Almost all older houses and quite a few new ones are fitted with sash windows – handsome, but prone to faults. Here’s how they work and how to repair them.

The sash (or double-hung) window was used a great deal on homes right into this century – almost to the exclusion of any other type. It’s a period feature, often adding adding a touch of authentic charm. Unfortunately, there’s a lot that can go wrong.

Sash windows actually consist of two separate windows – sashes is their proper name – each sliding vertically in its own channel. When both are closed, the sash in the outer channel is at the top, and the inner sash is at the bottom.

The channels are formed by three sets of beading, running round the inside of the frame. These are known (starting with the outermost one) as the and beads. The outer and staff beads lie flat on the window frame, but the parting bead is fixed on its edge. The outer bead, in fact, may well form part of the frame itself; the other two are always separate pieces, nailed in place. For easy removal they should never be glued, or maintenance of the window becomes impossible.

How sashes work

Counterbalancing weights, each pair of which weighs the same as the sash they’re attached to, ensure that the sashes stay in whatever position you choose and don’t come crashing down – perhaps with such force that the glass is shattered. There’s a weight on each side of each sash, hidden in a compartment inside the frame. Each weight is attached to its sash by a cord that passes over a pulley at the top of the frame and is nailed to the side of the sash.

The drawback of sash windows is that it’s almost impossible to make them fully draught-proof, although some success can be achieved with brush-type draught excluders. The only sure way is to install secondary double glazing – the type that fits within the window reveal and is hinged to, or slides in, its own frame. You can’t attach fixed double glazing panels directly to each sash because they won’t slide past each other. And even if you could, the extra weight would throw the sashes out of balance, preventing the inner one from remaining in the open position and the outer one from remaining closed.

Minor repairs

However, many lesser faults can easily be cured if you know what to do. Often you needn’t even dismantle the window.

Hacking out and replacing old, crumbling putty, and renewing a cracked pane of glass , are two such jobs. And if a pulley squeaks, the remedy is the obvious one: just oil it.

You can even repair a sash corner joint that has begun to open up, provided you wedge the sash firmly in place while you’re working on it. All that’s needed is a flat, L-shaped metal plate which you can easily buy: you just screw it across the corner. It looks a bit unsightly if left exposed; but you can conceal it by first chiselling out a shallow L-shaped recess to take it, and afterwards covering it with paint (not emulsion paint), cellulose filler and then a top coat of paint – in that order, so that the water in the filler doesn’t rust the metal and discolour the paintwork.

Filler will also take care of minor cracks, dents and other blemishes in the wood. You can do a certain amount of redecorating, too, without removing the sashes, but you’ll find it hard to get a neat edge as you approach the concealed parts.

Major repairs

Some jobs, however, do call for taking the window to pieces – a procedure that’s far easier than it sounds. One such task is silencing a rattle; the root of the trouble in this case is that the beads are too far apart and need repositioning.

Prise off first the staff bead and then the parting bead on each side of the frame. There’s usually no need to interfere with the sections of beading at top and bottom, but you’ll have to take out the inner sash to get at the parting bead. To remove a bead, cut down the angle with a sharp knife first to break the paint seal and avoid tearing off flakes. Then push a chisel between it and the frame, as near the nails as you can, and spring it out gradually.

The various beads may well have become damaged over the years. In that case you can simply replace them with new ones, bought from a timber merchant. To lessen the risk of splitting, drill pilot holes for the nails – oval nails are best. When re-fixing the beads, position them close enough to each sash to cure the rattle, but not too close, or you’ll bring about the second common fault: sashes which won’t slide freely, or at all.

The other and more likely reason for that, however, is a build-up of paint in the channels. You can’t just go on putting coat upon coat of paint when you redecorate them, and the only remedy when they jam is to sand or scrape off the paint where the r 2 – sashes are binding, leaving room for the primer and one or two further coats that will have to be re-applied to the bare wood.

Taking out sashes

By far the most serious possibility, however, is that eventually a sash cord will break and need replacing. When this happens you should replace all four, because if one goes the rest are sure to be near breaking-point. In any case the hardest part of the job is dismantling everything; fitting four new cords is very little more trouble than fitting one.

Begin by levering off the staff bead. Swing the lower sash inwards, tie a length of string to each sash cord just above the sash, and cut each cord below the knot, letting the weights down gradually to the bottom of their compartments. With the string now attached to the cord, there’s no danger of being unable to retrieve the weights from their pockets. Lift out the lower sash, remove the parting bead, pull down the upper sash and repeat the process. Lift that out too, and remove the old cord and fixing nails from each sash.

Now that you’ve got the sashes out, you can take the opportunity to do major surgery on them if necessary. Where a corner joint is rickety, dowels make a neater and more professional repair than a metal plate. You’ll need to cramp the sash firmly in place on a workbench first, both to hold it steady and to keep the joint tight while you drill the dowel holes. The joint will almost certainly be a mortise and tenon, so the best place to run strengthening dowels is sideways through the tenon, or perhaps lengthwise on either side of it.

If one of the sash members is cracked or rotten, it may be possible to remove the bad piece by sawing lengthwise, and to replace it with new timber – cut slightly too large, glued, nailed and finally planed off flush. For both these jobs, use urea-formaldehyde adhesive, which resists damp.

Sometimes a sash sticks in its channel because it has warped or swollen. In this case, removing a few shavings from the offending part with a plane may be the answer.

The only really tricky job (one you’ll be well advised to leave unless you’re quite skilled) is renewing the glazing bars which divide individual panes of glass within a sash. And if a sash is in bad enough condition to call for other major repairs, if may be more practical to replace it altogether. Getting a joinery shop to copy the old one is generally far wiser than substituting a modern window which may be quite out of keeping with the character of the house.

With the sashes removed, you also have the opportunity to make a thorough job of re-painting the sashes and the frame. Use a

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Blowlamp or chemical paint stripper to remove layers of old paint if it’s in bad condition, and then coat the timber with wood primer. Or just sand the old paintwork down and spot-prime any bare patches. Then apply the rest of your paint system in the usual way.

Renewing sash cords

Whether or not you’ve had to pause in order to repair a sash or to repaint everything, you’re now ready to carry on and fit new sash cords.

The first step is to remove the weights. To get at them, you have to take out the one or two pieces of wood covering each weight compartment – the pocket pieces. These are usually just a push fit, and you prise them out with an old chisel or screwdriver; in some cases, however, there’s also a retaining screw. Lift out each weight, untie the cord from it, and attach it to the free end of the string, making a complete loop. If there’s rust on the weight, you can rub it off with abrasive paper at this stage, but there’s no need to paint it.

You can buy new sash cord from almost any builder’s merchant or hardware store, but ask for it by name – don’t just use any old cord. To fit the new cord, untie the loop of string, tie the cord to it, and use it to thread the cord over the pulley and down into the weight compartment. Then tie the cord to the weight with a strong knot. At this stage don’t try cutting the cord to the correct length -leave it too long.

Most sashes have a groove, near the top of each side, in which the cord is fixed with small galvanised round-head nails. Either nail the cord into the groove and trim off the excess, or mark the groove length on the frame and trim the cord to the mark. Which-ever you do, the weight should hang 50mm (2in) above the base of its compartment when the sash is at the top of the frame. It’s the same for each sash. Note that the cord shouldn’t be fixed right to the top of the groove, or the sash won’t run all the way up. The topmost nail should be as far down from the top as the top of the pulley is from the top of the frame opening.

After fixing the cords at both sides of the outer sash, replace the parting bead. Then repeat the whole process for the inner sash, and lastly replace it and the staff bead in position. When fixing the beads, make sure the sashes have room to slide freely.

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