Getting condensation under control

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7 Dec 2019
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Hi,

We moved into our property three years ago and over the last few winters noticed some condensation. There is only about 5 boxes in the loft and it's a 3 bed semi-dethatched. I think it's the old bitumen roof felt and built around 1980's. Inside humidity is usually mid 50's usually, and no sign of condensation/damp in the house. I only noticed it this year only during the last cold snap (when I went to get decorations) where it was maybe -6c at night. It went as soon as it got above 0ish. One side of the roof has solar panels and soffit vents and no condensation. Loft hatch is just a bit of wood on a hinge (no insulation, so that is on next years list, as is a downlight in the bathroom).

Year 1 - we monitored the situation
Year 2 - Added soffit vents to the side that didn't have any (no insulation blocking it and we can see daylight)
Year 3 - I've added a 5 lap vents to see if that helps. Spread around the area that was worst for condensation (directly above the loft hatch) and one above the bathroom light. Although no condensation there if it can rise and be drawn right out that's got to be a good thing?

There is clearly airflow up there as I've just been up and it's got a steady breeze. I appreciate the difference with relative humidity but at the moment my loft is now the same temperature as outside (11c) and humidity is give or take what the forecast is showing (Forecast 91-86%, my loft 89%). I would think this would be almost the same as it's drawing air in from outside.

Three questions:
  • Do lap vents cause any issues with roofs?
  • I noticed a small line of water on some insulation today (it was drizzled today but nothing serious). It was wet/cold to touch but not soaking wet and the insulation underneath was dry. Could this just be the last bit of condensation drying out form last weekend? (It's between two rafters that have a felt lap in it, but the damp part is not directly below, maybe 5cm closer to the middle of the loft).
  • Apart from the loft hatch, down light, and bathroom fan, there are no gaps in the ceiling to loft. I'm presuming these are the best things I can replace to try and fix the issues?
 
Since its a semi, is it possible that the source is coming from the neighbour? A piece of PIR on the loft hatch will help. Its a 2 minute job to cut and glue.
 
 
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