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.

 

[JohnD]

OSB and bottom of sarking visibly wet but not as bad as previous years. It does eventually drip onto the boxes

Do you have a roof leak?

Some photos would help. Include the eaves vents

It might be coming from next door.

 

[Jda10]

Will get some photos tomorrow. Doesn’t leak when it rains just condensation when frosty or snowy. And if prolonged then it builds up and comes through the OSB. Where there isn’t OSB it drips from the breathable membrane or underside of the plastic tile vents.

 

[freddiemercurystwin]

What is the exact make up of the roof? What is the pitch? If you are sure the roof is not leaking and the the loft space is adequately sealed from the occupied rooms then it must be a lack of adequate ventilation. If you have a sarking board then it matters not that the membrane is breathable, you should treat the membrane as if it is non-breathable and you need to ventilate the loft adequately. Surely if you have a sarking board it should cover the entirety of the roof so why would there be areas without it? You've not mentioned anything about what existing ventilation the roofer had when the roofer finished?

 

[Jda10]

Exact make up maybe a bit technical for me. The gaps with no OSB I think are because he was running short. I’m told there is a gap between the breathable membrane and the osb, not sure what else between that and the tiles. I’m told the Marley ventilation track thing was put in the ridge and I can see places of daylight from inside the loft at the gutter edge. I was told that was normal and usual and that was suitable ventilation. 1yr on 3 tile vents put in on front and triangles cut in OSB directly underneath. Yr later another 2 high level added at front and at back. Again triangles cut through membrane and OSB so I can see the plastic underside from inside. There is also a gap in the OSB at the ridge - the 2 boards don’t meet, and a bit round the velux. It’s definitely drafty and cold up there. Going to be a busy summer figuring it out.