You’ve paid for new windows, the installers have packed up and left, and something doesn’t feel right. Maybe there’s a draught that wasn’t there before, or the handle feels stiff, or you’ve noticed condensation forming in places it shouldn’t.
Bad window installation is more common than most homeowners realise. The windows themselves might be perfectly good products, but if the fitting isn’t done properly, you lose most of the benefits you paid for.
Here are the warning signs to watch for, what causes each problem, and what you can do if your windows weren’t installed correctly. Expert advice from experienced double glazing installers in Glasgow.
Draughts around the window frame
This is the most obvious sign of poor window installation and the one people tend notice first. If you can feel cold air coming in around the edges of the frame, the seal between the window and the wall isn’t doing its job.
In a properly installed window, expanding foam fills the gap between the frame and the wall, and a bead of sealant on both the inside and outside creates a weathertight barrier. If the foam wasn’t applied evenly, or if the sealant was missed or applied too thinly, draughts get through.
Hold a lit candle or a strip of tissue paper close to the edges of the frame on a windy day. If it flickers or moves, cold air is getting in.
Pay particular attention to the corners and the bottom of the frame. These are the spots where poor sealing shows up most often.
Condensation between the panes
Condensation on the inside surface of your windows is normal in cold weather, especially in kitchens and bathrooms. But condensation forming between the two panes of a double glazed unit is a different problem entirely.
If you can see moisture or fogging trapped inside the sealed unit, the hermetic seal has failed. This sometimes happens because the glazing unit was damaged during installation, or because the unit wasn’t seated properly in the frame, which put stress on the seal.
A failed seal means the argon gas fill has leaked out and been replaced by damp air, which drastically reduces the window’s insulation performance. This will need fixed immediately to restore energy efficiency of your home.
Visible gaps between the frame and the wall
Look closely at where the window frame meets the wall, both inside and outside.
You shouldn’t be able to see daylight, feel air movement, or see gaps where the sealant has cracked or is missing.
Gaps between the frame and the wall are a clear sign that the installation wasn’t finished properly.
Any gap will allow in draughts, rain, and insects in, and over time they can lead to water damage around the window reveal.
Small gaps can sometimes be fixed by re-applying sealant.
Larger gaps, where the foam behind the frame is missing or has collapsed, usually need the trim removing so the cavity can be packed and sealed properly.
Water leaks during rain
If water appears around the window during heavy rain, the external seal has failed or the window hasn’t been fitted with the correct weather drainage.
Modern windows have drainage channels built into the frame and sill to direct rainwater away from the opening.
If these channels are blocked by debris or excess sealant from the installation, water backs up and finds its way inside. In exposed locations (which covers most of Scotland), even minor drainage issues can cause significant water ingress during a storm.
Water leaks should be dealt with promptly. Left untreated, the moisture soaks into the plaster and brickwork around the frame, which leads to damp patches, mould growth, and eventually structural damage to the wall itself.
Windows that are difficult to open or close
A new window should open and close smoothly with minimal effort.
If you have to force a handle, lift a sash to get it to close, or push the frame to get the lock to engage, the window probably isn’t sitting square in the opening.
This happens when the frame is misaligned during installation, either because it wasn’t levelled and plumbed correctly, or because the packers weren’t positioned properly.
A misaligned window is more than an annoyance. It puts uneven pressure on the hinges and locking mechanism, which causes premature wear. It also means the seal doesn’t compress evenly when closed, creating draught paths and reducing airtightness.
Increased energy bills after installation
New energy-efficient windows should reduce your heating costs, not increase them. If your energy bills haven’t dropped after a window replacement (or have actually gone up), something is wrong with the installation.
The most likely cause is heat loss through poorly sealed gaps around the frame.
Even small draughts add up across multiple windows, and your boiler ends up working harder to compensate for the warm air escaping around the edges.
Check for draughts around every window in the house, not just the ones that feel obvious.
Make sure the environmental impact of your uPVC windows is reduced with fully efficient thermal windows.
Mould around the window reveal
Mould forming on the wall around a newly installed window is a red flag. It indicates that moisture is either getting in from outside or condensing on cold spots created by poor insulation around the frame.
When a window is installed correctly, the insulation between the frame and the wall should be continuous, with no cold bridges where warm indoor air can hit a cold surface and condense. If the foam filling is patchy or missing in places, those gaps become condensation points.
Mould isn’t just unsightly.
It’s a health risk, particularly for people with asthma or respiratory conditions. If you’re seeing mould around new windows, get the installation inspected sooner rather than later.
What to do about poorly installed windows
If you’ve spotted any of these common signs, here’s how to approach the problem.
Go back to the installer first
Any reputable installer will have a guarantee on their workmanship, separate from the product guarantee on the windows themselves. Contact them, describe the issue, and ask them to come back and inspect the installation.
If the fault lies in the installation, they have an obligation to put it right.
Get an independent inspection
If the original installer won’t come back, won’t acknowledge the problem, or has gone out of business (which happens more often than you’d expect in this industry), get another installer to inspect the work and give you an honest assessment.
Look for an installer with a long track record and proper accreditations. A company that’s been trading for decades is more likely to give you a straight answer than one that set up last year.
Here at The Advanced Group, we have over 38 years of trusted double glazing experience. By choosing our team, you can feel confident that you’re in safe hands.
Contact your local building control
Window installations that don’t meet building regulations can be reported to your local building control office. They can require the installer to bring the work up to standard, or approve remedial work carried out by another contractor.
How to avoid bad window installation in the first place
Long trading history
Companies that have been fitting windows and doors for decades have a reputation to protect. They should also be highly experienced in installing windows.
If anything goes wrong with the windows, they should still be around to honour any guarantee.
Strong reviews
Always check Trustpilot and Google Reviews, and read what customers say about the fitting teams specifically, not just the sales process.
This should give you a heads up on what to expect from their services.
A written guarantee
Both for the product and the installation workmanship. Ask what’s covered and for how long.
A proper survey
A high-quality installation starts with accurate measurements. If an installer quotes without surveying, walk away.
For experienced installations, contact The Advanced Group
Here at The Advanced Group, we have been supplying and installing windows across Scotland for over 38 years.
Every installation is carried out by our own trained team, not subcontractors. That means every installation is carried out by people who take real pride in delivering high standards of workmanship and customer service, helping to maintain the strong reputation we have built over the years.
We are proud to hold a 4.8-star rating on Trustpilot, and every installation comes with a 15-year guarantee.
If you’re concerned about your current windows, or you’d like a free survey to discuss your new window options, call us on 01355 271 223 (Glasgow) or 0131 370 0444 (Edinburgh).
