Most defects you’re likely to encounter with sash and case windows will be apparent on close visual inspection. Timber decay is one problem that's less easy to spot.
It’s usually possible to restore even the most rundown windows. Most old sash windows were made from highly durable heartwood timber of a quality that’s now difficult to find. So it makes sense to keep and repair original wood as much as possible.
Maintaining sash windows is fairly straightforward:
Most defects you’re likely to encounter with sash and case windows will be apparent on close visual inspection.
Timber decay is one problem that is less easy to spot. If you suspect decay, e.g. a rotten windowsill, test the timber with a penknife. Sound timber will resist the blade.
A musty smell inside the weight box signals the presence of damp and the potential for timber decay. Open weight box pocket piece covers to check for this and to examine the condition of weights and ensure that the box is free of debris.
Decay may occur behind shutters, either as dampness in plaster or wood rot in the window case.
Sash windows should run smoothly. To check their operation, open sash fasteners and any other locking devices and operate both sashes, sliding for the full length of travel in each case. Note any stiffness or resistance as well as any signs of sashes dropping out of the control of the counterbalancing weights.
Draughts around sash windows aid the ventilation of a traditional building. Some degree of ventilation is necessary for the health of both the building and its inhabitants. Where windows aren’t in good condition, draughts can be excessive and may impact on energy efficiency and comfort. Learn about fitting draught proofing.
Most sash and case windows can be readily repaired. It’s usually possible to restore even the most rundown windows.
Most old sash windows were made from highly durable heartwood timber of a quality that’s now difficult to find. It makes sense to keep and repair original wood rather than replacing it wholesale with new wood, which may be more prone to decay.
It’s unlikely that you would carry out repairs to windows yourself. But you should inspect the window carefully before employing a joiner. This will help you to agree on the work required and how much it will cost.
Sashes are hung on cords that pass over pulleys and connect to weights hidden in the hollow sides of the case. Sash cords should be replaced when worn or broken. Chains were often used in larger, heavier windows, and these should be kept and repaired, though new ones are available if necessary.
Sashes must be removed from the window frame to replace the cords. This is a two-person job best carried out by joiners.
New sash cord must be of the same diameter as the old. Cotton cord is normally supplied pre-stretched and saturated with wax to reduce the risk of rot and to allow it to run smoothly. Braided cord is more durable than twisted.
Process for replacing sash cords
Remove one of the inner baton rods – it will be secured by secret nailing, screws, turnbuckles or easy-to-use fittings if Simplex hinges are fitted.
If replacing the cord for the top sash, prise out the parting bead on the same side as the removed baton rod – this allows the sash to be released.
Use a tack lifter to detach cords from the side of the sash while ensuring that neither the sash nor the cord and its concealed weight drop. Set the sash aside.
Remove the weight box cover next to the damaged rope – retrieve the sash weight from the bottom of the case and clear the weight box of any debris.
Thread an overlong section of the new sash cord over the pulley and down into the weight box until it’s visible at the bottom – tie it to the existing weight.
Adjust the length of the sash cord over the pulley – the weight should hang 75–100mm above the bottom of the weight box with the sash fully raised.
With the sash supported close to the window opening, pull down the new cord so that it’s slack, set it into the groove in the side of the sash and gently nail into place with large blued tacks.
Once both sash cords are attached, put the sash back into position and check it operates smoothly, and then reattach the parting bead and baton rod.
External window paint must be kept in good condition to protect joinery and putty from the elements.
Sash and case windows must usually have their exterior repainted every five years. Repainting windows in good time, before paintwork has begun to break down, will minimise the preparation required.
Window sashes can usually be prepared and repainted in situ. If a more thorough job is required, sashes can be taken out fairly easily. The process of removing and replacing sashes is the same as when replacing sash cords.
You should select a suitable paint for outside use. You may need to apply for permissions for work involving a change in the colour of exterior window paint.
Follow manufacturers’ recommendations about:
suitability and use of primers
applying shellac knot solution to knots and resinous patches
how many undercoats and finish coats are needed
When painting, ensure that the putty is completely covered and the glass to putty joint is sealed with paint. But avoid spreading the paint too far onto the glass surface and make sure you maintain a straight sight line.
All surfaces must be prepared for repainting, taking care not to damage the wood. Bear in mind that the layers of paint are a record of the decorative history of the building. This would be entirely lost by stripping.
Where existing paint is in good condition:
roughen the surface with sandpaper to help the new paint stick to it
remove dirt and grease using sugar soap or washing up liquid in water
Loose and flaking paint should be removed either:
with a thin bladed scraper
Sash lifts and other fittings can be removed if required. But leave the sash fastener in place if it’s in good condition – realigning this later is often tricky.
Sometimes all or part of the existing paint must be stripped back to bare timber.
Paint stripping may be necessary where:
windows have been badly neglected and paint has broken down
paint has been poorly applied and the finish is rough and unsightly
paint is thickly built up to the stage where mouldings are hidden
the smooth running of the sashes is affected by multiple coats of paint
Caution should be exercised when stripping paint to avoid damage to timber, glass, putty and surrounding masonry. Protective measures may also be necessary as older paints may contain lead.
Alternative methods of paint removal:
chemical paint strippers – aggressive caustic strippers are not recommended. More suitable chemical paint removers for hand application, e.g. dichloromethane and methanol solvent based products, are available
mechanical sanding and scraping – care must be taken to avoid gouging the wood and eroding decorative details
heat – using a blowtorch is not recommended. A hot air gun can be effective but a baffle must be used to protect the glass as it’s likely to crack even under this gentle heat
How to paint windows to prevent them sticking
Pull the top sash right down, push the bottom sash up past it.
Paint three sides of the top and bottom meeting rails, the lower half of the stiles and glazing bars, and the parts of the lower sash that you can reach.
Paint the inner sill and the lowest 75mm only of the pulley stiles.
Let the paint dry.
Swap the position of the sashes, i.e. bottom sash right down and top sash halfway up.
Paint the remaining parts of both sashes.
Paint the top half of the pulley stiles.
Do not paint the parts of the pulley stiles that are hidden by the sashes when they’re closed.
Let the paint dry, then paint the surrounding woodwork.
Closing internal shutters and heavy curtains can vastly reduce heat loss from sash and case windows.
Wooden window shutters were often installed alongside sash windows and help to improve security and the energy efficiency of a traditional building. Shutters have fallen out of fashion in more recent times, however, and many have been fixed in place or removed.
Original shutters may need a little help to work smoothly and effectively once again.
Shutter repairs and improvements
Tasks may include:
freeing shutters sealed in their boxes by years of over-painting – use a craft knife to carefully cut through and scrape back paint at shutter edges
freeing shutters fixed to their housing – gently unscrew or slowly withdraw any screws or nails fitted in the past
resolving slight movement that has led to shutters getting tight and rubbing – realign hinges slightly or lightly plane the shutter edges
realigning shutters that no longer line up properly where they meet – unscrew shutters from their housing to access the affected hinges
treatment of dry rot – but only after you have first found and dealt with the source of moisture
filling cracks or splits in shutter panels – use wood filler for small cracks and slivers of wood for wider cracks, and then sand smooth
You may wish to invest in custom-made replacement shutters where the original shutters no longer exist.
A skilled joiner should be able to make and install new shutters to complement the individual style and period of the house. Surviving original joinery in your property (and in comparable buildings nearby) should inform the design of replacement shutters.
Research has shown that replacing existing windows with double glazed units is not as cost effective as other energy efficiency measures. Your existing windows can be upgraded for less money to give you the same benefits while still retaining the original features and style that give character to your home.
Replacing the panes of glass in existing multi-paned sashes with double glazed panes is usually possible with the right type of slim profile double glazed panes.
The Engine Shed is accredited by the Scottish Qualifications Authority (SQA) and National Open College Network (NOCN).
The Engine Shed was supported by a grant from the National Lottery Heritage Fund. Thanks to National Lottery players, we have been able to share knowledge of traditional building materials, develop skills and raise standards in conservation for traditional buildings.