The opening lights of windows often suffer from the same defects as hinged doors — loose joints, faulty hinges, etc — and the remedies are similar. However, you have to proceed with more care to avoid breaking the glass, especially on repairs that involve driving in wedges.
But the most common defect is rot, usually in the window sill. If the rotten section is not too extensive then you can make a repair, but if it has spread, you may find that the best policy is to remove the frame completely and fit a modern replacement window.
If the rot is in the middle of a sill, make a saw cut about 75mm (3in) each side of the rot. The cuts should be at an angle so that you remove a wedge-shaped piece from the sill. You will then have to cut a new piece to fit. Timber merchants sell standard sill sections but in the case of older houses you’ll have to buy a rectangular section and shape it yourself.
Treat the new timber and the cut ends of the existing sill with preservative. The repair is held in place with dowels set at intervals of 100mm (4in) and fixed into the frame. Smear all meeting surfaces with adhesive before finally fixing in place. For additional strength on wider sills, fit steel repair plates to the underside of the repair. Corner repair pieces are fitted in the same way, except that they are slightly more difficult to shape to the correct profile.
Remember that the outside of any window is exposed to the weather so be sure to give any new timber a coat of primer and then a good coat of gloss paint to protect it. Older properties are more likely to have sash windows and for a complete discussion on how to repair these.