Serious Loft condensation

[Ultraviolet]

Hello

Since the cold snap, we've had serious condensation building up in our loft, which then drips down onto the insulation and any other items stored up there.. any ideas what might be causing this, and what I can do about it?

thanks

UV

[mk1fan]

The 'extreme' conditions at the moment are causing problems that under 'normal' conditions wouldn't be there.

Could be warm, moist air leaking out from the house into the loft. Have you recessed downlighters on the floor below?

Check again when conditions normalise. If it's still there then start checking for causes/solutions/repairs.

If the current 'extreme' conditions become 'normal' then there'll be a lot of remidial work for building owners!

[Hereward]

You need to ensure the eaves (edges) aren't blocked, so that fresh outside air can circulate into and then out of the loft area.

[Harpo]

Groundhog day! :

I asked similar at the start of the month with the last cold spell.
Mk1fan was spot on then and no doubt is spot on again!
My loft was bone dry as soon as the weather went back to normal.

By the way, there were some wasps still buzzing around, biggest I have ever seen. Had to beat a retreat to B&Q for some spray.

[Sam_68]

Do a search on this forum for the words 'loft condensation'; you'll find that it's been discussed in some detail before.

Sometime (often) it does indeed dry out as soon as the weather has changed, but sometimes, particularly in modern properties with very thick insulation, it doesn't, for the simple reason that once moisture has saturated 18" thickness of fibreglass quilt, it takes a very long time to dry out.

The basic, initial response should be twofold:

• Do everything possible to ensure that warm (moisture laden) air from the house is not leaking into the loft (make sure the loft hatch, any services penetrations etc. are properly sealed). As Mk1. Fan has suggested, the current fad for downlighters, particularly in bathrooms (which obviously generate a lot of warm, moist air) is a common problem.
• Do everything possible to ensure that air circularion within the loft is working as it should (make sure the eaves vents, if you have them, are not obstructed by fibreglass quilt, remove any boxes that could be restricting air circulation, etc.).

If, after reading the past threads, you have any specific questions, post them on this thread and we'll try to help.

Edited by Sam_68 on Saturday 18th December 08:56

[Spudler]

Ditto the above posters but worth adding- IF you have the bathroom extraction exiting through the roof check that all is sealed tight as should be.

[Globs]

Hereward said:

You need to ensure the eaves (edges) aren't blocked, so that fresh outside air can circulate into and then out of the loft area.

This extreme weather means that _any_ moisture that gets up there sticks to the felting. Currently my eaves are completely open and I have condensation too, just avoid opening the hatch too much as you let the humid house air onto the felt.

For you the only answer may be to empty the loft, the insulation etc will recover.

[jeff m]

Loft should be as close to outside temps as possible.
If your eaves are open and you have upper ventilation then check any down light "cans" they could be the unrated ones intended for use on the ground floor. Cans for use on a top floor are different, they are double skin.

In the States we use "how fast does the snow melt on our roof" as a good indicator as to whether our loft iinsulation is adequete and the ventalation is good. I like mine to melt slower than my neighbour.

[blackcab]

Just out of interest have you had cavity wall insulation recently, I know there are loads of issues surrounding these govt backed insualtion incentives - i.e being installed wrong and causing condensation issues

[Sam_68]

jeff m said:

Loft should be as close to outside temps as possible.

...Although we are now starting to encounter condensation problems that appear to be directly because of this.

Traditionally, loft condensation was due to warm, moist air leaking out of the house and into the loft space, with the moisture held within that air condensing out into the loft insulation on the way. This is called 'interstitial condensation'.

_If_ they are properly designed an built (and I realise that this is a big 'if'!), modern houses are so air-tight that this is no longer a major problem.

What we now appear to be encountering is that ceilings are so well insulated that because the loft temprature is very close to outside temperature, two things are happening:

• The air within the loft space cools off every night and dunps its moisture out as a 'dew', just like the dew that forms on your lawn.
• The actual surfaces of the roof radiate heat in such a way that they actually cool to below ambient temperature (this is something I have difficulty getting my head around, I must admit, but I am assured that the physics of it is genuine and well known). The inside surface of the roof therefore acts as a condensing surface, and the water droplets that form on it trickle down and drip onto the loft insulation below. It's possible that the air flow over and though the roof space ads to this problem, with the pitched roof surface acting as a crude aerofoil (with the low pressure areas cooling the surface still further: think wing icing on an aircraft).

Because the insulation thickness is so great, the water droplets settling on top of the insulation quilt soak down into it and once in, become very difficult to dry out.

The answer, or course, is to move to a warm roof construction, or use an insulation that is basically impermeable (eg. rigid foam), bit both are very costly and the UK housing industry is reluctant to bite the bullet and adopt such measures.

All of the above relates only to relatively recent housing in the UK (we only recently increased insulation levels to the point where it starts to create problems, and improved air tightness to the point where it became obvious that interstitial condensation wasn't the issue any more). If you are living in a house that's 5 years old, or more, the chances are its just good, old-fashioned interstitial condensation that's your problem.

Edited by Sam_68 on Saturday 18th December 19:26