I'm rehabbing an old shed and putting new windows on it. I framed in the windows and purchased some simple barn sash windows.enter image description here

I framed it in and left about a 1/4" - 1/2" gap on the sides and top/bottom per the window manufacturers recommendation. However, when I did it, I didn't think about a window sill. I see a few options, but I never really done this before and not sure if this is smart or if there are better options. Also, I don't plan to make these windows operable at all.

Option 1: I would recess the window a bit, perhaps into the middle of the frame, and slant the bottom 2x4 a bit. I could shim it so that it slants outward.

Option 2: I buy an actual window sill. With this way, I'm not sure if the window would sit on the window sill or not. In other words, would the window sill cover the entire 2x4? Or just the outside of it? Unfortunately, I didn't account for this with the measurements, so I might need to reframe or trim the window.

Option 3: Make the window flush with the exterior. I would put trim on the exterior and push the window all the way up to it. I'd put in my interior stops and the window would sit flush with the outside siding. In this case, there wouldn't really be an exterior sill at all. For the bottom trim I could miter cut the top of it so it slopes down and out. Then caulk between the window and the trim so that no water should penetrate.

Option 3 is how the old windows were framed in. See these pictures: enter image description here enter image description here

I'm thinking I'd prefer to just go with option 3 as it's how I've seen it done previously and that's basically how I have already framed it. But I'm not entirely sure on any of this. Option 1 seems a bit odd because the window wouldn't really sit very well on the 2x4 if it's slanted. I could possibly cut the bottom of the window though so it does sit flush.

Any thoughts or recommendations?

1 Answer 1


Buy or make a windows sill.

Use galvanized sheet in the width of the window and 5 inch deep

Bend one edge up (about 1/2 inch high)

Now other other side at 4 inch distance bend the sheet down also about 1/2 inch high.

Use plenty of caulk and place the sheet on the frame with the up bend on the inside and the down bend on the outside.

This will protect the 2x4 frame from rain.

Instal the window from outside

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