Green Building Forum - Sweating roof uncovered Tue, 19 Dec 2023 08:37:15 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300545#Comment_300545 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300545#Comment_300545 Wed, 01 Mar 2023 18:36:53 +0000 marsaday
Anyway i have taken out all the plasterboard ceiling and removed the 50mm PIR insulation between the rafters. The rafter depth is 85-90mm, so there was a decent breathing gap behind, but I think they may have pushed come insulation a bit too far into the slate area. There is no felt/membrane under the slates.

I have damp rafters in most of the roof, some bits worse than others. Even some of the roof lats are damp in places.

There was no vapour barrier and the insulation was not foil taped.

My plan is to extend the rafter with a 50x25mm roof baton (done today) and then fit 75mm between the rafters and underboard with 50mm. Then i will foil tape the 50mm sheets up.

There is a section of the flat where I cannot baton out so much, but rather can only add 10mm. In these areas i will have to use 70mm insulation between and underboard by 50mm. This mean in these two areas (bathroom and kitchen) the breathing gap will be 25-30mm. The rest of the flat will have 40-45mm.

Will i have the same issue as before ? Should i be looking at introducing some breathing slates in the roof to get more air flow in there ?

This photo shows the water staining on the rafter.]]>
Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300546#Comment_300546 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300546#Comment_300546 Wed, 01 Mar 2023 18:37:49 +0000 marsaday Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300548#Comment_300548 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300548#Comment_300548 Wed, 01 Mar 2023 22:09:38 +0000 chrisinbrighton Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300549#Comment_300549 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300549#Comment_300549 Wed, 01 Mar 2023 23:20:46 +0000 marsaday Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300562#Comment_300562 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300562#Comment_300562 Thu, 02 Mar 2023 15:13:56 +0000 revor
I have insulated between rafters with 170 mm rock wool (have 225mm trusses )then 100mm PIR boarded over and taped. It is difficult to get good sealing between rafter and insulation so if you can overboard with rigid insulation with rockwool in between you will be able to get a well sealed ceiling. Duplex plasterboard to finish off.
I am surprised that you have condensation as slates have lots off gaps between them allowing ventilation but having a kitchen and bathroom up there will add considerably to the humidity level I guess. Have you enough headroom to overboard? Don't know the feasibility of adding roofing felt between the rafters, could be fixed to the battens and down the edges of the rafters. Needs someone more knowledgeable than me on that one.]]>
Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300563#Comment_300563 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300563#Comment_300563 Thu, 02 Mar 2023 15:28:16 +0000 marsaday
Got BC coming to give me some advise on the issue as it was not noticeable with the insulation in place the other week.

Will def be underboarding so creating a better vapour layer.

Just thought the clued up people on here might give me some pointers]]>
Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300569#Comment_300569 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300569#Comment_300569 Fri, 03 Mar 2023 07:39:16 +0000 tony Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300570#Comment_300570 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300570#Comment_300570 Fri, 03 Mar 2023 08:00:39 +0000 borpin
A good tight vapour barrier will help. What about any warm air coming up from below in the eaves? There was a suggestion in a previous thread about using a spray foam insulation to seal and insulate a ceiling in a roof space.

I'd also think that some ventilated slates wouldn't make things worse.]]>
Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300573#Comment_300573 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300573#Comment_300573 Fri, 03 Mar 2023 09:18:14 +0000 tony
You can’t stop loft condensation by managing the humidity in the house]]>
Sweating roof uncovered http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300589#Comment_300589 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17763&Focus=300589#Comment_300589 Fri, 03 Mar 2023 21:55:48 +0000 marsaday

The flat roof is now a warm one. I have put 100mm insulation above the osb deck and redone the roof in fibreglass. So i cant now make it a breathing roof.

Messing with the ridges will be hard. I think breathing slate vents will be a lot easier to fit.]]>