Mudsill and Rim Joist

Building the subfloor comes next, but the first part of that job is putting up the mudsill and rim joist. For those of you who are not builders, the mudsill is the board that you see bolted down to the foundation walls or to the slab. Houses built with wood subfloors also have a rim joist, which sits perpendicular to the mudsill and goes all the way around the outside perimeter of the house. The regular floor joists “tee” into the rim joist and are nailed or screwed to it.

I’m using 2x10 floor joists so my rim joist is also 2x10. The mudsill is 2x8, which is about the same size as the top of the concrete block foundation wall. With the exception of the front porch area, the mudsill and rim joist are up all around the perimeter.

Every contractor I’ve ever seen toe-nails the rim joist down to the mudsill. It’s a lot quicker this way, but I don’t like toe-nailing because I’ve seen it done wrong too many times. Done wrong the wood splits which compromises the strength of the connection. I like screws much better than nails and am willing to take the extra time they require to use. To connect the rim to the sill with screws required that I build everything upside down, then pick it up, flip it over (upright), carry it over and place it on the foundation wall and finally then bolt it down. Not having a helper, I could do all the steps myself except hold the sill and rim together (properly aligned) while at the same time putting the screws in. For this reason I built a jig to hold the boards straight (Pic 1). Using the jig freed up both my hands which made it a lot easier to put the screws in.

Buying all those screws would be expensive, but one day at the local building supply center I found a drastically reduced price table with a 25# pail of 3” exterior grade wood screws. I weighed the pail to make sure it was full (it was). As these were the same screws I was going to buy inside I felt like I had really come across some good luck.

My mudsill boards are 14’ long, the rim joist are 12’ long. That means there are lots of overlapping joints in the boards. Everywhere there is an overlap I have to do some sort of toe-nailing, but I’m doing it with screws. To avoid splitting the wood at the toe-nail I used a ¾” spade bit to drill a pilot hole (1/4”-3/8” deep). Putting the screw in the pilot hole means there is more wood there for the screw to grab, which lessens the tendency to split the wood. I also drill down through the big pilot hole (on an angle) with a 1/8” bit. This further reduces the tendency for the wood to split. (Pic 2)

It seems most any wood you buy, even if it was straight as an arrow when you bought it; letting it sit stacked (even in a dry garage) for any length of time guarantees some of them will warp. But, I found that using the ¾” pilot hole trick could also be used to connect and align the top of two rim joist boards that didn’t want to line up perfectly. (Pic 3)

Solvitur Ambulando - latin for “finding solutions as we go”. Maybe that’s what this blog should be named. I’m finding “lots” of opportunity to solve problems doing this project -- more than I ever expected.