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Liz DeLay
what is the window sill groove?

Can anyone tell me what the quarter inch groove under my exterior window sill is? It is on every window sill and runs the length of the sill about 1 inch in from the edge. My wooden clapboard house was built in 1946. I am having the siding replaced by my contractor and he is going to put quarter round under the window sills but that will cover up the groove. Is it some drip thing? Is it ok to cover it up? Hope someone knows. I need to know soon so I don't do something that will hurt the sill. Thanks.

Re: what is the window sill groove?

I think it is a drip edge break of some sort.

It really depends on the siding you're putting on if this will cause trouble. If the sills slope I wouldn't think the groove would be necessary.

My grandmother's house had these. It was built about the same time.

A. Spruce
Re: what is the window sill groove?

That groove helps to prevent wicking as well as water running in behind the siding. The sharp edge creates a barrier that the surface tension of water won't cross, creating a drip line. As Debbie said, if the sill has enough slope and the leading edge is undamaged, then it may not be necessary to maintain the groove, though IMHO if it can be preserved it should be.

Re: what is the window sill groove?

Even with a steep slope on the sill this slot should be maintained. Water running off the sill and down the front , can, due to surface tension, travel along the bottom of the sill and into the siding. And yes water can run up hill (it is actually pushed by the water coming off the sill) in these circumstances.

Re: what is the window sill groove?

Do not cover the sill drip. Even if your contractor caulks the joint to prevent water from coming in. You will then be relying on caulk to keep your home dry. This will be a maintenance nightmare.

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