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Went up there today to do some DIY and noticed a large number of drips along one side. The insulation is about 200-225 deep with loft boards on top. I've been careful to keep the insulation away from the edges so the loft can breath and I added a vented ridge tile to suplement the original one when we insulated and boarded.
The bottom two rows of bitumen felt we're damp to the touch on one side.
Is is
1 knackered felt, leaky roof.
2 sweating due to a lack of air flow.
3 because I went up there and the hatch was open, I let warm moist air from the house up there which condensed on the frosty roof.
Please tell me it's 3, 2 at a push. Just don't tell me its 1. By the way, it was built mid 1980s, typical Barrett/wimpy affair.
number 3
I've just been up to get the decs down.. same sort of deal.. little raindrops everywhere..
Go back up mid day on a not so cold day and recheck. Check the timbers for moisture. If it was a leaky roof it'd be more isolated and making its way rheo the ceilings. Condensation isn't one to be ignored tho. Personally I dont like the idea of over insulating older roof spaces as I think it causes more problems than its worth..
Cold roof filed with warm moist air from inside the house, condensed onto the roof as it met the cold surface perhaps?
4) vampire bat piss, obviously
I get condensation on the nails that stick through the boards. It happens on cold dry days, but warm wet days its bone dry up there.
No evidence of old drips up there. Seems to have only started on the day I went up there.
Fingers crossed that it was just that.
Condensation. How do you know it's not happening on the days you don't go up there? Vent your house more, leave window trickle vents open / ajar, keep heating on. Oh, insulate the topside of loft hatch too.
Can you feel any airflow in the loft? Check the vents on the soffit boards - mine were clogged with years of muck. Brushed them clean, I could then feel air moving and condensation went away.