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What is a Sole Plate?

By Christy Bieber
Updated May 17, 2024
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The sole plate, also sometimes referred to as the sill plate, the mud sill, or the base plate, is the main supporting beam of a wall in the construction industry. Typically, these are the first piece of wood that is in contact with the masonry of the basement or foundation. Sole plates are important because they are the base of the building on which the outside walls and floors are supported. There are a number of different ways to construct these plates and a number of different things to look for when examining one in a home inspection or pest control operation.

Since the sole plate is the foundation of the frame or wood walls of a home, to build an effective house or wall, it is essential to begin with a solid foundation. Due to the importance of sole plates, it is vital that the proper type of wood be installed. It is also necessary to secure it properly to ensure that the rest of your construction project goes as planned.

It is common for modern buildings to bolt or lag the sole plate into the masonry below it. In the past, however, construction of these plates that were not bolted to the masonry foundation were considered to be acceptable. This was viewed as permitted since the walls themselves would weigh the plates down to the ground.

Under most modern building codes, builders are generally required to use large bolts or lags to secure the sole plate to the masonry foundation. Most builders will also put a piece of corrugated plastic or foam underneath the plate to help prevent water from wicking up through the masonry and into the wood. This type of material is called sill seal, and it is used extensively in modern home building.

Often, treated lumber or rot- and pest-resistant woods such as redwood or cedar are used as the sole plate in construction. If these woods have not been used, there is a possibility that the plates could rot out or be damaged by ants and termites, thus causing a potentially unsafe condition where the walls are no longer directly attached to the foundation. If this is the case, the sole plate can sometimes be replaced by jacking up the area and removing the rotted or damaged wood, then replacing it with fresh wood of the proper species or treatment to prevent future damage.

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Discussion Comments
By renoguy — On Nov 10, 2012

Your house is a dead weight. Worrying about your house frame shifting off a foundation is akin to waiting for your fridge to move from one place to another in your kitchen, even 1/4". Earthquakes not included!

As far as sill plates being made out of steel, I can say no for two reasons. First, steel is a conducting material and you would end up with frost inside your basement or behind your baseboards, depending on where the sill plate is. Secondly, the difference in cost would be prohibitive, not to mention the steel possibly rusting over time. To fight that possibility, you would have to paint the steel with a red oxide primer. So it would be quite a process from beginning to end, and that is not going to happen soon.

Building a garage around here requires a pressure treated sill plate on top of your concrete floor and the first two vertical feet of the walls using pressure treated plywood. That is to fend off the snowbank that may melt along your wall. That makes it unlikely that it will rot if the water starts wicking up your new garage wall.

The seal between the poured concrete and the framed wall sill plate is done by installing a strip of foam approximately four inches wide. That material is available from most lumber yards. Once the house is built, there is not much you can do to add some kind of a seal between the sill plate an the basement wall.

Finally, as far as lifting a house is concerned,

a lot of existing homes have concrete walls poured with the floor joists embedded in there. Good luck as far as trying to lift the house frame from the basement.

Regarding pressure treated lumber, as in 3/4" plywood, the manufacturer will usually guarantee it for 40 years (underground basement installation). What would happen after that time is anyone's guess.

I hope this will help you all with your projects.

By Emilski — On Jul 25, 2011

@TreeMan - Good question. The short answer to the lifespan of treated wood is -- yes. When we started remodeling our bathroom three or four years ago, we discovered that there was some water damage to the bottom plate, which was originally treated wood. I've also read that treated wood isn't necessarily termite resistant, either.

We don't have a basement, so I'm not sure how it would work then, but the repairman was able to replace the damaged wood without having to jack up the house, but I'm not sure if that's typical for every situation. I believe he replaced it with more treated wood, but said it should last for many more years.

By kentuckycat — On Jul 25, 2011

I think I would be scared to know that my house was not bolted onto the foundation. Like the article says, the weight of the house, would probably hold things in place, but in some wetter climates, I could see where shifting soil could potentially cause problems. The same would go for places where earthquakes are common. I'm sure in the past, though, it was very difficult to drill holes into masonry.

The article mentions sill seal being used between the masonry and wood, but how do home builders stop water from leaking in through other parts of the foundation? Is there some sort of caulking product that is used to make a waterproof seal so that no water can get into the basement?

By JimmyT — On Jul 24, 2011

What kind of machine do you use to lift up a house! Surely you would need something a little bit more heavy duty than a regular car jack, wouldn't you? I'm wondering how you would even get the jack under the house to begin with.

Has anyone ever seen this done, or know how they do it? Also, wouldn't lifting up the house put stress on the other joints in the walls and frame? How do the contractors make sure there is no damage to other parts of the house?

By TreeMan — On Jul 23, 2011

Is a sole plate always made out of wood? Since there can be so many problems, would it make more sense to use something like a steel or iron sole plate? Is there some reason that metal shouldn't be used?

Also, isn't there usually a lifespan on the length that treated lumber will last? Won't the treating agent leave the wood at some point and leave it open to rotting?

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