Condensation is the thing we get asked about more than anything else between October and March, and most of the time it is not a fault with the window at all.
There are three completely different problems that all look like water on a window, and they have three completely different answers. One of them is a repair. One of them is a change to how the house is used. One of them is not a problem at all and is a sign the window is doing its job. Before anybody quotes you for anything, it is worth knowing which one you have got, because we have lost count of the people who have been sold new windows to cure something new windows do not cure.
The five second test that tells you which one you have
Run a finger down the wet glass from inside the room.
If the water wipes away, it is on the room side of the glass and it is coming out of the air in your house. If the inside is dry and the outside face of the pane is wet, that is dew and the window is fine. If the glass is dry on both faces and the misting is still there, sitting in the middle where you cannot get at it, the sealed unit has failed and that is the one we come out and fix.
That is the whole diagnosis. It takes longer to read than it does to do.
Condensation on the inside of the glass
This is the common one, and it is not a broken window.
Warm air holds moisture. Cold air cannot hold as much. When the warm, damp air in a room touches a surface cold enough to take it below its dew point, that moisture stops being vapour and turns back into water on the surface. In almost every room in almost every house the coldest surface is the glass, so the glass is where it shows up first. That makes the window look like the culprit when it is really just the messenger.
The water itself comes from ordinary living. Showers and baths, pans on the hob, a kettle, washing dried on radiators, a tumble dryer that is not vented outside, and the people breathing in the house. A family of four puts several litres of water into the air of a house every day without doing anything unusual.
Here is the part that catches people out. Older windows leaked air constantly, and that accidental draught carried the moisture away before anybody noticed it. When a house gets new, well sealed windows the draught stops and the moisture has nowhere left to go. The condensation often appears within weeks of a good installation, which is why so many people conclude the new windows are faulty. They are not. The house has simply stopped ventilating itself by accident and now has to be ventilated on purpose.
What actually helps: open the trickle vents in the tops of the frames and leave them open, because they are there for exactly this. Run the extractor in the bathroom during a shower and for a while after it. Put lids on pans. Dry washing outside or in a vented dryer rather than on a radiator. Keep a low background heat rather than letting the house go stone cold and then blasting it, because it is the cold surfaces that do the damage.
When it is a window fault after all: if the rubber gaskets round the opener have gone hard and perished, cold air gets past them and chills the frame and the edges of the glass, and you will see the condensation worst at the bottom corners. If a hinge has dropped, the sash is no longer squeezing evenly onto the seal and you get the same effect down one side. If the trickle vents were never fitted, or have been painted over or stuffed with foam by somebody trying to stop a draught, the room has no way of losing moisture. Those are all small jobs and they are all things we do.
If water is running down and pooling on the sill day after day, do not leave it. That is how you end up with black mould on the sealant and, in a wooden sill, rot underneath the paint. There is a longer explanation of the mechanism in our article on condensation on the inside of windows.
Condensation between the panes: this one is a repair
If the misting is inside the glass and you cannot wipe it off from either side, the sealed unit has failed. This is our bread and butter.
A double glazed unit is not two loose sheets of glass. It is a factory made assembly: two panes held apart by a hollow spacer bar round the edge, with a perimeter seal bonding the whole thing together and making it airtight. Inside that spacer bar sits a desiccant, a drying agent, whose job is to mop up the small amount of moisture sealed in when the unit is made. As long as the perimeter seal holds, the cavity stays dry and the glass stays clear for decades.
When that seal fails, and they all fail eventually, damp air starts breathing in and out of the cavity as the unit warms and cools through the day. The desiccant absorbs what it can until it is saturated, and after that the moisture has nowhere to go. It condenses on the inside faces of the glass, so you get fog in the morning that clears in the sun and then comes back. Given long enough you get permanent tide marks and a chalky bloom etched into the glass that will not come off even after a new unit goes in.
You will find people online, and a few outfits selling kits, who suggest drilling the pane, blowing it out and fitting a little vent. Steer clear. The seal is still broken, damp air is still getting in, and you have now drilled a hole in a pane of glass that is holding the weather out of your living room. It clears for a few weeks and then drifts back.
The honest fix is a new sealed unit into the frame you already have. The frame stays, the hinges stay, the handles stay, and the window is as good as it was. It is a fraction of the cost of a replacement window, and anybody telling you a misted pane means a new window is either mistaken or selling something. We go through the whole job in more detail on our double glazing repairs page and in the article on misted double glazing.
A lot of the double glazing round Wishaw and the wider Lanarkshire area went in through the nineties and the early two thousands. Twenty five to thirty years is roughly where sealed units start to go, so if several of yours have misted within a year or two of each other, nothing has gone wrong with your house. They were all fitted the same week and they are all reaching the same age together.
Condensation on the outside of the glass
Nothing is wrong. Genuinely.
On a clear, still night the outer pane radiates its heat away to the open sky and ends up slightly colder than the air around it. When it drops below the dew point of the outdoor air, dew forms on it, in exactly the same way it forms on the roof of a car left out overnight. It shows up worst on the windows that face the open sky, it is most common in spring and autumn, and it burns off within an hour or two of the sun reaching the glass.
The reason it happens at all is that so little heat is escaping from inside the house to warm that outer pane. A poor window leaks enough warmth to keep its own outside face dry. A good one does not. If your windows dew up on the outside, the energy coating and the gas fill are working. It is annoying to look through at eight in the morning, it is not a fault, and no repair will stop it. There is more on it in condensation on the outside of windows.
Mould round the frames and black spots on the seals
Black speckling on the mastic and in the corners follows on from months of inside condensation. Clean it off with a proper mould treatment rather than bleach on a cloth, which tends to lift the colour out and leave the spores behind.
Cleaning it is only half the job. If the moisture is still arriving every night the mould will be back within weeks, so the ventilation and any perished seals have to be sorted at the same time. Where gaskets have gone hard and shrunk back at the corners, replacing them is one of the cheaper things on our list and it makes a real difference to how cold the frame runs. If the black marks are sealed inside the glass rather than on the frame, that is a different thing again and we cover it in mould between window panes.
What it costs
There is one figure we can put in writing, and we would rather be straight about the rest than publish a price list that falls apart the moment we see the job.
Replacing a failed sealed unit in an existing uPVC frame starts from £75. That is a starting figure and it is for a small pane, the sort of hopper vent that sits above or below a main window. A bigger pane, toughened glass, obscure glass for a bathroom, energy glass, or a shaped or leaded unit will all cost more, and how much more depends on the actual window.
Gasket and seal work, hinge adjustments and vent work are quoted on the job, because two windows that sound identical over the phone can need entirely different parts. There is a fuller explanation of what moves a price on our repair prices page, and the rest of what we do is listed under window repairs.
There is no call out charge. You do not pay us to come out, you do not pay us to look, and the quote costs you nothing. If you decide against it you owe us nothing at all. You pay for the work done and that is it.
Quick questions
Will a new sealed unit stop the condensation on the inside of my glass? No, and anybody who tells you it will is selling. Inside condensation is moisture in the room air. A new unit replaces the glass, not the air.
Does condensation mean my windows have failed? Only if it is between the panes. Inside is the house, outside is physics, in the middle is the unit.
Can you replace just the one misted pane? Yes. Units are done individually and made to measure, so there is no need to touch the rest of the window, never mind the rest of the house.
Every window in the house has gone at once. Is that normal? It is very common. They were all fitted at the same time and they all reach the end of their life at about the same time.
Will the new glass match the rest? It should. We match the specification of what comes out, including obscure patterns and energy coatings.
If the misting is between the panes rather than on them, that is a failed unit rather than a ventilation problem, and our misted double glazing repairs page covers it. For the wider picture on windows, see windows in Wishaw.
How long does it take? The glass is made to measure so there is a short wait between measuring and fitting. The fitting itself is usually well under an hour for a single unit.
Where we cover
We are based in Wishaw and work across North and South Lanarkshire, which takes in Motherwell, Hamilton, Bellshill, Coatbridge, Airdrie, East Kilbride and out towards Glasgow. The full list is on our areas we cover page. If you are not certain whether you are inside the area, ring and ask. It costs nothing to find out.
Send us a photo
The fastest way to a real number is a picture. Send a photo of the window on WhatsApp with a rough idea of the pane size and a line about what it is doing, and we will usually come back the same day with an actual price rather than a range. Most misted unit jobs can be priced without anybody coming out at all.
If you would rather talk it through, ring 01698 604 278, or use the contact form. It all lands with the same two people and we are open eight until five, Monday to Friday.