I just finished installing mudsills on a nearly square house—the foundation is 34 ft. by 38 ft. And fortunately, the concrete contractor did a nice job of setting right angles at the corners, so it was pretty close to square in that sense too. His lines weren’t so straight though, the top of the foundation was hardly flat, and the anchor bolts, though placed precisely where I asked for them to be along the length of each wall, were all over the place in terms of their distance from the edge of the foundation. Their depth was inconsistent, at best.
All-in-all, it was a pretty favorable situation.
And yet, mudsills are where framing takes off from the foundation and the more accurate the start, the easier the framing that follows. So, I was fairly methodical with the process, despite the project’s simplicity. Plus, it was important to do a good job of air-sealing the mudsills as they were installed them. The aim is a tight house and this is an area prone to leaks. What follows is a look at the approach taken, some notes on what the building codes have to say about mudsills, and some thoughts from a few experts I reached out to for comments on this all-important process.
Preparing the foundation is worth the effort
Mudsills, or sill plates, or sole plates, as they are referred to in Chapter 4 of the the International Residential Code (IRC), are the first piece of framing lumber installed on most projects. They are commonly bolted to the foundation to make the transition from concrete to wood. Because mudsills are installed close to grade and because they can wick water from potentially wet concrete, they are generally pressure-treated lumber. Most of what you’ll find on mudsills in the 2021…
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