It is rare to find an older property, for instance a Victorian home, with double glazed windows; many still have the original sash windows in them. As would be expected, most of the time these sash windows have seen better days, their frames may have warped slightly, the panes have probably been painted shut, and they could be a whole lot more drafty then you may like. Restoring sash windows can seem like a daunting job, but with a little know-how behind you, it can be a job you can do yourself.

If your windows look to be sound, it may be that they just need the weights re-hung. On some sash windows there is a knockout cover, which is a small rectangle, about 2″ wide, and approx 6″ tall, scored into the side of the frame – this cover is just big enough to get a weight into. If you are lucky enough to have one then it is an easy way to get to the ropes and weights in your sash window and means you don’t have to remove the window trim. The panel is usually situated between the stops of the frame, and you can identify it by finding a horizontal line, some knockout panels are held in with small screws which can be another indicator. If it has got several decades of paint over it, you may need to use a certain amount of force (as well as a sharp edge) to get it open, don’t panic though, it was designed for this reason. If there is no knockout panel, you may be able to create one yourself with a bit of care and small oscillating saw fitted with a wood-cutting blade.

However, if you need to get access to more then just the weights and ropes, you will have no choice but to start removing the trim around the sash window. When removing the trim and interior window stops, take your time and try to get them off intact so you can re-install them again later when you come to put the window back. Use a sharp tool to break through any paint or caulk that may be securing the trims in place and then using something like a paint scraper, gently start to pry the trim away from the frame. Again, take your time, make sure you gently work any nails out and unscrew any screws. Once you have some space clear of paint, you can start to use a flat crowbar to give you more force.

As you start to renovate your sash window, make sure you mark what piece goes where so that you know what order to put things back when you rebuild the window – a fine tipped marker on an area you won’t be sanding or painting is ideal.

Once you have the trims off of the window, you should be able to remove the lower portion of the sash. The next step is to remove the parting stops, if these are in good condition, carefully remove them with pliers once you have loosened them – if they are damaged, you can replace them using standard ½ inch x ¾ inch window trim that is available from most DIY stores. The top sash is the last part to be removed.

When both panels of your sash window have been removed, you can check the condition of your window frame. Bear in mind that old houses will have spent many years shifting and settling on their foundations so it is very unlikely that your window frames will fit snugly or even be square any more. Water seeping into any gaps in the window joints can cause screws to rust, and wood to rot, which in turn will cause the side jams to drift apart.

Square window frames are essential for smooth operation of your windows, so use a spirit level to and a right angle tool to indentify any twisting, once the problem areas are identified you can start to correct it by nailing in shims (thin, tapered wedges of wood) where needed – be careful not to place the shims near the window weight well. If the shims aren’t enough, you may need to add lattice strips, make sure these are positioned so that they won’t show once the window is back in place.

Once you have a square frame again, you can start the “clean up” process. Using something like a decorators 5 in 1 tool to remove any old glazing compound, caulk, nails, screws and broken glass from the frame. If the paint is very thick, you may need to sand it or use paint stripper to make sure that the sash window can operate properly. Be aware of the fact that some of the paint may be lead based and make sure you take the appropriate safety precautions. Once you have removed the paint, you can check the wood for any rot damage, scrapping this away, treating the wood and then filling the holes with putty or wood epoxy.

Any glass that is in good condition can be left alone, there is no point risking breaking the glass trying to fix minor issues. If you need to replace the glass, it pays to get a hardware store to cut it to size. If you can, salvaged glass is often a cheaper option then new, and often will have come from an older property so will have that slightly imperfect finish that will help make the windows look more period.

To secure the glass in the sash frame, use glazing compound in a caulking gun. Put a small bead of compound in the channel, this will secure the glass without you having to use pins. Then run the glazing compound around the window where the glass and wood meet. Smooth down any imperfections with your finger, leave it over night to set solidly and then run a razor blade over it to remove any excess.

Next you can repaint or stain the window pieces. By doing this while the sash window is being renovated will reduce the chances of you accidently sealing two pieces together. If you are trying to match in with an existing stain, make sure you test the colour in an area that it won’t be noticed before re-staining the entire frame. It is always best to paint the outside of the window to give the maximum protection against the elements.

It isn’t unusual for weights to be missing from sash windows, replacing them can be a bit “hit and miss” as it is normally a case of adding washers and nuts until you get the balance right. You may also have to re-shape some of your pulleys if they are bent, this can normally be done with a pair of pliers – it is also a good idea to give them a good spray with WD40 or some other lubricant. If the ropes need to be replaced it is better to use a cotton based rope then a nylon one as it tends to stretch less.

Once everything has been checked, repaired and replaced where necessary it is time to start putting the sash window back together. Start by re-attaching the stops with small nails (typically 16 or 18 gauge and approximately ½ inch to ¾ inch in length) – make sure that the nails long enough to hold the stops in place without going through to the weight well.

The rest of the window goes back together in reverse order to how it came out (which is easier if you marked the parts as suggested). The top sash panel goes in first, then you tie the weights on – this is a good time to check your work, slide the panel up and down to ensure it moves smoothly and doesn’t catch on anything, or stick in the frame. If you are happy with the testing, you can then replace the parting stops, the lower sash panel and the interior stops. The final step is to re-attach the interior trim – use longer nails the you used for the stops, and only use the nails you need to secure it, don’t go overboard with them or it will impair the look of the finished renovation.

Then you can stand back and feel pride in the fact that you have successfully finished restoring sash windows in your home. However, if all this sounds a bit too complicated or there seems to be a lot of damage or problems with your sash windows you would probably be better off approaching a specialist firm who will restore your sash windows for you.