? How to Install Window sill or stool - new windows

[Patrick McCarthy]

Greetings, posting here because more of a finish carpentry question, so wasn't sure the Projects thread would be appropriate.

We installed new Marvin windows and my question is: how do I attach the window sill? Biscuits? (have a Lamello), Dominoes? (could easily rationalize), pocket screws and plugs? (least inclined to do this . . but)

Old window were 1960's aluminum sliders; we went down to the studs, insulated, new sheet rock, etc. old window sill.jpg


The new windows are flush with the wall.New Marvin bath window.jpgIMG_1948.jpg

I want to have the sill meet/mate to the face of the bottom board, land the casing on the wings and put an apron underneath. I want a traditional look rather than just using mitered casing for a picture frame effect.

1. how do I attach the sill?
2. given the fact I will have a joint between the window frame and the mating surface of the sill, should I try putting a subtle V groove on the top mating surfaces or just accept that some joint will telegraph thru the enamel?

3. while I am at it, and you are still willing to read . . . . how do I treat the end grain on the wings of the sill? Probably using poplar; is it appropriate to cut a return at the end of the wing or do I just sand, fill, sand, prime, sand, paint, paint 2nd top coat?

My house, my time, so a journey and not a race. It will always bug me if I "cheap out" and not do it "right".

Thank you in advance for sharing your experience. Patrick

[Ken Fitzgerald]

Patrick,

There are some excellent videos on YouTube for trimming out windows and This Old House website has Tommy showing how to do it IIRC.

[Jerry Miner]

Patrick--- I've been a finish carpenter for a few decades, trimmed out a bazillion windows. My .02:

Keep the stool (not a "sill", a stool) narrow, like 1/2" deeper than your casing (shorter lever arm) and drop it slightly below the window's bottom frame member, creating a small "reveal".

A few finish nails or trim screws into the window frame will hold it tight, and the apron will provide support underneath.

I usually let the end grain be exposed---profiling to match the front edge as needed. Mitered returns here are trouble. I do put mitered returns on the apron if it is profiled. For square stock, cut clean, sand, paint.

[Patrick McCarthy]

Gentleman, thank you kindly for your suggestions.
Jerry, the reveal makes more sense, and would collect no dust, than the V groove idea. I was thinking about the old saying "if you can't hide it, accentuate it". Your suggestion is a much better solution.

Ken, as soon as I read yours I had one of those head slap "duh" moments.

Best regards to both of you, Patrick