Designing a British House for 35°C Summers AND -5°C Winters
Designing a British House for 35°C Summers AND -5°C Winters
The British house of the future needs to keep heat out in August — and keep it in during January
For generations, the central challenge of British house design was fairly straightforward: how do we keep warm?
We insulated lofts, fitted double glazing, sealed draughts and installed increasingly efficient heating systems. Much of that was sensible, and it remains sensible.
But the problem is changing.
The Met Office reported in July 2026 that in parts of south-east England we are increasingly coming to expect temperatures around 35°C during hot spells. The most recent decade, 2016–2025, was 1.33°C warmer than 1961–1990, while the hottest day of the year has warmed by more than 4.5°C across parts of south-east and eastern England.
Yet Britain has not suddenly become southern Spain.
We can still wake to frost, ice, freezing fog and temperatures below zero in winter. We still need heating. We still need insulation. We certainly don't want to design houses that throw valuable winter warmth away merely because summers are becoming hotter.
That creates an interesting engineering problem:
How do we design a house that is comfortable at 35°C outside in August but equally comfortable when it is -5°C outside in January?
The answer isn't simply air conditioning.
It is better design.
We Have Been Designing Primarily for Winter
Walk around almost any modern housing development and you will see enormous areas of glass.
French doors.
Patio doors.
Rooflights.
Floor-to-ceiling windows.
Large south- and west-facing windows.
They look wonderful.
On a bright February afternoon, they can also be useful. Solar radiation enters the house, warms surfaces inside and contributes some free heating.
But put exactly the same house through several cloudless days at 30–35°C and that beautiful expanse of glazing can become an enormous solar collector.
And unlike a solar panel, its output isn't necessarily wanted.
This is one reason England now has a specific Building Regulations requirement dealing with overheating in new residential buildings. Approved Document O addresses overheating mitigation, while Part L continues to address energy efficiency.
The challenge is therefore no longer simply:
"How little heating can this house use?"
It should increasingly be:
"How little heating AND cooling can this house require throughout the year?"
That is a much more interesting question.
1. Stop the Heat Before It Gets Through the Window
Perhaps the biggest lesson Britain could borrow from hotter countries is remarkably simple.
Shade the window from outside.
We tend to fit curtains and internal blinds.
They help.
But by the time sunlight has passed through the glass and struck the blind or curtain, much of that solar energy has already entered the building.
External shading intercepts the sunlight first.
CIBSE specifically recommends external shutters, awnings, external blinds and overhangs as effective ways of reducing heat entering homes, and notes that external shading is substantially more effective than relying solely on internal blinds.
That could mean:
- retractable awnings over patio doors;
- external roller blinds;
- traditional shutters;
- sliding louvred screens;
- pergolas;
- roof overhangs;
- brise-soleil;
- deciduous planting outside windows.
This doesn't mean making the house permanently dark.
That is the important point.
Good shading should be seasonal.
In July, block the high summer sun.
In January, allow the low winter sun inside.
2. The Humble Awning Could Become Much More Common
A retractable awning is almost absurdly simple compared with installing an air-conditioning system.
Extend it on a hot sunny day.
Retract it when you want daylight or winter solar gain.
Imagine a south-facing kitchen with large bi-fold doors.
Without shading, perhaps three or four square metres of glazing are exposed to strong sunlight for hours.
Close a curtain and the room becomes darker, but the glass and space between the curtain and window still become hot.
Put an awning outside and much of that sunlight never reaches the glass.
This is exactly the sort of modification that could make existing British houses considerably more adaptable without rebuilding them.
And importantly, when December arrives, roll the awning back in.
The sunlight becomes useful again.
3. Perhaps Shutters Deserve a Comeback
We sometimes think of shutters as a Mediterranean architectural feature.
But Britain may increasingly have good reason to reconsider them.
A well-designed shutter could perform several jobs.
During summer it could prevent direct solar radiation hitting the window.
During a storm it could offer additional protection.
On winter nights an insulated shutter could potentially provide another barrier between a warm room and the cold outdoors.
And unlike permanent solar-control glazing, it can be moved.
That last point matters enormously.
A house designed for Britain's future climate should increasingly include things that change with the season.
Fixed solutions inevitably involve compromises.
Moveable solutions can adapt.
4. Don't Abandon Insulation Because Summers Are Hotter
This is where overheating discussions can become confused.
If insulation keeps heat inside during winter, surely it keeps unwanted heat inside during summer?
Yes — but that doesn't mean insulation is the problem.
Good insulation slows heat transfer in both directions.
If your house is cooler than outside on a hot afternoon, insulation helps slow heat entering through the roof and walls.
The problem occurs when heat is allowed into the building through unshaded windows, cooking, appliances and occupants and then cannot escape.
So the answer isn't to remove insulation.
It is:
insulate well + control solar gain + ventilate intelligently.
That combination matters.
Modern overheating guidance similarly treats shading, glazing and ventilation as interconnected design issues rather than viewing winter energy efficiency in isolation.
5. The Roof May Matter More Than We Think
On a sunny summer afternoon the roof takes an enormous amount of solar radiation.
That makes loft insulation valuable in both winter and summer.
During winter it slows heat escaping upwards.
During summer it slows heat moving from an extremely hot roof and loft into the rooms below.
There may also be a growing case for thinking about roof colour and materials.
Dark surfaces generally absorb more solar radiation than pale or reflective ones.
That doesn't mean every British roof should suddenly become brilliant white.
Planning restrictions, appearance, materials, weathering and surrounding buildings all matter.
But when choosing roofing materials for new buildings or extensions, their summer thermal behaviour deserves much more attention than it often receives.
The same thinking applies to flat roofs, garages, extensions and conservatories.
6. Window Orientation Matters
Not all windows behave equally.
A north-facing window receives relatively little direct solar radiation.
A south-facing window can receive substantial solar energy, but it also lends itself quite well to carefully designed horizontal shading because the summer sun is high while winter sun is lower.
East-facing windows can create surprisingly hot rooms in the morning.
West-facing glazing can be particularly troublesome because strong afternoon and evening sunshine arrives when the building has already been heating throughout the day.
This is why simply saying:
"We'll put lots of glass on the back of the house"
isn't really enough.
We need to ask:
Which direction does the back face?
England's Approved Document O explicitly considers façade orientation and glazing area when assessing overheating risk.
For a new house, I would therefore think carefully before covering an entire west-facing elevation with glass.
The view may be magnificent.
The July temperature may not be.
7. Keep Some Winter Solar Gain
We shouldn't overreact and try to eliminate sunlight entirely.
Winter sunshine is useful.
Imagine a cold but bright January day.
Outside temperature: perhaps 2°C.
Inside target: around 19–21°C.
Sun streaming through south-facing windows can contribute towards warming the building.
If we permanently block that sunlight with oversized fixed structures or extremely dark glazing, we may simply increase our winter heating requirement.
The clever design is therefore one that says:
Summer sun: stop outside.
Winter sun: welcome inside.
A correctly positioned roof overhang is a wonderfully simple example.
The high summer sun strikes the overhang and shades the window.
The lower winter sun passes beneath it.
No electronics.
No motor.
No app.
Just geometry.
Sometimes the best smart-home technology is something that doesn't require electricity at all.
8. Cross-Ventilation Needs to Be Designed In
Opening a single small window in a hot bedroom isn't necessarily good ventilation.
For effective natural ventilation, we ideally want air to enter somewhere and leave somewhere else.
That means thinking about cross-ventilation.
Windows or openings on opposite sides of the house can allow moving air through the building rather than merely into one room.
Doors, landing layouts, staircases and high-level windows can all become part of the airflow pathway.
CIBSE recommends opening windows when the outdoor air has become cooler than the indoor air — commonly later in the evening, overnight and early in the morning — and using openings in different rooms to encourage cross-ventilation. It advises the opposite during the hottest part of the day when outside air is hotter than the interior.
That leads to a slightly counterintuitive summer routine.
At 6am:
Open the house.
At 9am:
Close it.
At 2pm:
Shade it.
At 10pm:
Open it again.
The objective is to trap the coolness rather than trap the heat.
9. Night-Time Cooling Could Become Part of Normal British Life
Many Mediterranean homes have long followed this pattern.
British households traditionally haven't needed to.
We may need to learn.
If a house can fall to perhaps 19–21°C overnight, then keeping windows and external shading closed through the hottest part of the following day can delay the rise in indoor temperature.
That is especially powerful when combined with thermal mass.
But security matters.
Noise matters.
Pollution matters.
Ground-floor windows cannot always simply be left wide open throughout the night.
So future houses might incorporate secure ventilation panels, protected openings, louvres or other features designed specifically to provide summer night ventilation without compromising security.
A window isn't merely a source of daylight.
It is becoming part of the home's climate-control system.
10. Thermal Mass: Make the Building Work Like a Thermal Battery
We talk frequently about electrical batteries in green homes.
Buildings can also store energy thermally.
Concrete, brick and stone can absorb substantial amounts of heat.
That can be useful.
Suppose cool night air lowers the temperature of a concrete floor.
The following morning the heavy structure begins relatively cool.
As the day heats up, the building fabric can absorb some of that energy rather than allowing room temperature to rise immediately.
Then, when night arrives, ventilation can remove the stored heat.
So the daily cycle becomes:
cool the thermal mass → absorb daytime heat → release it at night → repeat.
But thermal mass isn't magic.
A large mass of masonry that becomes progressively hotter during a prolonged heatwave can eventually become a liability.
It works best when there is some way to discharge that stored heat, particularly through effective night ventilation.
CIBSE has likewise argued for passive measures such as shading, reduced glazing and thermal mass to be considered before falling back on mechanical cooling.
11. Trees Could Become Part of the Heating and Cooling System
This is perhaps my favourite solution because it combines engineering with nature.
Plant a deciduous tree in the right place.
During summer it develops a canopy of leaves and shades windows, walls and perhaps part of the roof.
Then autumn arrives.
The leaves fall.
Winter sunshine reaches the house again.
That is remarkably sophisticated seasonal solar control from something that requires no motor, wiring or computer.
There are other advantages too.
Trees contribute habitat.
They provide shade in the garden.
They improve the appearance of the property.
Their leaves intercept rainfall.
But positioning matters.
We don't want roots damaging buildings or drainage.
We don't want to remove so much daylight that the house becomes gloomy.
And a newly planted tree won't provide instant shade.
This is planning for ten, twenty or thirty years ahead.
Which is exactly how we should be thinking about houses.
12. The Garden Around the House Matters Too
Climate adaptation doesn't stop at the brickwork.
Imagine two otherwise identical houses.
One is surrounded by dark paving, artificial grass, gravel and bare fences.
The other has planting beds, shrubs, trees and areas of natural vegetation.
Their immediate microclimates may feel very different on a hot afternoon.
This doesn't mean paving is inherently bad.
But it means we should start thinking about the garden as part of the home's environmental design.
Perhaps the future British garden isn't simply decorative.
It helps manage:
summer shade;
rainfall;
biodiversity;
wind;
water storage;
and the temperature around the home.
13. Conservatories Need Particular Attention
Britain has thousands of conservatories that were designed partly around the idea that collecting sunlight was desirable.
In spring and autumn, wonderful.
During a heatwave, less wonderful.
If designing one now, I would put far more thought into:
external roof shading;
solar-control glazing;
opening roof vents;
cross-ventilation;
insulated solid roof sections;
and whether the room really needs glazing on every available surface.
Again, the answer isn't necessarily mechanical air conditioning.
The first question should be:
Can we stop the heat getting in?
CIBSE describes this as a "passive first" approach: exclude unwanted heat, remove the heat that does enter, and only then consider mechanical cooling.
14. A House Should Be Able to Change With the Weather
Perhaps the biggest mistake would be trying to design one permanently fixed configuration that is perfect every day of the year.
Britain doesn't have that kind of climate.
Our homes need different operating modes.
Winter Mode
Curtains open when sunshine is useful.
Shading retracted.
Heating running efficiently.
Windows mostly closed.
Heat retained by good insulation and airtightness.
Solar gain welcomed where appropriate.
Summer Day Mode
External shading extended.
Sun-facing shutters or blinds closed.
Windows closed once outside becomes hotter than inside.
Heat-producing appliances used less.
The insulated building envelope helps protect the cooler interior.
Summer Night Mode
Shading opened where appropriate.
Windows or secure vents opened.
Cross-ventilation encouraged.
Stored heat purged from the building.
Thermal mass cooled ready for tomorrow.
That is the key idea.
The house isn't passive in the sense of doing nothing. It is passive in the sense of using physics before electricity.
15. What About Air Conditioning?
I don't think we should pretend that mechanical cooling will never be necessary.
There may be homes where passive cooling simply cannot provide sufficient comfort.
Top-floor flats can be particularly difficult.
So can heavily glazed apartments, urban homes affected by noise or pollution, and homes occupied by people particularly vulnerable to heat.
Heat pumps that can provide cooling may increasingly have a role.
But I would still treat mechanical cooling as the final part of the solution rather than the first.
Installing air conditioning into a badly designed house while allowing huge amounts of sunlight to stream through unshaded west-facing windows is rather like turning the heating up because someone has left the front door open.
Fix the building first.
Then determine how much active cooling is genuinely required.
16. Retrofitting the House You Already Have
Most of us aren't going to knock down our houses and start again.
That is why this subject needs to be practical.
If I were assessing an ordinary British house for hotter summers, I would work through the following priorities:
- Identify the hottest rooms. Which become uncomfortable first, and at what time of day?
- Work out which windows receive direct summer sun. West- and south-facing glazing deserves particular attention.
- Add external shading where practical. Start with awnings, shutters, screens or pergolas before expensive cooling equipment.
- Improve loft and wall insulation. It remains important in both seasons.
- Check whether cross-ventilation is actually possible. Can air travel through the house rather than entering one room and stopping?
- Develop a night-cooling strategy. Work out which windows can safely remain open.
- Reduce internal heat gains. LEDs, efficient appliances and avoiding ovens and tumble dryers during the hottest afternoon hours all help; CIBSE specifically recommends shifting heat-producing appliance use away from the hottest period.
- Add deciduous shade planting.
- Think carefully before adding more large areas of glass.
- Only then assess mechanical cooling.
That could become another element of the Green Home MOT: not simply asking whether the house wastes heat in January, but whether it collects too much heat in July.
17. My Own Thinking About the Green Home Has Changed
I have spent years thinking about how to make our own home more energy efficient — adding insulation, solar generation, battery storage, solar hot water and moving towards an all-electric home with a heat pump.
Much of that thinking naturally concentrated on reducing purchased energy and getting through winter efficiently.
But increasingly I think there is another question we have to ask:
What happens when the summer temperature outside is higher than the temperature we want inside?
At that point the problem reverses.
Instead of preventing heat from escaping, we are trying to prevent heat from entering.
The interesting part is that many of the investments still help.
Insulation still helps.
Efficient appliances still help.
Solar panels can provide electricity when cooling demand is greatest.
A heat pump may potentially provide both heating and cooling depending on the system.
But the building itself needs to become more adaptable.
I would now put summer shading much higher on the list of things I would consider when designing my ideal green home.
18. The Cheapest Cooling System May Be a Piece of Shade
There is something slightly absurd about allowing several kilowatts of solar energy to enter a room through the windows and then using electricity to pump that heat back outside.
Sometimes technology is necessary.
But sometimes the answer is an awning.
Or a shutter.
Or a tree.
Or opening the correct windows at the correct time.
Good environmental design doesn't mean filling a house with technology.
It means using technology where technology genuinely improves the solution — and using simple physics everywhere else.
19. What I Would Put Into a New British House
If I were building a house now, I would want the architect to model both winter and summer performance from the beginning.
I would ask about:
High insulation levels
to reduce winter heat loss and summer heat gain through the building fabric.
Careful glazing ratios
rather than automatically fitting enormous windows everywhere.
External retractable shading
especially on vulnerable elevations.
South-facing overhangs
calculated to reject high summer sunlight while admitting lower winter sun.
Good cross-ventilation
designed into the floor plan rather than discovered after construction.
Secure night ventilation
so the house can cool without creating an unacceptable security problem.
Useful thermal mass
combined with a strategy for cooling it overnight.
Deciduous landscaping
that increasingly shades the building as it matures.
Reflective or heat-conscious external materials
where suitable.
Low-temperature heating
such as a heat pump.
Solar generation
because the days creating the greatest risk of overheating are also frequently excellent days for generating solar electricity.
And I would want one final question answered:
What happens to this house during five consecutive days above 30°C?
Not simply whether it passes an energy calculation.
What actually happens to the people living inside it?
The British House Needs Two Personalities
Perhaps this is the real design change.
The traditional British house had one overriding job:
keep winter outside.
The emerging British house needs two.
In January it needs to wrap itself around us — insulated, airtight and efficient, holding onto every useful unit of heat.
In August it needs to become something different — shaded, ventilated and protected against solar gain.
It needs a winter personality and a summer personality.
That doesn't necessarily require futuristic architecture or enormous expense.
Some of the solutions have existed for centuries.
Shutters.
Awnings.
Deep eaves.
Trees.
Thick walls.
Courtyards.
Ventilation.
Shade.
What is new is Britain's need to take them seriously.
We shouldn't respond to hotter summers by building houses that are colder in winter.
And we shouldn't respond to cold winters by creating highly insulated glass boxes that become unbearable every July.
The clever solution is a house that understands both seasons.
Because the British home of the future won't merely need to keep heat in.
It will need to know when to keep heat out.
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