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Sill Options for Exterior Doors

Gregg Hoyer walks you through the sill options available to you when building an exterior door unit and the pros and cons of each. If you want your door unit to last, make sure the subsill is made from a composite material.


Today we’re going to be talking about sills. We have a variety of aluminum sills right in front of me and these are inswing sills.

The very first sill to look at is a non-adjustable sill. This is made out of aluminum, the cap is plastic, it doesn’t rise up or down, the sweep at the bottom of the door comes in contact with a cap and that’s it. I can’t adjust it, this is a lower cost sill and people typically will use it for cost reasons.

Then we get into our adjustable inswing sills. Our very first one is a hardwood adjustable sill. Now, these screws on top of the cap allow that cap to move up and down.  Once I set my door unit, if there’s any changes in the door unit I can adjust that cap so that I can get the right tension or the right pressure between the weatherstrip, the sweep on the bottom of the door and this cap. I’m not crazy about this sill and here’s the reason why, the bottom of this sill or the sub-sill is made out of wood. Even though it’s got a treatment process on it, it can take water, it will swell, it can twist and eventually degrade. So, I’m not crazy about it because of that.

Our next sill is an adjustable sill. The cap looks very different than this, it does have screws, it does have a composite bottom. To change the cap height, you take these caps off and a screwdriver goes down inside the hole and that allows this to be adjusted. The base or the sub-sill is a composite material. This is called the basic adjustable sill. It is very limited in options, I can only get it in a mill finish and I’ve got very limited widths. It is a very good composite adjustable sill for price point.

These next sills are the Tru-Defense composite adjustable sills from Therma-Tru. These also have that same adjustable screw that we saw in the hardwood adjustable. The sub-sill is composite, on this sill it’s this material, it’s a very dense material. On our aluminum, it’s got a different composite on the bottom. We don’t care what that material is made out of, it’s a mill option if you will, as long as the sub-sill is composite and both of these have the ability to adjust that cap up and down. One final thing about the Tru-Defense sills is we change their width and we change options with a sill nosing and this sill nosing can slide or snap into place to extend the width of the sill for different jamb widths. The other thing that this is used for is, if I wanted to do a horn sill, or a sill horn, where the jamb leg comes to the side of the sill and I want my brickmould or casing to come down on the nosing of the sill, I can use this setup.

We also have wood inswing sills. Here we have a basic blank, very often we will cut it in this shape to accommodate exterior casing with sill horns, it is a great look. This material is Sapele Mahogany, we also offer the same sill in Oak. There are two profiles for our exterior inswing wood sills, we have a high dam sill, shown here, and we have a standard or a lower dam sill. This capped area is often called a dam. On a high dam sill it rises higher and it’s a little bit more secure to stop any kind of water infiltration. This is a great product and it should be considered in bad exposures.

Sometimes people will order outswing door units. Why do the order outswing door units? Because they don’t have room for the door to swing into a room or a hallway and sometimes for very bad exposures. In an outswing door unit, the door swings to the exterior of the building and wind and rain will actually push the door against the weatherstrip. We have two types of outswing sills. We have this bumper sill, she’s made out of aluminum, but the sub-sill is wood, so we’re not crazy about that. You can see how the door pushes right up against the weatherstrip. The Tru-Defense outswing bumper sill is a much better sill. It has the composite sub-sill and it has this really nice flat cap that protects the weatherstrip.

Another sill that can be used for inswing or outswing that has a very low profile is called a public access sill. This isn’t great for stopping air and water, but its purpose is to keep a very low profile so that things can roll over it and it does not create any kind of impediment with wheels or anything like that.

As you can see with all the different sills, one of the things that we recommend is always thinking about the material in the sub-sill. It does not cost much money to get a better sill with a composite sub-sill in it. It’s very cheap insurance and it’s one more thing to think about when choosing the right door unit.

Exterior Frame, Preparation
Updated on March 8, 2019

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