling all the other holes combined. But we got it done.