Interior window seal need replacing? Here's how to DIY it...
Updated: Feb 18
Replace the sealant around your window frames to reduce heat loss and save on energy bills.
After noticing a draught, I replaced the window seal around the frame of a uPVC double-glazed bedroom window this week. This DIY job came about almost by accident. External temperatures had dropped and I'd ordered some more of the bargain DIY window insulation kits for our older windows. (Side note: Window insulation kits are super simple and easy to apply, but they reduce heat loss significantly by trapping a layer of air between the window pane and the film you apply, improving a home's energy efficiency. I'll put a link to a post with more info and a product reveiw at the end of this one.)
I was cleaning the window, ready to install the film, when I noticed a bit of a draught coming from around the frame, so I began to investigate. I quickly realised that the sealant had started to deteriorate and wasn't in great condition. Whilst the window seal wasn't in a terrible state (you can see from the 'before' images), it was bad enough to cause heat to be lost unnecessarily, making the room colder and resulting in higher energy bills. Anyone who's read my recent post about how to add foil behind a radiator to save money on your heating bills will know that I love a money-saving DIY, so I grabbed my tools.
I shared an update on Instagram about this little job and had lots of people message with old windows or a broken window seal to say they would like a step-by-step, but before sharing the process, I wanted to add the following notes...
Which window seal are we talking about?
The first important point is to clarify that I'm not talking about the rubber window seals around the glass panes (also known as a window gasket or rubber gasket). The seal I replaced was the layer of sealant that filled the gap between the window frame and the wall inside the house. Also, the timing wasn't great with it being freezing, but as it was the inside seal, it was ok - I wouldn't attempt a window seal repair / replacement on the outside in low temperatures as that can prevent the sealant from curing.
When not to replace a window seal
The window in question is very old; it was installed years before we bought the house, and there are no guarantees or warranties in place. Before you start a DIY repair job, it's worth checking how long ago the window was installed and if a guarantee covers it because you wouldn't want to invalidate that by doing the work yourself and the fix might even be covered. Check the guarantee from the window manufacturer if you have one, too; better to be safe than sorry.
If you rent you should always check with the landlord before completing a DIY project.
Check that the window is fully accessible and that it's safe for you to complete the job. You'll need to remove and reapply the sealant around the whole window frame so you might need a ladder and you don't want to be teetering around on a ladder at the top of the stairs for example (or maybe that's just a note for clumsy people like me).
How to replace a window seal
Here's an easy-to-follow tutorial on the best way to replace the seal on a window frame.
You will need
Utility knife - this is the one I used
Ladder (if the top of the window frame is out of reach)
Wet cloth
Dry cloth
Window sealant - this is the one I used
Caulking gun - like this one
Sealant spreader tool (optional - you can use a finger)
1. Remove the old seal
Use a utility knife or blade to break the seal on both sides. You can
then hook the blade under the edge of the seal and pull it away from the window edge.
Do this around the entire window frame before pinching the sealant and pulling it out as shown.
2. Clean the gap
Once you've removed the original sealant, wipe around the edge of the window frame and check that no residue remains. The sealant came out extremely easily in my case and in long strands. The fact that it came out so easily proved that it was a broken seal and definitely needed replacing. If you have issues removing the seal there are lots of things you can try from heat guns (or hair dryers) to acetone, or WD-40 , but always check the material of the wall and the window frame is suitable before you get too involved with attacking stubborn sealant!
3. Prep for new sealant
Before applying new sealant, ensure the gaps are clean and dry as any moisture or dust will prevent the new sealant from adhering which will compromise the window seal.
4. Apply new window seal
Load the window sealant cartridge into the caulking gun (steps on how to do that can be found here) then cut the end at an angle. Apply sealant to the gap working steadily from top to bottom on the sides and along the top or bottom. Once applied, press the pressure release catch on the caulking gun to prevent more product oozing out. See this Instagram reel for a hack on how to make that even more effective. Using a sealant spreading tool (or a clean finger) run along the sealant line to push it neatly into the gap and leave a smooth finish. You can run lines of masking tape along the edges of the gap to make sealant application even easier and holding your finger over the end of the cartridge means you can smooth as you go (see image).
5. Allow to dry.
The sealant I used is touch dry within the hour (great news if you are impatient like me!) and is paintable, too, meaning you can blend it into the wall by painting right up to the line of the window.
FAQs
Here are the answers to some frequently asked questions.
Can you replace window seals yourself?
Yes, you can replace window seals yourself as it's an achievable and affordable DIY, but first, check the age of the window and if it is covered by any guarantee. If the window seals have failed within the guarantee period don't replace them without first speaking to the installer. If your windows are very old, well past any period of cover, then a competent DIYer can save money by tackling this job. As with most home maintenance tasks, I'll add the following caveat... Before replacing a window seal, make sure you have a detailed plan on how you will do it and ensure that you have all the correct tools and materials to hand. You don't want to remove the seal and find you don't have the means to replace it fairly promptly. Once you have a plan, check you have all the tools and materials and that you are confident to carry out the steps.
Is it worth replacing window seals?
Yes, it's definitely worth replacing window seals, as once you have a window seal failure, you need a long-term solution to prevent air leaks, draughts and increased energy bills. If you don't feel competent to replace the seal around a window yourself, consider booking a professional.
Can you replace window seals without replacing windows?
Yes, you can replace the window seals without replacing the windows, as the seals have a shorter lifespan than the panes of glass and are cheaper and easier to replace than the whole window.
Is replacing window seals expensive?
Replacing window seals is not expensive and is much much cheaper than a replacement window. The only costs I incurred were for the tube of sealant as I already had the other tools. If you are a new DIYer, you'll need to invest in a putty knife / utility knife and a caulking gun as well, but these can all be picked up for under £20.
Is recaulking windows the same as replacing the sealant?
Yes, in the UK we refer to 'sealant' for the (often silicone) seal that runs around window frames and baths, and we use decorators caulk for tasks like filling the gap between a skirting board and the wall, however, in the US they use the term 'caulk' for both. Therefore, in the US, recaulking windows means to replace the sealant around the edge of the frame as discussed above.
How often should you recaulk windows?
Windows should be recaulked or have the sealant around the frame replaced every 5-10 years. Rather than setting a specific time, it's best to monitor the effectiveness of the caulk/sealant as you should replace it as soon as you notice issues (eg draughts coming through on a windy day or when the outside temperatures drop). A good seal is essential for reducing heat loss and keeping energy bills in check.
Is caulking windows worth it?
Caulking windows is essential for preventing draughts and moisture ingress that can lead to condensation and mould. Caulk is able to close gaps between the wall and window frame preventing outside air from getting in.
Do you have to remove old caulking before applying new around windows?
You must remove old caulk or sealant from around the window frame before applying a new layer. Failing to do this will result in a substandard finish that won't be effective. Take time to get the job done properly as it will save you time and money in the long run.
If you are looking for other ideas for saving money on your energy bills and reducing condensation and mould be sure to check these posts out...
Where next?
I hope you've found some of these ideas inspiring and useful, let me know in the comments if you try any of them. Be sure to scroll to the very bottom of the page & hit the subscribe button to receive my monthly newsletter which is packed full of tutorials, updates and offers.
