Need some advice about my house roof and insualtion. Any experts lurking?

We suffer with bad condensation on our windows and plasterwork around them. I have just been in the loft and found that the roof is covered in condensation. It appears the roof consists of a plastic sheet with the roof tiles / slates behind this. The plastic is wet and has water dripping from it. Pics attached.

I was planning on insulating the gaps between joist with fibreglass but worried it will just get damp. Will the fibreglass keep heat in and prevent the condensation or does anyone any other advice or tips? Will roof vents help?

Thanks

Its already damp so I doubt extra insulation will make much difference.

Ventilation should sort it. The alternative is a ‘breather’ lining but to install means removing all your slates.

I’m no roofer / builder but had exactly the same problem after insulating our attic room.

have you blocked the vents?

Can you feel a draft coming from from your sofits? You need ventilation. Maybe the are blocked in someway.

I had a similar problem at the beginning of this year when snow was on the ground. The roof was actually dripping and I had to cover everything with plastic.

The first roofing company only put one vent in and it was still damp. The second company I called out put more in, ie both in the front and back, and that seems to have solved the problem.

I would strongly advise using a roofing company that has been recommended or, failing that, use Checkatrade.

Sound like you just need to make sure you still have air flow, maybe pull the insulation back a little from where it meets the roof timbers. A vented ridge or roof tile will help with the air flow and not cost the earth.

Don’t insulate the space between the roof spars it will make it worse
You need more insulation on the ceiling and lots of ventilation into your loft space, soffit vents, tile and ridge vents
Or a reroof and have breathable felt put in

Plastic vapour barriers are supposed to be below the insulation so that moisture from the house can’t get to a cold part of the roof where it can condense. There should be a breathable membrane under the slates/tiles but not plastic! I’m not fully up to speed on the latest thinking on this though…
Each room should have an air vent (in window or wall) of at least 40cm/sq and be open at all times.

You got any more pics, specificaly from head height looking down the roof pitch??

have a look outside and see where the vents are, then go up in your roof and see if they’re blocked.

Thanks for the help so far. We have two air bricks (one at each end of the house) and thats it. No other vents. I will check the insulation at where the roof meets the soffits and see whats what in daylight. I’m thinking roof vents are a must then?