Ventilation Testing

Yes, if you have a new build domestic or non-domestic property, you will need to have the ventilation system tested to comply with Part F of the Building Regulations. This is usually requested by your building control body before the property can be signed off. Testing is not required for storage spaces, or garages attached to a single home.

The most common reasons for failure are poor ductwork design and installation. To give yourself the best chance of passing first time:

1. Avoid kinks and squashing flexible ducting. Ensure the ducting has a clear, straight run.

2. Keep ducting runs short. Any duct run over 1.5 metres will significantly reduce the performance of standard axial fans.

3. Use more powerful fans for longer duct runs. If you can’t duct directly through a wall, consider using more powerful centrifugal or inline fans.

Catching problems before the final test also helps considerably. On a recent nine-home Woodstock Homes development, rather than waiting until completion, we ran a diagnostic air test on a single plot ahead of final testing – the results flagged leakage risks at typical junctions and service entries early enough for the site team to act on them across the remaining plots. All nine units then passed first time, with zero retests required.

Around 60-70% of ventilation systems fail on the first attempt – usually due to pinched ductwork, excessive bends or undersized axial fans. If a property fails, you will need to complete remedial work and book a re-test, which incurs additional costs.

Rather than leaving you with a generic fail report and guessing at solutions, our team can provide ventilation strategy advice to diagnose the root cause and specify exact ducting or fan adjustments required to pass.

It depends how early you are in the project. Testing is a pass/fail check carried out once a ventilation system is already installed – by then, the design decisions are largely locked in. A ventilation strategy happens earlier, at the design stage, and covers a different question: which approach (natural, mechanical extract or MVHR) suits the building, and what extract rates it will need to meet Part F once built. Getting this right early matters most when ventilation has to be balanced against other design priorities.

The same principle applies to existing buildings: a recent whole-house assessment showed why ventilation had to be planned before any airtightness improvements went ahead, not added as an afterthought once the fabric work was already underway.

While both are important for a healthy and energy-efficient home, they focus on different things. Part L (conservation of fuel and power) is concerned with limiting heat loss and making the building airtight. Part F (ventilation), on the other hand, is about ensuring that, despite this airtightness, there is still enough fresh air coming into the building. The more airtight a building is, the more important a properly designed and installed ventilation system becomes.

While testing isn’t mandatory for existing properties, a survey is essential if you’re dealing with damp, condensation or black mould – or if you’re planning energy retrofits like insulation or draught-proofing. Making a home airtight without upgrading ventilation traps moisture and ruins indoor air quality.

Ventilation failures are usually invisible to the naked eye. On a recent home survey, our testing uncovered a system delivering just 9.34 l/s of extract ventilation against a 37 l/s requirement, alongside missing fans and unvented cooker hoods. A survey replaces guesswork about “stuffy rooms” with precise, actionable data to fix the root cause.

A certified engineer will use a piece of equipment called a balometer to measure the airflow rate at each extract vent in the property (e.g. in kitchens and bathrooms). The process is quick, and the results are available almost instantly.

Yes. Combining ventilation testing with an air tightness test is the most cost-effective option. Because our engineers complete both assessments during the same site visit, we offer discounted add-on rates compared to standalone ventilation visits – applicable to both individual properties and multi-plot developments.