Passive House Air Tightness Testing

Passivhaus is a world-leading standard for building energy-efficient homes. It’s a design and construction methodology that creates ultra-low-energy buildings that require very little energy for heating or cooling. A certified Passivhaus is built with meticulous attention to detail and features super insulation, minimal thermal bridging, and exceptional airtightness to provide maximum comfort with a minimal environmental footprint.

The airtightness standard for a Passivhaus is extremely strict. A building must not have more than 0.6 air changes per hour (ACH) when pressurised to 50 Pascals (n50≤0.6 h−1). This is significantly more stringent than the requirements for a standard new build in the UK.

While both tests use a blower door fan to measure air leakage, the Passivhaus test is much more rigorous. The key differences are:

– The Target: The airtightness target of 0.6 ACH is far lower and harder to achieve than for a standard build.

– The Method: Passivhaus testing uses ‘Method A’, which measures air changes per hour based on the building’s volume (m3/h.m3 @ 50Pa). Standard UK tests typically use ‘Method B’, which measures air permeability based on the building’s envelope area (m3/h.m2 @ 50 Pa).

– The Procedure: A Passivhaus test requires both a pressurisation test and a depressurisation test to be carried out. The final result is the average of these two figures. The data logging and environmental readings are also more extensive.

Unlike a standard build which may only have one final test, a Passivhaus project typically requires multiple tests throughout the construction process to ensure it stays on track. It is common to test at least three times:

1. Stage 1: After the initial air barrier is complete.

2. Stage 2: After second-fix works are complete.

3. Stage 3: At completion for final certification.

Testing at these key stages helps to identify and fix leaks early, which is critical for meeting the final target.

We took this staged approach on a North Cotswolds self-build pursuing Passivhaus Premium certification – a pre-completion diagnostic test recorded a promising 0.53 m³/(h·m²)@50Pa, giving the confidence needed ahead of a final certified test that landed right on the 0.60 target.

There are three main certification levels, each with increasing requirements for energy efficiency and on-site renewable energy generation:

1. Passivhaus Classic: The foundational level, focused on achieving exceptional airtightness and insulation to minimise energy use.

2. Passivhaus Plus: Builds on the Classic standard by requiring the home to produce as much energy as it consumes through renewable sources.

3. Passivhaus Premium: The highest and most demanding level. The home must generate significantly more energy than it uses, with the potential to be a net contributor to the power grid.

Yes. For retrofit projects where the original architecture makes meeting the full Passivhaus standard unfeasible, the EnerPHit standard can be used. This is a slightly relaxed but still very challenging standard for achieving exceptional energy efficiency in existing buildings.