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As I mentioned below, my house has a lot of old double-hung windows. They leak. A lot. And it’s endemic to the design of a double-hung window; there’s a lot of surface area to leak with very little way to seal it.

The standard weather-stripping approach is to use something called spring bronze, which is basically a 1″ wide bronze strip that you put between the window and the frame. I tried it with mixed results. Upside: less draft. Downside: it makes the window more sticky and results in a metallic screeching whenever you open or close the window. Screeching == bad.

Then I saw a company offering insulating parting stops (the square bit that keeps the upper and lower panes apart), and it got me wondering… could I do that? It turns out I could.

For reference: said company can be found here.

I looked at two options: weatherstripping the sash and weatherstripping the trim. The sash was attractive because it was bigger, but it turns out there isn’t a good way to get the edges weatherstripped because of how the ropes hung. That left me looking at the parting stop. That piece is 3/4″ wide by 1/2″ deep, and half the 3/4″ is buried in the wall. Was there enough left over? Yes. To the table saw!

I had weatherstripping (from here, specifically WS74) that was designed to fit into a 1/4″ deep, 1/8″ groove. I wanted this to fit as tightly to the stop as possible, so I also needed to hold the plastic shoulder of the weatherstripping. All together, I needed a profile like so:

where the light gray shows the part that’s buried in the wall and the dark grey shows the part I need cut out. Of course, I need to groove the front side for the lower sash and the back side for the upper sash. There’s also some overlap, but it all holds together.

I used the table saw and router. The saw can make a 1/8″ wide groove pretty effectively, but the end won’t be square. So I started with the table saw and made three passes per side, ending before the end of the groove. I then cleaned it up with a router and a 1/8″ bit.

Finally, I snapped in the weatherstripping and installed the parting bead. Miracle of miracles, it worked! Which mean I was halfway there – I also needed the top, bottom, and between the sashes.

I had expected to install the top edge weatherstripping by cutting a groove into the top edge of the upper sash and using tubular weatherstripping (specifically WS10). However, in at least two windows, the trim on the top edge was actually bowed and thus anything on the top edge of the sash would not seal. Instead, I installed it on the back edge of the top parting bead by milling another groove. It seems to work fine.

Niggly little detail: you want to be sure to weatherstrip the entire perimeter, so the pile weatherstrip actually fits into the top stop a bit. I freehanded the groove for that one.

Next up: meeting rail and bottom sash!

I spent most of the day yesterday milling new window trim. One of the nice things about older windows is that there aren’t a lot of fancy shapes involved; everything was made by hand, and so there were a lot of rectangles involved. And so when I decided to replace the window trim instead of putting on Yet Another Coat Of Paint ™, it was pretty straightforward.

Double-hung windows use three critical pieces of trim: the inside stop, the parting stop, and the outside stop. The inside stop attaches to the inside edge of the window and keeps the inner, lower sash from falling on to your head. It’s typically about 1″ to 1 1/2″ wide and 1/4″ to 3/8″ thick. If you go to a hardware store, you will probably find this simple rectangle will cost about a dollar a foot, which is pretty inexpensive; however, compared to raw lumber, it’s crazy.

As a side digression, lumber is typically priced by the “board foot”, which is the volume of a 12″ x 12″ x 1″ (thick) board. If we do math, the inside stop is… about 1/20 of a board foot per foot. Given that you can get paint-grade lumber for $2/bf, by making my own I’m looking at a) ten cents a foot (or even if you round up a lot, 20 cents) and b) better wood.

I started with some 8/4 (or 2″ thick) poplar, which is an excellent painting wood, and cut down the pieces I needed. Admittedly, this required a bandsaw (or table saw) and planer; but if you already have them making molding is a remarkably zen-like experience. There’s nothing finicky; you’re just cutting one piece out over and over. So after about an hour, I had a stack of molding ready to paint. I even did this nifty 45* chamfer.

The next piece is the parting stop, which keeps the sashes from hitting each other. Like the inside stop, the parting stop is a rectangle – in this case, 1/2″ x 3/4″. That’s even easier to work with than the inside stops, since you take a standard 1-by board and cut it into 1/2″ wide strips. As a note, I originally bought red oak to do this, because I’d heard that oak is rot-resistant; turns out that’s _white_ oak.

Finally, the outside stops I’m leaving in place. You don’t see them often, and so the many layers of paint aren’t as bad.

The takeaway lesson here? There’s two of them. First, once you put enough layers of paint on something, it ends up looking like… you’ve put a lot of layers of paint on it. It’s not that hard to replace the molding and it will look much better without spending a ton on replacing windows. Second, if you have access to a decent woodworking shop, you can do a lot of it yourself in a weekend afternoon.

Up next: weatherstripping the parting stops. I think that I can weatherstrip the stops instead of trying to groove the panes themselves.

Don’t you love that? “Under construction”. It brings back memories of the ’90s and the blink tag.

Okay, not so much.

While I get this working again, here are some links:

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