Stop Condensation in Your Loft ~ Ventilation & Vapour Control

Roger wants to show you how to get the vapour in your house under control and looks at what is happening and how to combat this age-old problem.
Condensation in the loft and loft ventilation are some of the most popular subjects on our website.
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#KnowYourHouse #Condensation #VapourControl
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[@xsbxsbxsb]

My dad (FSVA RICS) would have agreed with every word. This sounds like one of our childhood mealtime lectures. Spot on.

[@sicknote26]

😂😂 the good old boys love it

[@robru]

Thanks Roger for the video. Perfect timing as I’m having exactly this issue at the moment!

[@23sunderland]

5 pints love it . Makes me think he knows his way round building and the pub . Being a roofer for 30 years plus he's bang on

[@SkillBuilder]

I haven't been in a pub for over 6 months. It is not the drink I miss though I do like a nice English ale.

[@23sunderland]

@@SkillBuilder lol only joking mate good stuff

[@TT_PaulLarge]

Bought a house built in the 1950s a few years ago. Huge unaddressed mold problems and very steamed up windows in the evenings. I installed some soffit vents (there were none) and a PIV unit in loft. No more problems, cheap and easy to install as well.

[@protonsid2628]

Roger you're brilliant i hope the all mighty gives you very long life and you can go on teaching us,you are one in million i love yours and Robins veidos great job well done.

[@AntonyGoodall]

Experience, intelligence and expertise. Thanks for sharing Roger. Cheers.

[@stefanghiata9567]

Roger, the loft comment... Spot on. Your experience has proven time and time again you know what you are taking about. Great thanks!

[@rob2941]

So glad I followed your recommendation and applied Storm Dry to the outside walls of our 1960's bungalow last summer, what a difference it has made and the house feels warmer.

[@tullgutten]

Water is a excellent thermal conductor. And it makes bricks much more thermal conductive when it's wet

[@simonstones1918]

What has it done for you?

[@aaronharris5275]

So the water now runs and beads off the bricks better now does it? Saturated bricks allow the cold from the outside in. Is that what you have found?

[@danfall8233]

2 and a bit hours of KZbin and finally a video that explained this to me. Cheers Roger!!!

[@somedude-lc5dy]

fantastic video. perfectly explains the problems. your roof design skills are top notch.

[@fast_eddie3441]

Just bought a 50s bungalow and putting in an ensuite bedroom upstairs under PD.. Most of the airbricks have been covered up at the ground floor which has meant the floorboards and joists were soaking wet when we pulled the carpets up 🙄. New airbricks going in all around the perimeter of the suspended floor, membranes and in line extractor fans all round too. Thanks for the advice and explanation on the channel. Very helpful!

[@LEA-hr5tf]

Thank you so much, this was the best video about vapor control by far. Thank you for sharing your knowledge and explaining it so well.

[@tonymaraia5088]

Roger is a legend. Can’t get enough of his videos

[@marileaschofield7838]

Your video has really helped me to understand why I am getting so much moisture in my loft. I didnt realise I had such a problem until I went to get my christmas decs down yesterday. I was absolutely horrified and panicked, all I could see was loads of money and the big problem of trying to search for a proper decent builder to resolve the issue, with Christmas on the horizon, difficult. But after watching your video I calmed down and began to think how I coould tackle the problem sensibly. Been up there today and have a plan!! Thank you so much for your help Roger.

[@mattmecham]

Google lap felt vents. Fixed my problem in a few days.

[@hollow34]

Get rid of moisture sinks like cardboard, use plastic boxes, lay everything flat so air can move around your loft. Make sure loft hatch is sealed up good. Vent bathroom after a shower, get a dehumidifier on the landing, get a hygrometer to keep track of humidity levels upstairs. close the kitchen door when cooking, use the fan hood to vent cooking humidity.

[@007JHS]

For the first time this year as I got our Christmas decs down from the loft I noticed a lot of damp on the underside of the roof space.

[@gary8306]

@@mattmechamThankyou, never heard of of them before.

[@writecolour]

That half hour flew by! Genuinely interesting and pretty well explained. Your effort appreciated Roger. Stay safe. Paul, Newmarket, Suffolk.

[@SkillBuilder]

Thanks, will do!

[@liamsandie]

Absolutely Roger, another great video. I've had plenty of time now to observe how Stormdry is working effectively on my weather facing exposed brickwork on our 13 year old Redrow house. Last year at this time we were facing a complete mess with water penetrating the cavity. No such problem now and water literally bounces of the outside walls. No issues with condensation either, plenty of vents and air flow and as you rightly say Stormdry allows moisture to exit the bricklayer without allowing larger rain and water in. Simple physics really. Keep the videos coming :)

[@SkillBuilder]

That is great to know thanks for telling us. I am sure it will help others

[@ellis2792]

You bought a new build from red row. Good luck 😂

[@polizovski]

Excellent information, condensed into 30 minutes. Thank you very much.

[@Jm006a00061]

Roger, just wanted to say a huge thank you for this video. Very well explained and I finally understand why I’m getting damp issues. Have liked and subscribed which is not something I do often. Keep up the good work and awesome teaching techniques. 🙏😁

[@SkillBuilder]

Glad it helped

[@jamiefors5062]

Brilliant video buddy, I had this problem and used those vents you slide between the felt laps, problem solved 👍

[@fredwestbuilding2155]

Thanks Roger, very informative. The only thing missed is the Blue Peter solution for bitumen felt by using polystyrene wedges between the sheets to enhance the airflow.

[@SoledadSolary]

Perfect. I understood everything. Great advice.

[@eddjordan2399]

Great explanation. fantastic understanding of the problem. Every things relative.

[@rachelmorgan-smyth5593]

Thank you Roger, very informative and helpful

[@jetteraismabash4186]

Thanks Rogers, really great understandable video👍

[@buck8441]

Hi Roger, Ive lived in 2 bungalows that both suffered with condensation, I total agree with your information, old 60’s bungalow had cavity wall insulation at some time and loft full of insulation, windows streamed ever day, I solved it by clearing all the insulation jammed in between the roof rafters at plate level added 6 roof tile vents and good bathroom extractors. Job done. Great skill builder videos Thanks Tony

[@SkillBuilder]

Good result Tony.

[@rsmith02]

You can combine a vented loft with insulation at the floor level, just air seal the heck out of it first. Air movement is the biggest issue vs diffusion through solids.

[@foxyblonde73]

Thank you. I've just started noticing white spots on my loft interior roof ply. I thought I had a problem with my roof. This totally makes sense as I have downlighters in every room. Also the white dotting/clouding is mostly above shower room

[@lksf9820]

It's a very good presentation at conveying how difficult things are becoming and that what we see as modern designs are often no longer any good in some situations. You mention Canada as a place of extremes, but they are here in the UK too and becoming more common due to climate change. I live in a UK house which does get these weather extremes. It's old so has no felt or membrane under its stone slate roof and it's very draughty, yet condensation forms under it. One of the main reasons is we can have a lot of wind and rain for a long period of time. Recently it soaked the house, it even drove the rain through the Stormdry it was that bad. This was then followed by very still and cold weather so it couldn't dry out, it just sweated with condensation and continues to do so.

[@johnandcathyhill976]

POLYTHENE VAPOUR BARRIER DISINTEGRATING! Just discovered Skill Builder and most impressed, all seems very useful and sensible advice. I have one problem which I'd be interested if anyone else has experienced and what may have caused it. I had condensation in the roof of my 1980's-built house, on the underside of the bitumen roofing felt and roof timbers. So I installed soffit vents and also put clear sheet polythene under the fibreglass loft insulation, on top of the plasterboard of the bedroom ceilings, as described in the video. This has reduced the problem but some years later all the polythene sheet has become brittle and when exposed and touched just breaks into pieces - so it's usefulness as a vapour barrier is much reduced. I think the polythene was just standard clear polythene sheet bought from a builders merchant, not specifically sold as a vapour barrier. Does anyone know why this has happened? Is it some reaction between the polythene and the glassfibre? It's most frustrating having put all that polythene sheet in and it's now pretty useless. Any ideas, or similar experiences, would be appreciated.

[@pcranebmw]

I Always install a HRV (Heat Recovery Ventilator) Excellent video.

[@petemiddy4785]

Really good video and explanation of vapour barriers and breathable barriers,it's still complicated to me ,I was in propery maintenance and refurbishment for over 40 years and still find it hard to get my head around, as vapour goes where it wants and stopping it or redirecting it in older properties to cause the least amount of condensation is difficult.thanks

[@BRI535D]

I use a low energy dehumidifier to keep relative humidity at around 55%.I am amazed at the amount of water it pulls out of the atmosphere.Stops condensation on windows and eliminates potential mould and other nasties for wellbeing.I am very satisfied with the results.

[@abbyanderson4171]

Check your electricity bill...

[@craigchamberlain]

Yeah, we’ve got a dehumidifier which can pull 20L of water a day from the air but it costs (in Aug 2022) about £600 a year to run which is not great. What we’re doing now is only using it when drying clothes indoors where it becomes effectively a heat pump tumble drier without the “tumble”. We’ve actually got a heat pump tumble drier as well and I need to do an exercise to see which is actually more efficient! What worries me more is that, in our loft, the slate nails penetrate the sarking boards and droplets of water condense on the nail points in winter and drip onto the loft floor. I don’t see any signs of an effective vapour barrier between the heated part of the house and the loft so I think we need to improve that as best we can but also improve the ventilation of the loft which seems minimal at best. Why don’t surveyors find basic stuff like this when surveying houses for potential buyers? 🤷‍♂ Going back to the dehumidifier, if you are going to use one then don’t use it while simultaneously ventilating the house with open windows. If you do this then all you’re doing is dehumidifying the planet! which is an expensive exercise in futility. My suggestion is to dehumidify overnight when electricity is potentially cheaper and the windows are closed. And do it in areas of the house which can benefit most. But as Roger said, try to ventilate cooking steam or shower steam at source via ducted ventilation. We’ve been guilty of turning those off because the humming noise is annoying but I can see now that they are important. Thanks again Roger. 👍

[@rsmith02]

@@craigchamberlain Heat pump should be more efficient. Is there no option to dry outside or semi-outside or in a room with windows open and doors closed so the vapor goes outside vs around your home?

[@PaulSilvers-in4mc]

4:09 ​@@rsmith02I'm

[@dimchohvarchilkov683]

Thank you for the brilliant video/lecture! It answered all questions which have been running through my head for the last few years. I'm interested in the case which there is a solid brick wall with a 100mm external insulation, rendered with ciment+sand+lime? Many thanks!

[@wardy2002]

Another excellent stream. Just one question. Can you use Storm Dry on pebble dash. Or does it have to be on brickwork? And thanks again for an excellent channel.

[@TC-uq1rc]

Thank you for a very informative video. Should help with my flat roof ventilation problems.

[@changingmatrix8687]

I've been looking for two months for this EXACT video! Thank you! Thank you! God bless

[@barrydoherty636]

Another great video, well done.

[@pioneerservices510]

Well explained. Thanks Roger

[@iulixxx]

Great video....absolute great.Thank you!!!

[@joejoey316]

Great bit of info thanks!!

[@alanbarlow8232]

Great video and love your no nonsense approach! Putting an extractor in a roof will remove the air and stop moisture building up, but it also defeats the point of the insulation since cold air will constantly be drawn in lower down the building from outside to replace the lost air. I put open cell foam into my roof and vents behind that, which stops the massive airflow of an extractor but still allows the roof to breathe and get rid of the moisture. It also costs nothing to run. For me at least, it solved the problem since it's like goretex but insulated.

[@SkillBuilder]

The fan in the loft blows air into the house to put it under positive pressure thereby forcing the airborne moisture out through the windows and doors provided they have trickle vents

[@charlieshore231]

@@SkillBuilder always a pleasure to watch you informative videos Roger. We have a condensation issue in the winter, would you recommend the PIV extractors in the loft to help with the situation as the bungalow has no membrane in the roof, it has fully boarded feather board which the tiles hang off. No leaks but does smell musty in the loft so presuming the extractor will help keeping a constant airflow around the house? Many thanks

[@onlymise2758]

Thanks Pal another very interesting vid .... keep them coming

[@charlesvonroretz1270]

Love the 'fewer' bit! Less of a problem will give you fewer (number) of problems! I have taken a lot away from this vid including a bit of grammar so thanks. I am researching new boilers so came to this via one of your other vids. BTW I am still trying to find your vid on how to stop that turkey in my bathroom sink!

[@sandrarobbins8233]

Thank you, brilliant information

[@45graham45]

Excellent video. Thanks.

[@richard1441]

brilliant I really understand how it work now, I learn more from illustrations

[@SN-hx4mg]

You are Absolutely right sir . I agree with every word you said .

[@AtulShetty]

very informative- thank you.

[@gusolive]

Love this channel 💪

[@solo-repair9374]

Excellent lesson there thank you

[@lstephens1788]

That was really interesting, been thinking about what to do in our 1890 cottage, decided to leave it as it was built, only lambs wool in the loft, its draughty and sometimes cold but bang the woodburner on and its toastie, cool in the summer too. Old tech is sometimes the best tech.

[@SkillBuilder]

You can't beat the woodburner

[@nevillewebb2856]

No rant - very calm and useful thanks 👍

[@davidrobertson7964]

Got problems with my loft! Been thinking for ages. Also got a job coming up to stop damp and insulate corner of a house. Thanks for that! Explains alot! The grey grey area and lots of opinions on condensation. Never thought of a membrane on top of ceiling joists. THANKS!

[@SkillBuilder]

Normally the membrane is put on the underside of the joists and the plasterboard goes over it,

[@johnnyrogers5066]

I trust Roger more than anyone else, his advice and explanation is spot on.

[@SkillBuilder]

Thanks John, I try to be honest but personally I am a great believer in getting a few opinions and then working out who is telling the truth.

[@cpk3050]

Thank you learnt a lot from this

[@445fhn]

I've never used a vapour barrier to the loft. I simply make sure the loft area is well ventilated with soffit vents etc.

[@kevinrobertfrasier1309]

Lets say a builder plants a lump of 5x2 along the width of the properties behind the facia board which blocks off the air vents and air flow then that has created a problem. This is the case on new builds in entire rows and these properties suffer badly from moisture in the loft spaces causing moldy ceilings

[@thetessellater9163]

@@kevinrobertfrasier1309 - not sure what you mean, Kevin, I've never seen anything behind the fascia, they're usually fixed to the rafter ends, and the vents are underneath on the soffits. Builders also use plastic under-felt vents between the joists allowing air to pass by keeping the insulation from blocking the ventilation path. At least in the UK, though you may be referring to builders in other countries?

[@mattychapatti7342]

@@thetessellater9163 this is what my loft is like. (5 year old redrow house) but the insulation had been shoved right down into the eves squashing the plastic vents closed. We had bad condensation when we moved in 8 weeks ago but I unblocked these added felt lap vent, re secured the fan hose vent. And so far so good no more condensation

[@GeorgeEI7KO]

Great video Roger. Regards from Ireland

[@danielbolton6905]

Vapour migrating through the building fabric is also responsible for heat loss though it’s not a huge factor it all adds up. Great vid. So many builders get confused when it comes to vapour barriers and condensation. I’m a chippy and I’ve lost count of the times I’ve had to explain all of this to a contractor. Only thing I’m not convinced of is how often is it warmer outside the dwelling than inside. Without a/c where I live on the south coast uk I suggest it’s very rare indeed.

[@danhamjam]

What about a pitched cold roof in a loft conversion? Using solid PIR between Rafters and other layer of PIR below rafters, why would you want to trap the vapour in the loft?, would you not want it to travel through the roof and out via ventilation gap in the pitched roof. I'm looking at diagrams even from Regulations stating a vapor barrier is needed even in this senario but i cant get head around it. All this PIR has foil fronts and is taped by aluminium tape, gaps filled by filler or gafo tape. Why is a vapour barrier needed in this system?

[@danielbolton6354]

The PIR under the rafters is a vapour barrier when the seems are taped with foil tape.

[@venenareligioest410]

I have just fitted 10 x felt lap vents for £25 - worked wonders 👏🏻👏🏻👏🏻

[@pokepals4840]

Brilliant, thank you 👍

[@danshinsplints940]

Brilliant explanation Roger, I wish you had of been my school teacher.

[@SkillBuilder]

sadly I was a very disruptive pupil and gave my teachers a hard time. I would like to go back and apologise but it is too late.

[@antog123]

What a video of information. Question : I live in an old house, no roof vents and the style of roof prevents facia vents, I noticed recently moisture on insulation i installed 3 years ago. Would It help by installing gable vents or vented extraction fans and if so would they both need to be extraction or would one have to be just vented for circulation? Would appreciate any advice, many thanks from Ireland

[@beverleymckenzie8436]

Great video, very informative. In winter I get lots of condensation in my attic (crappy 1903 terraced). The “felt” is a grey rubbery/plastic material, definitely non breathable. There are 3 roof vents already in & when I had plastic soffit & fascia board capping done the builder inserted vents about 12” apart, probably 15 in total. Because of the layout they are only on one side. Didn’t improve things so I’ve tried installing 20 odd felt lap vents but still no appreciable improvement I am topping up loft insulation (adding 200mm to the existing 170ish) & adding loft legs & loft boards as & when I can afford it (it’s a large area) but am now concerned that this may add to the problem? There seems to be a suggestion that more insulation causes it’s own problems. Do I need to take it all out & put a vapour barrier in? I have been seriously tempted to just cut the felt to somehow get more air flow into the attic. My old house had a thin layer of polystyrene bead insulation, no roof felt at all……. & no damp problems 🙄

[@garyreid8871]

Another great video.

[@migsvensurfing6310]

Thank you. It answered a question i left in the comments on a later video. I dont know why I didnt see this video when it was uploaded. I want to build a cavity wall without plastic but with Rockwool and ventilation. For rainproofing I want to use lime.

[@mickyork41]

The ‘he means fewer problems’ caption absolutely made my day. My wife and I always argue about this. I say it should be fewer, and she’s wrong. I’d never criticise a word a legend like Roger says obviously, but still...

[@SkillBuilder]

Dylan and I have a running joke about this and I can't believe I got it wrong. Dylan put in the correction and he is right. The rule is very simple. If you can quantify it with a number it is 'fewer' if you can't then it is less. So "fewer people came to the concert this year which made it less crowded." My five says we have less money because fewer customers are willing to pay my extortinate rates.

[@mickyork41]

Spoken like a true journalist Roger. I did 13 years on a local paper and went from being told off to doing the telling off on that one over that time. I have a damp porch built less than two years ago. The builder has been back a few times already and hoping he’ll have it sorted soon but wondering if some of your wisdom in this video is relevant. Will take those down lighters out and have a nosy inside the flat roof...

[@thetessellater9163]

Waitrose had "five items or fewer" checkouts until recently; proper speak!

[@bencoughlan3187]

This guy is incredible.

[@malcolmsmith1588]

Yes good explanations roger ive just done a warm and cold roof at home no vapour barriers although I think p I r insulation has a barrier on it anyway I would say it’s worth mentioning that on a cold roof cross vent with battens is essential and with a warm roof I’ve done exactly as you explained the only problem I get is a bit of friction between the insulation and the ply when the sun gets on it and makes a bang as it warms so may need something between 👍

[@paulmarjoram2258]

Interesting Rodger. I live in a mid 70s detached. Cinder block and brick construction with a 30 x 14 flat roof extension which I had re boarded and GRP’d some 20years ago. 22 x 14 of that roof is in one room opened into the existing kitchen and dining room, so it’s a fairly large space where we spend a lot of time breathing, cooking etc. The flat roof has continuous vents on the underside of the over hang on three sides but not sure if any holes were put in joists. The joists are running perpendicular to the original house meaning without holes in the joists there wont be an through flow of air in most of those voids. Should I worry and if so,is there any simple fix you can suggest.

[@MrTurboSAAB1]

Perfect explanation Roger. We bought 1958 end terrace house with bitumen felt under concrete tiles.Previous owner never had dampness in the attic,that was only storage place thanks to little insulation on joist level....hardly 100mm.I have put another 350mm and loft legs and boarded. This winter there is lots of condensation on rafters and some black mould.. I have to mention roof is unvented. If I replace tiles,put there new breathable membrane like Tyvek and install over the fascia vents and dry vented ridge,will it solve the problem? Can I after that put some kingspan PIR between the rafters,if course keeping 40mm vent gap , to keep loft storage bit warmer?

[@jaydee7367]

Another super video Roger, thanks. Is a loft vapour barrier needed for an older solid wall house with sheep wool insulation? I'm trying to keep the house ventilated, but don't know it that applies to the loft too

[@robwilton8001]

As always, well as most often :-) great content and practically informative. So useful to peruse your videos for a bit of no nonsense on subjects I’ve not dealt with for a while combining a good bit of ‘old’ wisdom and useful modern methods that actually pan out as worth learning… What are your thoughts on adding external ROCKWOOL with a timber (thinking charred larch) or cement panel rainscreen over painted pop block with cavity wall insulation. My thoughts are converting the inner walls into more of a heat store by wrapping the walls in a fireproof blanket and allowing whatever moisture working through the walls into the cavity fill to migrate out into the ventilated ROCKWOOL over time. My only concern is whether I need to remove the existing white masonry paint surface before ROCKWOOL goes up as the latest coat has been in place for over 10 years over the previous 10 year coats and it still looks as good as the day it went on (live in Cornwall where nearly all exterior walls are white) I’m concerned it has created an impervious barrier for water movement outwards. Perhaps drill a few holes and add a stick of compressed felt to wick moisture out of the walls to evaporate into the ROCKWOOL? What do you think Roger? Or anyone else reading the comment…

[@paulburton6832]

Hi Roger and thank you, I have got A-frame trusses with W style supports inside the trusses and the non-breathing roofing felt so we do get the condensation on the underside of the roofing felt this condensation does make the trusses wet to an extent. The block and brickwork at the ends of the house have about 150mm square of ventilation i.e. not much. What do you think about sheep's wool insulation between the trusses? I believe the wool insulation would absorb the moisture and release it when the weather heats up spring and summer. Can you advise how much ventilation is required per cubic meter in the loft space in this situation? My roof slopes front and back and overall is about 8m long, detached house. I have electric bathroom heater fans and extractor fans and we open windows to get rid of bathtime condensation. Kitchen has an extractor hood, lounge has an open fire so all in all fairly good ventilation, washing is dried outside.

[@wandango5913]

Great video, we’ve just moved into a 1930’s solid 9” brick wall house with suspended floors, high moisture content of +80%, fitted the Nuair PIV which has made a difference but not to the extent that others are experiencing, the loft is well insulated but the tiles are just lime mortared would it improve the moisture content if I added facia vents?

[@AccountantDoesDIY]

Loved this video Roger. I’m a novice DIYer having a crack at building myself a fully insulated garden gym. I’m doing cold roof given the 2.5m max height under PD makes a warm roof difficult. Everything you said reinforced what I’ve learnt from hours of scouring KZbin - great to have it all in a sub30min video together. I’m coincidently fitting the VCL to the ceiling and walls this weekend.

[@SkillBuilder]

If you ventilate above the insulation you will be fine

[@AccountantDoesDIY]

@@SkillBuilder yep. 6b2 rafters with 3inch to 0inch firrings on top. 4b2 noggins. 90mm PIR flush against the bottom of rafters. Min air gap of 2inches. Max air gap at end of firrings 5inches. Circular soffit vents at front and back of each rafter run. Also quite a breezy bit of the garden so reckon I’m all good. I am however guilty of the downlights :-) I’ve cut 100mm square holes in the PIR for them and pushed 40mm of PIR back into the hole to sit behind the light. Will take care to polythene tape the VCL edges around the hole into it as best I can. Suspect there will still be moisture leakage but the ventilation above the PIR should help with that anyway.

[@davidfincham5181]

Before I retired I worked as a building inspector for the NHBC. When I witnessed a vapour check installed at ceiling level below a roof space I asked the builder to remove it as it causes mould to build up in the ceiling as the moisture struggles to escape.

[@michaelcameron2553]

Thanks, another insightful video. I'm getting quotes to have my roof retiled (mid 1970s house with disintigrating felt under tiles). Current practice around here is to cover with OSB then membrane followed by tiles, with dry verge system. Only one roofer so far has pointed out the requirement for either adding some vented tiles or leaving every 3rd rafter secion without OSB. I've watched several roofs being done round here with full coverage OSB and no sight of any additional vents. What's your opinion on leaving sections of rafters without OSB.

[@bryanwyer2961]

Hi Roder.. im after reroofing a house using tivek membrane its a standard a roof..im now going to slab the ceiling with 38mm insulated slabs ..should i use foil back slabs or not ?

[@abbyanderson4171]

Interesting stuff,well presented......

[@normanboyes4983]

Nice one Roger.👍

[@pippathedog7801]

You can seal areas of your house to prevent water vapour inside travelling to other areas such as the roof or walls. But you do not stop condensation problems, only move the problem to another part of the house.. Seal one area, water vapour with find the next coldest area and condense, seal that area, the vapour will the next coldest part of the house and so on. My house house is well sealed, but I have am am the extremes of the problem, where the coldest part of my house is now the hinges on the external doors and windows, and I have pools of water here. There is only one way to stop condensation, seal the house, but add a heat recovery system, it will remove the worst of the vapour with the benefit of heating cost savings and filtered air.

[@paulmartin4285]

I recently had upvc cladding done on the soffits fascias and barge board, cracking job until I went in the loft and found it literally dripping with condensation. Bit of research and found out the continuous air gap under the soffits had been completely compramised by cladding over and replacing with 8 circle vents. Got in touch with company to rectify problem and they didn't have clue about the mm2 formula for ventilation. They eventually turned up and at my request added 32 vents in total, Problem fixed. Basically don't ever cover the soffit vents !

[@craigalexander4747]

good video on the technical side of how moisture forms but would like to see what you can do and what products you can use to help reduce moisture to a current property with moisture on the felt inside

[@markmarlow]

Skill builder could you do a video on what type of vapour barrier should and shouldn’t be use on flat roof there’s loads out but I do feel the knowledge on these is very hit and miss even the building inspectors say all different things

[@lewisbarry461]

I am building a single storey extension with pitched roof and looking to use fibre cement tiles. Half the structure is fully vaulted half has a flat ceiling. Part cold, part warm roof if you like. What membrane (felt) would you recommend? A breathable or non-breathable? Cheers

[@bamsebrumbamsebrumen5403]

Great that you covered this area. My personal experience is that when you are in as much of tiny a doubt then vent… and never put outside wall dressing directly up against the wall, without a airgap, if the inside of the house is dressed with plastic because that wall will require desert climate if to ever dry up.

[@pingu99991]

So I'm moving into my first home soon and planning what I need to do get get my bills as low as possible - I want to insulate my roof, it's a typical pitched roof bungalow so insulation will really help due to the larger surface area to living space they have. I wanted to know if I should put in vapor barrier underneath the insulation but going over the joists? In that case what do you do about the struts that come down from the rafters to the joists? do you tape it to the wood to try and get the best seal you can or is this something I'd need to pull the plaster board off the ceiling and put in between the joists and plasterboard the way you described? (Something I'd rather not do if possible) I should also say that I'm planning to put in a MVHR system so that should help keep the property drier than normal without venting all the heat/AC that I'm paying for into the atmosphere, but that also requires the better air sealing that the vapor barrier would provide. This is because I want to put in a heat pump - I know you're not the biggest fan of those but I have Multiple Sclerosis which is impacted a lot buy heat so I need AC in the summer - I feel like I might as well heat my home with the same system and get off gas as I don't like the look of the gas market's volatility long term. Do you think a MVHR system and good insulation could help alleviate some of your problems with heat pumps? Thanks for all the great info!

[@michaelcrowley2247]

great video

[@terrythorpe346]

Hi Roger, Thanks for explaining the science of vapour control. What is your view on dehumidifiers to control moisture content and what is an ideal RH level to aim for?

[@SkillBuilder]

Hi Terry 45% is probably about right but in the summer it may go up and in the winter you might drop to 35% because there is less humidity. If you have a dehumidifier it will not extract so much moisture in the winter because there is nothing much drifting in fromm outside. I would think it is fine to leave the dehumidier on because it adds heat to the building and won't end up making you into a crisp.

[@fazerstorm-oap]

Ventilation is key but it costs money if you have to keep the heating on. Interesting article, thanks.

[@tullgutten]

Cost less than rebuilding the house from water damadge

[@Winkie_Designs]

hi @ Skill Builder I am building a craft wooden penthouse overhang shed that will be heated by electric... I have watched so many tutorials but all give different answers so I wondered if you could give it to me straight... i'm wanting to know how to do all the layers etc ... like cladding / batten / Tyvek / batten / insulation / then my inner wall plasterboard or T&G etc is this correct? plus when you were saying about cold roof, if I put vents in each of the spaces in between the roof joist at the front and back will this be enough? many thanks in advance

[@chunlichun]

What about positive air flow fans in loft to stop condensation buildup on timber rafters and bitumen felt?

[@avfczoff]

Really appreciate this video and it’s a big help! I’m not a builder but a sparky and I’m trying to gain as much knowledge on this subject as I can for my own house. How would you arrange a vapour barrier if the internal walls are solid brick? In one room (bedroom for example) there is one stud wall & three solid walls. I wasn’t too sure if a vapour barrier should be taped continuously around the ceiling and all walls but then how would plasterboard be fixed to solid walls with a vapour barrier behind? Its very much out of my comfort zone so any help is more than appreciated 😬 It fry’s my brain! Thank you

[@NikolayBoyanov]

Hello I'm in a brick house, the question is what do you have behind the bricks? Is it a ventilated facade, is it siding, is it plastered, etc. In general, you should not worry about vapour escaping through the walls when they are tightly plastered. Steam vapors go up and it is good to have a vapor barrier on the ceiling. The question here is whether your ceiling is a wooden structure or solid. Plastderboard is placed on a structure above this structure is placed a vapor barrier.

[@paula.the.wannabe.hauler]

Thanks Roger, how would you manage the light fittings etc without have to cut holes in the membrane?

[@shafserious2805]

Mad video love it

[@Alexnse10]

Roger, I have a 1930s bungalow solid brick construction,one room has 3 external walls and a bit colder than the rest of the bungalow. I want to use insulated plasterboard to try and make the room a bit more comfortable but read different views on how to and it will cause more problems long term . Have you any advice. Alex Hennessey .

[@wisher21uk]

Hi I’m glad I found this Our loft has a vent on the gable end that basically a black plastic hole that’s brick size, it looks proper not just made up, also our boiler is in an airing cupboard that has a vent on the ceiling of the cupboard for the the boiler that goes into the loft. Now the 5 yr old boiler is a condenser boiler does it need the vent for the boiler on the ceiling and is the the hole in the wall ok? As we get wet spots on the insulation that’s dripped down I’m assuming

[@bluestar.8938]

Thank you : )

[@westwonic]

Originally, Bathroom and extractor fans relied on manual on/off switching, and then were improved with a timer device that kept the fan running for an extra 20 minutes or so after switching off. Nowadays there are humidity controlled extract fans that switch on/off automatically whenever the humidity levels rise. Surely this should be a requirement written into the building regulations?

[@martinconnelly1473]

I added a flow switch to a hot water feed to a bath and shower that triggers the bathroom fan. This means it comes on when it is most needed and does not require anyone to remember to switch it on or off.

[@thisismyuniquestory]

To Nick, I was into industrial ventilation from day 1 at work in a tannery, smells, steam, and the more the merrier. That was 1963 and industrial buildings leaked but if the fans ran no mould. 1968 Powrmatic manufactured a comprehensive range of industrial fans. As an R&D engineer I had to address the more scientific approach. Large buildings weren't so well sealed and large large volumes of air extracted and more attention to replacement air was for 340 days in the UK at a lower RH, relative humidity, each year. 19 years and more attention involved with gas and oil combustion for heating and process, tiles,ovens, gas registration with CORGI was a minor nuisance in my life (Roger), Involvement with Modecon Boilers in Poole, the first commercial industrial GAS condensing Boiler in the world as I believe the history as I was Dr Harry Cheetham's boiler to be. I was Harry's service engineer and each module was 50kw and multiple modules were the new science commencing with one, two three and on. Harry did build 23 module unit back to back with another 23 module it was that flexible. (A FOOTNOTE - Harry sold of Stelrad who produced the same modular unit as the Concord Super to this day. Hamworthy were miffed with Harry's development of the boiler during the time of his employment so an intellectual rights began and Hamworthy produced with the Wessex modular for the next 26 years, 2021.) Air conditioning was a serious involvement for me, industrial to the tune of computer halls for the MOD and pharmaceuticals and Roger was correct about the temperature differentials and crossing the vapour barriers of air con with any size of all buildings. I moved to Vent Axia with a progressive MD Peter Norris and he saw where leisure and ventilation was heading. The Solo 100mm diameter fan range with modular controllers including variable speed fan control. Brilliant for many public sector houses, expensive electric heating, double glazing added,the result, black mould. Cured with variable speed humidity control improving living conditions for 10,000s problem properties including my own property. That was 1987 and so much of the intervening years not enough attention to ventilating all properties and industrial buildings. Kids with asthma, allergies and other illnesses nor that I've medical knowledge other than acquired knowledge building the environmental control systems a and building the air con systems for isolation rooms for identifying allergies. To that end and for your own homes, VA had one control option and it may still be an option, a two speed toilet fan either with a pull cord for high speed during use the bathroom/toilet. When the light is off the slow speed runs 24 hrs very low energy but not ,zero. The RIBA, the architects body was all home's required on air change per hour, every hour. Before double glazing, plastic doors, air bricks with Hit & Miss ventilation control to slide in the coldest weather. Sweden, a colder country had better insulation in 1936 which we matched around 1980. They knew an RH above 75℅ was the top limit. Google how much water people exhale every hour plus pet, sweating, cooking, hot drinks, airing clothes. A long list, washing, bathing ,showering and on. Covid 19 - I've printed q Permanent negative ventilation, extract, for homes and every building Taking your option Martin with a flow switch for fan control is a useful control without wishing to sound patronising. Humidity does maintain after a shower if the RH is measured knowing steam does hold a great deal of moisture if it's weighed and will attach to all cold surfaces and mirrors are the prime demonstrator. This is a waste product in my list of definitions of products that aren't good for our well being, all included by the Swedes but sometime they recovered 70℅ of the heat with an air to air heat exchanger. VA did get in energy saving for public housing with Southampton City Council with their Hot Rocks project to produce heating and hot water from a bore hole, my involvement was the ventilation and reclamation o heat back into warm the fresh make-up air to save tenants outlay. All Swedish thinking from years back. My last thoughts about the containments we live with and its the produced ts or by products of our homes. I've had air tests done for something like 80? gases, new car

[@MaintenanceENG]

I have a slope in my bedroom ceiling, which there isn't any insulation above. I assume that there isn't any insulation because its right at the edge of the roof eaves, for airflow. But, this area gets cold and lets warm air in loft. How can i dral with this? Will a vapor barrier board over top work?

[@craig5832]

Hi Roger, I've just bought a 1930's dormer bungalow and I'm adding room in roof insulation. I'm replacing the rock lath with insulated plasterboard and adding as deep insulation boards as I can between the rafters. There is no felt under the tiles, does this mean I should leave more or less of an air gap? I'm looking at leaving a 50mm gap at the moment but the rafters are only 125mm deep. I might even end up adding battens along the underside length of the rafters to get a little bit more depth for the insulation boards. At the moment the only insulation in the roof is a small amount above the ceiling which doesn't seem great! But I don't want to cause additional issues by adding all of this insulation