Bright Choices: Using Daylight Analysis to Shape a Better Loft

When approached by a client to explore ways of enhancing their loft conversion, the ambition was clear: introduce as much natural light as possible while celebrating the spectacular views across the surrounding countryside. Early design discussions centred on balancing spatial quality, daylight access, budget, and how the changes would impact the existing roofline.

Design Option 1 - Velux Balcony Windows

The first design concept proposed the use of Velux balcony windows. These offered a clever and cost-effective solution that allowed an immersive connection to the outside without significantly disrupting the existing roof structure. The beauty of this option was in its simplicity: when closed, the windows sit flush with the roof; when opened, they unfold into mini balconies that invite the outdoors in. It was a low-intervention idea with high experiential value.

Design Option 2 - Dormer roof with standard glazing

The second design explored the construction of two dormer roofs. These would open up more usable floor area by increasing head height while allowing for larger windows to flood the rooms with light. Within this dormer strategy, two different options were proposed: one with a more restrained amount of glazing and another fully glazed, maximising transparency and visual connection. While visually striking, these came with added complexity. Dormers required a more substantial removal of the existing roof, the construction of new external walls, and bespoke framing for the larger window units, particularly in the fully glazed option, which also included custom mullions and specialist glass.

Design Option 3 - Dormer roof with bespoke glazing

To help guide the decision, daylight analysis tools were utilised, with a particular focus on understanding solar gain and annual sun exposure. As all glazing faced south, there was a risk of overheating, particularly in the fully glazed option. By simulating how much direct sun each scheme would receive during the hottest times of the year, we could quantify the trade-offs between light, heat, and comfort. The analysis showed that the Velux balcony windows brought in significant daylight without dramatically increasing solar gain, while the dormer options offered higher light levels throughout the rooms but also increased exposure to potential summertime overheating.

Quantified Results

The daylight autonomy analysis revealed significant differences between the three options. Using Bristol Airport weather data to accurately reflect the Long Ashton location, the simulation showed that Option 1 (Velux balcony) achieved 65% daylight autonomy, Option 2 (restrained dormer glazing) reached 78%, while Option 3 (maximum glazing) delivered 89% daylight autonomy. These percentages represent the proportion of occupied hours (8 AM to 6 PM) when natural daylight alone could maintain the 300 lux threshold required for comfortable living spaces.

Daylight autonomy analysis comparing three loft conversion options, showing the percentage of occupied hours when natural daylight maintains adequate illuminance levels (300 lux). Results demonstrate the impact of different glazing strategies on daylight distribution across the floor plan.

Bright Ideas, Early On

One of the biggest takeaways from this process is the value of carrying out environmental analysis early in the design stage. At this point in a project, ideas are fluid, and decisions can be tested quickly and affordably. Using climate-based simulation tools allows architects and clients to visualise how daylight, sun, and heat interact with different design proposals: something that's hard to understand from drawings alone. This means we can avoid costly changes down the line and make confident decisions that are backed by real-world performance data.

Counting the Costs

Alongside comfort and aesthetics, cost was a key factor. The Velux balcony solution proved to be the most cost-effective of the three proposals, involving minimal intervention, less labour, and lower material costs. By contrast, the dormer roof options, especially the fully glazed design, required more extensive structural work and bespoke glazing solutions, leading to increased build time and a higher price point. This cost difference was an important consideration, but the design value and long-term comfort benefits of each option also played a central role in the final decision.

Power on the Roof: The Solar Panel Trade-Off

An important layer to the conversation was the roof's south-facing orientation, which made it ideal for installing solar panels. However, each design impacted the available roof area differently. The Velux balcony solution preserved more uninterrupted surface, meaning more panels could be accommodated. The dormer roofs, while adding interior volume, reduced the usable roof space for solar technology. This trade-off introduced another balance between architectural expression and long-term energy performance. In the end, this became a crucial factor in the decision-making process, especially with sustainability as a shared ambition between architect and client.

A Room with a Virtual View

Another invaluable aspect of the process was the use of a detailed 3D model, which enabled the client to explore each design option from the comfort of their own home. Rather than relying solely on drawings or descriptions, they could navigate through the proposed spaces and get a tangible sense of how each scheme might feel in real life. Being able to virtually "walk around" the loft helped them appreciate not only the layout and flow of the rooms, but also the quality of light, the extent of the views, and the overall atmosphere. This immersive experience brought the design concepts to life in a way that was both accessible and engaging, and it proved instrumental in giving the client the clarity and confidence to move forward with their chosen design.

The Client's Choice

After careful consideration of all factors, the client is leaning towards Option 3: the fully glazed dormer design paired with external shutters for solar control. While this option presented the highest risk of overheating, the combination of maximum daylight access and controllable shading offered the best balance of light, views, and comfort. The shutters would provide essential flexibility, allowing the client to manage solar gain during peak summer months while maintaining the spectacular countryside views that originally motivated the project.

Permissions, Planning & Practicalities

As with many loft alterations, we also considered the planning constraints. Velux balconies often fall within permitted development rights, especially when flush with the roofline, while dormer extensions, particularly glazed ones, can require planning approval. These considerations were part of the wider feasibility review, and clients appreciated that design ideas came pre-checked for viability, reducing the risk of delays later in the process.

More Than Just Sunlight

While daylight was a key driver, we also assessed the thermal and visual comfort implications of each proposal. Excessive summer sun can create overheating, glare, and discomfort, especially in highly glazed spaces. Our early climate analysis helped flag these risks and supported balanced decisions that kept future use and comfort in mind. This holistic approach ensured the design was not just beautiful, but also liveable and efficient.

Looking Ahead: Why This Matters

For clients, these early-stage studies aren't just a luxury; they're a powerful tool to de-risk decision making, quantify trade-offs, and balance ambition with performance. For architects, they unlock a richer dialogue with clients, allowing creative exploration backed by data. As part of our service, we include climate-based environmental modelling and 3D walkthroughs to empower our clients with the insight they need from day one.

This project reinforced the importance of integrated design thinking, where environmental performance, cost, and architectural quality are considered together from the outset. The combination of quantitative analysis and immersive visualisation proved essential in helping the client make an informed decision that balanced their aspirations with practical constraints.