How can I insulate a sash-weight window in a 1900 house?

February 16, 2008 1:17 AM

How can I insulate a sash-weight window in a 1900 house? (I wish titles showed up on the main page so they didn't repeat the question....) Seems like you kind of have to leave a big hole there for the weight. But a lot of cold air is getting in there. I'd rather keep the weights if I could.
posted by msalt to Home & Garden (11 answers total)

I'm not sure I understand the question. Are you saying that cold air is coming in through your window molding, through conduction, and that the solution that comes to mind is filling the weight cavity with insulation, except that you don't want to do that because you want the window to still work?

My house has sash windows, c. 1908, and I haven't noticed the weight cavity as being a problem. Cold gets in around cracked glazing, around the sides, where the old felt insulation needs replacing, and straight through the thin single-pane glass. Have you dealt with all of those vectors already?
posted by mumkin at 1:42 AM on February 16, 2008

Does the window have original glass in it? That old Victorian-era stuff is worthless as far as heat loss goes. You can do better with more modern single pane.
posted by mrmojoflying at 4:27 AM on February 16, 2008

No problem. First, look inside of the weight box and check for leakage between the exterior piece of trim and the inside of the weight box. I could see daylight when I looked into mine, especially at the bottom. I used a few squirts of Great Stuff to address those.

Then, I cut a piece of Johns Manville 1" R-6.5 foil-faced insulation (I found mine at Menards) to fit perfectly within the weight box. Used some foil tape to seal the edges.

(Since you are already adventurous enough to check behind the trim). If you can check behind the trim under and over the window, those are notorious for having leaky gaps, too. I used Great Stuff to seal those off.

Studies have shown that pairing older (and restored) wood windows with energy efficient storm windows can approach the energy efficiency of a double glazed window. Without ugly and eco-awful vinyl replacements needed. Here's my take on the subject.
posted by jeanmari at 5:19 AM on February 16, 2008 [1 favorite]

Break it into two issues: heat that's lost by being conducted through the solid materials, and cold air that is infiltrating through leaks. There's a decent chance that most of your problem is with air infiltration, and caulk and weatherstripping can make quick work of that. The lack of insulation in the cavity is a relatively small problem, because even thought the R-value is low, the surface area isn't very big.
posted by jon1270 at 5:36 AM on February 16, 2008

We've been using this company to do a weather stripping treatment. As others mention, you need to determine where your heat loss is happening. So we've done mostly weather stripping and will be going to insulated glass for some windows. On some, though, we've removed the weight system and installed "jambliners," which is specifically what you're asking about. Here are some pictures of horizontal weather stripping, vertical weather stripping, and jambliners.
posted by cocoagirl at 6:12 AM on February 16, 2008

Best answer: Check the fit of the brick molding. If there is a gap, I would caulk it. That will address any issues with the weight pockets. I would not try to fill in the weight pockets with any insulation.
I restore these windows for a living. We use a router to grove the sides of the sash so that the sash can move along an interlocking metal track. I'd guess that most of the heat loss and drafts you are getting are coming from the sides of the sash and the meeting rail.
Make sure the top sash is sitting all the way up. If it isn't, your meeting rail isn't working. If the weights are cut, just slam it up and fire some screws under the rail.
Unfortunately, if you aren't a woodworker this is a lot of work. It's still a lot of work for us. But there are companies out there that will restore your windows to full function without replacing them. And a true double-hung that works properly is a treat. You can email me if you've got any specific questions.
posted by princelyfox at 8:10 AM on February 16, 2008

You can also DIY weather stripping in old wood windows using a combination of relatively easy to find materials, a router and a slot cutter. If I, an expert in being an amateur (no pre-existing skills except curiosity and desperation), can pull this off while pregnant, good heavens, anyone can. Here is the after shot of how smoothly they work once I completed this project.
posted by jeanmari at 8:17 AM on February 16, 2008

Sorry, princelyfox, I should have previewed. But I don't think it is as difficult to learn as you are implying. Though, heaven knows, for the non-DIY inclined, thank God companies like yours exist in the world.
posted by jeanmari at 8:19 AM on February 16, 2008

Yeah, it's not really difficult. There's just a lot to it.
posted by princelyfox at 11:28 AM on February 16, 2008

Response by poster: Thanks so much for all the advice!! To answer the first question, yes, you're understanding it correctly. No sign of any felt insulation, which might be (a big) part of the problem.
posted by msalt at 10:00 AM on February 19, 2008

Here is a video of the technique that I used. I've had these in for three winters now, no drafts, works smoothly. The foam board insulation helps a great deal when there is only two pieces of trim (exterior and interior) and an empty weight box between you and the Great Outdoors.
posted by jeanmari at 8:26 PM on February 21, 2008