Condensation in loft.

MisterNick

As the OP here, I thought I would update on my position.
I went in the loft yesterday and there was no condensation on the felt.
The boards had mostly dried out, and I couldn't see any signs of the exposed insulation being wet. I haven't been able to look at all of it yet, but I was encouraged by what I saw.
I haven't got any lap vents yet, but it is on the to do list.
Also the felt (I think you still call it felt as its the black bitumen type) is looser at the seams than some of the pictures from the vent vendors, but they are not so loose that they are flapping or at risk of ripping. I think Ashe discussed it.
Thanks again for all the replies and support, I understand the problem much better now. 

MisterNick

rross1
Hi, it looks like you need require additional ventilation. From previous experience from our previous house, there was a design of vents which you can fit into the insulation to aid this. May have been covered above already. Hope this helps.

Interesting, I wonder how vent in the insulation works. - I just made sure there was a gap between the top of the insulation and the bottom of the loft board.

gutovicky

Yup, thank you everyone for the excellent feedback (& MisterNick for the thread itself).

I'm particularly grateful to grumbler & Norman_Castle for the clear and comprehensive explanations.

Yes, I'm plugging those gaps into my loft - around pipes & light fittings.
Yes, I'm planning to lay more (thicker) loft insulation.
Yes, I'm going to stop worrying so much about the water pipes in my loft - which are (after some recent patching-up) reasonably well-lagged.

Cheers all.
Wishing you a Happy New Year, Vicky

_Sam_

Condensation has disappeared from our loft too once the wind has picked up, at some point there was a musty smell due to all the wetness and it is now gone too - it seems indeed the unusual weather that contributed to all of this.

littleboo

Just to add my experience, I mentioned back on the 13th Dec that I would take a look in the loft, and a day or two later I did and had condensation on the felt of the north facing side. That was with lap vents installed on both sides, one between each pair of rafters but alternating between the two sides, so they are staggered,if that make sense.
However, now, with the warmer temps and more airflow externally, its very dry and there is a very noticeable breeze as soon as I poke my head through the hatch. So I believe the lap vents work providing there is sufficient air movement outside but on their own aren't enough for very cold, still weather. But then would anything else fare better?

badatDIY

Update on this from me - installing felt lap vents and sealing the perimeter of the (very leaky!!) loft hatch seems to have done the trick - dry as a bone up there now (including the rafters having dried out).

Proof in the pudding will be whether the condensation comes back if we have a prolonged cold snap again, but for now seems to have worked.

Can't remember if I said, but I also moved the felt lap vents a couple of times - first time I installed them the felt overlaps were way to big to actually create any more ventilation so when putting them in make sure they are actually helping.

Mistral001

It looks like the present eaves ventilation is insufficinent.  I put five small (38mm dia.) eaves vents front and back in my house and it transformed the air quality in my roof space overnight.  The air was no-longer musty but as fresh being outside.