I’ve always appreciated the workmanship evident in old houses (although it’s often offset by a lot of sloppy corner cutting), and I’ve really been enjoying one aspect of our recent weatherization efforts: restoring our old double hung windows.
I say “weatherization efforts”, but the window project actually started with a desire to add colored glass to some of our windows. Our house has a number of decorative touches, including lead came cathedral style windows in the bathroom.
Several of the upstairs windows have decorative upper sashes, with diagonal diamonds framed by mullions. We’ve thought for some time that those diamond shaped pieces should be colored glass, and an architecture student who visited several years ago said that solid color window accents were fairly common at the turn of the century. So I did some reading, put together a list of supplies, and ordered tools and a few square feet of English Muffle glass from Delphi (nice selection, but punitive shipping prices, I now shop locally at Art Glass Emporium in Winder).
Replacing the glass meant removing the sashes, so it has turned into a full restoration job, and the first window took a lot longer than I expected. I’ve only done a few so far, but I’m amazed at how well designed these old windows were, and how few people (including the previous owners of our home) understand how the original windows worked.
First the double hung design: with a double hung window both sashes move, so that you can raise the bottom sash to let air in the bottom (or yell at a barking dog), or you can lower the top sash to let hot air out (while lessening the chance of rain coming in, since it’s protected by the overhanging roof). You can even do both, providing some air circulation in a room with only one window through the chimney effect. (Hot air exits through the upper opening, pulling in cool air through the lower opening, one of the reasons for those tall floor to ceiling windows you see in many old houses).
What some people don’t understand is that the easy adjustment of the sashes was facilitated by counterweights hidden in the framing of the window. (There were other options, but I’m going to describe the hardware used in our 1897 Queen Anne.) A sash weight, usually a cylindrical cast iron billet about 1.25 inches diameter , was suspended behind the window frame by “sash cord” (so that’s where that came from!) that ran from the weight up over a pulley near the top of the frame, and then down to an attachment point on each side of the sash. There was a weight on each side, a pair for each sash, and the beauty of this design is that each sash weight was about 1/2 the weight of the sash, so the weight of the sash was perfectly counterbalanced at any position.
Unfortunately this design did suffer from at least one weak link, which is that sash cords fray and eventually break, and when they do the window no longer functions. If it’s the lower sash it won’t stay up when raised, and if it’s the upper sash it slides down whenever the window latch is undone. Since the sash weight is hidden in the frame, the homeowner often underestimates what an easy repair this is, (and what functionality they’ve lost) and they just live with it, propping the lower sash open with a stick when they want to raise it, and painting, nailing or caulking the upper sash in place to keep it from sliding down.
That’s what was done with our windows. Most of them lack sash cords (suggesting that the weights have dropped down into the frame), and a lot of the sashes are sealed in place. On the first window I initially started by cutting through the paint layer, hoping to free the stuck sashes, but found that both of them were caulked in place, and the upper sashes even had nails holding them up. Once I cut through the paint and caulk, and pried the face trim off I was able to remove the lower sash. Removing the upper sash required prying out the parting beads, thin wood strips on either side that hold the two sashes about 1/2 inch apart.
The sash weights were accessible, even inside the casing of the window, because there are removable hatches in the face of each side frame, held in place by a single screw. (Here’s a nicely illustrated page that might help.) Once you remove those hatches (in our case one for each side of each sash, four per window) you can reach inside and pull out each sash weight. Replace the sash cord, route it through the pulley and reattach it to the side of each sash, and you’re ready to hang the sash in position. (Obviously you need to measure the original cord, or determine the appropriate cord length by trial and error.)
Since I was replacing the small diamond panes in the upper sash I had to remove the glazing putty, and sand and repaint once the glass was replaced. While working with the sashes I noticed other design features that contribute to the performance of double hung windows. The sash lock that holds the two pieces in place also pulls the top rail of the bottom sash firmly against the bottom rail of the top sash behind it, which locks the two pieces in place. And these two rails (also known as the check rails) are not flat, the facing surfaces are angled so that they wedge against each other, blocking drafts when the lock is closed.
The final step in the restoration was adding weatherstripping, and I chose single leaf spring bronze from Killian hardware. It took a few days to get the first window done, so we had some experience with the functional window before we installed the weatherstripping, and it was striking how much weatherstripping improved the function of the window. Not only does it stop drafts, but it also prevented rattling of the sashes on windy days, and smoothed the motion of the sashes in their tracks. We installed strips in the tracks on each side, added a strip on the top rail of the upper sash, on the bottom rail of the bottom sash, and a strip on the face of the upper sash check rail.
Single leaf stripping is nailed down on one edge and then the other edge can be pried up with a putty knife or painters tool, standing up off the surface to block air infiltration. On the face of the rails it’s compressed against the stool or jamb (or matching check rail) when the sash lock is closed, and installed in the side channels it presses lightly against the edges of the sashes as they slide up and down, preventing drafts from sneaking around the sashes.