Sash windows are part of what sells a Victorian terrace or a Georgian flat. On a viewing, they usually get a glance, yet they affect how warm and quiet the home is and what you are allowed to change.
Ten minutes at the windows will tell you whether you are looking at routine repairs or a major cost.
Open every window you can
Ask to open each window, top and bottom. Both sashes should slide and stay where you leave them.
- A sash that will not move is often painted shut.
- A sash that drops or will not stay up usually has a broken cord.
- A window that rattles in its frame has gaps that let in draughts and noise.
None of these is a reason to walk away. They are routine repairs, but they show how well the windows have been looked after.
Look low for rot
Rot usually starts at the bottom, where rainwater sits. Look at the outside sill and the bottom rail of the lower sash for flaking paint, cracks and soft timber.
Decay in one section does not mean the window is finished. Historic England’s guidance on traditional windows says they can often be repaired simply and economically, usually for less than replacement. A firm that carries out specialist sash window repairs can cut out the decayed timber and splice in new sections.
Check for draughts and noise
Hold your hand near the middle of the window, where the two sashes meet, and around the edges. Then close it and listen to the street.
Draughts can be fixed without new windows. Research commissioned by English Heritage at Glasgow Caledonian University found draught-proofing cut air infiltration through a sash window by as much as 86%. Secondary glazing, fitted on the inside, cut heat loss by around 60% in the same research.
Treat a draughty window as a cost to budget for, not a deal-breaker.
Find out what you are allowed to change
What you can do to the windows depends on the property type, and many London period homes come with restrictions.
- Planning permission is not usually needed to repair windows or replace them with ones of similar appearance, according to the Planning Portal.
- Flats and maisonettes. Those allowances do not apply. Councils including Greenwich and Lewisham say planning permission is needed to replace windows in a flat.
- Conservation areas. The council may have made an Article 4 Direction removing the usual rights, even for houses.
- Listed buildings. Listed building consent is needed for any significant works, inside or out.
- You may need permission from the landlord or management company, so check who is responsible for the windows under the lease.
Rules differ between boroughs and sometimes between streets. A specialist who regularly works on period homes across South London, or wherever you are buying, will usually know how the local council treats sash windows.
Ask for the paperwork
If any windows have been replaced, ask the seller for the certificate. Building Regulations have applied to all replacement glazing since 1 April 2002, as the Planning Portal explains.
The work should have been certified in one of two ways: by an installer registered with a competent person scheme, such as FENSA, or by building control. In a flat, a conservation area or a listed building, also ask whether planning permission or consent was obtained. Your solicitor can raise both points.
One more check applies to old paintwork. Lead was used in some paints for windows and other woodwork until the mid-1960s, according to Cambridge City Council’s guidance. Flaking paint should not be dry-sanded, and young children and pregnant women are most at risk.
Put a number on it before you offer
Most original sash windows fall into one of three groups, and each carries a different cost.
- Overhaul and draught-proof. The window is sound and needs servicing, new cords and seals.
- Repair and upgrade. Decayed sections are repaired and secondary glazing is added for warmth and quiet.
- If the window is beyond repair, replacement timber sash windows are made to match the originals, subject to the permissions above.
Ask a sash window specialist to survey the property and quote before you exchange contracts. A written quote turns a vague worry into a figure you can put into your offer.
