Q: I would like to replace my old wooden double-hung windows with new wooden double-pane windows, retrofit if possible. Do I need to take out the old sash, plus stops, then replace them with a complete new window unit, squaring with shims and screwing it into the old opening? Or can I make the replacement with just the new sash and glass and stops only. In this case, why do I need shims or screws?

A: Replacing your old single-glazed windows with new, more energy-efficient double-paned glass is a good idea – and a good do-it-yourself project.

First, a quick course on window nomenclature. A sash is the frame the window goes in. Sashes are almost always made of wood, steel, aluminum or vinyl.

Stops are the narrow strips of wood that the sash butts against to hold it in place. If windows are divided into more than one pane, each pane is called a lite. The strips of wood or metal that hold the lites in place are called muntins.

We’re assuming that your sash, stops, lites and muntins have seen better days. Over time, wooden window parts tend to warp or rot.

You certainly can replace the old sash in the windows. No screws or shims required. The trick will be to find a manufacturer who can provide the double glazing.

A double-glazed window will take more of the width of the sash, so you’ll need to satisfy yourself with the looks of the new sash. If the aesthetics are acceptable, installing the new sash in the existing frame is not that difficult.

One warning: Old-style, double-hung window frames are drafty by nature, so what you gain in energy efficiency with the double glazing, you may lose in the design of the old windows. Explore methods of weather-stripping to make the new sash as energy-efficient as possible.

If you decide to replace the old sash with new and you’re careful, you can save the old stops. We assume your windows have many coats of paint on them. To remove the old stops, score the seam where the stops meet the frame and then try to gently remove them with a flat pry bar such as a Wonder Bar, a must-have tool for any do-it-yourselfer.

Start with a thin putty knife to create a gap so you don’t damage the frame or the stop. After the stops are removed, the bottom window should tilt out. Remove the bottom sash, then remove the stop that holds the top sash in place, again by scoring the seam, but this time gently removing the stop with a pair of pliers. Go slowly here; this part of the job can be tricky. Reverse the process to install the new sash.

We’ve always found it best to paint or varnish the new sash both inside and out prior to installation. Also, if the windows are operated by sash cord and window weights, this is a great time to replace the ropes.

A problem you might encounter is that over the years, the window may have gotten out of square. Measure carefully, taking into account the bevel on the bottom sash, and you should be able to trim the new sash to fit the old frame.

Tip of the week: When replacing sash cord, put a 16d nail into the end of the cord before feeding it through the pulley. The weight of the nail is enough to allow the cord to easily get to the bottom of the window so you can attach the sash weight.

Bill and Kevin Burnett will attempt to answer your questions, although the volume of e-mail sometimes makes this impossible. Contact them at sweat-equity@comcast.net.

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