Double hung windows are a great energy saver and if the need arises, replacing double hung window glass yourself is not difficult. Double hung windows have an upper and lower sash (the sash is the moving part of the window) allowing the window to open from the top or the bottom. The design of a double hung window consists of two grooves in the sides jambs (a jamb is part of the window structure) that allow each sash to slide over the other and to move separately from one another.
Most double hung windows will come with manufactures installation instructions so be sure to read those as well to verify what is required for your specific window type.
Remove the Old Sash or Window
The first step is to remove the old window or sash. First, you will need to remove the center stop. If you have difficulty removing the stop due to caked on paint or sealant use a pair of pliers to loosen the hold. If replacing the entire window then remove the top sash first. Remove only one sash at a time, and work on one side of the sash at a time to remove the sash cord, weights and ties if there are any.
Preparing to Replace a Double Hung Window
When replacing the entire double hung window or just one sash, measurement is the first and a very important step. The new window is going to fit into the old jambs and window space, so it needs to fit properly. Measure the length in three places and the width in three places and use the smallest measurement to order the new window or sash.
Prepare Window for New Sash
Check the window sill for any damage as this is the best time to repair it. As well, if there is old caulking or sealant in the frame or sill, remove this as well. Pre-drill any holes that will be necessary and then install the new brackets into the window frame for the window. Next, if you are replacing the lower sash, you will need to install the filler blocks for the lower sash by nailing them into place. As well, install the jamb liners (which provide the channel for the lower sash to move up and down) into the window frame making sure that the liners fit firmly against the frame. If only replacing one sash, these steps will only pertain to the area of the frame that corresponds to the sash you are replacing. If you are replacing the entre window then these steps apply to the entire frame.
Install the Sash(es)
Once the frame is ready, install the lower sash of the window first if you are replacing the entire window. Slide the pivot pin into the appropriate furrow in the jamb liner and then snap the pin into the sash balance on each side of the sash. Next, lift the sash into place and verify that it slides up and down. If you are only replacing the lower sash, your task is complete. If you are replacing the upper sash only then follow the steps above for the upper sash. If you are replacing the entire window, then repeat the steps above to install the upper sash into the frame as well.
The Finishing Steps
After completing installation for the double hung window or new sash, you will need to caulk around the window to create a weather barrier.