Serious condensation in loft and I tried everything

[Jda10]

So I got a new roof in November 2021, and there was condensation but I thought it’s winter the roof has just been off and so it will take a while to properly dry out. Fast forward winter 2022 with awful snow for a week and my upstairs ceilings were wet. I investigated condensation dripping everywhere insulation soaking. Roofer came out and added 3 tile vents to the front where it was the worst.. need more ventilation he said. 2023 winter brings the same problem but not as bad (not as bad a winter) roofer comes back puts in another 2 vents in the front , higher this time and same in the back. Summer 2024 I rip out all the manky lift insulation and have folks install 300mm of new stuff. Winter 2024 and the frost arrives and you guessed it!! OSB soaking, where you can see the breathable membrane it’s dripping condensation and where you can see the underside of the vent tiles they are dripping too. Added ventilation, replaced insulation and now I’m stumped. Rafter insulation next? New roof (again)?

 

[JohnD]

CONDENSATION IN LOFT (ANSWERS)

This seems to be the time of year for condensation in lofts, so instead of replying to lots of queries I though I would write this "one-size-fits-all" post. Please also see //www.diynot.com/wiki/Building%3ACondensation-in-Houses Condensation in lofts occurs when the amount of water...

www.diynot.com

 

[Jda10]

Thanks John. I have seen that advice before. Holes have been sealed, no tanks up there but there are pipes which have been lagged, and holes sealed, no downlighters. Blockage of soffits cleared when old insulation removed and new put in. No drying washing upstairs and definitely not over radiators (downstairs in dryer or in front of dehumidifier), extractor on and window open when using bathroom. Vent in velux window in loft permanently open, 7 tile vents, ridge vents at point of construction, 7x sheets of flooring running down middle raised with insulation underneath and air gap. Humidity sensor in upstairs rooms is 40% with temp of 19, loft temp 6 with humidity of 90%, outside temp 1. No water ingress when it rains etc. like I said I’m stumped. After adding all the ventilation and cutting holes in OSB, roofer now says try heating the loft space.

 

[aveatry]

Is there a disconnected or otherwise extractor hose with a hole in it pumping moisture from the bathroom into the lost instead of outside.

 

[JohnD]

There is water vapour in the loft.

Heat does not remove water.

I do not know where yours is coming from, but you have to ventilate it out faster than it arrives. A loft should be cold and windy, like outdoors. Opening the eaves on both sides usually gives ample ventilation.

Your water must be coming through the ceiling, or a wet wall or chimney, or a leak in roof or plumbing.

You mention OSB so I guess you are in Scotland with sarking. This can make a very good roof and damp patches should be visible.

 

[Jda10]

Yes, I’m in Scotland - Glasgow. Extractor goes straight out the wall so no vent pipes in loft. Most of the wet is at the front (North facing) and OSB and bottom of sarking visibly wet but not as bad as previous years. It does eventually drip onto the boxes I have up there though and the flooring as you can see the stains or puddle from near the window. In 2022 I had an inch of visible wet on the rafters and both the rafters and the OSB needed brushed and bleached to get rid of the white mould that formed. Not the chimney breast itself but the party wall beside it has started salting too. I guess I need another rip out and proper investigation in the summer. Also thinking of replacing upstairs ceilings adding new vapour with new plasterboard. That would also give everything a reseal again. Next door has a loft conversion, if that was poorly done would that generate heat and moisture through the party wall? It’s a 1950s house so all cavity walls (not filled) and has 50mm kingspan external cladding the council put on. In the old roof the felt under the tile was disintegrating, tiles porous and I was getting moss from the tiles coming in which is why I replaced it.