When renovating a period property, you will usually need to pay attention to the original fixtures and fittings, including sash windows. Being able to restore your sash windows will mean you get to keep these as a feature of the period property and also reduce your utility bills as you make the building more energy-efficient.
Sash windows became a popular feature in houses as an alternative to the lead latticed casement windows. As casement windows came back into fashion due to their natural ventilation, sash windows were no longer installed in modern houses, but should you own a period property, there are a number of ways in which you can restore them to their former distinction.
Depending on the what the problem is with your sash window, you should only try fix the part that needs attention rather than try renovate the whole window.
If your sash window is in fairly good condition, then it may be that you only need to replace the weight and pulley. Look around the inside of the frame for a rectangle scored in the wood.
If your frame has had a number of layers of paint over the years, this may make it harder to find, but you are looking for a panel around 15cm tall by 5cm wide. It may need to be unscrewed but otherwise should knock out to allow access to the weight. Replacing the pulley and sash cord with draught-proof nylon pile will also ease the movement of the window.
If your window frame is in poor condition, then it may need a full restoration. The trim and interior stops should be removed first. Unlike a casement window such as those from https://www.firmfix.co.uk/windows/casement-windows/, the frame on a sash window may have settled over time or been warped by moisture so no longer fits square and snug.
It is important for a window to be well fitted, so placing wedges into the frame will correct the misshaping of the wood and allow it to fit back into the available space once the layers of paint have been sanded back.
Finally, ensure the outward facing frame is covered with weather-resistant paint and fix your frames back into place. Check that the window is in full working order before putting the trim back around the frame.