Planning a home extension is an exciting opportunity to transform how your home flows, with more space, natural light and a stronger connection to the outdoors.
But while many homeowners focus on layout, doors and finishes, some of the most important design decisions are often overlooked early on. Daylight, ventilation and heat control can have a huge impact on how comfortable and usable the space feels once it’s built.
To help you navigate what really matters, we spoke to Mark Hood, Director of Architecture at Resi, to share practical advice on designing an extension that balances all the important elements.
- Design daylight around how the space will be used, not just layout
- Roof windows help bring consistent light deeper into extensions
- Ventilation and solar control are essential for year-round comfort
Mark’s top tips: Simple ways to make sure nothing’s missed
How do architects design extensions that work day-to-day with light, airflow and comfort built in?
“When architects start designing an extension, we’re usually thinking about how the sun moves across the property throughout the day, from east to west, and how that aligns with how the space will actually be used.
For example, where will someone have their morning coffee? Where will children sit to do homework? Where will the family gather in the evening?
Those everyday activities help determine where natural light should fall. Roof windows often play an important role because they bring light deeper into the space and provide consistent daylight throughout the day.”
Tips:
- Track the path of the sun when planning your roof window placement
- Design daylight around how the space will be used
- Roof windows can deliver more consistent daylight than façade windows
- Position openings so the light reaches deeper areas of the extension
How can you make a deep or north-facing extension feel bright?
“One challenge with relying only on façade glazing is that the light entering from the rear can be affected by shade from neighbouring buildings, trees, fences or walls.
Roof windows capture daylight from above when the sun is highest in the sky, which means they can bring far more consistent daylight into the space, especially in deeper extensions.
They help prevent the middle of a room from feeling dark.”
Tips:
- Facade glazing can be affected by surrounding buildings or trees
- Roof windows capture daylight from above throughout the day
- Roof windows can significantly increase daylight in deeper rooms
- Use roof glazing to brighten the centre of the extension
What common design mistakes do homeowners make with extensions?
“A common issue is that people accept having a darker middle space without realising it can be solved through design.
Architects can introduce solutions like light wells, high-level windows or stepping the extension to create small voids that bring daylight and ventilation deeper into the building.
Without those strategies, the centre of the space can feel dim and sometimes even stuffy.”
Tips:
- Avoid creating dark middle zones in deep extensions
- Light wells can introduce daylight to central areas
- High-level roof windows can brighten deeper parts of a space
- Designing voids can also improve ventilation
Should you prioritise roof windows or bifold doors?
“It’s not really a choice between one or the other, both can work together.
Homeowners often prioritise full-width bifold doors without thinking about how deep the space will be. Large doors mainly bring light into the first few metres of the extension. Beyond that, daylight levels drop off quickly.
Roof windows solve that by bringing light directly into the deeper areas of the room.”
Tips:
- Bifold doors mainly light the front of the extension
- Roof windows help illuminate deeper spaces
- A combination of both often works best
- Leave enough wall space for kitchens or furniture
What would you prioritise when designing your own extension?
“The first step would always be setting a realistic budget and understanding how the extension affects the value of the property.
After that, I’d focus on how the space will actually be used day to day, where people gather, eat or relax.
Once those activities are mapped out, you can design light and ventilation around them, so the space feels comfortable and functional all year round.”
Tips:
- Set a realistic budget early in the process
- Consider the property’s long-term value
- Map out how the space will be used
- Design daylight and airflow around daily activities
Why do some extensions overheat or feel stuffy and how can good design prevent it?
“When you add more glazing to a home, solar gain becomes a real factor, especially in summer. If heat control and ventilation aren’t considered early in the design, the space can become uncomfortable.
Ventilation is something homeowners often overlook because it isn’t a visible feature, but it plays a huge role in how comfortable a space feels day to day.
Openable roof windows can help regulate both temperature and airflow, particularly when paired with blinds or smart systems such as VELUX ACTIVE, which automatically adjust windows and blinds based on temperature, humidity and CO₂ levels.
Thermal comfort is sometimes called invisible architecture, you don’t notice it when it works well, but you definitely notice when it’s missing.”
Tips:
- Plan solar control at the design stage
- Blinds can help regulate temperature in summer
- Managing solar gain prevents overheating
- Comfort depends on both daylight and heat control
Who are Resi?
Resi is the UK’s leading architectural service for home extensions, helping homeowners design, plan and deliver their projects with confidence.
From initial concepts and planning applications to technical drawings, Resi supports homeowners at every stage of the extension journey. Explore Resi and start planning your extension- https://resi.co.uk/
Currently only available in England and Wales