dehumidifier in attic?

Hi, my attic has previously been fine, and I have loads of stuff stored up there. Now it seems to be damp and paperbacks are curling etc. Would it be any good to buy a dehumidifier to put up there? Or does a dehumidifier only work in an airtight space? I'm assuming it's the wet weather we've had recently that's caused it. (I've been looking at €80.00 ones, 10L from B&Q etc)

A dehumifier only treats the symtom and not the cause. Sounds like you may have blocked vents in the attic space when you were picking stuff.

Hi Davy

No the attic is only floored in the middle bit, which is where everything is stored. Apart from me looking through boxes, there's been no work done up there at all!

Hi Gordanus

<great sounding nic btw>

DavyJones has given you some sound advice.
Some condition must have changed in your attic to cause the dampness if it wasn't damp before as your post seems to suggest.

Here's a non-exhaustive list of some likely causes of damp in attics; -

• warm moist air travelling into a colder attic space
• leak at gutter, upstand, penetration or in roof
• additional insulation without vapour check
• inadeqaute venting of the attic space
• work to adjoining properties [vague]

Issues can arise from a myriad of causes and I list some to try and jog your memory on stuff you might have done.

• downlighter installation
• flexible duct from bathroom fan disconnected or blocked [book fell on it]
• flashing on chimney or pipr penetration working loose in wind
• broken slate or tile, block eaves vents [if there are any]
• adding insulation [will lower attic temperature]
• pipe leaking internally
• valley gutter or blocked and water getting under valley boards or into eaves boxing.
• eaves gutter blocked and water getting into eaves boxing

The last two may not actually "wet" the place, but will tend to contribute to air-borne water vapour in the attic.
Anyway, do a check on these and revert.

ONQ.

onq said:

Some condition must have changed in your attic to cause the dampness if it wasn't damp before as your post seems to suggest.

Click to expand...

• warm moist air travelling into a colder attic space - due to wet weather?
• leak at gutter, upstand, penetration or in roof - haven't yet clambered around on joists to look...
• additional insulation without vapour check - nothing done
• inadeqaute venting of the attic space - was always fine before...
• work to adjoining properties [vague] none...

Issues can arise from a myriad of causes and I list some to try and jog your memory on stuff you might have done.

• downlighter installation - nope, no work done
• flexible duct from bathroom fan disconnected or blocked [book fell on it] - bathroom ventilated by window!
• flashing on chimney or pipr penetration working loose in wind - o dear..might have to send someone onto the roof!
• broken slate or tile, block eaves vents [if there are any]- o dear..might have to send someone onto the roof!
• adding insulation [will lower attic temperature] - insulation untouched for years
• pipe leaking internally - no marks on ceilings below
• valley gutter or blocked and water getting under valley boards or into eaves boxing.- haven't yet clambered around on joists to look...
• eaves gutter blocked and water getting into eaves boxing- haven't yet clambered around on joists to look...

Thanks Onq for your very detailled reply! Guess an inspection is necessary. Will call out my builder. Aaargh! All this on top of pay cut!

Gordanus said:

Thanks Onq for your very detailled reply! Guess an inspection is necessary. Will call out my builder. Aaargh! All this on top of pay cut!

Click to expand...

For condensation issues, contact an architect.

ONQ.

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hi.. I have a similar problem with condensation on the north facing felt.. i put in two vent slates to help with ventilation but the problem still exists (if not worse).. was thinking about using a de-humidifier during the winter months!

Condensation in habitable rooms is the result of three things.

(i) water vapour in the air
(ii) relatively inadequate insulation
(iii) relatively inadequate ventilation.

Inadequate insulation causes surfaces to remain cool and moisture in the air to condense as dewpoint is reached - on cold surfaces in unheated bedrooms and landings for example.

In attics the situation is slightly different.

(i) water vapour in the air
(ii) relatively adequate insulation
(iii) relatively inadequate ventilation.

Insulation at ceiling level prevents heat reaching the attic, lowering the dewpoint to allow moisture to condense on colder surfaces - the felt under slates for example.

Water vapour in the air in the attic can be reduced by installing appropriate vapour checks on the warm side of the insulation.

Downlighters at 1st floor level will tend to make matters worse.

Ventilation can be increased by ensuring the eaves vents are maintained at 50mm clear and introducing vent tiles or slates at high level.

HTH

ONQ.

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