Skylights and roof lights are popular architectural features, bringing in abundant natural light, enhancing aesthetics, and creating a sense of openness. However, when it comes to Energy Performance Certificate (EPC) assessments, homes with an excessive number of skylights often face unexpected penalties that can lower their energy efficiency rating.
Let’s explore why EPC software tends to view too many roof lights as a negative factor—and how homeowners can mitigate these effects.
The Appeal of Skylights: A Double-Edged Sword in EPCs
While skylights offer excellent daylighting, reducing reliance on artificial lighting during the day, they present two key challenges in EPC assessments:
Higher Heat Loss Potential
Increased Overheating Risk in Summer
EPC software is designed to model a building’s year-round energy efficiency, and excessive glazing on roofs raises concerns on both fronts.
Key Reasons Why EPC Software Penalizes Excessive Skylights:
1. Higher U-Values of Roof Glazing
Even high-performance triple-glazed skylights generally have worse U-values (thermal transmittance) compared to insulated pitched or flat roofs. In EPC calculations, large expanses of glazed roof areas contribute to greater heat loss during colder months.
2. Uncontrolled Solar Gains
While solar gain can be beneficial in winter, too many skylights increase the risk of overheating during summer. EPC models apply penalties if large glazed areas face orientations that receive high solar exposure, especially without shading devices.
3. Assumed Thermal Bridging Around Skylight Frames
If skylight installations lack documented details on how thermal bridging is minimized, EPC software applies default bridging factors, which further downgrades the property’s thermal efficiency score.
4. Daylighting Benefits Often Undervalued
While skylights reduce the need for artificial lighting, EPC calculations tend to give limited weight to this benefit compared to the penalties for increased heat loss and potential overheating.
5. Documentation Gaps for Advanced Glazing Technologies
If skylights with advanced coatings (low-E, solar control films, etc.) are installed but not documented with performance data, EPC software defaults to conservative assumptions, negating their real-world efficiency.
The EPC Reality Gap: Design Elegance vs Energy Calculation
Architecturally, skylights enhance living spaces by flooding interiors with daylight. However, EPC software simplifies complex building physics into rigid calculation methods, which can penalize even well-designed roof glazing installations.
How to Minimize EPC Penalties for Skylight-Rich Homes
Provide Certified U-Values for Glazed Areas: Ensure skylight performance data (U-values, g-values) are available and submitted.
Document Shading Strategies: Include blinds, overhangs, or glazing films used to manage solar gains.
Use High-Spec Thermal Break Skylights: Skylights designed to minimize thermal bridging can help offset losses.
Conduct Daylight Analysis Reports: Supplement the EPC with lighting energy reduction reports to support efficiency claims.
Choose Assessors Familiar with Glazed Architecture: Experienced assessors can input nuanced data and ensure performance benefits are properly considered.
EPCrate: Specialist EPC Assessments for Architecturally Unique Homes
At EPCrate, we understand the complexities of assessing properties with significant roof glazing and skylight installations. Our EPC services ensure your architectural features are evaluated with precision.
Explore our pricing and schedule an assessment through our online booking system.
Book an EPC Assessment for Skylight-Intensive Properties
Ensure your home’s design elegance doesn’t get penalized unfairly. Contact EPCrate to arrange a professional EPC assessment that understands glazed architectural elements.
