When aiming for a high Energy Performance Certificate (EPC) rating, most property owners focus on insulation, heating systems, and glazing. However, air tightness and ventilation strategies play a crucial — often underestimated — role in determining a building’s EPC score.
A well-balanced approach between sealing air leaks and ensuring healthy ventilation can dramatically influence a building’s energy efficiency, indoor air quality, and EPC rating.
In this article, we’ll explain how air tightness and ventilation affect EPC outcomes and what property owners can do to optimise both.
For expert EPC assessments that consider advanced air tightness and ventilation solutions, visit our Services page.
1. What Is Air Tightness and Why Does It Matter in EPC Assessments?
Air tightness refers to how well a building prevents uncontrolled air leakage through gaps, cracks, and joints in the building envelope. Excessive air leakage leads to:
Heat loss during colder months.
Increased heating and cooling demand.
Drafts and occupant discomfort.
EPC software uses assumed air permeability rates (m³/h.m² at 50Pa) for existing buildings. However, newer buildings (or those tested for air tightness) can benefit from better scores if air leakage rates are low.
2. How EPC Assessors Evaluate Air Tightness
For Existing Buildings: Assessors apply default air leakage rates based on construction age and type, unless specific air tightness tests are provided.
For New Builds (SAP assessments): Air permeability test results are mandatory and directly influence the EPC rating.
For Extensions and Conversions: RdSAP assumes standard air tightness unless evidence is provided for enhanced sealing.
If you’ve conducted an air tightness test or have undertaken air sealing measures, it’s vital to provide documentation to your assessor for an accurate EPC result. Book an EPC assessment that factors in your air tightness improvements.
3. The Role of Ventilation in EPC Ratings
While air tightness reduces uncontrolled heat loss, properties still need adequate ventilation to:
Maintain indoor air quality.
Remove excess humidity and pollutants.
Prevent condensation and mould growth.
EPC assessments consider various ventilation types:
| Ventilation Type | EPC Impact |
|---|---|
| Natural Ventilation | Standard assumption; may limit EPC potential. |
| Intermittent Extract Fans | Common in older homes; modest impact on EPC. |
| Passive Stack Ventilation | Can reduce EPC penalties for mechanical fans. |
| Mechanical Extract Ventilation (MEV) | Improves air quality but uses more energy. |
| Mechanical Ventilation with Heat Recovery (MVHR) | Significantly boosts EPC scores by recovering heat from exhaust air. |
MVHR systems are increasingly popular in new builds and retrofits for properties aiming for EPC Band B or A.
4. Achieving the Right Balance: Air Tightness vs Ventilation
Over-sealing a property without appropriate ventilation leads to:
Stale air and poor indoor air quality.
Risk of condensation and damp.
Potential health issues for occupants.
Conversely, excessive ventilation without heat recovery increases heating demand. The ideal EPC strategy is:
Minimise uncontrolled air leakage.
Implement controlled, efficient ventilation (preferably with heat recovery).
Learn how we assess and optimise these aspects for your property on our About Us page.
5. Practical Steps to Improve Air Tightness and Ventilation for EPC Gains
Air Tightness Measures:
Seal gaps around doors and windows.
Use airtight membranes and tapes during renovations.
Draught-proof loft hatches and floorboards.
Ensure professional sealing around pipe penetrations.
Ventilation Upgrades:
Upgrade to MEV or MVHR systems in airtight properties.
Use extract fans with humidity sensors in wet rooms.
Maintain balance between airflow and energy recovery.
Document all upgrades and provide them during your EPC assessment to ensure improvements are recognised.
6. Real-World Example: Air Tightness and MVHR Boost EPC from D to B
A semi-detached property built in the 1980s initially had an EPC rating of D due to:
Poor air sealing (high air permeability rates).
Inadequate ventilation (basic extractor fans).
Post-upgrade:
Air leakage reduced by professional sealing works.
Installed MVHR system with 85% heat recovery efficiency.
EPC rating improved to B, meeting MEES targets and increasing property value.
For a detailed breakdown of EPC improvement strategies, view our Pricing page.
Conclusion
Air tightness and ventilation are pivotal to achieving high EPC ratings, yet they’re often overlooked. Sealing uncontrolled air leaks while ensuring efficient mechanical ventilation can enhance thermal efficiency, improve indoor air quality, and elevate EPC bands — making properties more valuable and compliant with evolving regulations.
At EPCrate, we ensure these critical factors are assessed thoroughly in every EPC inspection. Schedule your assessment via our Booking page or reach out through our Contact page for tailored advice on optimising air tightness and ventilation for your property.
