Hi there, I've been on this forum before but on a different section about the above problem the history is its always had condenation dripping from the slate nails all house around here that are slated this but over time I insulated it and the timbers on the north pitch bacame damp. I had vents installed at the low level on the North pitch with no improvement then i had three larger vents fitted at a low level on the south pitch and 3 more fitted at a high level on the North pitch.
I was up there in mid November and it only had drips from the nails and I went up the other night and not only was the North pitch damp but the South pitch was damp from the apex to midway down, ok in the last four weeks we have had 2 weeks with the roof covered in snow and blocking the vents with a brief thaw and then another week of snow and on going again blocking the vents, it probably doesn't help that the sun is blocked from hitting the south pitch fro about 2 months of the year. My house is an end terrace of four and is probably the best insulated. and any moisture can travel freely from loft to loft as the dividing walls are not right up to the under side of the roof but when I improved the vents I thought this would have countered this. So I'm not sure what to think now but when the snow goes I'll open the loft hatch.

you can see the slate nails? have you got sarking felt or similar? or bare slates & back pointed to the lats?

Hi Chris, its sarking with felt between the slates and boarding, the nails on the south pitch were all white with frost, I feel like hauling out some of the insulation, Im hoping its because the vents are blocked, no thaw here until Sunday.

Thanks for the reply

Yeh...i haven't a clue either what to do next, hope the thaw is quick to get the vents clear and the hatch open.

I may have to consider soffit vents however they are made of asbestos cement! I remember the days when I was on roofs cutting

big six with a angle grinder! and cutting asbestolux inside, (once only) no protective measures and the building full of dust.

A shortened life span I guess!

So the nails which protrude through the sarking get cold, the moisture condenses and then freezes on the nails. It sounds as though there is excessive moisture in your loft space, which could easily be because of your neighbours, if there is no separation between your loft and theirs.

I've just had a new slate roof done with plastic vents all the way round the top of the fascia, but I don't know if you can fit this retrospectively.

Hi there, thanks for the input, I've been floored by flu for the last week but as i speak I have left the loft hatch open to allow some heat to help it dry, some wouls say drastic but there's no heat to move the damp and the sun won't hit the foof fully for another month. I have a brick dividing wall between me and my neighbour bit it doesn't finnish right to the top, the gap varies, I could use expanding foam for some of it but will need some bricks and mortar, would any one reccomend a foam to use, it will seal a gap between brick and sarking, I'm also looking at fitting soffit vents and maybe a couple of air bricks at the gable end to help the loft ventilate when covered in snow. Another suspect is I had the guy fromm around the corner fit a new bathroom and he fitted an extractor and vented it to the soffit and I've yet to check that it actually connected, didn't bother him drilling the asbestos! well, he is 80 and won't stop working!

Any help appreciated.