Heritage buildings present unique challenges when it comes to Energy Performance Certificate (EPC) compliance. While internal storm windows are often added to improve energy efficiency without altering a property’s historic exterior, they introduce certain complexities during an EPC assessment.
If you’re looking to book an EPC in London, our EPC Assessors understand how to evaluate heritage properties with sensitivity to both energy regulations and preservation requirements.
Why Internal Storm Windows Are Used in Heritage Buildings
Internal storm windows are secondary glazing units installed on the inside of existing windows. They are often chosen for:
Preservation compliance – avoiding changes to the external façade.
Thermal insulation – reducing heat loss through single-glazed windows.
Noise reduction – providing extra sound insulation in busy urban areas.
However, while these benefits are real, EPC assessments don’t always give them full credit due to how they are modelled in the Standard Assessment Procedure (SAP).
EPC Assessment Challenges
1. Limited Recognition in SAP Modelling
The SAP software used in EPC calculations may not fully account for the energy performance boost of internal storm windows, especially if the system’s thermal properties aren’t officially documented.
2. Ventilation and Condensation Concerns
Heritage properties often lack modern ventilation systems. Internal storm windows can trap moisture between glass layers, creating condensation risks — an issue assessors must factor in when evaluating overall energy performance.
3. Interaction with Other Retrofit Measures
In some cases, combining internal storm windows with other upgrades (like secondary heating controls) can influence EPC results. Our Residential EPC service ensures these combined effects are properly documented.
Improving EPC Scores in Heritage Properties with Internal Storm Windows
If you want to improve your rating, consider:
Providing manufacturer performance data for storm window units.
Pairing with draught-proofing to reduce air leakage.
Upgrading insulation in roof and floors to offset limited wall/window improvements.
For urgent upgrades before a sale or rental, our Same-Day EPC service ensures you meet compliance deadlines without delays.
Final Thoughts
Heritage buildings deserve careful EPC evaluation to balance energy efficiency with historic preservation. Internal storm windows can be an effective solution — but only if assessors properly capture their benefits.
If you own or manage a heritage property and need expert EPC guidance, contact us for tailored advice.
