Condensation in the loft – what solution?

I went up into the loft earlier today and there is condensation on the roofing underlay – enough to have then dripped off onto the boarded area. I assume the issue is just that warm moist air is finding it’s way into the attic and hitting the cold underlay. It is old style non breathable underlay btw. The attic is insulated with 300mm (or equivalent) rock wool.

So what solutions?

Increase ventilation?
– current ventilation is from the eaves past with an air gap in an 18inch skilling that cuts across in the upstairs rooms. possibly put in some ventilation tiles in combination with a ridge tile?

Increase insulation?
– Perhaps insulate the roof itself and and then put a membrane over the insulation to stop any moist air finding its way anything cold and therefore no condensation?

Does anyone have an opinion on the best way forward?

There was recently a thread on this subject, it would be worth your while hunting around in the last week or so.

I had the same problem at the beginning of the year and had some extra vents put in. Has cured all the dripping.

From too many years ago when a student, I recall doing thermal calcs for various wall types and the idea was always to get the dew point to be at a point in the cavity or external brick work elements.

We did this by calculating the “K” value of each element, plaster, block, cavity insulation, brick, render and with internal and external temperatures to work from and to, you could calc the temperature drop through the wall and hence find the dew point location. A poor wall had this inside the plaster or internal block wall.

There shouldn’t be any need insulate the roof underside as I guess most houses don’t and I doubt you could get the dew point to be outside a roof or in the tiles so therefore it must happen in the roof space.

I’d be inclined to increase ventilation.

I could be talking loblocks though as it was more years than I care to mention.

Reduce humidity in the house using kitchen/bathroom extractor fans.
Make sure the loft is sealed from the rest of the house e.g seal off downlighters, and gaps and seal the loft hatch so that warm humid air cannot get into the loft. Make sure any water tanks in the loft are covered. If this doesn’t work you need more ventilation in the roof. Get some tile vents installed. If you want to DIY then i’ve found LAPVENT to be a good product in that you can install them from inside the roof.

http://www.singletrackworld.com/forum/topic/any-builders-or-roofers-on-here-advice-needed

Id be looking at increasing ventilation in the loft area.
Dont cover the existing insulation with a membrane as you will cause condensation on the inside of this membrane and soak your insulation.
The condensation isnt caused by damp air leaving your house its the heat it contains causing the moisture in the air in your loft causing the moisture.
So if you have heat rising somewhere you must have some gaps in your insulation.Loft hatch ok?

Thanks all. Great info. Ventilation it is then. Tile vents sound like the sensible option cost wise.

Need to check mine had vents put in last year so need to check it’s gone, but was advised to add ventilation.

i had this exact problem. the ridge tile is supposed to be vented as well as the vents at the soffits. sometimes roofers lay the felt over the apex of the roof and thus block and ventilation through the ridge tile. this was what was wrong with my roof and it caused lots of condensation like you described whenever it was cold. my neighbour is a roofer and he said to simply make a cut in the felt with a stanley knife or similar and take around a 1cm strip of felt out all along the ridge and under the ridge tile – worked a treat. I’ve had around 600mm of insulation already and this worked for me.

vent tiles

Is it in a new house? Some housebuilder use a breathable roofing membrane which is about as much use as a chocolate teapot. Do you have vents in the eaves and has the insulation been pushed tightly into the corner of the trusses? Best bet is to put in tile vents but be careful about the membrane where you cut it as it’s the second defense line if a tile leaks.

Ho ho ho, I spoke too soon. 🙁

Loft is full of condensation again so have been trying to cover up contents with plastic sheeting.

Silly question – if I removed the hatch for a bit to allow some warm air to rise, would it make any difference?

Worse. (Hot, damp air on cold roof.)

OK, thank you.

Same problem here, just been in loft and its like a shower room.
Fitted soffit vents, 300mm insulation, air bricks on gable ends, boxed in the down lighters that were sticking into roof void, fitted bathroom extractor fan, might try a for sale sign and let it be someone else’s problem.
What crouisk said might be worth investigating. My roof has a shallow pitch and I can only kneel upright in the very center, lofts with more space might not condense up as much.

I can sympathise bear!

Shallow pitch roof here too and I’ve just been crawling around on all fours checking for drips.

I only realised when water was again dripping through bathroom extractor fan. Fortunately I don’t use it anyway so just covered over carefully with plastic sheeting.

Do wonder if problem is original underlay (house is 30 years old) but loft is well insulated and also have cavity wall insulation.

I had this problem after adding thick loft floor insualtion.

Eaves vents in soffits all along didn’t really fix the problem. I only cracked it after adding a ridge top vent. Easy to do. Hoof it up onto the roof and choose a ridge tile. Drill a big long slot in the centre and make sure it goes go right through the ridge board. Cement on another ridge tile on top with air gaps to leave the slot. It sucks air out a treat.

(Or you can get vented ridge tiles, but they do the same thing).

Also Make sure you have foam seal all round your loft door, and there are no air gaps round pipes going up from the airing cupboard.

Dry loft.

My parents seem to get this a lot in their loft but I don’t seem to get any at all. Curious.

I can’t believe no one has mentioned a vapour barrier. This is standard building practice now. The idea is to place a impervious plastic sheet on the warm side of the insulation which stops moist air from reaching the dew point. This is much better done at the original building stage though 🙁

How much moisture is too much?

I have a few drips (formed into 2 or 3 lines along the roof pitch) that drip onto the insulation and a couple of the trusses look like they’re damp with soaked-in water. It’s not a problem with making stored stuff wet.

Ben

and a couple of the trusses look like they’re damp with soaked-in water.

only too much if you care about the roof rotting and falling in…