Are my windows to blame for mould?

28 Oct 2010
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South Glamorgan
United Kingdom
Hi all, new here.

The guy that fitted our windows is a friend but I'm not too sure he did such a great job.

Over time, the silicone seal has broken around the frame where it meets the wall so there are gaps and the windows whistle in the wind a lot.

I'm going to completely reseal one window after bits of plastic trim fell off. I removed this plastic trim ready to reseal to find there were large gaps around the side of the windows with a cold draft blowing through! These gaps were just covered with plastic trim, presumably so he could save using lots of sealant plugging the gap.

Also, for a few years now we've been getting excessive build ups of mould in the corners of our upstairs rooms. This problem seems to have worsened since our new windows were fitted.

Does anybody know if it is a problem with the windows which is causing the mould? Also, should I fill these large gaps with sealant before attaching the plastic trim again?

Thanks all.
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I would just like to add a few things...

I've been reading a lot of threads on this forum and I think I should point out that we have no extractor fans in the bathroom or kitchen. We also have no trickle vents on any of our windows. I've always wondered if I should have trickle vents and extractors fitted.

Other members of my household hate opening the windows for ventilation as they get cold so the windows are usually left closed in the colder months. We also dry washing indoors regularly.
I understand that.

Essentially, is my house poorly designed? It was never fitted with these trickle vents or extractor fans.

Are we cursed to sit cold in our homes all winter because we need to leave windows open for ventilation?

It is this that I don't understand.
I don't want a mouldy home, but I don't want a cold home either with a huge heating bill.

(The house is a 1960's semi-detached.)
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When your house was designed, it might have had an open fire, or a gas fire with a chimney, which provides a lot of ventilation. It would have had a washing line in the garden, and washing would have been done about once a week. People would have had fewer baths and showers, they would have had wooden windows which leak a bit, and a housewife would have opened the windows to air the house while hoovering, mopping the floors and making the beds. There might not have been central heating. With no double glazing the occupants would have had water or ice on their bedroom windows in the winter, they would have accepted it as normal.

With modern heating, your house will be warmer; with more baths and showers it will be steamier; with closed windows it will be worse ventilated, and with buckets of water draped about the house or hung over radiators soaked into washing, it will be far wetter.

You ought to have trickle vents; and you must have at least a bathroom extractor. However if you continue to drape wet washing about the house, it will always be damp and mouldy. This is the worst, and most common cause, and no-one but the occupier can cure it. Save up for either a tumble drier, or a washing line. If you prefer you can buy a dehumidifier, but this will work out more expensive.

I am not being intentionally rude, but that's how it is.
Is an extractor fan cheap and easy to install in a bathroom?
I've suggested we get one of those installed for months but it has been put off due to more important things going on.

As for the washing, we have a washing line too but good old Welsh weather means it gets used very little. We also have a tumble dryer but its expensive to run and we've had problems with it in the past.

Also, can trickle vents be retrofitted to normal uPVC windows? If so is this a cheap and easy job.

Thanks for the advice.
if your house is made of brick and block, you can hire a core drill that will make a neat round hole to fit the duct in less than half an hour. Do the kitchen, bathroom, utility room, place where tumble drier or cooker hood is/might be, you can do them all within half a day's hire. the rooms that you don't have extractors in yet can have a cowl fitted to the outside and a hit-and-miss vent fitted to the inside. You can close or open that depending on whether you want ventilation or not. A plastic duct has to be fitted to line the hole. If you have loose cavity insulation, stuff the hole with an offcut of fibreglass loft insulation first.

An extractor fan in a bathroom should be fitted by a qualified electrician who is a member of a self-certification scheme, for legal reasons. Do not fit it directly above a bath or shower, or where it might get squirted or sprayed with water, otherwise you will have to fit an ineffective low-voltage one, or an expensive waterproof one. Put it as high as you can, and as far from the door. It will draw dry air in under the door to replace the moist air which it extracts (water vapour rises). I recommend you have it connected to come on every time the light switch is used, as some people have an aversion to ventilation and won't turn fans on. You can get a fan with a timed overrun. If you have wet towels or splashy shower, it can take 20 minutes to get reasonably dry. If you leave the fan running, you can, if you insist, hang damp washing in there. Centrifugal fans are generally quiter and more powerful than axial fans, but not as cheap.

Trickle vents are basically holes in the frame, though you can get plastic covers to make them look neater of keep flies out. You can probably drill yours, being careful not to touch the glass. Some plastic frames have steel reinforcers, usually at corners or hinges, which you must avoid.
Whatever ventilation you go for - it'll still take heat out of the room so just leave the windows open. I thought they were tough in the valleys.

It's the end of October and I haven't had my heating on yet. Toughen up Boyo.
Thanks for the information.

I like the idea of the extractor fans and trickle vents on windows and I am seriously considering getting these fitted by competent tradesmen as soon as possible. (But not the guy who fitted my windows)

As for the vents in rooms, that seems a bit more complicated and I may wait a while on that one.

Also, I mentioned in my original post about large gaps around the sides of the windows under the plastic trim, shall I plug these holes with sealant before replacing the trim as a lot of noise and cold draft is coming through these gaps.
I'd use expanding foam.

clean out all dust and loose material, and spray with water first.

if you put wide tape over the gap on both sides of the wall, this will help it to expand into the gap rather than falling out. You can poke the nozzle through a small hole in the tape.

It is very sticky and expands more than you think possible, so cover the floor, tape newspaper or clingfilm to the wall and frame, have several clean pairs of disposable gloves - once you touch the sticky foam you will have to throw the sticky gloves away. It will stick to hair, skin, eyeballs, clothes, shoes, carpets etc. If you get it on you, apply water to harden it and pick off later. Do not try to clean it up while wet or it will just smear around and get worse. You can buy a foam-eating solvent for any hardened bits in the carpet.

once it has hardened and filled the gap, you can cut it flush with a breadknife or surform, and paint, decorate or fill over it. Externally it has to be painted as sunlight degrades it.
You aren't getting the message. The more draughts you plug - the bigger your mould problem will become and it's a genuine health hazard. Ventilation means bringing fresh cold air in from outside - inviting draughts into the house. That's what ventilation is - a controlled draught. Trickle vent (all but useless) air-bricks (that most people block up). It's all about making your house draughty. Get it yet?
but in this case, draping water about the house and over radiators will make the problem insoluble.
You aren't getting the message. The more draughts you plug - the bigger your mould problem will become and it's a genuine health hazard. Ventilation means bringing fresh cold air in from outside - inviting draughts into the house. That's what ventilation is - a controlled draught. Trickle vent (all but useless) air-bricks (that most people block up). It's all about making your house draughty. Get it yet?

Umm, yes, I understand...

I've already thanked JohnD for his advice and I'm considering getting the work done ASAP.

But I want to ventilate my own home of my own accord and not have draughts and noise coming through the side of my windows because they have been poorly fitted.

I will gladly open some windows to get some ventilation, but I dont want large gaps around the side of my windows. I'm not trying to make my house airtight.

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