kaye Posted January 23, 2021 Posted January 23, 2021 HI all, Wondering if your collective brains have any knowledge on condensation in a cold roof in a passive timber frame house. We have tons of insulation in the loft floor, slate roof, when we opened the loft hatches to do the second fix electrics up there this week there was a deal of condensation. Is this normal in a new build timber frame and should i be doing something to prevent it? We have only just got the electric on and plastering has only just finished but with it being airtight i am assuming moisture should not have escaped from the house into there from that. The loft space is boarded out and we were intending using it for storage (the proverbial xmas tree and assorted other junk that its difficult to part with). Appreciate any help or advice any of you have on this.
ProDave Posted January 23, 2021 Posted January 23, 2021 How have you sealed between the warm house and the cold roof? how have you sealed the loft hatch? I am a huge fan, you could say a convert, to the concept of a warm roof where this problem goes away completely.
A_L Posted January 23, 2021 Posted January 23, 2021 6 minutes ago, kaye said: but with it being airtight i am assuming moisture should not have escaped from the house into there from that No, airtight does not necessarily mean vapour tight. It depends on the exact nature of the airtight layer (and possibly other layers). The loft hatch would also definitely be a suspect.
kaye Posted January 23, 2021 Author Posted January 23, 2021 1 minute ago, ProDave said: How have you sealed between the warm house and the cold roof? how have you sealed the loft hatch? I am a huge fan, you could say a convert, to the concept of a warm roof where this problem goes away completely. its all totally airtight, taped to within an inch of its life by the timber frame company, (the airtest was very good 0.5). It has warm cell insulation (installed by MBC) The loft hatches are airtight and insulated, albeit not the prohibitively expensive ones - dolle clickfix with a u value of 0.49.
kaye Posted January 23, 2021 Author Posted January 23, 2021 4 minutes ago, A_L said: No, airtight does not necessarily mean vapour tight. It depends on the exact nature of the airtight layer (and possibly other layers). The loft hatch would also definitely be a suspect. ah ok, this is a learning curve for me. I will ask the timber frame company on monday what they suggest on this.
Dan F Posted January 23, 2021 Posted January 23, 2021 If it's MBC, they used this membrane on our build, just a couple of months ago: https://www.partel.co.uk/product/25/1/izoperm-plus-pha-vapour-control-membrane Is the roof-space vented?
kaye Posted January 23, 2021 Author Posted January 23, 2021 45 minutes ago, Dan F said: If it's MBC, they used this membrane on our build, just a couple of months ago: https://www.partel.co.uk/product/25/1/izoperm-plus-pha-vapour-control-membrane Is the roof-space vented? Thanks Dan - they used this in our build too. Not sure if the actual roof is vented tbh, i dont think so, its not something i was aware of as required. .
TonyT Posted January 23, 2021 Posted January 23, 2021 You have introduced a lot of water while building/plastering , it may just need a dehumidifier running for a while to remove this extra moisture, then the normal ventilation will cope....
Dan F Posted January 23, 2021 Posted January 23, 2021 1 hour ago, kaye said: Thanks Dan - they used this in our build too. Not sure if the actual roof is vented tbh, i dont think so, its not something i was aware of as required. . Are they natural or man-made slate? Do you remember what membrane was used below batterns on pitched roof? Was it this one? https://www.partel.co.uk/product/23/1/exoperm-mono-150-breathable-monolithic-membrane
Mr Punter Posted January 23, 2021 Posted January 23, 2021 3 hours ago, ProDave said: How have you sealed between the warm house and the cold roof? how have you sealed the loft hatch? I am a huge fan, you could say a convert, to the concept of a warm roof where this problem goes away completely. Mostly, pitched roofs are either cold roof + cold loft with insulation at ceiling level or cold roof warm loft, where the insulation is between and under rafters. To be a proper warm roof, all insulation would be above the rafters. @kaye has cold roof + cold loft and needs ventilation at eaves, plus a bit at the ridge.
kaye Posted January 23, 2021 Author Posted January 23, 2021 (edited) 2 hours ago, TonyT said: You have introduced a lot of water while building/plastering , it may just need a dehumidifier running for a while to remove this extra moisture, then the normal ventilation will cope.... thanks tony, we kept the loft hatches closed to help keep it snug to dry the plaster, this is a good idea Edited January 23, 2021 by kaye
kaye Posted January 23, 2021 Author Posted January 23, 2021 1 hour ago, Dan F said: Are they natural or man-made slate? Do you remember what membrane was used below batterns on pitched roof? Was it this one? https://www.partel.co.uk/product/23/1/exoperm-mono-150-breathable-monolithic-membrane natural slate. and yes it was this membrane.
Dan F Posted January 23, 2021 Posted January 23, 2021 45 minutes ago, kaye said: natural slate. and yes it was this membrane. You should be good then (without any air vents) as that membrane is vapour permeable and natural slates alllow ventilation of batton zone, even if you dont have a dry ridge systen with ventilation. As long as you haven't put anything vapor impermeable on top of expoperm (?). Agree with @TonyT, its likely temporary.
ADLIan Posted January 23, 2021 Posted January 23, 2021 (edited) Slates are quite well sealed and I believe even with a breather type membrane the roof void should be ventilated unless the membrane is certified (BBA or similar) to allow use unvented. construction moisture drying could be part of the problem. Edited January 23, 2021 by ADLIan 1
SimonD Posted January 23, 2021 Posted January 23, 2021 Mirroring what others have said, this is most likely entirely normal. It could just be down to a recent rapid drop in ambient temperature together will moist air within a new building. Keep an eye on it but you'll no doubt see it disappear soon. 1
kaye Posted January 23, 2021 Author Posted January 23, 2021 1 hour ago, Dan F said: You should be good then (without any air vents) as that membrane is vapour permeable and natural slates alllow ventilation of batton zone, even if you dont have a dry ridge systen with ventilation. As long as you haven't put anything vapor impermeable on top of expoperm (?). Agree with @TonyT, its likely temporary. Thanks Dan - i do hope so. There is nothing above the membrane except the warmcell insulation (about 350mm minimum as i remember). The loft is partially boarded though, not sure if that would make any difference. lets hope it magically disappears!
kaye Posted January 23, 2021 Author Posted January 23, 2021 40 minutes ago, SimonD said: Mirroring what others have said, this is most likely entirely normal. It could just be down to a recent rapid drop in ambient temperature together will moist air within a new building. Keep an eye on it but you'll no doubt see it disappear soon. Thanks Simon, will keep a close eye.
Dan F Posted January 23, 2021 Posted January 23, 2021 25 minutes ago, kaye said: Thanks Dan - i do hope so. There is nothing above the membrane except the warmcell insulation (about 350mm minimum as i remember). The loft is partially boarded though, not sure if that would make any difference. lets hope it magically disappears! I meant between exoperm and battens/slates. I can't see how partial boarding woule have an impact.
goatcarrot Posted March 11, 2021 Posted March 11, 2021 Did it dry out yet ie was it moisture from the plastering?
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