Case Study

Airtightness testing when retrofitting existing homes

The FES Group is a construction compliance, sustainability and acoustics services company operating nationally with offices in York, London and Edinburgh.


Established in 2007, FES offers support on both new build residential and non-residential schemes, as well as having an Existing Buildings department dedicated to supporting retrofit and refurbishment schemes. Clients include the UK’s largest construction companies as well as many architectural practices, M&E consultants, housing associations, local authorities and planners.

Traditionally the core business of FES has been to serve large volume house builders and mid to top-tier contractors with new build compliance-related services such as airtightness and acoustic testing. However, increasing legislation and ever-growing wider societal pressures are also beginning to open up new opportunities in the retrofit and refurbishment sectors that have not traditionally recognised the value offered by on-site testing and measurement. Of course, with some 27 million existing homes in the UK compared to the 200,000 new homes built per annum, not only is there immense market growth potential there are a set of very different operational challenges as well as opportunities.

Driving the growth of the residential retrofit market in the UK is the introduction of the PAS2035 standard in 2021 which applies to all publically funded retrofit programmes such as ECO. The standard is also being adopted voluntarily by many housing associations, private landlords and investors. Crucially, PAS2035 encourages a whole-house approach to retrofit and places property assessment and design of a joined-up solution at the heart of all retrofitting activity. One such area where joined-up thinking is particularly needed is in appreciating the interrelationship between insulation, air tightness and the ventilation needs of properties.

The FES Group have identified offering air tightness testing services and related support and advice in the retrofit market as a key growth area for its business. To make it work, however, the company targets carrying out tests on between 12 and 18 properties per day and called for a solution that would cause minimal disruption to what are typically occupied homes.

Pulse pressure test in a house

In late 2021, FES Group chose Build Test Solutions’ Low-Pressure Pulse equipment as its tool of choice for testing the air tightness of existing buildings. Pulse is a portable, modular compressed air-based system designed specifically to measure air leakage rates and enclosure integrity directly at low pressure; this means the system provides an air change rate measurement that is representative of normal inhabited conditions, helping to improve understanding of energy performance as well as background ventilation.

Using 2 complete Pulse systems, FES has completed 768 Pulse tests (up to the end Oct 2022) and successfully manages them using the Pulse Online system. Pulse Online is a secure, cloud-based online reporting system for displaying test information, viewing diagnostics charts and printing reports to give to the customer.

Ben Wood, Operations Director at FES Group comments:

Retrofitting of existing homes is incredibly important and the scale of the opportunity is immense, both in terms of environmental and wider societal benefits but also commercially for us as a business in terms of our continued growth. Innovation has always been at the heart of how we operate at FES and with new markets come opportunities to try new technologies and equipment. Pulse is an incredibly clever piece of kit that we consider to be particularly well-suited to serving the retrofit market. Side-by-side with the existing fan technology we see not only efficiencies in the speed and simplicity to operate the hardware but also end customer benefits in terms of how the equipment presents on-site and the lesser disruption that it causes.

Working with The FES Group and other well-established airtightness testing businesses as early adopters, Build Test Solutions is continually seeking to build on the strengths of the system with work in the pipeline to further enhance the speed of the test process and to strengthen the features and functionality of the software and reporting platform. There has also been a new background ventilation testing protocol established in partnership with Trustmark and the Insulation Assurance Authority, further helping to grow the overall retrofit testing market.

Ben concludes...

True scaling of air tightness testing of existing buildings is still in its early days but it’s such an important measurement in terms of helping us to understand not only energy efficiency improvement potential of buildings but also where they stand in terms of risk of over or under ventilation and the issues such as mould, condensation and poor indoor air quality that comes with this. We’ve invested heavily in blower door fan technology over the years but we see this work as a natural extension of our business so with new work comes the need for new capacity and new equipment. When faced with that investment choice, Pulse is absolutely the front-running option.


Luke Smith

Luke Smith

Managing Director

FES Group case study statistics

Facts and statistics about this case study:

Pulse kits
2 x
Properties per day
12 - 18
Pulse tests (to date)

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