For heritage properties and listed buildings, upgrading energy efficiency is a delicate balance between preservation and modern standards. Since replacing original single-glazed windows is often prohibited, secondary glazing becomes a popular solution. However, when it comes to Energy Performance Certificates (EPCs), the benefits of secondary glazing may not always be fully recognized.
Understanding how EPC assessors evaluate secondary glazing is essential for homeowners aiming to improve their property’s rating without compromising historical integrity.
What is Secondary Glazing?
Secondary glazing involves installing an additional pane of glass on the inside of existing windows, creating an insulating air gap. Unlike double glazing, which replaces window units, secondary glazing preserves original frames and aesthetics, making it an acceptable upgrade in conservation areas.
How EPC Assessments View Secondary Glazing
EPC assessments primarily rely on U-values (thermal transmittance) to gauge window efficiency. Secondary glazing can improve the U-value of single-glazed windows, but the degree to which this is reflected in an EPC rating depends on several factors.
Key Considerations for Assessors:
Type of Secondary Glazing System
Fixed panels, hinged units, sliding sashes, or magnetic systems all vary in thermal performance. More robust, airtight systems are credited with better insulation properties.
Air Gap Thickness
The air gap between the primary window and the secondary glazing significantly affects heat retention. Larger air gaps generally offer better insulation but must be documented.
Sealing and Air Tightness
Secondary glazing that is poorly sealed or leaves gaps may be treated as minimally effective by EPC software. Proper installation details are critical.
Default Values if Specifications are Missing
Without precise U-values for the secondary glazing system, assessors may apply default values that offer limited benefit over single-glazed assumptions.
Impact on Draught Proofing
Secondary glazing can improve a property’s air permeability, but unless airtightness tests are conducted, these improvements may not be fully credited.
Why Secondary Glazing Might Not Boost EPC Scores as Expected
Even though secondary glazing can reduce heat loss and draughts, its EPC impact is sometimes modest compared to replacing windows with modern double glazing. Additionally, EPC software may not fully credit its effectiveness if installation data and specifications are incomplete.
How to Maximize EPC Benefits from Secondary Glazing
Provide Certified U-Values: Ensure product specifications include U-values for the installed secondary glazing system.
Document Installation Details: Include air gap measurements, sealing methods, and draught proofing enhancements.
Consider Airtightness Testing: Demonstrating improved air permeability can help offset software default assumptions.
Work with an Experienced EPC Assessor: Choose assessors who understand heritage building constraints and can input secondary glazing details correctly.
EPCrate: Specialists in Heritage Property EPC Assessments
At EPCrate, we specialize in EPC assessments for listed buildings and heritage properties. Our EPC services ensure that upgrades like secondary glazing are fully considered in your energy rating.
Explore our transparent pricing options and schedule a professional assessment through our online booking system.
Book an Expert EPC Assessment for Your Heritage Home
Ensure your secondary glazing efforts are accurately reflected in your EPC. Contact EPCrate to book a specialized assessment tailored to heritage property requirements.
