Condensation in loft

pledgeX

Evening all.

I went up in my loft today to store some stuff and it smelt a bit damp. On further investigation, the cause of this seemed to be the loft hatch itself - the top of the loft hatch was wet to the touch. The hatch is made out of about half an inch of wood (plywood maybe?) and attached is about 3 inches of loft insulation wrapped in a plastic bag.

I've only been in the house for 7 months and this is the first time I've noticed it. About a month or so ago I insulated the loft, so I assume something I've done has caused this - although it may have always been like this, but having not lived here last winter I'm not sure if this has always happened...

I've read that condensation in lofts is usually caused by a lack of ventilation. When I insulated, I checked the edges of the loft to see if there were ventilation ducts. I could not see any, but left a bit of a gap just in case. In the top of the roof there's some kind of vent which I can see daylight through so it's definitely getting some air in there.

I had a bit of a feel round the loft and the loft hatch was the only hint of dampness I could find, so perhaps I just need to insulate it better?

Any advice on how to get rid of the dampness?

Thanks.

ariba10

We fitted a couple of ventilation tiles, in the roof tiles,

We are lucky enough to have a young and energetic neighbour who did the job off a roofing ladder.

The_Pedant

It's usually warm moist air meeting a cold surface or cold air.
If it is just damp around the hatch then I'd be inclined to think you have warm air from the house escaping around the hatch to the attic. I'd probably try checking the hatch & the opening is draught-proof and properly insulated to prevent the warm air from the house meeting the colder air & surfaces in the attic space.

London_Town

Yes, I'd agree with the Pedant. When I had my loft insulation increased last summer, the firm that did it made great efforts to insulate my loft hatch. I didn't understand at the time, but it makes sense to me now.

keystone

The bigegst source of warm humid air in a roofspace is the loft hatch.

OP needs to make sure that there is more than "just a bit" of space in the eaves. There should be no insulation stuffed into the eaves at all. It compromises cross ventilation and leads to condensation.

Cheers

pledgeX

The_Pedant wrote: »

It's usually warm moist air meeting a cold surface or cold air.
If it is just damp around the hatch then I'd be inclined to think you have warm air from the house escaping around the hatch to the attic. I'd probably try checking the hatch & the opening is draught-proof and properly insulated to prevent the warm air from the house meeting the colder air & surfaces in the attic space.

Forgive me if this is incredibly dim, but bear with me. If its being caused by the hot air from the house meeting the cold air in the loft, wouldn’t the condensation form on the ‘house-side’ of the hatch, not the ‘loft-side’ like I’m getting? Just like when you get condensation on the windows – you get in on the inside as the house is warm, not the outside.

As for insulating the hatch further. I can’t add any more insulation as 3-4 inches is the maximum as any more than that wont fit under the access ladder above. Maybe I could use some of those insulation sheets instead of the offcuts of insulation rolls from the rest of the loft? How do those sheets perform in comparison?

And I’ll make sure to pull away any insulation from the eaves but I’m pretty sure there’s enough space there anyway.

Thanks for the replies.

Leif

To digress a little, if there are holes in (bungalow) ceilings where heating pipes used to go, would it make sense to stuff something into the holes to prevent warm air escaping into the loft? I had assumed a little ventilation would not be bad, but forgot the warm air might hit a cold roof and cause condensation.

NewJones_2

We had our loft insulated by a 'large energy company' a few months back and they put a draught proof strip around the house side of the loft hatch to stop air transfer. Unfortunately when we went up just before Christmas to get the decs down it was soaking wet up there and a lot of our things were ruined. We're having vented tiles fitted next week to try and fix the problem.

ormus

always leave at least a 50mm gap in the insulation at the eaves. this will cure most problems in lofts.
air vents in the tiles or ridge tiles is another possible answer.

The_Pedant

pledgeX wrote: »

Forgive me if this is incredibly dim, but bear with me. If its being caused by the hot air from the house meeting the cold air in the loft, wouldn’t the condensation form on the ‘house-side’ of the hatch, not the ‘loft-side’ like I’m getting? Just like when you get condensation on the windows – you get in on the inside as the house is warm, not the outside.

My thinking is this (I'm just thinking on my feet here):-
- Warm air can hold more moisture than cold air.
- The hatch itself does not conduct well enough to be cooled sufficiently for the warm air to condense on the underside (like your window example)
- Cold air entering the living space of the house would be warmed by the bulk of warmer air which can absorb any cold moist air creeping around the hatch
In the window example you give, the glass has been cooled by the outside temperature. Therefore any warm air meeting it would cool rapidly, causing the excess moisture released curing cooling to condense.

Without trying to remember a whole host of calculations from 20 years ago, that kind of explains it in my own (some might say warped) mind