While there's no disputing the charm of original sash windows, if you've moved into a period property, due to their potential age, you may find them less energy efficient than other types of windows.
Employing all kinds of draught proofing measures around your home is always a task worth doing, but with sash windows, there's a number of different ways you can approach the job.
We explore how the experts draught proof sash windows, as well as explaining the more simple tips and tricks you can take to do the job yourself. Say goodbye to cold and rattling windows and hello to a warm and toasty home.
DIY methods for draught proofing sash windows
There are several ways you can draught proof sash windows yourself, and it's always a job you should consider doing as the rewards far outweigh the time and cost. That said, it is a job that requires little more consideration than when insulating windows of other styles, such as casement. This is because the sliding motion of the windows can cause adhesive draught strips to come loose relatively quickly.
"Draughts are one of the most common problems with sash windows, caused mainly by the 3mm gap between the sash and the frame," explains Maximilian Schwerdtfeger energy expert at The Eco Experts.
"We lose a lot of heat and energy through our windows, sometimes as much as 30% depending on the age of the house and the windows," he adds. Although we'll come on to explain some specific products and techniques, it starts with taking care of what you have, says Maximillian.
"The best protection against this is to regularly clean and maintain the frame to stop that gap from expanding and to prevent cracks from making it worse."
"Over time wooden frames naturally bend and bow, or building movement creates gaps as the box frame is shifted and sashes remain relatively square. Over painting can also result in windows not closing fully over time," adds Brian Turner at London Sash Window Repairs Ltd. It's why keeping on top of your window maintenance is essential.
The other methods and products you can use to draught proof sash window are:
- Silicone sealant / decorator's caulk
- Self-adhesive weatherstrips
- Brush seal weatherstrips
- Temporary window sealer
1. Apply silicone sealant or decorator's caulk
Although using silicone will provide a secure seal and prevent cold air from entering your home, it's not always for everyone due to its permanence.
"If you're quite happy having your window fixed shut because it’s rarely, or possibly never, used then you can seal the window closed with a silicone," says Brian Turner.
"This completely eradicates the draughts and will have a big impact on the temperature of your room when you crank up the heating. The transformation will be quite shocking and by far produces the best results of all DIY sash window draught proofing – and instantly too."
Silicone sealant is readily available and easy to apply, but once it is in place, it is not so easy to remove. Bear in mind that if the window is needed as a fire escape this is not a viable option.
"A cheaper alternative is decorators caulk and will do the same thing," suggests Brian. "It comes with the added benefit of being paintable. If you decide to reverse your decision it will be notably easy to cut with a utility knife too."
However, if you are hoping sealing your windows will improve your EPC energy rating, there's a fair chance it won't be seen this way.
"The other problem might come in the form of not being able to claim an energy efficiency upgrade on your EPC certificate," says Brian Turner. "Despite the fact sealing a window shut is more efficient than a draught proofing system, and is going to offer the same reduced carbon footprint, it might not be recognised as such."
2. Use self-adhesive weatherstrips
A really popular method of draught proofing sash windows is to use self-adhesive weatherstrips. These are usually sold in rolls and are designed to be cut to size and stuck into place.
One really useful thing you can do is to use foam or rubber stripping on the sides and top of the sashes, which will stop air escaping," agrees Maximillian Schwerdtfeger. And, it's one of the cheapest methods to hand.
"A rubber seal on the inside of your sash window can cost as little as £5, and the savings of cutting out draughts can save as much as £85, depending on the circumstances of your home," says Maximillian.
However, it's potentially not one with great longevity warns Brian Turner.
"Stick on draught proofing isn’t always that effective long term because as you use your windows, the movement can potentially dislodge the draft seals, but it certainly is cheap and very easy to install, says Brian Turner.
"But, the good news is almost anyone will be able to successfully draught proof their sash window using this DIY sash window draught proofing method. On top of that, if the install is neat and tidy, it shouldn’t effect the function of the sash window all that much," he adds.
3. Attach brush seals
Another option for anyone after a DIY method to draught proof sash windows is to use metal or plastic strips with brushes or pile strips attached – known as brush seals or strips.
These come in many different guises. They are commonly sold in two parts, with a self-adhesive 'pile carrier' – rebated plastic or metal strips – designed to be stuck around the window frame into which the fluffy brush or pile strips are slotted to stop draughts.
While these do prevent draughts, as with self-adhesive strips, do bear in mind that they many need replacing in time, depending on how often you open and close your windows.
Metal and plastic strips with wipers or 'V-strips' are also usually better suited to casement windows rather than sash windows.
4. Temporary solutions
There are several products on the market now that are designed to seal up sash windows during the colder months before being removed again when the weather warms up and you want to open the window.
One such product is Gapseal. It comes ready to fit into window gaps between 2mm-7mm and with all the tools needed to secure it into place. Once fitted, it expands to fill the entire gap yet can be taken out when no longer required.
Maximillian joined The Eco Experts in 2024 and has written extensively about sustainability and energy efficiency across a wide range of topics.
Brian Turner is a sash window expert at London Sash Window Repairs, a company who prides itself on its professionalism and service.
Shop for products to draught proof sash windows
This 6m length of T-shaped draught excluder is suitable for many types of windows and doors
Seals gaps up to 7mm, easy to cut to size and flexible finish to help with window opening and closing
Heavy duty sealant applicator with 290ml white flexible caulk for filling gaps and cracks around windows
Professional techniques for draught proofing sash windows
As with repairing sash windows, if your windows are in need of more than just a little attention, the best option when it comes to draught proofing them is to call in the professionals. Not only will they be able to offer advice on the best method for your particular windows, but they should also be able to repair damaged sections in order to improve their efficiency even further.
"Professional systems use draught seals that are machined and rebated into the original sashes," explains Brian Turner. "Parting beads and staff beads are then replaced with a like-for-like mould that has a draught seal hidden and pre-installed.
"Brush pile is inserted into all perimeters of your sash window to achieve a complete seal. The top of the top sash, meeting rails, lower rail of lower sash, parting bead, and staff bead all have draught seals installed," he continues.
"We use a pile carrier that is glued in situ, and then once set firmly, a brush pile is inserted into the channel. Using this two tier system, as opposed to directly installing into the sash creates the additional benefit that if a draught seal is damaged or painted and is no longer effective, replacement of the draught seal is a two minute job and can be done by the homeowner, costing just a few pence.
"Plus, all reputable companies, including ourselves will guarantee the functionality of the draught proofing for five years. With a few caveats like ensuring a decorator doesn't just paint them stiff," he adds
Costs to draught proof sash windows
"Making the decision to draught proof sash windows is one of the best things you can do to save money on your energy bills, plus it's important to note that it's 0% vat rated," explains Brian Turner.
"We hope that this cost saving will remain in place until 2027 and makes it one of the best ways for reducing your energy costs,. In fact, only loft insulation per pound is arguably better," he adds.
However, the method you choose will ultimately dictate what you pay to draught proof sash windows. DIY methods are in the realms of tens of pounds, while professional methods will naturally be more.
Costs will vary depending on the size and style of your sash window, your location and whether any additional repairs are needed to make the draught proofing more effective.
The London Sash Window Company quote the following guidelines to help you budget should you need professional help.
Prices below include full service, replacement sash cords, new sash window furniture, and timber moulds with a pre-installed draught proofing carrier and pile.
- Small/medium sash windows (under 1.8m in height and under 0.9m in width) – £328.00 – £588.00 per window
- Large sash windows – £488.00 – £888.00 per window
- Venetian sash window – £888.00 – £1388.00 per window
- Sash windows on spiral balances – £488.00 – £888.00 per window
Other options to enhance the energy efficiency of your sash windows include looking at specialist secondary glazing, which is something I've considered as I have single glazed sash windows. Although they have been well maintained and have the necessary draught proof seals in place, secondary glazing would help reduce the heat loss through the actual glass. So whilst not a draught proofing method as such, one that would certainly help save money on my gas bill.
For more advice on keeping your home warm this winter, check out the other places where heat loss in a house happens the most, and do make sure your loft insulation is to the required levels to stop heat escaping upwards.
