Adding Piece to Window Sill/Stool

[Rich Riddle]

I am finishing a four-season room for my wife (hopefully in time for our anniversary next week). Most all of the windows came lacking the inside framing, but Andersen sent one window with the inside members already in place. That's fine on the sides and the top, but they didn't have the sill/stool wider like most homes have for a ledge.

I need to add a piece to a window stool/sill. It will run parallel to the piece already there directly in front of it. I have a biscuit jointer somewhere in the shop, but that doesn't sound like the best way to do it. I don't have a Domino, and it seems expensive to purchase one just for this project. Any ideas on how to do it? I contemplated removing the factory work but the process might destroy the window.

In the pictures below, you can see the one window pre-framed by Andersen in the first two pictures. It's stool/sill isn't wide enough. The third picture shows the stool/sill I made for other windows. Just look at the 90 degree joints where the corners meet the bricked area to see the differences. It's a bit difficult to tell in the photos if you don't know where to look at the differences.

Thanks for any insights.

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[Peter Quinn]

Seems like it would be easier to fix if the window were not in place. I'd guess you could remove the factory stool and replace with an appropriate type. Seems many many modern window manufacturers assume you will be be picture framing the trim, I prefer the stool/apron/casing lands on the ears of the stool approach like a traditional window. I suppose you could use biscuits and finish nails to attach a stool extension, would look fine for paint grade, less fine for stain grade. Pocket screws could also work, though either way you might have to open the window and clamp the stools in place from inside to outside of building. Is there enought clearance below the hardware to sneak in a 1/2" piece with a thicker piece glued to the leading edge, like a nosing for a second story stair landing? This would give you a continuous look, you could create the ears for the casing, it would trick the eye, I would still want some glue and finish nails involved to joint the two pieces. A router with a slot cutter might be easier, you could run a 1/4" slot into both edges and use a plywood or solid spline to joint the extension to the existing stool.

[Rich Riddle]

Peter, thanks for the input. Removing the factory pieces intimidate me not because of making new ones (did that for all the other windows and it's essentially a sun room) but because I wouldn't want to damage the window itself. I cannot see how they fastened the framing to the window. The windows will be finished, not painted.

I do have 1/2" of space below that no one would see. You offer a good idea. Thanks for the idea of the router cutting a 1/4" slot as well. Hadn't thought of that but have a trim router in the shop. Anything done will get glued to say the least.

You are correct about window manufacturers thinking everyone wants a picture framed window. Not sure why they do it that way these days.

[Rich Riddle]

A router with a slot cutter might be easier, you could run a 1/4" slot into both edges and use a plywood or solid spline to joint the extension to the existing stool.Peter,

If I understood you correctly, this is what you recommended. Whiteside makes a "slot cutter" attachment to a router shank in various sizes. This is the result of 1/4" "slot cutter" work in the horizontal bottom sill/stool. Is this what you meant? Hope so because there is no going back.

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[Mark Bolton]

Rich, those extension jambs are just stapled in place. There is generally a small dado to register the extension jam. Window manfacturers dont ship windows with stool on because they have no way to allow for horns/returns/projections and so on, plus they wont fit in the standard packaging.

If you just pry down on that lower extension jamb it will likely just come loose. As a general rule they arent glued or anything.

If your wanting a sill on your windows you have to order them with a "stool prep". They simply staple a scrap in the stool location and land the side ext. jambs on the scrap. You pry out the scrap and install your stool on site after the window is installed.

[Mark Bolton]

Whats going to suck is its a complete crap shoot if you'll get a tight butt joint there with a piece of nosing though I guess you could open the windows and clamp from the exterior to draw it in tight.

If you dont have too much time invested I would to a little prying and I'd guess you'd pop that lower extension jamb off in no time and simply make a one piece stool however deep you like.

Just my 0.02

[Rich Riddle]

Mark,

Thanks for the input. I might go out there and try prying it in a bit. Hopefully Andersen didn't glue that stool onto the window. There is the dado you discuss because the other frames I made had to have them in it. Thanks again.

[Mark Bolton]

I would be very shocked if there was glue even on a mull'd unit. We just did a job with Pella's and they are the same way, shallow dado, extension jambs have a rabbet on the outside edge (face away from glazing). The Pella's however dont have a dado at the sill, I cant remember if Andersen does or not. Its been a long time since weve used Andersen but again, I highly doubt they're glued.