condensation in loft

[auldsy]

Hi
I have read other posts but just wanted to double check.
As you can see there is alot of condensation and it leaves the ceiling above the windows mouldy.
There is no moisture rising up from the rooms below, there are two vents on the roof, water tank is covered etc.
The only reason I can think that is causing the moisture is too much insulation.
Is there supposed to be insulation between the wall and roof?
(insulation is always damp and it is not an external wall)
many thanks

condensation in loft

• auldsy
• 19 Jan 2010
• 1

Untitled

• auldsy
• 19 Jan 2010
• 1

Untitled

• auldsy
• 19 Jan 2010
• 1

 

[mointainwalker]

On what basis do you say ...

" no moisture coming up from below " ?

 

[auldsy]

we dont dry clothes in flat
there is an extracter fan in the bathroom ( although the bathroom has no windows and the duct is about 6 metres )
there are no leaks in roof or holes in ceiling etc

 

[mointainwalker]

But is there a vapour barrier on the loft side of the ceiling and underneath any existing insulation ?

 

[JohnD]

start by pulling out that insulation in pics 2 and 3

With luck you will get a nice draught of fresh air blowing through the loft. This remove the damp air and let the loft dry out.

It is OK for lofts to be cold and draughty above the ceiling insulation. Lofts are not heated spaces.

Also pull away some of the insulation at the edges, it is usual to have ventilation at the eaves, but this depends on the design and build of your roof.

As long as the loft insulation covers the plaster of the ceilings below, and overlaps slightly onto the tops of the walls, it is OK. it should not be stuffed into the eaves.

BTW yes, moisture will be rising from the house below. Ceilings and hatches are not airtight. If there is no ventilation of the loft, then the water vapour cannot escape so it forms condensation on the cold surfaces.

Also your bathroom ventilation might not be enough. When does the fan go an and off? Are the towels still wet when the fan is stopped? Does the bathroom mirror get steamy? If you go outside on a cold day, do you see steam blowing strongly from the outlet? Is the fan motor in the wall or ceiling, or is it in the loft?

 

[auldsy]

cool I will pull out the insulation and see if it helps.
the bathroom ventilation might actually be a problem. its an internal bathroom with no windows and a fan on the ceiling. its goes on with the light and stays on for 10 minutes after the light is switched off, the condensation on the mirror is usually gone at this point.
the fan is connected to piping which travels accross the loft for about six metres and exits through a hole on the wall.
would I need a more powerful extractor fan?

 

[JohnD]

if the mirror is clear, that is usually a good sign. If the fan comes on with the light, this is also good as it avoids the risk that someone might fail to turn on the fan (some people have an aversion to ventilation)

However the towels and bath may still be wet, and this water has to go somewhere.

If you want to increase the ventilation because the duct is rather long (a photo of your current fan, or any make and model you can see will tell us how powerful it is), you can get a Centrifugal (these are generally more powerful and quieter than Axial fans) in-line fan, which is fitted in the loft

this sort of thing which has more than twice the power of a cheap little fan

you can even mount them in an insulated box standing on foam to cut down on noise even more

Any ducting in the loft is going to be cold and prone to internal condensation, so preferably use rigid pipe (not flexible) and run in with a slight fall to the outside so that any water can drip out, and flop loft insulation over the duct to prevent heat loss and condensation.

BTW check any joints in the duct while the bathroom is in use in case it is leaking steam into the loft.

edited to correct speling eror

 

[auldsy]

thanks mate
plent of things to go on there.
my current fan is an axial - not at home at the moment so dont know which make or model.
will have a look at the duck and will probably insulate it. would there be any point in reinsulating the whole loft?
cheers

 

[JohnD]

if the loft has 150mm of insulation all over, I wouldn't bother. Current recommendation is for 250mm but the incremental benefit is small for the cost and effort (you may get a grant though)

 

[auldsy]

ah good didn't really want to go mad and reinsulate everything.
thanks for all your help and advice John. Appreciate it.