I've been spending some time insulating the loft of late, and it gets rather hot and muggy in there. I discovered why: there is no ventilation. No air bricks, no soffit vents, no tile vents, nothing. There are a few gaps where the roof isn't perfectly airtight, and the can be pressure buildup from one side of the roof to the other when it's windy, but it seems like there's no free flow of air. There's a few holes for old pipes etc in the ceiling that aren't filled meaning some air is likely escaping into the loft (mostly plugged with wool, should probably do a better job), which are likely about the same size as the gaps in the roof. There are actually two lofts (east and west sides) with habitable space in between, so there's no path for cross ventilation (I could install a drain pipe under the floor, but it wouldn't be very much).
There are no dampness problems in evidence, but I wonder if I should be putting in extra ventilation as well as insulation? Would soffit vents be sufficient, given the lack of cross draught?
Or can I get away without it? Some of the existing insulation isn't very good in a way that's hard to fix (access is really awkward), so there is some merit to keeping the heat in, but there are no vapour barriers beyond the regular plasterboard.
Will soffit vents help, or hinder? Or something else?
Thanks Theo