Airtightness in existing homes
What is air tightness?
Infiltration is the unwanted movement of air through the building fabric and “air tightness” puts a number on it. Infiltration is more than draughts, discomfort and increased energy bills – it can stop insulation being effective, create cold spots where mould starts and can shorten the life of a building.
Retrofit performance gap
Retrofit measures are usually based on the assumptions used to produce the EPC (Energy Performance Certificate). In the case of air tightness, these assumptions are based on age and certain building characteristics. This is great if your property is on the average, but there is a wide variation in air tightness across the UK housing stock and it should not be assumed that all older buildings are more leaky.
If a property is more airtight than the assumptions, there may be unintended consequences from measures such as condensation and mould. If the property is leakier than the assumed average, the opportunity to tackle cheap to address issues is missed. Testing the building overcomes these unknowns and can assist all retrofit routes – Retrofit Assessments, PAS2035 led social housing retrofits, DIY, architect led single projects.
Light retrofit and heat pump installation
Light retrofit is usually defined as sufficient measures to enable a switch to a heat pump without the fuel bill increasing. The key building issues to understand for a light retrofit are property specific: identification of issues which offer best return on capital invested (usually easily remedied airtightness problems created by earlier works on the building, often accounting for 20% of heating energy use) and whether any measures are likely to create condensation or mould issues.
The property specific, easy to tackle measures are not identified in the current retrofit specification routes. However, the inclusion of a baseline test in the process would address this gap.
The uptake of heat pumps in UK owner-occupied properties remains poor, despite the financial incentives. Part of the lack of confidence amongst householders is due to contrasting positive and negative feedback on heat pump effectiveness and the impact on fuel bills. Key factors influencing heat pump effectiveness include the quality of design and installation, the heat loss calculation method and the underlying performance assumptions of the building – building air tightness is one of the components of this last point, so baseline testing of the building can be seen as also contributing to the level of confidence in domestic heat pump use.
What is a baseline pre-retrofit test?
The test uses blower door air tightness test equipment and thermography to create a picture of an individual property – quantifying the air tightness and identifying the key issues for the property being tested (infiltration and thermal performance). The test (including feedback to householder / retrofit professional) takes 4 hours or less for a 3 or 4 bed property.
Skills shortage
Air tightness testing in the UK is focused on the certification of new buildings and this is reflected in the training available. Current accredited testers do not generally have the knowledge, skills or experience required to provide a picture of an individual building pre-retrofit.
A new generation of tester is needed – one with a good awareness of how buildings perform and a wider range of skills with different equipment, allowing the performance of a building to be assessed rather than just a focus on producing a certificate. The NOCN accredited Baselining Buildings© training has been created to address this gap.