How to repair and maintain timber framed windows

It is essential to keep timber-framed windows in prime condition—if neglected, the wood will quickly deteriorate. And if signs of decay are left uncorrected, rot may set in.

A neglected window spoils the appearance of a home, causes draughts and damp, and can tempt intruders. If the signs of decay are not detected and dealt with at an early stage, further deterioration will make repair more difficult.

Types of window

The two basic types of timber-framed window are the casement type and the double-hung sliding sash window.

The sliding sash window operates by means of cords, pulleys and weights which counterbalance the sashes—the opening parts of the window—as they slide up and down. Two sets of headings —thin lengths of wood—hold the sashes straight in the frame. Covers or caps in the lower part of the inner edge of the frame are usually provided to allow access to the compartments containing the weights. Where this is not so you will have to remove the inside frame cover.

A casement window is attached to the frame by hinges and is held open by means of a stay which is designed to allow progressive adjustment.

Working considerations

The most common problems affecting timber-framed windows are decay from wet rot, loose joints in the sashes and —in the case of sash windows—fraying or broken sash cords. To repair these faults you have to remove the sash so that you can get at the individual components of the window or work on the sash itself—difficult or impossible if it were left standing in the frame.

Where a section of a sash is decayed, you can strengthen it by cutting out and renewing the affected part of the wood. If the joints which hold the sash together are working loose, you can reinforce these by knocking them apart and re-assembling them with fresh adhesive. But if the decay is particularly widespread, rot may have irreparably harmed the timber fibres and the only solution is to discard the sash and fit a new one.

If you have modern casement windows, replacing a decayed section of the casement may be difficult because there is insufficient wood to work with. In this case, it may be quicker and probably more effective to replace the faulty casement altogether.

If you are dealing with a window affected by rot, it is best to carry out the work during dry weather as the timber remains swollen in damp conditions, making any repairs less than perfect after eventual shrinkage in dry, warm conditions.

Before starting work, identify the type of rot. Wet rot is more common in window frames but you may find dry rot in which case treatment must be more drastic.

Removing a casement window

Older types of casement windows are constructed from thick timber and are therefore heavy. So, if you have to remove the casement for replacement or repair, the work must be tackled with great care.

Begin by passing a strong cord around the window, under the top hinge, and tie this to the upper part of a step ladder to prevent the casement from falling to the ground.

Before you attempt to remove the screws holding the hinges in place, use an old paintbrush to dab a small amount of proprietary paint stripper on any paint around the screw heads.

If the screws prove particularly obstinate and difficult to turn, try to tighten them slightly first to help loosen the threads, or give the end of the screwdriver a few sharp taps with a mallet. If all else fails, apply some penetrating oil and leave it to soak into the screw holes overnight.

Remove the screws which fix the hinges to the frame first—those in the casement are easier and safer to remove once you have taken the window i1 !’ out of the frame. Loosen each of the screws by one full turn and then unscrew two from each hinge, leaving one screw in each.

Now, starting with the upper hinge, remove the remaining screws. Give the casement extra support with one hand under the outer corner and then swing it sideways into the room or, if you are working on the ground floor, lower it to the ground.

Removing a sash window

If a sash window is neglected, it becomes difficult to open and close properly and eventually its cords may fray and snap. To cure these problems, it is usually necessary to remove both sashes from the frame.

Start by removing the fixing beads around the inside edge of the frame. Beginning with a long piece, use an old chisel to prise it away starting from the middle of its length. Bring it out to a distance of about 25mm from the frame and then tap it smartly back into place. This should cause the bead’s fixing pins to rise up through the surface so that you can remove them with a pair of pincers.

Repeat this procedure for the remaining pieces of beading, then take out the inner, or lower, sash and rest it temporarily on the window sill. Ease the parting bead which runs between the two sashes from its housings then slide out the outer sash.

Sashcords are usually nailed into grooves in the sides of the sashes. To detach the cords of the inner sash, make pencil marks on the front of each sash to show where the ends of the cords reach to, then make corresponding marks on the outer frame.

Afterwards, remove the clout nails which hold the cords into place and— unless you intend to replace the cords —immediately tap the uppermost nails into the edges of the frame to prevent the weights on the other end of the cords from falling down behind the stile boards.

With both cords removed from the inner sash, you can take it from the frame and repeat the procedure for the outer one.

Replacing sash cords

If the frame of a sash window needs attention, it is likely that the sash cords are also in a poor condition and need to be replaced. And if one of the cords has already snapped, it is possible that the others are frayed and about to break, so it is best to replace all four at the same time.

For renewing the cords, buy a slightly longer length of pre-stretched wax cord than you need to allow for waste. You will also need a lump of lead or a large nail to act as a weight for dropping the new cords down into the pockets.

Eemove the sashes from the frame, as described above, and begin work on the cords of the outer sash. To get to the weights to which they are attached, unscrew the pocket covers—or lever them out if they are simply nailed or wedged into place—then pull the weights through the pocket openings and remove the cords.

Check the pulleys to make sure that they run smoothly and, if not, apply a little oil to the pivots. If the window is in particularly bad condition, the pulleys may have rusted and you will have to replace them altogether.

To fix the first new cord, tie your nail or lead weight to a piece of string about 1.5m long and feed it over the groove of the outer pulley wheel until it falls down behind the stile. Tie the new sash cord to the other end of the string and pull it over the pulley and out through the pocket opening. Now untie the string, secure the cord to the original weight and replace this inside its compartment.

Pull the weight up about 25mm and half drive a nail through the cord, into the edge of the frame to hold the weight temporarily in position. Cut the cord so that it is level with the pencil mark on the frame, made when you first removed the sashes.

Next position the outer sash so that you can fit the cord into its groove, align the end of the cord with the pencil mark on the front of the sash, then fix the cord in place with four or five clout nails. Repeat the procedure for the other cord, remove the temporary nails and lift the sash back into place within the frame.

The procedure for renewing the cords of the inner sash is almost the same but in this case pull the weights up further, almost to the pulley, before fixing the temporary nails.

Then replace the pocket covers, parting bead, the inner sash and then the outer beading. Grease the channels with a little candle wax to aid smooth running.

In some windows, the cord may be knotted into a hole in the side of the sash. The method of replacing is much the same, but tying the knot in exactly the right place might require some trial and error.

Strengthening a sash

If the mortise and tenon joints of a sash become loose, water will eventually penetrate the gaps causing decay in the sash and possibly the surrounding timber as well. Extensive and costly repairs could then be the result of an initially minor fault.

Do not be tempted to strengthen a loose-jointed sash simply by filling the gaps. To do the job properly, remove the sash from the frame and chip away the putty holding the glass in place. Remove the glazing pins and the glass, then use a shave hook to scrape away all the remaining putty from the edges of the timber.

Now knock the joints apart, using a mallet with a timber offcut to protect the sash, and clean all the old glue from the tenons with wire wool. The joints in sashes are usually reinforced with two small wedges in each mortise to ensure a firm fit. Remove these and clean the inside of the mortises with an old, blunt chisel.

Using the removed wedges as a guide, mark up and cut replacements slightly longer than the originals to allow for trimming. When you have cut all the replacement wedges, coat the tenons with a waterproof woodworking adhesive and slide them into position in the mortises.

Tap them home with a mallet, again protecting the timber with a piece of waste wood, then apply some glue to two of your new wedges. With the angled edge of each wedge facing inwards, tap them into place with the mallet then trim off the ends with a chisel.

Fit the remaining wedges, and check that the sash frame is square by measuring the diagonals—which should be equal. Cramp the sash carefully as described previously. Once the glue has set, you can reglaze the window and rehang the sash.

Renewing decayed timber

If part of a sash is affected by wet rot, make a probe into the wood with a bradawl to check the extent of the damage. Providing the decayed section is small and is spread over no more than half the thickness of the rail, you can cut out the affected wood and replace it with new timber.

Knock apart the joints as described above to remove the rail which needs repair from the rest of the sash frame. Use a combination square to mark a 45° angle at each end of the decayed area. Then mark horizontal lines slightly below the depth of the decayed section. Make these lines on both sides of the rail.

Next, secure the timber in a vice and saw down the angled lines to the depth line with a tenon saw. Use a keyhole saw or a jigsaw to cut along the depth line and, with the waste wood removed, smooth down the sawn edges with a bevel edged chisel.

Use the cut piece of wood as a pattern to measure up the replacement timber, then mark the cutting lines with the combination square.

Angles of 45° are easiest cut using a mitre box to guide the saw blade, but if you do not have one, continue the cutting lines around all the faces of the timber, then secure it in a vice and cut the replacement section. Plane down the sawn edges of the new wood and check its fit in the sash rail. If it is slightly oversize on any of its faces, sand down the unevenness.

The replacement wood is fixed into place by two or three screws, countersunk below the surface. Drill holes in the new section for these, staggering them slightly, then apply some glue to the underside and angled faces and cramp the section into place. Extend the screw holes into the sash rail to a depth of at least 12mm, drive in the screws and sink their heads well below the surface of the wood.

When the glue has set, remove the cramp and plane down the surfaces of the new wood until it is flush with the surrounding timber. Afterwards, fill in the screw holes and reassemble the sash, as described above.

Sticking windows

Apart from the faults already described, casements and sashes can stick because of a build-up of old paint or because the timber in the frame swells slightly.

The former problem is easily solved by removing the offending frame, stripping off all the old paint and then repainting. But swelling is a problem which can come and go with the weather. On casement windows, where it occurs most often, swelling can usually be allowed for by adjusting the casement hinges—a far less drastic solution than planing off the excess.

Mark the swollen part of the casement and judge whether increasing or decreasing the depth of one of the hinge recesses will bring it away from the window frame.

To increase the depth, pare away 2mm or so of wood from the recess with a sharp chisel. Try the casement for fit again before you start to remove any more.

To decrease the depth, cut a shim of cardboard or thin hardboard to the shape of the recess and fix it in place with a dab of glue. Punch or drill screw holes through the shim then replace the casement. Do this with great care to ensure a proper fit.


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