Condensation in loft space - Page 1
Forum section: electronics / general

author: akis
author_rank: Frequent Contributor
timestamp: November 27, 2023, 07:27:38 am
content: I have a serious issue on my new built house where there is a lot of condensation in the loft. This happens in the (warm) mornings after very cold nights (down to 0C or thereabouts).The loft is habitable and the insulation is in between and under the rafters.The house is not finished yet, is not heated, and no one lives in it.This condensation is created on the underside of the membrane under the roof tiles. The membrane is at outside temperature and in the mornings warm and humid air condenses as it contacts it. This happens on both sides of the membrane, but it is the inside surface we care about. The underside of the membrane gets soaked, and it starts to run down the rafters until it finds a point where it drips onto the floor (and that is how I see it).This is morning dew but it happens inside the house.To combat this you are supposed to ventilate the underside of the membrane with eaves vents and ridge vents and a gap between the membrane and the insulation. As the house is under construction, there were areas of no insulation at all in between the rafters, and that was the maximum ventilation one could hope for. Yet, it condensed. I also saw a little condensation on the inside of brand new roof windows.I am not sure how to proceed. If anyone has experience with rooms in the loft and condensation please help!

author: IanB
author_rank: Super Contributor
timestamp: November 27, 2023, 09:45:54 am
content: What do you mean by "the loft is habitable"? Is it actually fitted out as an extra room in the house, of is it just partially finished as a storage space?If it is an actual room for living in, like a bedroom, then it should presumably be very thoroughly insulated with no outside vents or membrane visible on the inside? So I'm a bit puzzled by your description. It seems like you should probably talk to the builder about it, as they should be most qualified to discuss the issue?I do recall when I moved into a new home in the UK, the builder gave all owners a leaflet about condensation, saying that it was a common concern in new houses. I think the issue is partly that there is a lot of residual moisture left inside a home after it is built, which takes time to disperse, and that houses are thoroughly insulated and sealed to prevent drafts and heat loss, and this can trap moisture inside. I think the advice was to open windows for ventilation, and to wait for the house to dry out and reduce the problem.

author: tggzzz
author_rank: Super Contributor
timestamp: November 27, 2023, 10:13:11 am
content: A couple of observations, with no definite conclusion. I am not a civil engineer, but I did replace my roofWhere do you think the water is coming from?, e.g. is some part of the construction still "drying out"?Are other properties suffering the same issues?The membrane between the rafters and the tiles should be breathable, i.e. porous to moisture but not to rain. Examples: Tyvek, Daltex.Your statement "...there were areas of no insulation at all in between the rafters, and that was the maximum ventilation..." is too loose to be correct.There is a difference between a "warm roof/loft" and a "cold roof/loft". Different designs have the temperature gradient in different places (i.e. thermal insulation is in different places), and humidity barriers are placed so as to ensure that the dew point occurs in a safe place. You need to understand where the humidity and thermal barriers should be.Do not assume that the building has been built correctly and to design. There are many many examples of on-site people cutting corners and/or just doing what they've done before. The former allowed an entire cul-de-sac in Sadly Broke to be built with only 25% of the specified cement in the mortar => mortar could be abraded by fingers, and (IIRC) Lovell had to buy all the properties back. The latter was the source of the "high alumina cement" building failures. You may have heard the phrase "Jerry built", referring to poor design/construction. That originated in the 20s/30s and referred to the various problems found in homes rapidly constructed after WW1.I suggest that your first step should be to complain the builders and the NHBC - with other people if they are affected too. If there is a problem, do not expect the builders to respond easily. If that fails, then you will need to find a structural engineer/surveyor and solicitor that are prepared to take on the case. That may not be easy, since the building industry is a small community (think Masonic Halls).If you can back out of a purchase, you might like to consider that. I wouldnotrely on a builder's statement that "it will be alright when finished", unless they statewhythat will become the caseandyou believe the cause and effect.

author: Gyro
author_rank: Super Contributor
timestamp: November 27, 2023, 10:27:21 am
content: I suggest checking out the Skill Builder channel on YouTube...https://www.youtube.com/user/skillbuilderchannel/videosI agree with tggzzz on the 'official' route to follow, but it would be helpful to have a bit more background on construction practices.

author: tggzzz
author_rank: Super Contributor
timestamp: November 27, 2023, 11:32:43 am
content: Quote from: Gyro on November 27, 2023, 10:27:21 amYes, you need to know how to demolish bullshit explanations and fob-offs."The David and Charles Manual of Roofing" isn't a bad starting point, but manufacturer's application notes will be more up to date."Defects in Buildings" by HMSO/PSA is more general, and will make you wonder why there are any buildings left standing

author: tszaboo
author_rank: Super Contributor
timestamp: November 27, 2023, 12:19:14 pm
content: Condensation in a new built isn't unusual. Everything needs to dry out, paint, mortar and so on. It also depends a lot on which season they were doing the work, and how much rain the unfinished house got. I wouldn't worry about it for now.You should get a dehumidifier, and run it 24/7 while you move in. There are a few that can drain the water, or you can maybe convert a regular one to it.If there are issues a year and a half in, after a summer (however miserable an English summer is), then it's time to look for construction issues.

author: tom66
author_rank: Super Contributor
timestamp: November 27, 2023, 12:43:26 pm
content: Just be aware that with this kind of thing the NHBC insurance will be critical but IIRC, the first two years it's 100% the builders responsibility and afterwards NHBC takes over but there is a quite a high minimum claims value (~£1.7k) which would cover major structural design errors but may not cover having a professional locate the issue and fix it. This situation is one major reason I did not buy a new build home (not that old homes are trouble free - it just tends that their problems are more due to wear and tear rather than design flaws which have been fixed over time.)

author: Dan123456
author_rank: Regular Contributor
timestamp: November 27, 2023, 12:51:19 pm
content: If it’s reasonably complete and sealed off from the outside world, you could grab a few of those damp rid things (basically just a bunch of calcium chloride in a bucket) and place them up thereThey absorb the moisture from the air and you often see them in storage area’s etc. just to keep the air nice and dry so things don’t go mouldy

author: akis
author_rank: Frequent Contributor
timestamp: November 27, 2023, 05:17:43 pm
content: Thanks for all replies.The house is still being built. It has no heating and has never been heated, however we did have a hot summer.The loft contains liveable rooms and bathrooms.The roof is standard rafters with insulation in between and under. There is (supposed to be) a gap between insulation and membrane to allow ventilation and reduction of condensation.The membrane is Tyvek Supro. It is the most expensive and apparently allows warm air to escape outwards and no water in, even without gap between it and insulation. In some houses they do spray foam insulation between rafters, which closes down every possible air gap.The condensation forms inside the loft, on very cold objects, past the dew point, even a cold glass of beer or the underside of the membrane. We can deal with the glass of beer on the table but we cannot deal with the membrane being soaking wet. It started to happen the very same night after we fitted windows upstairs, no air circulation, I went in next day and the whole floor was wet.The condensation happens in winter, and it must be close to 0C during the night. The membrane is at 0C, warm air touches it and condenses. Even if it is a "breathable" Tyvek Supro.As the house is still being built (very, very slowly), there were places in the loft with no ceiling boards and no insulation in between the rafters. You could look up and see the underside of the membrane and it was all soaked. As was everything else "cold" inside, like steel beams, glass of beer on the table etc.If the extra extra humidity comes from the house itself, then after it dries, the problem will go away.But if the humidity is simply in the air, then we have a problem, during the very cold nights followed by a warmer day. It is like morning dew, but inside the house.I will be having heating put in soon, and hopefully it will help dry things out. I will also get a couple of dehumidifiers, but am not sure if the humidity comes from the house or from the environment.

author: IanB
author_rank: Super Contributor
timestamp: November 27, 2023, 05:35:05 pm
content: I think what you are describing is physics.Warm air can hold more moisture than cold air. So during the day, the house fills with warmer, more humid air. At night, the outside cools down much faster than the inside, and so inside air forms condensation on cold surfaces.I think when the house is finished and heated, the problem will perhaps not be apparent. The inside surfaces will be much warmer, and the inside air will be dryer, and any moisture inside will have to diffuse through walls/ceilings before it can reach cold surfaces.

author: tggzzz
author_rank: Super Contributor
timestamp: November 27, 2023, 06:52:35 pm
content: If it only condenses where there is no insulationat the moment, that isn't a problem per se.When insulation is installed, there will be a thermal gradient across the insulation. If the air is humid, and the dew point is inside the insulation, then any water from the house will condenseinsidethe insulation. Oops.To prevent that, there must be a vapour barrier on the hot side of the insulation. Amateurs often put it one the cold side, which is disatrous.

author: IanB
author_rank: Super Contributor
timestamp: November 27, 2023, 07:10:13 pm
content: Quote from: tggzzz on November 27, 2023, 06:52:35 pmYes. I think in general, that membranes on the outside behind roof tiles or wall cladding should block liquid water, but be permeable to vapour so it can get out. Membranes on the inside behind interior walls should be impermeable to prevent the problem mentioned above.

author: Neutrion
author_rank: Frequent Contributor
timestamp: November 27, 2023, 07:22:30 pm
content: Quote from: tggzzz on November 27, 2023, 06:52:35 pmOr if someone builds a new house at minimum a ventilation with heat recovery should be installed especially if you renew the heating anyway. It also spares a lot of energy.If it is a small house one entry and one extracion point is enough if at the opposite end of the house.And of course if you are installing a condensing boiler for heating make sure the minimum heating capacity where it can modulate down is as small as possible. Ariston have some with 1-2 kW minimum capacity which is quiet rare.But of course a water-air heat pump is a better thing especially in England with the "cold" 0 degrees in winter.

author: tggzzz
author_rank: Super Contributor
timestamp: November 27, 2023, 07:30:27 pm
content: Quote from: IanB on November 27, 2023, 07:10:13 pmYes, exactly that.

author: Bud
author_rank: Super Contributor
timestamp: November 27, 2023, 08:05:57 pm
content: Google for Rafter Vents. They are channels that create air gap between the roof underside and insulation, providing unrestricted air flow from eaves vents to ridge vents. Once you install rafter vents between rafters, you can put all insulation you want under them.

author: pickle9000
author_rank: Super Contributor
timestamp: November 27, 2023, 08:24:47 pm
content: Sounds like no vapour barrier. That is a plastic sheet between the studs and drywall.

author: akis
author_rank: Frequent Contributor
timestamp: November 27, 2023, 08:41:50 pm
content: Quote from: Bud on November 27, 2023, 08:05:57 pmThat is the first resolution we tried to the problem. We fitted sections of plastic tubing over rafters, under membrane, to allow passage of air sideways from rafter to rafter wherever we saw a "blockage". A blockage is interruption to the flow of air due to roof construction, eg roof windows, dormers, porches, noggins, insulation too deep etcThe second step was to drill holes at the top ridge to allow passage of air from and to the the two main sides of the roof.The third step was to remove the main ridge tiles, cut the section of membrane over lapping the ridge, and repositioning the ridge tiles. The ridge has a dry ridge system (breathable fabric type thing).None of these measures worked. None oif these measures would be needed if Tyvek membrane did what it's supposed to do.I forgot to mention this condensation has so far only happened on the north side of the roof, never the south.Quote from: pickle9000 on November 27, 2023, 08:24:47 pmThere is no vapour barrier in the plans, and I have never seen one used so far. The typical UK cold roof is made of : roof tiles, over battens, over membrane, over rafters, insulation in between and/or under rafters, (insulated) ceiling boards screwed into the rafters.Which means condensing vapour under the membrane will run uninhibited down the rafters / into your ceilings.

author: Neutrion
author_rank: Frequent Contributor
timestamp: November 27, 2023, 10:16:54 pm
content: Forgot to mention: I meant the single "metal box" units to be installed somwhere with pipes, not the pseudo ones installed on the walls because those make almost no difference. If there is a bathroom it makes sense to have the extraction point there.Even better is to have the ventillation system built into the fume extractor in the kitchen because if you use the fume extractor you need a lot of incoming air anyway, and you don't want to cool down the house completely.

author: Bud
author_rank: Super Contributor
timestamp: November 27, 2023, 10:38:58 pm
content: Quote from: akis on November 27, 2023, 08:41:50 pmSorry what you describe is totally different. Rafter vents are installed along rafters, not across.

author: IanB
author_rank: Super Contributor
timestamp: November 28, 2023, 12:59:58 am
content: Quote from: akis on November 27, 2023, 08:41:50 pmThe vapor barrier would go between the ceiling boards and the rafters. This is what stops moisture from inside the house diffusing through the ceiling boards and insulation and reaching the outer membrane where it can condense. This is what tggzzz meant in the post quoted below:Quote from: tggzzz on November 27, 2023, 06:52:35 pm