CONDENSATION IN LOFT (ANSWERS)

[JohnD]

This seems to be the time of year for condensation in lofts, so instead of replying to lots of queries I though I would write this "one-size-fits-all" post.

Please also see
http://www.diynot.com/wiki/Building:Condensation-in-Houses

Condensation in lofts occurs when the amount of water vapour rising in the loft exceeds the capacity of the loft ventilation to remove it.

Water vapour is lighter than air so it will tend to rise up through the house until something stops it.

So one or both of the following applies: (1) Excessive water vapour load and/or (2 )inadequate ventilation

Common causes are:

1.

Excessive water vapour in house due to occupants draping wet washing about the house or over radiators. Cure: Stop doing it

Excessive water vapour in bathroom due to occupants not using an extractor fan until the room is dry (including the towels). Cure: Use an extractor

Excessive leakage into loft due to hole in ceilings, e.g. downlighters, pipes into loft, ill-fitting loft hatch. Cure: Seal the holes

Plumbing faults causing tanks in loft to contain hot or warm water, and/or water tanks without tight-fitting lids Cure: Ask the plumbers

Leaking roof or plumbing dripping into loft

Bathroom extractor fan duct has become disconnected from the fan so the warm damp air from the bathroom is being blown into the loft.


2.

Eaves ventilation blocked by loft insulation. Cure: Pull back the insulation a few inches and cut it so it can't flop back

Inadequate ventilation since house was built. Cure: Cut soffit vents or hire a core-drill to make hole in gable walls. Or a roofer can fit tile or ridge vents (warning: unskilled roof work may cause leaks)

Older house where roof was originally not felted (so was ventilated by gaps between tiles) but a new roof has been fitted. Cure: As above

 

[meditatinghamster]

Hi John D,

Good link, with some good common sense solutions.

Wet coats hanging up: solution = umbrella

Tumble drying is not always a solution as it can cause clothes to shrink,
Solution: tumble dry what will not shrink and use a clothes horse + dehumidifyer for those that will. That way you will probably be able to keep it to just one room that has wet clothes in.

We lived in a rented place that had terrible damp and mould problems. A reasonable quality dehumidifyer worked wonders..

I'm sure a one-size fits all wiki entry is possible and would be really useful for everyone.

 

[swbjackson]

You've missed one important and very dangerous cause of condensation within lofts, faulty flues.

If a flue from a gas appliance fails within a roof space it will create severe condensation within a very short period of time. The occurrence of flue failures within lofts seems to be increasing as more people are having condensing boilers with vertical flues fitted to replace old open flued boilers. Most modern boiler flues are push fit and if not supported properly can come apart.

If you suspect that a flue from a gas appliance is causing the problem shut off the appliance and call a registered gas installer in to check the flue.

Mike

 

[sympology]

Another one.

A poorly sealed Loft Hatch.
Fix - Seal it up better. Door sealant does a fine job.