Stop Condensation in Your Loft ~ Ventilation & Vapour Control 

😂😂 the good old boys love it

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

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.

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.

@@mattmechamThankyou, never heard of of them before.

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.

@@SkillBuilder lol only joking mate good stuff

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

What has it done for you?

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?

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

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

Check your electricity bill...

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. 👍

@@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?

4:09 ​@@rsmith02I'm

Thanks, will do!

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.

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...

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

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.

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.

You can't beat the woodburner

Cost less than rebuilding the house from water damadge

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

@@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?

@@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

Old working chimneys are an excellent way of getting fresh air into a building and moisture out. Thats some of the problem nowadays as there little to no ventilation in some houses 👍

@@tmgromit4007 they can also et a lot in if it has an open chimney pot have a rain cover

Or Mrs. Bushy giving off moisture 😉

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.

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

Glad it helped

Good result Tony.

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.

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?

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

External wall insulation. That is an interesting one. I did a training course with Weber so it would be a good idea.

Skill Builder I'm thinking about insulating the inside walls of a double brick house which doesn't have a cavity. Im in a conservation area so can't put anything externally, but worry about causing moisture. I think there are lots of people in a similar situation, where the heat loss means the house is never comfortable - either too hot or cold, or with cold areas when the rest of the house is too hot!

I’ve seen this bodge so many times 😬😬

If you ventilate above the insulation you will be fine

@@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.

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

@@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

you just have to do it intelligently. that's very easy with new builds if you know what you're doing. it's tricky/difficult with retrofits.

The best way to achieve this is with counterbattens and even 25mm is enough. The water that condenses on the underside of the tiles drips onto the breather membrane but the gap between the tile battens (laths) and the membrane allows the water to run down the membrane to the gutter rather than collecting behind the battens. It is a strange anomaly that our often stringent Building Regs overlook this requirement. In Continental Europe it is almost unheard of not to use counterbattens. If you use counterbattens you can push the insulation board against the felt.

@@SkillBuilder thanks for replying Roger. I didn’t think of counterbattens, wish I had. But I think what I’ve done must be working anyway as haven’t had any repeat of the puddling issues inside the loft that I was having before in particularly cold and still outside weather.

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

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.

Alistaire Cook It will be the North facing side of the roof. I miss your Letters From American. I am a huge fan of your work.

@@SkillBuilder You are 100% corrrect it is the North facing side. Unfortunately I'm not the Alistaire Cook your thinking of 🤣🤣🤣 or even the Cricketer.

The downlighters are allowing a lot of air up there

Yes it is better to use Celotex. I used Rockwool for convenience but Celotex is warmer.

@@SkillBuilder cheers Rog much appreciated👍 M