How low (energy) can you go…
By Adam Grover
When you’re working on a new build, achieving Passivhaus standards is relatively straightforward. You can control every aspect of the design—from wall construction and orientation to the size and placement of windows—ensuring the building is as energy-efficient as possible. With a Grade 2 Listed Building in Central Bristol, not so much!
When it comes to retrofitting many existing buildings, the Passivhaus Institute’s EnerPHit standard is the go-to. EnerPHit allows compromises to full Passivhaus but still enables significant energy efficiency improvements despite the restrictions that come along with working with an existing building. Other great retrofit standards include the AECB’s Carbon Lite Retrofit approach, and LETI’s Retrofit Guide.
But what happens when your existing building is listed, in which case there are numerous restrictions limiting what you can change? This is precisely the challenge we face with our project on Queen Square in central Bristol, which has secured planning permission and listed building consent and is now going into Technical Design for Building Regulations Approvals, and Tender.
Front Elevation - Restoration
Our aim is to transform this historic property into two energy-efficient homes, while preserving its historic features. We want to reduce the cold, draughts, and high energy bills common with historic properties, within the limits of a listed building and planning restrictions. The challenge is to establish how much energy efficiency can be achieved when both the exterior and interior are protected against change.
Images showing the existing interior, original cornicing, stairs, skirting and other protected period features.
Rooms have recently been used as office space, and need restoring and enhancing.
Restrictions and Limitations
Grade II listed buildings, like Georgian townhouses, have strict rules determining what can and cant be changed. For our project, both the exterior and many interior elements have to stay intact. Other challenges include:
Poor orientation: Unlike new builds, we couldn’t adjust the property’s orientation to improve natural light or heat gain.
Historic fabric: No external insulation is allowed, as the original materials have to be preserved.
What Can Be Done
Even with significant restrictions, there are still practical ways we are working to enhance energy efficiency:
Secondary glazing: Regulations often prohibit changing windows, but secondary glazing can improve thermal performance while preserving original window frames if they can’t have replacement double glazing units.
Floor insulation: Adding insulation between floors reduces heat loss and improves efficiency, especially where heat escapes through old floorboards.
Rebuilding extensions: This property has a poorly built rear extension that we propose to rebuild with much higher levels of insulation and high quality modern windows.
Upgrading heating systems: Energy-efficient heating drastically cuts energy use for heating and hot water and can dramatically reduce the environmental impact and bills.
Draught exclusion: Sealing gaps around doors and windows helps keep out draughts, making the home more comfortable and energy-efficient. It is important to ensure controlled ventilation to the fabric.
Internal wall insulation: While we can’t add external wall insulation, we will propose breathable, natural internal wall insulation where possible, helping to retain heat during winter.
Exploded Concept Diagram
Key Takeaways for Clients
Know the limits: Listed buildings come with restrictions, so expect limitations on changes.
Focus on incremental gains: Small improvements, such as better insulation or modern heating, can make a big impact.
Work with experts: Retrofitting specialists are key to navigating Listed Building Planning and Building Regulations - following an approach such as LETI or AECB can help guide decisions and the best process.
Sustainability is possible: While Passivhaus standards might not be attainable, tailored improvements can still enhance energy efficiency and comfort.