Condensation on inside of windows

[amfisted]

As stated elsewhere on this forum, we've at last managed to buy a property with cavity walls, after decades of living in draughty, condensation-affected Victorian properties with solid brickwork.

We've just had our first genuinely cold evening since the Spring, and I was rather disappointed to find extensive condensation on the inside of the double glazing units. These units are UPVC, have probably been fitted within the last 20 years and are beaded on the outside, although security-wise a local fitter has reassured me that the units are secured with clips. Point is, why would I have ANY condensation with cavity walls? Is it because the inside walls are warmer, and therefore the only place for any water vapour to go is on the cold inside pane of the glazing units? In our last house we had little if any condensation on the windows, but a dreadful problem with condensation on the walls which I could only address by having a dehumidifier running for several hours a day.

 

[Gazman16]

Sounds like it may just be the way you live then, Creating lots of moisture and not getting rid of it.

Do you:
Vent/open a window while cooking/showering?
Do you dry clothes inside?
Have indoor plants?

Heres a post I made on an old forum compiling some of the best information I have found about the causes of condensation.

http://www.double-glazing-forum.com/topics.aspx?ID=34

Easiest option is probably to open windows more often or buy a dehumidifier though

Read more: //www.diynot.com/diy/threads/fitting-a-trickle-vent-in-a-tricky-place.413944/#ixzz3FRcYRYVh

 

[amfisted]

Thanks for all that.

The kitchen has a very efficient extractor fan but the bathroom doesn't, and I intend to address that; though I won't be going with plan A and fitting it myself. We don't have any indoor plants and our clothes are dried in a condensing tumble dryer.

Having read your links, it seems that the best bet in the short term is to carry on using the dehumidifier for an hour each evening. I had hoped to be able to pack it away once we moved into a house with cavity walls, but no such luck.

Long term I guess we'll just have to breathe a bit less.

 

[JohnD]

Open the windows more.

Especially the bedroom every morning after you have thrown the bedclothes back

Use trickle vents all the time.

For the bathroom, a ducted extractor above the ceiling can be both quieter and more powerful than a typical wall extractor.

 

[dishman]

What you need to concentrate on is a combination of good heating control, insulation and ventilation.

If you are already getting condensation on dg windows, it will only get worse as the outside temperature drops unless you change your living habits a bit.

Get a bathroom extractor with a humidistat, this will ensure it stays on untill the humidity is at the correct level.

An average family can produce up to 15 litres of water vapour per day! Warm air holds more water vapour then cold air. So, as air cools (especially near windows and other cold surfaces) it condensates as water. You may also, as the temperature drops further, begin to get damp on walls if your not careful.

How do you control the heating? Do you keep some areas of the house hot and others cold? Do you maintain a good constant temperature around 18C or above?

Shut the door when you use your condenser dryer and put the kitchen extractor on. Condenser dryers often leak warm water vapour into the air.

Basically, before you become reliant on a dehumidifier, change your living habits and this should improve things a lot.

This guide should help...

http://www.bolton.gov.uk/sites/DocumentCentre/Documents/Condensation and Mould.pdf

 

[amfisted]

Thank you both.

I do try to remember to leave the window open a crack at night, but its easy to forget, especially when the wind is blowing a hoolie outside. I'll try to remember to open it in the morning also, once Mrs Van Winkle has risen.

I always assumed that condensing tumble dryers kept all the moist air within the machine, but thinking about it, if they exude warmth during operation then some of that air must contain water.

Humidistat controlled extractor fan...makes sense, thanks. In our last house we had a ceiling fan connected to the bathroom light, and it kept condensation, at least in the bathroom to a minimum. This is a much smaller property which is on just one floor, so such a device might help to keep the rest of the property dry also.

We've not long been here and are yet to work out exactly how the central heating roomstat, timer and boiler combine to the best effect, and I may be posting a question about that elsewhere on this forum.

I intend to have all the pre-Fensa dg replaced over the next few years, and when I do order the new units I'll make sure that they have trickle vents. In the meantime, I believe that they can be retro fitted?

 

[Gazman16]

Trickle vents should be an absolute last resort!

It is basically just a big hole straight through your expensive windows with a flap of plastic to stop drafts and spiders.
Not many company's bother to tell you but once you add a trickle vent to a window you can wave good bye to an A,B,or C rating. Technically they should be against regulations for how badly they affect the energy rating but you don't have to have them tested with a vent fitted.

There is talk of banning them (thank god). I'm really not a fan of them.

 

[amfisted]

Thanks again. I must admit, the thought of spending all that money to seal the inside of the house against the outside then putting a hole in it doesn't appear, on a basic level, to make much sense. The relative merits or otherwise of trickle vents is obviously an ongoing debate, of which, for now, I would prefer to remain an impartial observer; at least until I'm absolutely persuaded one way or t'other.

I'm interested in this phrase "cold bridges". Is this where the double glazing unit comes into contact with the side of the frame, and therefore with the wall, when its being fitted?

 

[JohnD]

Opinions differ.

A tightly sealed home with no ventilation will become stuffy and stale, but more importantly, none of the water vapour created by the occupants will get out. Many people complain that condensation starts when they replace their draughty old windows with tightly sealed new ones, because they have never consciously needed to provide ventilation.

Trickle vents allow a small and controllable amount of ventilation. They are especially useful in bedrooms. They are certainly not "a big hole"

 

[Gazman16]

Or you could just open the window and put it on the night latch every now and then. I open a window while showering and leave it open for at least half an hour after. Also I sleep with the window open as I like fresh air.

Personally I think a 4000mm2 hole is quite big (the average size for a trickle vent) most window now have 4-9 chambers within them and the hole breach's all of them allowing cold air to circulate around the whole of the window frame. Yes technically trickle vents should be sleeved but in reality no company does it and in a retro fit scenario it would be damn near impossible.

So in the case of the windows I fit you go from having 6 insulating chambers in the frame to none, Just 4mm of pvc between the outside air and yourself.

Then you have all the bugs and spiders that set up home in them.
They look awful
They get very dirty, are a pain to clean.

I would only recommended trickle vents where:
They are required by law.
In tenanted property's (for the sake of the landlord as tenants rarely open windows).
Where there would be a security issue with leaving windows open (like bungalows in rough areas).

 

[dishman]

The fact is, as you increase insulation and "air tighness" you reduce uncrontrolled ventilation.

This causes a problem as water vapour is trapped inside the house for longer. The water vapour will condensate on any cold surface which (due to it being an older property) acts as a cold bridge and cannot be insulated.

So as you reduce uncrontrolled ventilation, you must increase controlled ventilation. This is done by targeting specific areas where a lot of moisture is produced, such as the kitchen and bathroom. The extractors must be correctly specified to work correctly and move enough air.

The problem is that you have to find a balance between extracting the moiture and loosing the heat (which you are trying to avoid). In my mind, on an older property, this is a trade off I am happy to live with.

It is neigh on impossible to get an old property to a level of air tightness by which heat loss though an extractor fan would/should become a issue or a concern. Therfore a good extractor fan with a humidistat is a must.

You can actually get self contained heat extraction (mvhr), extrator fans if you are really concerned about this. They extract the air but put some of the heat back into the room.

It is only modern properties, where the livel of air tightness is such that you have whole house mvhr, which would be able to extract moisture and retain all the heat at the same time.


With regards to the op's property. As it is a small flat, any moisture you produce, will be concentrated into a much smaller space as water vapour. So the issue may be more pronounced. Water vapour can move around a propety quite quickly. For example, i have period single glazed windows but I have no damp or exessive condensation issues in my property. However, when Iuse the gas cooker on a cold day and I forget to put the extractor fan on or open the window a crack in the kitchen, the upstairs front bedroom windows quickly begin to steam up! The kitchen is downstairs at the back of the house. So, this shows you how quickly air can carry water vapour through the house, cool and condensate. If I put the cooker extractor on, I do not have this issue.

 

[pinenot]

The reason trickle vents were invented and fitted to windows is because so many people blocked every vent hole to try cutting costs/comfort, not realising that ventilation is an absolute nessesity for keeping down condensation and eventual rot.
Condensation is a result of poor ventelation, high moisture born air and cold surfaces which condensation forms on, reducing any or all of the above prevents it. Easy to say but not so practical sometimes. Dehumidifiers will bring down the moisture content, at a cost. Heating will help warm the cold hard surfaces, but hot air carries more moisture than cold. Again well sealed double glazing will help, but is not the be all and end all. Fitting and using good curtains to windows prevents the moisture from condensating on the cold widow frames, glass etc. but some moisture loaded air always gets through. THE DILEMMA
The best approach is all of the above, as is most suitable in each particular case, as each one can affect the formation of condensation...pinenot

 

[amfisted]

Fascinating discussion and again, thanks.

Incidentally, we have moved to a detached bungalow, not a flat, and now of course we have four outside walls. One wall in particular seems to be very cold; I've found this out because whilst decorating the garage conversion I've found that on the bottom of one wall, which is on the inside of an exposed outside corner, emulsion paint dries very slowly indeed. I had a similar issue if, in any season other than summer, I attempted to paint the gable end corners of the bedrooms in our old house, those corners being on a particularly exposed outside wall.

My plan as of now and having read all the excellent advice above is thus: have those relatively old windows which have been particularly badly affected by condensation replaced with new units, hang curtains because at present we only have blinds, and to fit an extractor fan in the bathroom; humidistat if not too expensive. Then breathe in and hope for the best, breathing out only when absolutely necessary.

 

[JohnD]

if you buy new windows, get trickle vents. You can always close them if you feel you have more ventilation than you need.

On a rainy day, look at the cold wall for signs of gutter or downpipe spillage.

Unless the walls are defective, CWI will greatly cut heat loss, and the inside surfaces of the walls will be warmer. You might get it free or subsidised from BG even if you are not their customer.

 

[dishman]

My plan as of now and having read all the excellent advice above is thus: have those relatively old windows which have been particularly badly affected by condensation replaced with new units,

Just a point: When you say "badly affected by condensation", do you mean the windows have become mouldy, discoloured, damaged? Or do you mean that there is condensation inside the double glazed unit, if so, this is a different issue and can be solved by replacing the glass unit.

If it is none of those, and the window is just prone to condensation, it may not be worth going to the expense of replacing/upgrading the whole window.

Taking the advice here and the guide I posted (or any others you have read), may prevent condensation forming on them.

As JohnD says above, I would first look into getting your walls (if they have a cavity) insulated. Same with the loft (check it is up to modern thickness standard).