How to Prevent Overheating in a New Build Home
- Ian Knowles
- 1 day ago
- 8 min read
If you're designing a new home, you'll probably spend a lot of time thinking about how to keep it warm in winter.
Insulation, airtightness, high-performance windows and reducing heat loss are all important parts of designing an energy-efficient house.
But there is another question that should be asked much earlier in the design process:
What will this house feel like during a hot week in July?
Overheating is becoming an increasingly important consideration when designing new homes in the UK.
A highly insulated house with large areas of glazing can perform brilliantly during winter but become surprisingly uncomfortable during hot weather if solar gain, shading and ventilation haven't been properly considered.
The answer isn't necessarily air conditioning.
In many cases, the best place to tackle overheating is on the drawing board.
Why Do New Build Homes Overheat?
Modern homes are deliberately designed to retain heat.
Better insulation, improved airtightness and high-performance windows all reduce unwanted heat loss during winter.
That's exactly what we want.
The problem comes when significant amounts of solar energy enter the building during summer.
Sunlight passes through the glazing and warms floors, furniture and internal surfaces. A well-insulated building can then be very good at retaining that heat.
Combine this with large windows and limited ventilation and internal temperatures can continue increasing throughout the day.
Common factors contributing to overheating can include:
excessive areas of glazing
poorly positioned south or south-facing windows
large unshaded rooflights
limited external shading
rooms with windows on only one elevation
insufficient opportunities for cross ventilation
an inability to safely ventilate the house overnight
building and landscape design that hasn't considered the movement of the sun
The important point is that overheating isn't simply a Building Regulations problem.
It starts with the architecture.
1. Start With the Orientation of the House
One of the first things I look at when developing a design is the relationship between the site, the proposed house and the sun.
Orientation costs nothing.
But it can fundamentally change how a house performs.
The sun behaves very differently on each elevation.
South-facing elevations receive significant solar exposure, but the high summer sun can often be controlled using horizontal shading.
South-facing glazing can be particularly challenging because the lower afternoon sun can penetrate much deeper into a room.
This is also happening late in the day, after the building has already been warming for several hours.
That doesn't mean we should avoid south or South-facing rooms.
It means their glazing needs to be designed deliberately.
When we're developing a new house, questions such as these should be considered alongside the floor plan:
Where will the afternoon sun fall?
Which rooms need the best views?
Where do we actually need large windows?
Can the architecture provide its own shade?
These decisions are considerably easier to make at concept design stage than after planning permission has been granted.
2. Bigger Windows Aren't Always Better
Large areas of glazing have become a familiar feature of contemporary homes.
And used properly, they can be fantastic.
They can provide daylight, views and a strong connection between a house and its garden.
But more glass doesn't automatically create better architecture.
Every large opening should have a reason for being there.
I like to ask:
What is this window actually doing for the room?
Is it framing a particular view?
Providing useful daylight?
Allowing ventilation?
Connecting a kitchen or living space with the garden?
Or has it simply become large because large windows look impressive on an elevation?
Sometimes reducing a window by 20% has very little impact on how the room feels while substantially reducing the amount of unwanted summer solar gain.
Good design isn't about maximising glazing.
It's about putting the right amount of glazing in the right place.
3. Put the Shade Outside
Once sunlight has passed through the glass, much of its energy is already inside the building.
Internal blinds and curtains can help with glare and comfort, but external shading can prevent a significant proportion of that direct sunlight from reaching the glazing in the first place.
This is where architecture becomes particularly interesting.
Solar shading doesn't necessarily need to look like an environmental technology bolted onto the house.
The building itself can provide the shade.
4. Use Roof Overhangs to Control Summer Sun
A deeper roof overhang can protect windows from high summer sun while still allowing lower winter sunlight to penetrate beneath it.
This can work particularly well on south-facing elevations.
The result can be a simple architectural feature doing several jobs:
providing solar shading
protecting the building envelope
creating a sheltered external space
giving the elevation greater depth
strengthening the architectural character of the house
This is the type of passive design decision that can be relatively inexpensive when incorporated from the beginning.
5. Recess Windows Into the Building
Window position matters too.
Rather than placing glazing close to the outside face of the wall, windows can sometimes be set deeper within the opening.
The head and side reveals then provide a degree of natural shading.
On a red brick house, for example, a deeply recessed window can create strong shadow lines across the elevation while simultaneously reducing direct sunlight reaching the glass.
It creates architectural depth and has a practical purpose.
That's something I particularly like in residential design: one detail doing several jobs.
6. Think Carefully About South-Facing Glass
South-facing glazing deserves particular attention.
During the afternoon, the sun is much lower in the sky.
That makes it harder to control using a conventional horizontal roof overhang.
Depending on the site and design, solutions might include:
reducing the overall area of south-facing glazing
deeper window reveals
vertical fins
external shutters
timber screens
strategically positioned trees
designing rooms so they can be cross ventilated later in the day
There isn't one standard answer.
The solution depends on the house, site and how the rooms will actually be used.
7. Don't Forget Rooflights
Rooflights can transform a plan.
They're particularly useful for bringing daylight into the middle of deeper houses and extensions.
But because they face towards the sky, they can also receive considerable solar exposure.
A huge rooflight isn't automatically better than a carefully positioned smaller one.
When designing them, I would consider:
orientation
size
glazing specification
shading
whether the rooflight can open
whether it can contribute to high-level ventilation
Again, the aim isn't to avoid glass.
It's to use it intelligently.
8. Design for Cross Ventilation
Stopping excessive heat entering the building is only half of the equation.
We also need to get unwanted heat out.
Opening one window doesn't necessarily ventilate a room effectively.
Where openings can be provided on different sides of a house, pressure differences can encourage air to move through the building.
This is cross ventilation.
It is something that can influence the floor plan itself.
A dual-aspect living space, for example, can potentially be ventilated from two directions rather than relying on one large set of doors.
High-level openings can also help.
Because warm air rises, opening rooflights or high-level windows can allow warmer air to escape while cooler air enters lower down.
The position of the windows can therefore be just as important as their size.
9. Design for Night-Time Cooling
On particularly hot days, external temperatures may simply be too high to provide much useful cooling during the afternoon.
Once temperatures fall overnight, however, the house has an opportunity to release some of the heat it has accumulated.
That makes night-time ventilation important.
But there is a practical issue.
Can the occupants actually leave the windows open?
Security, noise, privacy and the position of windows all affect how people use a building.
Ground-floor windows might not be suitable for leaving fully open overnight.
Bedrooms facing busy roads may have noise issues.
Good design therefore needs to consider how ventilation will work in reality, not simply on a drawing.
10. Use Thermal Mass Intelligently
Materials can also influence how quickly temperatures inside a building change.
Dense materials such as:
brick
stone
concrete
dense blockwork
can absorb and store heat.
This is known as thermal mass.
Used correctly, it can help stabilise internal temperatures by absorbing some heat during the day and releasing it later when temperatures fall.
But thermal mass isn't a solution on its own.
If excessive sunlight continues entering the building and there is no effective way of cooling it overnight, that material can eventually become warm too.
The best approach is usually to consider:
solar control + thermal mass + ventilation
as parts of the same strategy.
11. Use Landscape Design as Solar Shading
Some of the most effective shading doesn't need to be attached to the building at all.
A carefully positioned deciduous tree can provide substantial shade during summer.
Then, once its leaves fall, it can allow more sunlight to reach the building during winter.
That makes planting potentially useful as part of the environmental design of the house.
Pergolas, climbing plants, hedges and tree canopies can also create cooler external spaces immediately around a home.
This matters particularly around large glazed openings and terraces.
It is one reason I think the house and garden should ideally be designed together.
Landscape shouldn't simply be whatever space is left once the house has been designed.
It can actively contribute to how comfortable that house is to live in.
What Does Approved Document O Mean for New Homes?
Overheating is now specifically addressed within the Building Regulations for new residential buildings in England through Approved Document O: Overheating.
Its purpose is broadly to reduce unwanted solar gains during summer and provide appropriate means of removing excess heat.
But simply achieving Building Regulations compliance shouldn't necessarily be the ambition.
Compliance is the baseline.
For me, the more useful question is: Will this actually be a comfortable house to live in?
That means thinking beyond calculations and considering how someone will experience the building.
What will the kitchen feel like at 5pm in July?
Can the bedrooms cool down before bedtime?
Can windows safely remain open overnight?
Will that large south-facing window become uncomfortable in the afternoon?
Will the terrace actually have somewhere shaded to sit?
These are design questions.
And they are much easier to answer before the house has been built.
When Should Overheating Be Considered?
Ideally, from the first concept drawings.
This is where the biggest opportunities exist.
At concept stage we can still:
rotate or reposition the building
move rooms around
alter window positions
reduce unnecessary glazing
deepen window reveals
extend roof overhangs
introduce cross ventilation
position rooflights differently
coordinate trees and landscaping
consider how the house will perform throughout the year
Many of these changes have little or no additional construction cost.
Once planning permission has been obtained and the technical design is complete, the available solutions become much more limited.
That's when relatively inexpensive design decisions can become expensive retrofit solutions.
Planning a New Build Home in Norfolk?
When I design a new home, I don't think the starting point should simply be how many bedrooms can fit onto the site.
The aim should be to create a house that responds to the site, orientation, views, landscape and the people who will live there.
Summer comfort is one part of that.
So are daylight, winter energy performance, materials, practical room layouts and how the house connects with its garden.
Getting those fundamentals right during concept design can produce a better house without necessarily producing a more expensive one.
If you're considering a new build, self-build or replacement dwelling in Norfolk or Suffolk, I can help explore the potential of the site and develop the project from early feasibility and concept design through planning and technical delivery.
Have a site or an early idea for a new home?
Get in touch with Ikonic Architecture to discuss what might be possible.
Because good architecture shouldn't just look good on a drawing.
It should feel good in July as well as January.
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