Modern architecture increasingly favours glass-heavy designs — from panoramic windows to entire glass facades. While visually stunning, properties with high glazing ratios often struggle with energy efficiency, making it difficult to achieve favourable Energy Performance Certificate (EPC) ratings. This article explores how extensive glazing impacts EPC assessments and what property owners can do to mitigate these challenges.
If you need expert EPC assessments for glass-dominant structures, explore our Services page.
1. What is a Glazing Ratio?
The glazing ratio refers to the proportion of a building’s external envelope covered by glass compared to opaque elements like walls or cladding. Properties with high glazing ratios — typically over 40-50% — are common in contemporary commercial offices, luxury flats, and modernist homes.
While aesthetically appealing and excellent for daylighting, these glass surfaces often become the weakest link in thermal performance.
2. Why High Glazing Ratios Negatively Impact EPC Ratings
The EPC assessment process evaluates how well a building retains heat in winter and avoids overheating in summer. Glass surfaces, even double or triple-glazed units, typically have higher U-values (greater heat loss) compared to insulated walls. This results in:
Increased heating demands during colder months.
Solar heat gains leading to cooling requirements in summer.
Higher reliance on HVAC systems for thermal comfort.
EPC software models these losses and penalizes properties with large glass-to-wall ratios unless robust mitigation measures are in place. Learn more about how EPC evaluations work on our About Us page.
3. Key EPC Challenges for Glazed Properties
Excessive Heat Loss: Even energy-efficient glazing falls short compared to insulated walls.
Thermal Bridging Risks: Improperly installed glazing frames can create points of significant heat loss.
Overheating in Summer: Without adequate shading or solar control glazing, buildings can overheat.
Ventilation Complexity: Balancing air exchange without further heat losses becomes challenging.
For an accurate EPC assessment that considers these factors, book a professional visit with our experienced assessors.
4. Solutions to Improve EPC in Glass-Heavy Buildings
While high glazing ratios inherently pose EPC challenges, several strategies can mitigate their impact:
a) Upgrading to Triple Glazing
Where feasible, replacing double-glazed units with triple-glazed panels can lower U-values significantly, thus reducing heat losses.
b) Solar Control Glass & Low-E Coatings
Utilising low-emissivity coatings and solar control glass can limit unwanted solar gains while improving thermal retention.
c) External Shading Devices
Architectural elements like brise-soleils, external blinds, or louvres help control solar gains, especially on south and west elevations.
d) High-Performance Window Frames
Switching to thermally broken frames reduces heat loss at glazing junctions.
e) Optimising HVAC and MVHR Systems
Well-designed mechanical ventilation with heat recovery (MVHR) systems counteract heat losses efficiently.
We incorporate these factors in our tailored EPC assessments. Get a quote on our Pricing page.
5. EPC Software Limitations: Why Real-World Performance Might Differ
It’s important to note that EPC assessments (especially those based on RdSAP for domestic properties) rely on standard assumptions and may not fully reflect the performance of advanced glazing technologies or custom solutions.
For complex glass structures, dynamic simulation modelling (DSM) might provide a more accurate reflection of energy performance. While not part of a standard domestic EPC, this can be vital for larger developments or commercial buildings.
Our team offers guidance on which assessment method suits your property best. Reach out through our Contact page.
6. Special Considerations: Listed Buildings and Conservation Areas
In heritage or conservation contexts, replacing original windows may be restricted. In such cases, secondary glazing, internal thermal blinds, and draught-proofing become essential strategies to balance aesthetics with energy performance.
We’ve assisted many property owners in these sensitive projects. See how we approach these unique challenges on our Services page.
7. Step-by-Step: Preparing for an EPC with High Glazing Ratios
Document Window Specifications: Provide U-values, glazing types, and frame details.
Demonstrate Solar Control Measures: Include shading devices, films, or coatings in the documentation.
Optimize HVAC Controls: Ensure efficient heating/cooling systems are correctly documented.
Pre-assessment Consultation: Book a pre-EPC advisory session for tailored recommendations.
Conclusion
Properties with high glazing ratios present distinct EPC challenges due to inherent heat loss and solar gain issues. However, with smart design interventions and a thorough assessment approach, it’s possible to mitigate these effects and achieve compliance with EPC requirements.
If your property features extensive glazing and you’re concerned about your EPC outcome, contact our expert team for a professional evaluation that understands these complexities. Visit our Contact page to get started.
