Box sash windows were popularly used in construction during the Victorian and Georgian eras and are still found in older homes worldwide. A pulley and weight, concealed in a box and installed in the window frame, open and close the windows. Weights can be adjusted by removing the box pocket, and beads called parting and staff beads help the window operate smoothly. Replacing or repairing a box sash window can be challenging, but you can accomplish it on your own with household tools.
Cut carefully along the paint joint between the staff beads and box frame, using the knife. Set the chisel behind the staff bead, and use the mallet to tap the beads toward the window's centre. Repeat until all beads are removed, then remove the nails in the beads by hand or with pliers and set aside.
Remove the bottom sash. If you are replacing the cords, cut them carefully one at a time, knotting the end with the weight and lowering the weight until the knot meets the pulley. If you are reusing the cords, remove the attaching pins and tie a knot in the cord, letting the knot rest at the pulley.
Slice the paint between the parting beads and box frame with the knife, and carefully pry the parting beads out of their groove. Be careful to avoid nails or rough paint edges when removing the beads.
Remove any nails or screws holding the top sash in place. Cut along the paint joint of the top sash with the knife. Tap the sash carefully with mallet and chisel to release it from the frame, then remove the cords and beads as you did with the bottom sash.
Slice paint joints around the box pockets and pry them out gently. Untie the knot near the pulley and carefully remove the weights.
Inspect the frame and sashes for damage and repair any damaged wood by removing it and filling with epoxy. Replace timber as needed and nail it into place. Treat the entire frame with wood preservative. Scrape off excess paint and sand all surfaces with medium grit sandpaper, then fine grit sandpaper.
Prime and paint the wood, then spray the pulleys, beads and runners with lubricant. Balance the sashes by comparing weights; if they are out of balance, you can add or remove weight. The top sash should be heavier than the bottom sash.
Run replacement (or original) sash cords through the pulleys and pockets, using a weight if necessary to guide the cord. Attach the weights and tie with a knot. Cut the other end of the cord and tie in a knot so it doesn't slip through the pulley during installation. Reinstall the dividing strip between weights, preventing snagging.
Rehang the top sash by pulling the sash cords until weights are at the top of the box and against the pulley, and pin into place. Position the sash and affix cords with pinning into the groove with a carpet tack. Replace the parting beads and seal any noticeable gaps with caulk, using a caulking gun. Dispense caulk evenly along the length of the gap, until all is flush. Silicone-based caulks are recommended, because they are durable and resilient to temperature change. Pull the sash to test its movement, ensuring smooth operation.
Rehang the bottom sash, following the same top sash steps. Replace the staff beads, nailing them into place. Use common or casing nails.
Use caulk to eliminate any drafts or gaps. Spray lubricant on pulleys and tracks to ensure smooth movement.
Some windows may have been permanently fixed shut due to broken or damaged pulleys and cords. In these cases the windows may suddenly drop out of place when you remove the nails or paint surrounding them. Be extremely careful during disassembly -- there will likely be old nails, screws or splinters that jut out. Further, if you are working with older windows, take precautions in regards to any hazardous materials used in the construction, such as lead paint.