I'm an old pro at rehabbing double hung wooden sash windows. Our old house was a prairie craftsman in Chicago and we rehabbed nearly every single window in the house. The first window took us about two hours to disassemble, but by the end I could disassemble a window in about 15 minutes flat. We took the part stops out, removed the sashes, then repaired the dry rot (sometimes going so far as to make duplicates of various parts of the sash that were too dry rotted to save), then reglazed the sashes, and re-assembled the window. Re-habbing each sash could take anywhere from a couple of days to a couple of weeks, depending on the condition of the sash (and how much free time we had available).
The windows in this house are complicated by the fact that they are painted, and always have been painted. Many have been painted shut. The windows in this house also have old fashioned tin weather stripping. In later posts I will talk about how to disassemble this kind of window, because it has to be done carefully in order to preserve the tin weather stripping to use it again. So far I have been successful in this, but I am willing to bet that I will screw things up taking apart at least one window and ruin the tin weather stripping. It is hard to find, so I hope I don't do this.
The windows in this house are old fashioned double hung sash windows counterbalanced by iron sash weights that are contained in recesses hidden by the window trim. In our particular windows, the recesses are faced on the outside by the outside trim around the window. This means that you can get serious drafts around the perimeter of the window if the window trim isn't absolutely flush with the shiplap sheathing underneath the cedar clapboard on the house. In our house there is about a 3/8" gap between the outer trim and the sheathing....our windows are incredibly drafty.
I will talk in a later post about improving the weather tightness of double hung sash windows. In this post I will talk about preventing drafts coming from the sash weight recess, because if you don't stop up that major source of drafts, there isn't much point in improving the weatherstripping on the sashes. Once you have stopped up the drafts coming from the perimeter, then weatherstripped the sashes, old double hung sash windows with a storm window are nearly as weather tight as modern windows. Put appropriate window treatments on that let light in in the winter and keep light out in the summer, and you will further dramatically increase the energy efficiency of your windows.
There are two ways to stop up drafts coming from the sash weight recesses. One is to caulk around the outside window trim from outside. This works if you can actually access where the window trim rests against the sheathing of your house. In our case, I would have to rip up the clapboard siding. This isn't really an option at the moment, but we will be replacing the clapboard in the next year or two, and at that point we will caulk around the exterior trim of each and every window.
In the meantime, for the worst windows in the house (all of which face either west or south), I have worked out a way to caulk the windows from the inside by removing the interior trim. In the first picture below, I am removing the part stop that holds the lower sash in place. Unless the inner part stop is attached with decorative screws, you can't save it. Expect to be buying new part stops. In our case I wanted to replace them anyway because whoever installed them must have been using scrap pieces of part stop...none of the pieces are more than three feet long and it looks really sloppy.
In the second picture below I am beginning the process of removing the inside window trim that hides the recess for the sash weight. It pays to be very patient as you do this...carefully move your crow bar up and down the window, easing the trim off slowly and evenly. The third picture shows the trim from the side about halfway trhough the process of removing it. You can see a couple of nails holding it on around the middle of the picture.
I included the fourth picture showing me removing the trim only because I just noticed now it shows my left pinky finger that I buggered up last year removing window trim...I accidentally slammed that knuckle into the window frame when the crowbar slipped and I busted up my knuckle. My left pinky finger doesn't work right and hangs at a funny angle and I need hand surgery to fix it.
The moral of the story; be careful when doing this.
When you get the window trim off, save it. If you accidentally split it while removing it, glue the split together and clamp it while the glue dries by wrapping the piece of trim with duct tape and then sand it smooth and repaint when the glue is dry. Because the trim in this particular room is painted a hideous colour of blue, I will be taking this opportunity to take the trim down to our workshop to strip the paint off.
The fifth picture shows the horror that lies behind the window trim. Note that the air infiltration is so bad into the sash weight recess that the cellulous insulation that was blown into the walls has totally infiltrated that cavity. I will vacuum it all out then wash out the cavity with a damp cloth to remove much of the accumulated grime of 110 years. In a later update, I will add a description of how to insulate and seal this cavity using spray foam insulation.
In later posts I will describe how to disassemble the window and reglaze the sashes, and also describe how to remove the paint off of the metal window hardware. The windows in our house have lovely Eastlake hardware that has been painted over many times...it looks really nice when it is cleaned up.