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« Hot spot or not - Josh 335 | Main | Truth and the green »

Keeping the heat out

An article in the Mail tells the story of the number of people - apparently large - who are choosing to decamp rather than continue to live in their ecohouses.

When Emma Taylor was offered a two-bedroom apartment in an award-winning block of flats, she couldn’t wait to move in.

Newly built, she was informed the building had been constructed to such high eco-standards that it would cost just £1 a week to heat. Unfortunately, as she’s discovered to her extreme discomfort, keeping warm is the least of her problems.

Because unlike most Britons, 23-year-old Emma has come to dread the summer months. Her ground-floor flat in Coventry is so well insulated that when the sun shines the temperature inside rockets — regularly over 25C, a point at which experts say health can suffer.

The Mail article seems to suggest that this can be a lethal problem:

To understand the impact heat can have on mortality rates, turn the clock back to 2003.

That August, much of Europe sweltered under a heatwave, with temperatures in northern France exceeding 40C.

The result was 15,000 heat-related deaths, the vast majority among older people. Research later revealed at least half could have occurred due to exposure to heat in people’s homes.

However, there is research out there that claims to have shown that as far as the 2003 deaths in France are concerned it was lack of insulation that was a risk factor. The UK government seem to concur and official advice is to get your walls insulated to keep the heat out.

The National Housebuilders organisation have looked at this question too, but their report raised more questions than it answered:

There is increasing evidence that new and refurbished properties are at risk of overheating, especially small dwellings and flats and predominantly single-sided properties where cross ventilation is not possible.  However, there is also evidence that prototype houses built to zero carbon standards are suffering from overheating, which shows that overheating may also become an issue where cross ventilation is not achievable in lightweight, airtight houses with little or no solar shading.

In many cases the lack of ability to reject the heat build-up from normal occupant activities means that a risk of overheating exists in summer.  However, in some instances the gains are such that the overheating occurs for most of the year and is therefore independent of the external temperature.

I'm guessing that because of the relatively low numbers of people who live in eco-houses at present, their risk of frying the occuptants alive was not picked up by studies of the French heatwave. Certainly, the one cited above only had a category for buildings "Built after 1975".  It may be that there is an optimum level of insulation, above which the risks of overheating outweigh the benefits in lower fuel bills.


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Reader Comments (57)

The mechanisms of heat gain within buildings are all very well understood. However, existing guidance and MODELLING TOOLS appear unable to predict overheating in all cases, and more work is needed to develop them based on robust practically proven research.

Who would have believed it ?

Jul 10, 2015 at 2:15 PM | Unregistered Commenteresmiff

Junior's room is prone to overheating too. Now the problem might as well be the subsidised loft insulation I got installed maybe 10 years ago. I will have it removed.

Jul 10, 2015 at 2:19 PM | Registered Commenteromnologos

There are as I understand it - standards for ventilation (number of air changes per hour) which aren't actually much adhered to.

Heat pump systems should be able to work in both directions - my dentist has one such system in his surgery which works well.

I'd say that the "over insulation" = you fry issue is related to the heating / cooling system provision which is a cost component that cheapskates swerve around. A building that retains heat is equally capable of retaining cold.... - but cooling systems are easily red-pencilled - the occupants find out that insulation is a two way street the hard way :-)

Jul 10, 2015 at 2:19 PM | Unregistered Commentertomo

"regularly over 25C, a point at which experts say health can suffer."

Health can suffer above 25C? Maybe this is just the perspective of someone who grew up without air conditioning in the American Midwest, but 25C doesn't sound particularly uncomfortable to me. Even now at my advanced age my air-conditioning thermostat is set above 24C in summer.

Of course, that's still air conditioning, meaning the indoor humidity is kept low, so maybe that passage sounds right to a Brit?

Jul 10, 2015 at 2:29 PM | Unregistered CommenterJoe Born

I believe there is an optimum level of insulation however it is so site specific that it's not useful to say eg R40 in ceilings/R30 in walls is optimum.

My house in rural Virginia has about R40Ceiling/R20 walls and is relatively easy to heat. However the kicker is in the summer when I'm also forced to use AC at times. So there's really no CO2 savings to be had. I have mature trees in my southfacing front yard so the house is in shade most of the day and that makes a large difference. Most summer house heating is by interchange of inside air with outside hotter air during the day and the reverse at night. Because of the amount of insulation (which is quite high for these parts) there is a considerable lag. With less, or no insulation the effect is much more immediate.
This week temperatures are in the 90s days/ high 70s-low 80s nights. With no cooling the inside temperature eventually comes close to the outside temperature and may exceed it after sundown when outside cools off faster than inside. But not every site, especially in urban UK has large shade trees. One must also consider the UHI effect which must be quite noticeable in urban UK. Here houses are set apart from one another sometimes by quite a distance; my recollections of urban and even suburban UK are that that is not the case.

Given all of this I can quite see that with temperatures in the 90s, an airtight overinsulated house without AC in an urban environment would become unlivable. However this state of affairs is not likely to continue for long. The recent (or is it still current?) UK heatwave is quite an anomaly - although one suspects not as bad as the heatwave of August 1911.....

Jul 10, 2015 at 2:33 PM | Unregistered Commenterchris moffatt

What might surprise most people is that insulation works both ways! It not only keeps the heat in on cold days, but it also keeps the heat out on hot days. What you do have to do is to ensure that your house is well-ventilated, to prevent heat build-up from your own activities (If you can’t stand the heat, get out of the kitchen – would that ring any bells?).

Jul 10, 2015 at 2:35 PM | Registered CommenterRadical Rodent

I'd add that I've been asked in to look at a couple of eco-standard newbuilds where the GSHP installers were morons and the system settings and configurations were resulting in the houses having to leave the (triple glazed) windows open :-)

If the insulation heat budget is modified past the point where say the radiative heat (that greenhouse effect) through large windows is large compared to losses... eventually a thriving market in blinds emerges - folk who own conservatories which are in the sun for much of the day are only too well aware of this (it's that sun again).

I find the traditional Venetian blind quite effective....

(UK!) Housebuilders.... the people who build "garages" where even the owner of a Smart car can only get in and out of their vehicle if it has a sunroof.

Jul 10, 2015 at 2:36 PM | Registered Commentertomo

25C is unhealthy...really? We set our air conditioner to cool our house to 25C. My house is a modern Canadian home so it is very well insulated and sealed..and why we have a air exchange system (to remove odorous air). On a hot summer day (over 30C), if the house is empty, we leave the windows closed and covered and it stays cool all day. We will only use the a/c when people are home and the appliances/electronics are in use...and the main benefit is lowering the humidity.

Jul 10, 2015 at 2:38 PM | Unregistered CommenterMike W

Are "apparently large" people more vulnerable to changes in temperature, than those who "apparently" are not?.

Couldn't "apparently large" people get a green grant for ears the size of elephants, to help them cool down? Obviously they might also need larger doors to get into their houses.

Jul 10, 2015 at 2:46 PM | Unregistered Commentergolf charlie

A one storey villa (so called) in the Oman I once used had shrubs growing on one side and not the other. Those shrubs really protected the rooms their side. Air con wall units on other side rooms were useless. 45Deg C, but the sea was nearby luckily....and the beer!

A flat I have in London (top floor of two) fries usually with 4 inches insulation on...another 8 inches to go on next. Cannot grow anything near the flats of course, so its exposed badly.

Just imagine..air con units sucking on windmills?

Jul 10, 2015 at 3:19 PM | Unregistered CommenterEx- expat Colin

Australians everywhere are shocked to learn that their health has been endangered for at least six months of every year when the ambient daytime temperature and in many places thoughout most of the nights have hovered above 25C. Oh dear, how sad, never mind, don't cry. Once again, bulltish baffles brains.

Jul 10, 2015 at 3:19 PM | Registered CommenterMique

Can we remember the libertarian issues here as well as the eco-rubbish?
The insulation in my house is no business of government provided it reaches minimum standards, neither is the extent to which I recycle waste, the speed at which I drive (safely), the fuel I choose to burn (if it is safe for other people), the salt,sugar and fat in my food, the type of engine I have in my car. Are we free people or slaves?

Jul 10, 2015 at 3:29 PM | Registered CommenterDung

Someone should have posted the Fahrenheit equivalent of 25C so us Americans could understand the point. Okay. It equals 77F. Now, if that poses a health problem there would be no Mexicans left to migrate north.

Jul 10, 2015 at 3:30 PM | Unregistered CommenterJimB

Those who live in summer over-heated EcoHouses should go to church more often.

The traditional type, with small % window-area, solid walls 1.5m thick, stone floor without carpet, and a poorly insulated roof 4.5m above their head.

Jul 10, 2015 at 3:30 PM | Unregistered CommenterJoe Public

Yes, I had a chuckle about the 25C thing, too. We Aussies must be tough lot - not to mention hundreds of millions of Asians.

The trick is to keep the house closed and windows covered during the day, and open everything up at night. But I imagine that in dwellings where there is poor or no cross-ventilation, the cooling effect at night would be greatly decreased.

That said, I do use aircon in summer - but our heatwaves are an annual event and last considerably longer than yours.

Jul 10, 2015 at 3:39 PM | Registered Commenterjohanna

Not just ecohouses but well insulated old houses will have the same problem. The temperature in my living room last week was approaching 30 degrees C.

I wonder how many on the "Green Deal" will suffer from heat stroke in future hot weather.

Jul 10, 2015 at 3:46 PM | Unregistered Commentercharmingquark

Can't she open a window?
Isn't it cold more often than warm?

Jul 10, 2015 at 3:50 PM | Unregistered CommenterMikeN

It is not just insulation, but ventilation. One of the ways they achieve such great insulation is to reduce windows or only have them on one side of the building. This eliminates cross-drafts which are necessary to cool. To say you are "keeping the heat out" is only sensible in the short-term (hours). After that, your apartment will equilibrate to the outside with some lag. In addition, any dwelling gets warm from lights and appliances. Insulation keeps this in.
There is generally wisdom in the historical style of housing in use in an area. In very cold climates, steep roofs let the snow slide off. In the US South, the old style (pre-air conditioning) house had wide-roofed porches all the way around which acted like wearing a hat--it kept the sun off but allowed air in. They also had high ceilings. This made them act like a cave and kept the cool night air in longer. In general, the focus of eco-houses is on one season only, like winter, to save on heating bills, and they ignore summer.

Jul 10, 2015 at 3:50 PM | Unregistered CommenterCraig Loehle

I don't think this story's got legs Bish. I have a fully insulated house and provided we keep the curtains drawn and prevent as much sunshine coming into the house as possibleon sunny days it stays cool. As for 25C being bad for your health - sounds like the sort of stuff the greenies put out hoping no one will check.

Jul 10, 2015 at 3:56 PM | Unregistered Commentergeronimo

Many houses in Belgium have white external blinds on south facing windows. Is that not the obvious answer for well insulated houses. Stop them warming up during the day? Or is that too obvious?

Jul 10, 2015 at 4:08 PM | Unregistered CommenterTed

Cross-ventillation is the solution, because you're fine provided you can open enough upstairs windows on two sides of the house in the evening.

Of course you then can't go out and leave the house unattended, because it's not secure against burglars with its windows open, so you may want to fit wrought iron grills across some of your windows like in hotter parts of Asia.

Jul 10, 2015 at 4:17 PM | Unregistered CommenterPete Austin

Passive ventilation

That's why sash windows were invented, seen any lately?

Open the top and bottom panes a little, hot air flows out the top and fresher air comes in the bottom.



Jul 10, 2015 at 4:27 PM | Unregistered CommenterGG

What's wrong with insulated curtains, whitewashing the windows as per greenhouses (readily available at garden centres and DIY stores), and opening the windows and curtains at cool times of the day/night. For the 2/3 weeks of the year when it gets quite warm in the UK a little effort works wonders.

I was aiming for 25'C in the house during winter months, nice and warm and no need for a pullover.

Jul 10, 2015 at 4:30 PM | Unregistered CommenterSandyS

How is it that my French house built 100 years ago with 18" thick stone walls and wooden shutters is currently 22 degrees inside whilst it is 31 degrees outside in the shade? Did these old builders hold some secret knowledge that has been lost in the mists of time?

Seriously. I have double glazing, 2" insulation on the inside of 18" stone walls inner white plastic shutters and exterior wooden shutters which I shut onto the latch in the hot weather. The people opposite me have new houses and they all open all their windows when I shut mine at 11 am. I stay cool and they get cooked. Rocket science it ain't.

My house in Cornwall says it is 22degrees outside there according to Nest. They think they are having a heatwave!

Jul 10, 2015 at 4:33 PM | Unregistered CommenterIvor Ward

People talk about ventilating the space yet the same Daily Mail ran an article during the recent heat-wave (!) saying that windows should be left closed as the outside air was undoubtedly warmer than the air inside so all you were doing was allowing warmer air to heat your house. D'oh. Written by someone with not a very good grasp of how air movement works.

Jul 10, 2015 at 4:50 PM | Unregistered CommenterHarry Passfield

In South Wiltshire at 400' I have not been as cold in summer under my double thatched roof as I was in Milnathort in June in the early '90s. I have to go outside to warm up - or it's fingerless mitts & hat on at the desk

Jul 10, 2015 at 4:52 PM | Unregistered CommenterVictoria Sponge

Anyone else see the irony that zero carbon construction creates greenhouse conditions????

Jul 10, 2015 at 4:56 PM | Unregistered CommenterAJStrata

In underground mines where heat conduction from hot exposed rock heats the air to 28C companies are required to cool and circulate air to prevent worker heat stress. Normally they'll refrigerate incoming air to below 20C and make sure it keeps moving. Stagnant non-moving air is the problem area and so in many mines you could almost fly a kite in many drifts.
I would think an eco-house should have some form of an air circulation system or the owner can simply install a fan in a window to make it move. Seems rather silly that the occupant hasnt thought of this??

Jul 10, 2015 at 6:01 PM | Unregistered Commentermikegeo


Grew up in Central America, about 835 miles north of the equator. Nocturnal temps only dropped below ~80F for a couple weeks in January and early February. Daytime highs are persistently in the body temp range, ca. 98F, no relief ever, and the humidity is dauntingly wet.

A well built house has large roof overhang, no insulation, and interior courtyards also with large overhangs. Clerestory windows without shutters serve as heat vents on most of the outside walls.

Dwelling temperatures are kept manageable by two methods. Unglazed tile floors are wet mopped once or twice a day. You have to be there to understand the enormous power of evaporative cooling, even in a high humidity environment. The afternoon storms from late May to November always knock down the temp by 15F or so, and produce cool downdrafts that flood into the courtyards and displace the warmer air out the clerestory windows.

The first time I went to Europe, I was gobsmacked by the insanity of zipping up a house to keep out the heat. What a quaint notion. I was not surprised at the high mortality rates from the '03 heatwaves. The mechanism is well known, warmth causes sweating that dehydrates the person. Can be lethal for old people. Just look up the age distribution of the extra mortality from that summer, and location... Many died in lightly staffed nursing homes, where many staff were on vacation. Lack of hydration can be deadly, not heat per se.


Jul 10, 2015 at 6:37 PM | Unregistered CommenterGlennDC

It's these air-tight houses that you have to worry about ...

But in a normal modern 1970s house with small windows and plenty of insulation, it is too hot to sleep upstairs during warm summers, even with the windows open. There is just not enough air movement outside to ventilate. If I ever build a house for myself, in the current climate of building regs, the bedrooms will be downstairs.

But hey, can't we run air conditioning off solar panels? The perfect free energy, when the sun is hottest, that is when we need the most AC? Anyone got figures for this. With a roof-ful of solar panels, can that fully run AC on a sunny summer day?

Jul 10, 2015 at 6:48 PM | Unregistered CommenterMax Roberts

Also in the Mail: "Climate change deniers are conspiracy theorists and are damaging the public debate on global warming, study claims".

Jul 10, 2015 at 7:06 PM | Unregistered CommenterBudgie

People that complain about 77F could well believe the world is doomed.

Jul 10, 2015 at 7:30 PM | Unregistered CommenterTmitsss

I start to melt around 21 C. I live in the 2nd wettest/2nd cloudiest place in the UK. Summer heat is a problem for me, even here. Especially at night. I will be more vigilant about airflow in the future. I understood it, but didn't take it seriously enough.

Jul 10, 2015 at 7:54 PM | Unregistered Commenteresmiff

Air temperature is a long way short of being the whole story, the body gains a lot of heat from condensation of water vapour, some from one's own evaporated sweat, some from ambient humidity.

The modern trend is towards air-conditioning, but for me a key (possibly life-saving) technology is a large electric fan, to blow away most of my evaporated sweat and layer of hot air before it can act back on me.

Jul 10, 2015 at 7:54 PM | Unregistered CommenterMikky

[OT]Disappointed to see no mention of the emetic 7:20am Toady interview with Richard Allen in which he impartially assures listeners that the 'pause' no longer exists because it's been renamed and anyway the heat is hiding in the oceans, and that we must all wish godspeed to our gracious rulers when they meet in Paris to save us from our immoral consumerism later this year.

Jul 10, 2015 at 8:02 PM | Unregistered CommenterJake Haye

Stay in any modern hotel and the rooms are horribly warm. The first thing I do when I get into one is make sure the heating is very definitely off, and if there is AC then that goes on. Otherwise its open the windows as wide as you can, which in many modern hotels is not far, if at all.
Our neighbor commented at Christmas that he had noted we had the window to our bedroom open at night, we live in a stone built Victorian detached in Huddersfield, even in winter its still to hot for me at night.

Jul 10, 2015 at 8:41 PM | Unregistered CommenterDaedalus

"...the sort of stuff the greenies put out hoping no one will check."

They seem to do that a lot, and of course the media helpfully doesn't check, and in fact most often declines to listen to anyone who does check.

Jul 10, 2015 at 11:42 PM | Unregistered CommenterPiperPaul

Just install a fan to evacuate the loft space in the hottest days.

Jul 10, 2015 at 11:53 PM | Unregistered CommenterMooloo

Law of unintended consequences - thermal insulation qualifies, along with; diesel cars, biofuels, pollution from manufacturing PV cells, wind turbines et bloody cetera - as they say.


As Dung said [I think], that if, you like a drafty house with single glazed windows and old stone walls, is cool in summer and a bollock freezer in winter and you don't mind the bills - that's your choice, innit?

It takes a time to get used to the tropics, if you are lucky enough to travel.

When we have warm weather in the UK, we need to take time to adjust, having good insulation can be a curse in new build houses but particularly flats and apartments - where you cannot adjust aught particularly if you are one of the unfortunates - ie renting.

But cripes, if it is warmer outside - don't open the bloody windows [unless you live in a Moorish built villa] and particularly if there is no through draft ventilation - you are going to make the inner Temp increase.
I find 25°C is bearable but not comfortable, humidity levels are what usually makes life uncomfortable but fortunately a British summer only lasts 3 days, any longer and you have to get used to it and make damn sure you visit vulnerable friends and loved ones to make sure they are drinking enough fluids - and: water only during the day.

It does get warm in the UK - sometimes and we should embrace it - but then what would we do - we'd have nothing to moan about - NATURAL Global warming its so f*****g luverly!

Jul 11, 2015 at 1:45 AM | Unregistered CommenterAthelstan.

Most appear to be thinking home insulation is cause of overheating. Hmm. Insulation just stops the transfer of heat across the "delta T" (change in temperature) direction. Hot to cold or cold to hot. Ventilation--by design or through leaky windows, or other flaws, is the other path for heat to move across the "delta T". Without looking at the specs for he new homes, it's probably they have inadequately designed and operating ventilation?

Jul 11, 2015 at 5:54 AM | Unregistered Commenterrms

Average day time temp in SW France (summer) 27°C. It regularly passes over 35°C. Deaths in 2003 were due mostly to lack of intake of water.

The French vacate Paris in the summer leaving their elderly on their own. Many apparently did die but the temp was regularly above 38°C by day and not below 28°C at night. Insulation standards are still very poor in france but new houses have to have similar levels to the UK.

Jul 11, 2015 at 9:59 AM | Unregistered CommenterStephen Richards

Watching 'green' accredited houses proclaim themselves as hermetically sealed and pass the acid test of minimal leakage under positive pressure is a recipe for auto-digestion, sickness and fetid accumulation. Contrast the elegant house in the tropics, large verandas, open walls and endless shade, allowing anabatic and katabatic breezes free reign. In colder climes, hermetic sealing is not the answer. Energy is the answer, both for heating and for management. Otherwise, pack your bags and head southward.

Jul 11, 2015 at 10:05 AM | Unregistered CommenterManfred

As a child many years ago I remember holidays in southern Europe. In the heat of the day, a visit to an old church or castle was always pleasant. Great big thick walls, stone floors, high ceilings and narrow windows made them nice and cool in hot weather.

Of course when the Normans started building in similar style in England, it made for cold and drafty buildings in winter, that remain expensive properties to heat for their current owners.

Jul 11, 2015 at 10:36 AM | Unregistered Commentergolf charlie

Irish Air Conditioning here in Dublin operates as follows. (we have a bungalow).

Open front door fully. Keep door open with heavy item.

Open back door fully. Keep door open with heavy item.

Check both doors open.

Open internal kitchen door (leads to hallway) and air begins to flow.

Open other room doors and windows off hallway as required.


Jul 11, 2015 at 11:04 AM | Unregistered CommenterPeter Walsh

Budgie (Jul 10, 2015 at 7:06 PM): it is refreshing to note the number of sceptical comments – we are not alone. I do wonder in the DM is deliberately stirring it to raise awareness amongst the sheeple.

Jul 11, 2015 at 11:29 AM | Unregistered CommenterRadical Rodent

Peter Walsh, and others, if you live in a pitched roof house, and are able to open windows (or doors) downstairs) then opening the roof access hatch normally creates a mild chimney effect, drawing cooler air in, and allowing it to rise and exit through the ventilated roof.

Insulated roof spaces do get hot in sunshine, and stay warm during windless nghts, s there is no up draught of cooler air from the lower floors.

Not advisable if your roof space is occupied by maneating mice/pigeons/wasps etc

Jul 11, 2015 at 11:31 AM | Unregistered Commentergolf charlie

Just wait for it... build cave homes. Take the dirt, make farm land or fill in the Channel. Great Green stuff.

Jul 11, 2015 at 12:20 PM | Unregistered Commentercedarhill

Unfortunately the worst offender in this respect is not insulation, but triple glazed and LARGE picture windows. These are added in to the equautions of 'low energy' on the basis that winter sunlight can actually warm a room,. and so indeed it does, but unless you keep it OUT of summer rooms, it warms them a whole lot more, and indeed opening the windows is not the answer, because te air temperatures outside can also be well in excess of comfortable.

The answer is to add something that is in no building regulation at all. Lots of concrete or other thermal mass INSIDE the insulation to act as both a heat bank in winter and a cold bank in summer.

The optimal low energy house has a highly insulated shell, with heat recovery ventilation, and large windows BUT it also should have masses of concrete or brick inside the shell to stabilise day to might temperatures, and it should also have overhanging eaves to let low level winter sunlight in, but keep summer sun out. Also shutters and curtains help.

This does not really fi with cheap flats however. Perhaps balconies could provide the overhang, but its rare to have significant internal mass in a flat. Unless its all built out of steel and concrete,.

Jul 11, 2015 at 12:22 PM | Unregistered CommenterLeo Smith

The "award-winning" architects should of course be required to live in one of these sweat-boxes before foisting them on the less well off.
Trouble is they all aspire to a nice Georgian town house or a Victorian country vicarage with all the original windows and with biomass boiler so you can actually make money the more fuel you use.

Jul 11, 2015 at 3:20 PM | Unregistered CommenterJack Savage

Interesting, Leo. I once lived in a beautiful passive solar house, designed by a local disciple of Frank Lloyd Wright. Nearly it's entire south side was glass with a large overhanging eave which perfectly blocked summer sunlight and perfectly admitted winter sunlight.

It was also built in an era of extremely cheap natural gas. When I replaced the roof, they told me the original R factor was one. The gorgeous two sided fireplace drew poorly and we abandoned its use.

Wish I still lived there.

Jul 11, 2015 at 3:38 PM | Unregistered Commenterkim

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