black mould at windows

HI,

I have a 15 year old house. I've done all the home improvements including new double glazing (3 years ago) and 12 inches of loft insulation. Only thing left now is cavity insulation.

Now I was plagued by black mould and condensation in all of the upstairs windows when I had the old windows. These were hardwood frames with sealed double glazing units inserted like a single pane of glass.

There are three windows in total upstairs, front bedroom, back bedroom and landing.

I had specified trickle vents and grade A energy rating glass for the new double glazing due to the condensation problems I had.

I am still plagued by condensation when the outside is cold even with the new double glazing.

Its so bad that there are pools of water on the window shelves. I of course ended up with black mould again on the emulsioned plasterboard where it meets the wooden window shelf.

I've scraped off the mould and painted benzalkonium chloride on in an effort to kill the mould and prevent regrowth.

Last year I invested in a dehumidifer thinking that it was the moisture from sleeping peoples breath that was the cause as the downstairs windows did not suffer from condensation

Now that the outside is colder, I had it running all the time to dry out the air and it did reduce the condensation significantly.

But the other half is complaining she is waking up with a headache due to dehydration and is gasping for water all day whilst at work.

I've changed the humidistat to 30% humidity on the dehumidifier. This is on the landing . The other half's headaches have improved but the condensation has come back somewhat, with a thin smearing at the bootom of the window panes

I am keen to avoid a return of the black mould as I have asthma. I have noticed that the plasterboard in the two corners where wood window shelf meets the UPVC window feels cold to the touch. Although there is no mould (yet) the benzalkonium chloride I painted on seems to have become tacky.

How can I banish this condensation once and for all?

Stephen.

Reply to
Stephen
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Bloody hell, mines set to 70%.

What you need is to open the windows a bit.

Then you may need to have a little more heat.

Reply to
dennis

When you did the windows did you ensure there was no cold bridge or a void with a draft from the outside in it?

Reduce the moisture content of the air inside. Where is this mositure coming from? One assumes that the bathroom and kitchen have extractors and they are used during and after bathing/cooking. Do you dry clothes indoors? Try to remove/eliminate the moisture at source.

After that reduce the vapour in the air either by ventilation or by a dehumdifier. Ventilation is the prefered option as that brings fresh air into the house.

Reply to
Dave Liquorice

Good advice.

Cooking, showering, washing, breathing etc all put dampness in to the air.

You can extract it via extractors, windows or dehumidifiers. Otherwise it will simply condense on the coolest surfaces in the area.

Reply to
Hugh - Was Invisible

Condensation occurs when the temperature of a surface drops below the dew point.

For example, if your house is run at 20 degC, and it is 60 percent humid, there will be (very nearly) 20 x 0.6 = 12 grams of water per cubic metre. This represents 100 percent humidity at 12 degC, so if your windows drop below 12 degC on the inside, condensation can form.

There are at least two things you can do, apart from re-engineering the windows:

Lower the humidity in the house (this will lower the temperature at which condensation takes place)(this can he helped by keeping moist air from the kitchen and bathroom out of the rest of the house by keeping the internal doors closed)

Draw curtains over the windows (this stops the humid air reaching the window in significant amounts if done properly (no gaps at top, bottom, or sides).

Terry Fields

Reply to
Terry Fields

What you need to do is buy a half dozen humidity meters from Amazon (they are only a few quid each) and scatter them around to get a picture of what is happening. If you have readings above 70% then you are going to have condensation problems. But beware, whereas digital meters tend (I think) to be accurate, the analogue ones need to be calibrated. (Buy a digital one to calibrate them with).

Good luck.

Brendan.

Reply to
Rednadnerb

a) determine where excess moisture is coming from, and sort it out b) run the dehumidifier Ventilation is good in summer, this time of year its a lot more practical to use the dehumidifier.

NT

Reply to
NT

Just over a year ago I put up various curtains etc. The front door, which is fully glazed, gets far more condensation with double net on the door and curtain over the recess than it ever did when 'naked'; the same applies to other glazing. I run the downstairs rooms at ~16 - 18C and upstairs at ~14 - 16C and there's only me in the house and v. little cooking. I assume that the extra condesation is due to the glazing (20-yo double) being much colder. The advantage is that the moisture can be mopped up and got rid of and that the other surfaces are a bit warmer than they were and so get less condensation.

Reply to
PeterC

I'm convinced that this sort of thing is due to a chimney-like effect, but in reverse.

When the curtains are pulled across, warm air behind them cools due to the heat loss through the door/window/frame. This sinks down, cooling as it goes, to emerge as cold air at the bottom.

Meanwhile, warm moist house air enters at the top, cools, and sinks to the bottom.

The bottom of the door/window/frame is the coolest part as the top is heated by the room air, and if it falls below the dew point, moisture will condense out. The colder the outside temperature, the further up the window etc the condensation starts.

However, heat is also lost by conduction through the frame, and as a consequence the nearer the frame, the cooler the glass and the greater likelyhood of condensation. When the curtains are pulled back, the condensation is typically in a U-shape.

That's why I suggested to the OP that ensuring there are no air gaps at the sides and bottom (and at the top too, if that can be arranged) in order to stop this happening by cutting off the airflow.

Terry Fields

Reply to
Terry Fields

Why is that if you are removing at source?

Reply to
ARWadsworth

Leave the internal doors open and a window or two so air can circulate and remove the moisture. The problem could be steam from a shower? Something somewhere is generating moisture.

Reply to
Pakistan Cricket Scam

If you can reduce damp enough without a dh, fine, but often thats not the case.

NT

Reply to
NT

Yes, it will work like that to some extent but no where near as fast as a bare window. Many times on here we've had mention of needing sufficient gap behind a radiator (and in front, e.g. not putting furniture close) to allow the air to circulate. The flow is weak over a rad. with up to 60C difference; a window at max. 30C most of the time would be far less. Adding even an ill-fitting net curtain will slow that enormously.

I decided to add layers when I noticed the difference made by possibly the worst addition: vertical blinds. They're loosely mated and have gaps on 3 sides but the difference on a cold morning between inside and windowside was striking. Last Winter there was far more ice on the windows than I'd seen in the previous 19 years; as the glass is obviously much colder than it was without the extra layers there is less loss of heat. The chimney effect is slowed and is less than a bare panel, although it still adds some heat to the window of course.

Reply to
PeterC

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