Listed buildings, with their historic architecture and cultural significance, are often subject to strict regulations regarding alterations and energy upgrades. To improve energy efficiency without altering external appearances, many property owners opt for modern internal insulation systems. However, when it comes to Energy Performance Certificates (EPC), these internal insulation solutions come with hidden risks that can negatively impact the property’s rating.

Why Listed Buildings Face EPC Challenges

The EPC assessment methodology is designed with modern construction standards in mind. Listed buildings, with their solid walls, single-glazed windows, and ventilation complexities, often don’t fit into the assumptions made by EPC software. Even when modern internal insulation is installed, these improvements may not always be reflected accurately.

Hidden Risks of Using Internal Insulation in Listed Properties:

1. Lack of Recognized U-Value Data

If the installed internal insulation system doesn’t come with certified U-value documentation, EPC assessors are forced to use conservative default values. This can negate the energy efficiency gains achieved through insulation upgrades.

2. Thermal Bridging Concerns

EPC software accounts for potential thermal bridges where internal insulation may be discontinuous—such as at floor junctions or around windows. If not properly detailed, these areas can reduce the perceived effectiveness of the insulation.

3. Air Permeability Assumptions

Older listed buildings often have higher assumed air leakage rates. Even with modern internal insulation improving airtightness, unless airtightness tests are conducted, EPC assessments may still apply default high permeability values.

4. Moisture Risk Overcompensation

While internal insulation improves thermal efficiency, it can introduce moisture and condensation risks in historic structures. EPC assessments do not consider whether these risks have been mitigated (e.g., with vapour control layers), leading to cautious efficiency estimations.

5. Incomplete Recognition of Partial Insulation

If only selected walls are internally insulated, EPC software may dilute the improvement across the entire envelope, resulting in a lower-than-expected rating despite significant work being done.

Real-World Efficiency vs EPC Outcomes

Owners of listed buildings often find that, despite investing in high-spec internal insulation, their EPC ratings show minimal improvement. The combination of software limitations and cautious default assumptions means that actual energy savings may not be adequately reflected.

Steps to Ensure Fair EPC Ratings in Listed Buildings

  • Provide Full Technical Documentation: Ensure that all insulation materials and systems are backed by certified U-values and installation details.

  • Conduct Airtightness Testing: Supplying empirical air permeability results can help reduce penalizing default values.

  • Highlight Comprehensive Insulation Strategies: If you’ve implemented moisture control or thermal bridging solutions, make sure these are documented and presented to the assessor.

  • Work with Specialist EPC Assessors: An experienced assessor familiar with listed buildings can ensure the correct inputs are used and explain nuances that might otherwise be missed.

EPCrate: Trusted EPC Assessors for Listed Buildings

At EPCrate, we understand the intricacies of assessing listed properties with modern internal insulation systems. Our EPC assessment services are designed to capture every improvement while navigating the challenges of historic construction.

You can check our pricing options and schedule an assessment through our online booking system.

Book a Specialist EPC Assessment for Your Listed Building

Ensure that your energy-saving investments are fairly recognized. Contact EPCrate for an expert EPC assessment tailored to the unique needs of listed buildings.