External Wall Insulation ~ The Ugly Truth?

I was a property manager and we decided to EWI a whole estate of 1920`s solid brick houses which were suffering with excessive damp and mould (also the properties externally were looking old and quite depressing) We specified that any obstructions to the insulation must be removed and insulated 100% of the external walls. It was a huge success resolving years of problems as well as modernising the appearance. That was 25 years ago and driving past recently I noted that the properties are still looking really good.

Nice to see you are insulating your thumb 👍🏽

I worked in social housing for almost 20 years. Black mould and condensation was the bane of every repair officer's life. Even when we'd insulated the stock, installed the most efficient condensing boilers and double glazing, some tenants still suffered from condensation and black mould. Often, you'd have two adjoining houses, one mould free, the other full of mould. Regardless of the witch hunt in the tabloid press, it's mainly a lifestyle issue. Cooking with pan lids off, not using extractors in bathrooms and kitchens, drying clothes on racks and radiators, not opening windows to vent a bathroom after use, or using the heating to avoid cold surfaces. Most often, black mould is directly related to poverty. When all else failed, I found one product was amazing in removing internal moisture laden air to avoid condensation and mould growth. It was the Nuaire Drimaster (for houses) and Flatmaster (for apartments). They extract continuously and use incredibly low amounts of electricity. My own parents bought a bungalow which had terrible mould growth behind wardrobes and on external walls. I installed a Drimaster in their hall ceiling and it immediately resolved the problem. I'm not making some marketing pitch on their behalf, but on this I'm absolutely certain. No other humidistat or extractor came close. They are absolutely brilliant. They're not cheap to buy, costing £300-400, but I've never seen anything work better. They're ridiculously cheap to run, literally a few pence per day and are silent.

Great video, thanks. I’m an Architect and fitted external wall insulation to my 1929 house 8 years ago. I did it at the same time as a major extension and rebuild which avoided most of the problems. Fortunately because of that I haven’t had any issues with condensation or mould. We doubled the size of the house and halved our heating bills. More importantly we have a lovely warm and draft free house which is very good for my wife’s arthritis.

We bought our house around three years ago, black mould all over the inside walls and absolutely sopping with moisture. solid concrete and small so only possibility was to do ewi, they give a 6k grant here in Ireland to do it, absolutely great job, but because we had just bought the house I was able to take absolutely everything off it, got new windows in and mounted them flush with the exterior face of the original wall, had to put a meter cabinet in as power was coming in onto gable of the house, do I left meter cabinet proud 110mm. Got the insulation done, and it absolutely transformed the house, no cold spots at all. What did happen though is all my moisture flecked off into the attic and I had mouldy patches where all the rafters were coming down to the top of the walls. Cored a couple of holes in each gable and made sure I was getting ventilation through my soffit, attic absolutely bone dry now and not a patch of mould anywhere, also added benefit of ewi is the thermal mass of the walls gets put to use, house stays warmish for a good three days with no heating on now.

In Canada, with new build homes, we have to install air exchangers, so as to manage the moisture issues. I used to go on house calls with people in older updated insulated homes and they would complain about moisture on their new windows. I had to explain that they had made their homes more airtight and that the house needed to breathe. One couple were upset with one another sash having moisture and the one next to it had none, I explained that the fly screen was trapping moisture, they removed the screen and shortly after the moisture evaporated. You are correct, making your house more airtight, needs some attention to air flow control.

I've got a few flats with EWI. No issues with moisture at all. Soil stacks are plastic, boiler flues obviously warm enough, and no issues with damp or mould anywhere. If the EWI did anything it got rid of damp on inside walls that was there before and made the flats so warm that heating is no longer required. Nothing but good things to say about EWI. Tenants love it when they hear there are low or no heating bills, especially with the cost of living crisis. Recommended.

Totally agree - I brought a 1970s build with empty cavity as part if the huge renovation we decided to have both internal and external insulation fitted to lower energy requirements , great until you realise the humidity increase. First off regarding flue and soil pipes prior to arrival and because it wasn’t occupied, the soil pipe and glue were extended. For the flue it ment getting a gas engineer in to size one up and cut to the new length needed. This one was easy since we were Also fitting a new system boiler , with the external soil pipe removal and extending was essential or it would have to have a larger box section fitted , but thankfully we had a fitter who was happy to work with the team so they could pre cut to size , but there’s little to do about fitting around the sewer inlet other than to fit a box with the internal insulation plug sockets or new outlets must be planned and run , but we still had to retrofit a new heat exchanger in the dining room /living room . The kitchen extractor on when cooking and washing up and a green room dehumidifier 8kwh running plumed in , this fills up a 10 litre in about 4 days when people stay and sleep over . I was thinking of a house hvac exchanger but retrofitting now is Awkward now that second fit onwards so please plan ahead if you plan on doing the same also when having air tightness talks for external find out what they are using to close the gaps or if they fit external edging on these sheets like internal rated for , trust me you can’t get a good fit with a saw no matter what they say , it’s no say labour job it needs planning and working well on site it took a week to do everything external to get it all in . And it’s not cheap to do this 5 bedroom cost 18,000 external and 9 k for inside . For a team of 3 , plus Plummer and gas engineer. And please don’t forget to super insulate your cold feed it’s a condensate magnet otherwise

One of the first retrofits I did was install heat recovery ventilation. It made my house less drafty, helped keep my heat and improved indoor air quality. Insulation is great, but ventilation is key.

Finnish housebuilder here. This is so very true. Nice and simple explanation how it works.

I insulated my solid wall house 4 years ago. Although there are no cold bridges, it definately gets more humid. If that moist air makes it into the loft it condenses on the roof and drips down. I've put a lot more ventilation in my loft and try and do regular air changes. Getting rid of cooking and shower moisture at source is important too. It has been brilliant on the whole, during cold weather the outside of my house has ice crystals in it as the heat loss is so low!

You hit the nail on the head: insulating and air-sealing older homes is very, very challenging. I've done it and never again, thanks! We built a new super-insulated home and never looked back.

Hi there. I work doing ewi and yes we do have a plumber that moves the pipes . We do take the fence or gate post from the walls that’s my job. Yes I am a carpenter. We rebuild from new the fence and gates that we remove . We do on some properties work with wales and west utilities to move same gas boxes and insulation is behind. Sorry we do move most things and put them all back when it’s finished. I hope this explanation is good for you and keep up your good work as I always enjoy your videos and I hope your thumb gets better .👍👍👍

Well done Roger, as someone who works in the construction industry I appreciate your commentary. This whole area is fraught with risk if the principles at play are not understood and you explain the building science extremely well!

Hello Roger from a GC across the pond. Great video. It's important for people to understand that there are no singular silver bullet solutions. All solutions need to be comprehensive. You explained it well.

Hi Roger, We have had 3 and 2 bedroom flats (looks like a large Semi from outside) done last year. We removed the down pipes, svp, lights, gate etc. We then fitted new SVP on 97mm spacers , two new boiler flues which interestingly they put rock wool around to approx 600mm all around it. We removed the original 9 x 6 wall vents. The building was then insulated and rendered with a silicone render (luckily we had deep soffits) which appears to be self cleaning in heavy rain. We have trickle vents on all windows anti back draught (non shutter type) extractors in both bathrooms, anti back draught extract to outside fans in both kitchens, new down pipes with rawl plug, screw and adhesive clips & new 32mm vertical external condensate pipe running down to a mini soakaway, 1st floor flat roof space was insulated with wool to current standards..... My word what a difference it has made both flats, much cooler in the summer and much warmer in the winter & ZERO condensation. Alot of work, cost us £9K plus the £10K grant (which is another long storey for another time) but I now run the heating via the Vaillant combi boilers at 58 degrees (well below dew point) without the tenants knowing a thing!!! If done properly and not the way you are suggesting it is worth it. Next step is to redecorate flats which will also involve over sizing rads to 35-40%

Fantastic video - thank you for taking the time to explain the pitfalls of non-optimal EWI installations!

So pleased you mentioned this. I had this issue when moving into my current home. Dehumidifiers are useless. The internal wall insulation caused this. It's also caused damp under floorboards which has also led to an internal wall having damp. I sleeved vents and added new vents to solve the sub floor issue to some extent but a neighbour has had all his floorboards rotted away because of this insulation. I solved the humidity and constant mould growth via a positive input ventilation device in the loft. This pulls in less moist air from outside and pushes the moist air out as a result. Really cheap to run but make sure you get the one with a heating element to temper the air. Beware with insulation because the humidity and mould caused me to develop asthma after being in good health before moving in. It's very hazardous to health. Just constantly cleaning the mould is not enough.

I live in Canada but your points remain just as relevant. I bought an older house and one of the previous owners did the external insulation. The points you bring up around awareness of such areas as electrical, plumbing and other such wall penetration is invaluable. So is moisture content. This past winter I had no issues with it because I made sure I had a dehumidifier going. But, I was able to identify areas of heat loss. It is early spring here so I am going to address those issues before it gets too hot! Good vid. Thanks.

Had EWI installed 8 years ago. 1930's built solid brick house. They did it properly. They even put a bend in the soil pipe. There are no "blank" spots. It's been nothing but positive. We used to get mould in the corners before in most rooms where condensation would meet cold walls. Despite having humidistat extractors and running two dehumidifiers. The day the insulation went on (Feb), I had to turn the central heating thermostat down by 2 degrees as it was getting too warm inside. We have no more mould growing in any corners. The only fly in the ointment was the patio doors no longer swing all the way open like they used to as the insulation stops them opening beyond about 95°. But I have a cunning plan to remedy this when I come to replace the doors.