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.

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

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.

Great video thanks! Home ventilation is one of the most overlooked aspects of construction. You can buy cheap moisture traps in the high street pound shops and these are a great indicator of just how much airborne moisture there is in your home. See how long one takes to fill before and after you make changes to your insulation or ventilation systems.

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 .👍👍👍

hi Roger thanks for covering this subject up.May be more of my clients are going to accept replacing and extending all the pipes because most of them don't accept the extra cost and it can have a big impact on the system.Thanks i always follow your advice

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

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.

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.

Good information, thank you. I’m on a small island off of the west coast of British Columbia Canada (yes, my father was a lumberjack)… I have been considering external insulation for a while and this helps.

Roger, please take into account the 'Saturated Vapour Pressure' that forces the wet air through any gaps. It does not just float around! great video by the way, keep up the good work!

Great video roger as usual. My thinking would be, Control layers of any building have to deal with Water, Air, Vapour and Thermal in that order only. Air tight envelope comes before insulation. Insulation is cheap and insulating is easy as compare to doing an air tightness and making sure it passes the air tightness test. If cold air moves around the building meeting warm air is going to be the biggest issue. Also if cold air moves around, it will reduce the effect of insulation that supposed to hold warm air. Unless we understand the building science, I am afraid we will actually end up ruining our existing housing stock.