Summary
Delivering the Warm Homes Plan at scale requires confidence that every domestic retrofit project is safe, effective, and aligned with long‑term net‑zero goals. Evidence from recent programmes shows that installation quality and in-use performance do not always match design intent, leading to avoidable cost, performance shortfalls, and reduced confidence in outcomes. Performance testing provides measured evidence of how homes actually perform.
This white paper explains why testing matters: from improving design accuracy, to supporting ventilation performance, appropriate heat pump sizing, and reducing the risk of costly remediation. With targeted testing costing as little as £750 per home, performance testing offers a low‑cost, high‑value solution to reduce delivery risk and support warm, healthy and efficient retrofitted homes.
The paper has been developed in collaboration with retrofit experts from Leeds Beckett University, University of Salford, Build Test Solutions, and BSRIA’s Applied Engineering team
Key Insights
Why Performance Testing Must Underpin the Warm Homes Plan
Performance testing reduces uncertainty by informing key decisions before retrofit and validating performance on completion of works. Pre-retrofit testing provides measured values for fabric performance and heat loss that can be used directly to inform design decisions. Post-retrofit testing verifies that installed measures are performing as designed. Together, these stages improve outcomes and reduce the likelihood of performance shortfalls remaining undetected across domestic retrofit programmes.
Closing the Performance Gap with Building Performance Testing
Thermal imaging, airtightness, heat loss, and ventilation testing reveal defects, incorrect assumptions, and design issues that visual inspections alone cannot detect. These tests provide measured evidence of fabric performance, air leakage and ventilation rates, allowing performance issues to be identified and addressed.
PAS 2035 and the Risks of Assumption‑Based Design
The white paper highlights how current assessment processes still rely heavily on estimated U‑values, infiltration rates, and fabric performance. Where estimates are inaccurate, this can lead to oversized heat pumps, ventilation non-compliance, and unexpected running costs. Using measured performance data at appropriate stages reduces reliance on estimation and improves confidence in design decisions.
The Cost of Getting It Wrong — and the Savings of Testing
Incorrect insulation assumptions or oversized heat pumps can add significant upfront cost and increase lifetime running costs. Identifying performance issues earlier in the process reduces the likelihood of unnecessary capital expenditure and avoids the need for corrective work following completion.
Why Airtightness and Ventilation Testing Are Essential for Healthy Homes
Ventilation non‑compliance remains widespread within domestic retrofit. Combined airtightness testing and ventilation verification identify insufficient air change rates, and poor commissioning, reducing the risk of damp, poor air quality and inefficient system operation.
A Framework for Testing Before, During & After Retrofit
The white paper sets out where testing delivers the most value across the retrofit process. It will support organisations involved in planning, funding, delivering, or assuring domestic retrofit projects, including:
- Central and devolved government departments providing retrofit funding
- The Warm Homes Agency
- Policy makers
- Housing associations and local authorities
- Retrofit assessors and designers
- Retrofit installers
It gives advice relevant throughout the retrofit process, including:
- Retrofit audits: Identify quality issues early, reduce rework, and strengthen governance.
- Design stage: Improve design confidence with measured fabric data, accurate heat loss calculations, and informed heat pump sizing.
- Tendering & procurement: Specify testing requirements to ensure consistency and accountability from contractors.
- Building Regulations Part F (Ventilation) compliance: And performance verification.
- Training & competency development: Build skills in measurement‑based retrofit practice for coordinators, assessors, and installers.
- Post‑occupancy evaluation: Use monitoring data to validate performance, optimise settings, and reduce ongoing operational costs.
Building Performance at BSRIA
BSRIA has decades of expertise in building performance evaluation and leads the industry in developing standards, best practice, and independent testing methodologies. We combine technical rigour with practical insight, ensuring our recommendations are realistic for real‑world delivery.
Choosing BSRIA means benefiting from:
- Independent, accredited testing and evaluation
- Expertise across ventilation, airtightness, thermal imaging, U‑value measurement, and heat loss assessment
- A proven track record supporting housing providers, local authorities, and government programmes
- Guidance designed for measurable impact, not theoretical assumptions
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FAQs
1. What is performance testing and why is it important?
Performance testing uses physical measurements - such as heat loss testing, airtightness testing, and ventilation testing - to understand how a home actually performs. It replaces assumptions with real data, improving the quality of retrofit design and installation.
2. How does testing support the Warm Homes Plan?
Testing ensures that publicly funded retrofit upgrades deliver better results. It reduces the risk of failure, avoids costly remediation, and increases resident confidence by verifying that homes are warmer, healthier, and cheaper to heat.
3. Is performance testing required under PAS 2035?
PAS 2035 requires assessors and coordinators to establish performance, but many assessments still rely on visual inspection. Testing builds on PAS 2035.
4. What tests offer the greatest value for money?
Airtightness testing, ventilation flow testing, thermal imaging, and a whole‑house heat loss test (or SMETER-based assessment) deliver significant insights for a modest cost per dwelling.
5. How does testing prevent oversized or undersized heat pumps?
Heat pumps must be matched to the actual heat loss of the home. Without measured heat loss data, systems are frequently oversized, causing higher capital and running costs, or undersized, leaving homes hard to heat. Testing reduces these risks.