how would you correct sag in a wooden window sash?

Hello all,

With all the news of natural gas prices kicking into arm and a leg price range, I've been trying to cost effectively work on this 1918 house I bought in February. I like the look of the old double hung wooden windows, but they have not been well maintained over the years. Replacement is not currently an option, but I bought some decent triple track storms to put in on the outside.

I'm taking this time to strip all the bad paint jobs over the nice old wood while I have the sashes out for reglazing, and repair. I've stripped the first lower sash, and removed the upper sash (storm window is keeping the hole sealed up), but this window in particular has a pretty bad sag in the lower part of the sash. it has pulled away from the glass and trim in the middle.

Here's one picture of the problem that pretty much sums it up:

Sagging Sash

You can check out some more pictures here: (don't mind the first two, they are of the resident groundhog).
Image directory

I'd like to get these sashes repaired, sanded, stained, and poly'd in short order. I also need to replace (edit) the sash ropes (possibly with copper or other metal chain so they don't rot again), and clean up the tracks. I know all of this is tedious, but I can't spend 200-500 dollars a window for replacements right now, and I enjoy the refurbishing process.

Any help would be appreciated!

 

It looks to me like the first thing you should do is totally remove the glass. Once you have the glass and the old glazing and caulking removed, then you will be able to tell if the vertical mullions have rotted off on the bottom or not. If they've rotted off, you'll need to replace them. It's more likely that the tenons have just separated from their mortises. It's also likely that the bottom rail is permanently warped and will need to be replaced.

Bar clamps would be helpful to tighten the sash, bringing all the mortise and tenon joints together. Before clamping it, apply a generous amount of Titebond II or Titebond III wood glue, (which is an exterior grade glue) to the tenons. Once it's clamped together the way it should be, you might try nailing through the mullion tenons with a small 4d galv finish nail to hold them in place. Keep the sash clamped overnight. If it springs loose when you unclamp it, you'll need to replace the bottom rail. This would involve fabricating a duplicate rail and making new mortises for the tenons... difficult for a DIY'er, but not impossible provided you have a lot of woodworking tools... Table saw, router, bits, sanders, chisels, drill press, etc. Hope this helps.