Planning Permission granted for hempcrete ecohouse in Bristol

We’re pleased to share that, after two years of persistence, negotiation, and redesign, planning permission has been granted for a new hempcrete eco-home dwelling on a constrained infill site in inner-city Bristol.

Tucked behind a row of terraced homes and accessed via a shared driveway, the previously derelict site will soon be home to a compact, sustainable family house. It reuses the existing garage structure on site and introduces a timber framed house with hempcrete infill, which will be a unique construction in the city of Bristol.

An Eco-Home that Works with Its Site

The project is defined by its responsiveness both to its tricky site constraints and to the environmental challenges facing the built environment today.

The building has been carefully designed to:

• Minimise embodied carbon, using a timber frame construction and hempcrete insulation, a breathable, biogenic material that will store carbon for the lifetime of the building. We have estimated that the walls alone will store 2 tonnes of carbon.

  
  

• Maximise passive solar gain The dwelling is orientated to face exactly south which allows the house to benefit from passive solar gain. Large roof overhangs mean that the house can benefit from heat from the sun in winter whilst minimising direct sunlight on the hottest summer days.

  
  

• Control overheating through the use of louvre system to reduce incoming sunlight in summer. Deep window reveals and thermal mass of both the concrete base and thick hempcrete walls ensures that the home remains comfortable year-round without mechanical cooling.

  
  

• Minimise heat loss through energy conservation and high levels of insulation which far exceed the minimum levels for building regulations. 500mm thick hempcrete walls have a u-value of 0.13W/m2K.

  
  

• Generate its own energy with photovoltaic panels and solar thermal panels installed on the pitched roof positioned to capture maximum solar exposure through the year.

  
  

• Enhance biodiversity on site through two green roofs, located on the stair tower and flat-roofed garage extension. These provide rainwater retention, thermal buffering, and habitat creation, while softening the building’s visual impact.

  
  

• Reuse existing materials, including the former garage structure, to reduce demolition waste and integrate the new home with the memory of the site.

  
  

The design strategy here isn’t just about ticking sustainability boxes, it’s about designing a home that works intelligently with its environment, built for comfort, durability, and low ongoing energy demand. The aim is to create a low-energy house in both the construction and the dwelling's life span.

The Many Benefits of Hempcrete

Hempcrete is a fantastic material choice which provides a myriad of benefits including carbon sequestration, insulation and thermal mass, to fire protection and sound absorbtion. It is unusual for a material to provide the benefits of a "heavy" material like masonry whilst also providing insulation benefits of a 'light' material which can far exceed the levels required by building regulations for a new-build, which makes it a great choice for an eco home such as this one. We will be sourcing the hempcrete from the UK with some of the first ever UK made hempcrete blocks from Ty Mawr in South Wales.

A Small Site, a Big Effort

Despite the home’s modest footprint, the journey to consent was far from simple. Concerns from planning officers included overlooking, privacy, access, and overdevelopment; challenges familiar to many urban infill projects.We engaged in early pre-application discussions, neighbour consultations, and detailed design revisions, working closely with planning officers across multiple submission rounds. The proposal was ultimately approved for its sensitive relationship to context, thoughtful use of materials, and clear sustainability agenda.

Next Steps

We’re preparing to progress into technical design, to develop detailing strategies that deliver on the project’s low-energy ambition.

Construction is expected to begin late 2025, and we look forward to bringing this carefully crafted, low-impact home to life.

If you’re exploring how to unlock difficult urban sites for sustainable living, or want to understand how eco-materials like timber and hempcrete perform in real-world settings, we’d love to hear from you.

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.

Retrofit Works - An Overview to External Wall Insulation and why you should use it.

If you are thinking about undertaking a retrofit project or looking to self-build a new dwelling, you might be thinking about whether to apply internal, external or cavity wall insulation to the walls in order to improve the energy efficiency. In this post we will explore why you might choose external wall insulation (EWI) over the alternatives and what the various considerations might be for using this approach on your project.

What is External Wall Insulation (EWI)?

External Wall Insulation (EWI) is a way to make a building more energy-efficient by adding insulation to the outside walls of a building, which will reduce heating costs and improve the building's appearance. Insulation boards are simply fixed to the outside of the existing walls and then render or cladding is applied over the top. This creates a high quality and attractive finish.

Woodfibre EWI applied to a passive house project at Wellington Lane

A question we are always asked is whether to apply insulation internally or externally on the exsting walls. EWI is not necessary the right approach for every project but we will explore the potential benefits and the things to consider in deciding whether to take this route.

Benefits of External Wall Insulation over Internal Wall Insulation.

• Increasing the thickness of the wall externally means that you are not loosing valuable space inside your house. As long as you have the room outside then you can make a great contribution to U-value improvement without impacting upon the sizes of rooms.

• Insulating externally brings the opportunity to improve the appearance of a property with an attractive fresh new look.

• Insulation on the outside potentially makes a huge improvement to the internal air quality and health of your building and reduces the risk of mould growth in dwellings. This is because the dewpoint is pushed to the outside of the wall build-up rather than being located somewhere within the building fabric. If you choose to use IWI instead then you need to be really careful about vapour control to avoid condensation forming within the fabric of the wall.

• EWI often provides a much better continuity to the insulation compared to IWI. Often with IWI there are floors or internal walls which are impossible to avoid and creates a cold bridge. With EWI there is opportunity to connect with connect well with "warm roof" buildups.

Considerations and Challenges with EWI

There are some instances where EWI can be more challenging or needs additional work to succeed.

• EWI needs careful coordination with other building elements. Particularly roof eaves, door and window cills. These items should be extended and enlarged to oversail the thickness of the insulation.

• Other building furniture such as gutters, downpipes lean-to structures will need to be removed and then reinstalled, refixed to the outside of the new EWI.

• If you have a cavity wall construction then it is important to make sure that the cavity is filled with a materiel such as cavity wall insulation or the top of the cavity is capped to prevent heat loss through air movement. This can be undertaken during the retrofit.

Lime render finish applied to woodfibre insulation at Wellington Lane

Choosing the Right Insulation Material

There are several types of insulation materials to choose from, each with different benefits. The best option for you depends on your building type, budget, and priorities such as breathability, fire resistance, or affordability. Some common materials are:

• Expanded Polystyrene (EPS): A cost-effective choice for modern homes, lightweight and easy to install

• Phenolic Foam: Offers high insulation performance with a thinner layer, making it ideal for properties with limited space.

• Mineral Wool: Excellent fire resistance and soundproofing, often used in high-rise buildings

• Wood Fibre: A breathable, eco-friendly option that works well for older or heritage buildings. Woodfibre is normally used with a breathable finish such as a lime based render.

 Cost of External Wall Insulation

The cost of EWI depends on the insulation material, wall condition, and project size. The table below provides a general price guide:

Insulation Type	Cost per square metre (including installation)
EPS	£80–£120
Phenolic Foam	£120–£160
Mineral Wool	£100–£150
Wood Fibre	£110–£160
Cork	£130–£180

Designing Woodfibre EWI into a project

How External Wall Insulation is Installed

1. The wall is cleaned, and any loose materials are removed.

2. Insulation boards are fixed to the wall using adhesive and mechanical fixings.

3. A base coat is applied over the insulation, with reinforcing mesh to prevent cracking.

4. A final render or cladding is applied for protection and appearance.

Many considerations need to be made of how the EWI will interact with other building elements such as windows, doors, roof eaves, and the ground.

Is External Wall Insulation Right for You?

External Wall Insulation is a good investment for homeowners looking to improve energy efficiency and reduce heating costs. The best material and approach depends on your property type and budget, as well your sustainablitiy aspirations, . We as architects can help guide you through this process, ensuring you choose the right materials and meet all necessary regulations. Get in touch to see how we can be of help in guiding you through this whole process.