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Why modern British homes are getting mouldy

Britain's unique climate calls for unique housing solutions. Credit: Getty

May 31, 2024 - 10:00am

As a brief glance at the window will remind the reader, Britain is a cold and damp country. Our climate is a natural product of our position at Europe’s Atlantic fringe: left to its own devices, much of the country would naturally be covered by rainforest. Yet the recent drive to retrofit insulation in Britain’s houses, widely condemned by green pressure groups as the coldest and draughtiest in Europe, is, counterintuitively, likely to dramatically worsen living standards.

A recent BBC investigation alleging that poorly-fitted cavity wall insulation is causing health-damaging mould to grow inside houses outlines the symptoms while misdiagnosing the cause: the problem is not that the insulation fails to work, but that it works too well. 

Around 25% of Britain’s housing stock was built before 1919, the highest proportion in Europe. These houses were built according to time-tested techniques to manage the ambient moisture of Britain’s Atlantic climate through air flow — that is, the very draughts we now spend money attempting to eradicate. Air-permeable lime mortar between brick and masonry and lime plaster on the walls allowed moisture from within the home to evaporate outside, much like a high-tech wicking fabric. Draughty single-pane glazing allowed air to circulate, preventing the build-up of mould: the problem of heating draughty houses was efficiently solved by the simple, if now unfashionable expedient of burning vast amounts of wood, and later coal in open fires.

But after WWI, when many skilled tradesmen had been killed in the trenches, housebuilders adopted the newly-introduced solution of gypsum-based plasters and cement mortar, as cheaper and quicker to work with. Because both are impermeable to moisture, houses began to be constructed with air cavities and external vents or air bricks for circulation. Over time, the old skills were lost, and houses built before 1919 — perhaps including yours — were renovated with impermeable gypsum plaster, and overlaid with non-breathable plastic-based paint.

Draughty windows were replaced with sealed double-glazing and chimneys were bricked up in favour of central heating, reducing air flow further. The result was an explosion of damp in British homes, and whole new industries of damp-proof courses and chemical injections — none of which work — aiming to resolve the newly-introduced problem.

Rising energy costs and aspirations to minimise climate change are now driving a new campaign for retrofitting insulation to homes that were explicitly designed to be breathable. Believing that they were upgrading their homes, householders took up government grants for spray foam insulation in lofts, which by blocking air flow, caused moisture to build up, rotting roof joists and making their houses unmortgageable

The same issues are now growingly apparent with foam cavity wall and other retrofitted insulation: effectively, taxpayers’ money has been wasted on making British homes increasingly unliveable. While the intentions were good, the results are disastrous: the entire insulation campaign, which has even seen well-meaning activists resort to blocking roads, is a scandal in the making. Low energy solutions that may work well in continental Europe’s largely dry climate cause major problems which, when applied to Britain’s Atlantic climate, their advocates still struggle to understand.

What’s the solution? Short of demolishing and rebuilding a quarter of Britain’s housing stock — often the most valuable and desired British homes — government grants wasted on introducing damp problems where they had never existed would be better spent on retraining tradesmen in traditional breathable techniques, currently a highly-paid boutique industry

Equally, supporting breathable insulation like sheep’s wool instead of impermeable foam and foil would be a much-needed lifeline for British farmers. Even grants for introducing dry, circulating heat from solid fuel-burning stoves — currently maligned by Net Zero advocates — would make draughty British homes warm and liveable without plaguing them with damp and mould. As is so often the case, the simplest, timeworn traditions are often the best– and the well-meaning innovations unintentionally disastrous.


Aris Roussinos is an UnHerd columnist and a former war reporter.

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William Cameron
William Cameron
17 days ago

If you have an old house do some simple things to keep it dry.
Open the windows often. Yes I know it’s cold but dampness requires ventilation to get rid of it.
Have a warm house. Nice log burner in winter very good. Ignore the folks that say dry wood is dangerous it isnt.
Lower the ground levels all round the so that any old slate damp proof courses are at least two bricks clear of ground level.
Make sure external air bricks which allow ventilation below your wooden floors are kept clear- or you will get dry rot.
Put flooring in your loft for storage and then have insulation on top of that in the bits you dont want storage. This stops squirrels eating your electric wires- which they love for some reason and it costs a fortune to fix.
Check old chimney breasts have open ventilation through air bricks and ensure that chimneys have cowls on top to keep the rain out.
Mop the condensation off window frames every day .

Jerry Mee-Crowbin
Jerry Mee-Crowbin
17 days ago

I live in France where it’s customary to have a very low power extractor fan running permanently to remove damp air. My house was built of stone around 1890 and until I insulated it some ten years ago it was impossible to live in it during the winter months. There was also problem with a build up of condensation. So in went the inexpensive fan which operates in the kitchen and bathroom.
Insulating the interior is a well understood and common practise in France and is well within the capacity of an average DIY person. Steel rails are set in the floor and ceiling with vertical rails inserted. The insulation was glass fibre, 10 cm thick and then plasterboard was attached and painted.
Job done, I now live in it permanently with a wood burning stove keeping the house pleasantly snug.
Why the DIY companies the UK can’t take a look across the channel to see a massive market opportunity escapes me!

Utter
Utter
18 days ago

Open the windows and air the place, every day.

Paul Smith
Paul Smith
18 days ago

I can’t have been too difficult to incorporate the requisite improvements in ventilation into the subsidy system, could it? There’s no such things as an over-insulated house, only an under-ventilated one.

Stu N
Stu N
16 days ago
Reply to  Paul Smith

Garbage. How many houses have you built or renovated? There is very much such a thing as an over-insulated house, such as the ones I’ve seen wrecked by having cavities and roof spaces gunked up by sprayed-on crap. And try spending half an hour in an over-insulated house on a hot summer day without expiring.

More ventilation means more draughts, thus negating the over-insulation you think is just lovely. Amateurs who think they’re experts should stay away from building, we create gaps and vents for very good reasons. If it gets cold in winter then heat the bloody place, we’re in northern Europe.

Katharine Eyre
Katharine Eyre
18 days ago

In modern, non-draughty homes where the air doesn’t circulate, open the windows wide for several minutes at least once a day. Open the bathroom window after showering. Don’t dry clothes on radiators and use the extractor fan while cooking, opening the window too if poss.

Gerry Quinn
Gerry Quinn
16 days ago
Reply to  Katharine Eyre

Drying clothes on radiators or cooking as you please are no harm. Just open the damned window!

Simon Blanchard
Simon Blanchard
18 days ago

I have a friend who jacked in his job as a state school music teacher to retrain as a traditional lime-based bricklayer. He’s doing very nicely indeed, largely putting right crimes against architecture perpetrated by modern bricklayers and damp-proofers.

Veronica Lowe
Veronica Lowe
17 days ago

Wool for insulation. I have long wondered when someone would suggest this. It is a scandal that the wonderful wool industry that flourished for centuries has been allowed almost to disappear, with farmers burning fleeces for which there is no market. Thanks for a fascinating insight.

miss pink
miss pink
15 days ago
Reply to  Veronica Lowe

Wool insulation is available here in New Zealand. Highly recommended by my builder husband.

Kathleen Burnett
Kathleen Burnett
18 days ago

The basic problem is condensation; that is, moist air cooling and turning into liquid. In modern-build houses, the single cavity does two jobs: reduce heat flow to the outside, and stop water getting in. The flaw in the design is that the moisture condenses in the cavity where the insulation sits, thereby wetting the foam insulation (sheep wool would be the same). The reaction to this amazing discovery was to line the inside walls with a plastic sheet. Out of sight, out of mind.
The perfect solution to a problem with two components is to solve each one separately. That is, to have two cavities. An outer one with air and open at the eaves, and an inner one with insulation and closed at the eaves. A knowledge of physics will guide you to choose thicknesses and materials such that the condensation occurs in the open cavity. This will give you a relative humidity inside the house in the 30’s to 40’s level (possibly too dry for some).

Mike Downing
Mike Downing
17 days ago

My neighbours had their cavity walls filled with foam years back and have been plagued with damp ever since.

Despite being hounded by salesmen for weeks, we decided not to bother.

John Robertson
John Robertson
17 days ago

Good article. Sheringhams’ ventilator was invented 1849 in response to finding out the reason why a girls school had a higher mortality rate than the boys bording school. The boys would more often break the windows allowing fresh air in.
The Sheringham ventilator was used in some victorian bedrooms. Industrial factories started to have the central square of window panes inserted with a hinged window.

Point of Information
Point of Information
17 days ago
Reply to  John Robertson

Intriguing. More detail or a link please.

John Robertson
John Robertson
17 days ago
Ann Looker
Ann Looker
17 days ago

I’m glad someone has written about this. I’ve knownabout it for years and have watched in horror as my neighbours set up future problems for themselves while trying to save the planet.
I live in a Victorian terrace. The house next door is run by a housing association which decided to clad all their houses with insulating panels. A few months later my neighours had to be moved out because of a massive infestation of dry rot. The spores had probably been lying dormant for years just waiting for some nourishing condensation to start the bloom! I have a large open grid over a soakaway into the cellar so I have a constant airflow (and Welsh rainfall) into the house. I’m the only person in the street who hasn’t blocked the grid.
I wish I’d known about lime plaster 40 years ago when I had the front rerendered. I have signs of penetrating damp in the front room – but no mould thanks to the draught from the cellar. I just wish I could afford to fix it.

UnHerd Reader
UnHerd Reader
18 days ago

So were the government putting money in the hands of their loyal supporters, the Big Builders? Like when we had the bonfire of the regulations, followed by Grenfell?

UnHerd Reader
UnHerd Reader
17 days ago
Reply to  UnHerd Reader

Think it’s the architects not the builders who are responsible

Adam Grant
Adam Grant
17 days ago

Here in Canada, new homes are often fitted with heat-recovery ventilators that transfer some of the heat from the stale humid air being expelled to the fresh air being pulled in.

Colorado UnHerd
Colorado UnHerd
17 days ago

An interesting article, with an illuminating historical perspective. I sent it to an asthmatic friend in Michigan’s Upper Península, who is always monitoring her little cabin for mold and adequate ventilation, and in winter balancing that concern against warmth. Thankfully, she is old-school and installed a small woodburning stove.

H W
H W
21 hours ago

Environmentalism ought to have something to do with awareness of one’s environment. Vancouver, Canada, is located in a rainforest British temperate climate zone. Other parts of the province, British Columbia, are semi-desert or have temperatures that fluctuate between -40 c and + 40. For decades, the province-wide building code was Californiaesque and resulted in ‘leaky condos’: apartment buildings rotting because of roofs not having enough overhang to protect stucco walls from heavy rain. Now we have chemical and plastic ‘vapor barriers’ encasing us and our warm, damp air in our over-heated homes. But it is nigh impossible to get folks to open windows, or use blankets, sweaters and socks to keep warm.

Matt M
Matt M
18 days ago

Bring back coal fires! I have one and it is in constant use from October to May- best thing in the house.

UnHerd Reader
UnHerd Reader
17 days ago
Reply to  Matt M

I lived in Ankara Turkey in the early seventies, and everyone used coal to heat their homes. We lived on a hill overlooking the city, and it was covered with black coal dust. I could run my fingers through my hair and they would come out black. If everyone use coal, lung diseases would be common.

UnHerd Reader
UnHerd Reader
18 days ago

For sure, nothing heats as well as a coal stove.

Ian_S
Ian_S
17 days ago

A nice story of unintended consequences — given extra delight when it is revealed that the old trades — Britain’s version of traditional indigenous knowledge — had it all over present-day Green-voting architects in black turtlenecks.

Dougie Undersub
Dougie Undersub
18 days ago

Good article, Aris. Now have a tilt at the renewable energy fiasco.