PAS 2035 (2023): Do any of your domestic buildings require an airtightness test?

What is PAS 2035?

PAS 2035 forms part of the retrofit standards framework and details how to carry out quality energy retrofit work to existing domestic dwellings (where PAS 2038 concerns commercial buildings). It sets out to encourage a shift from individual and ad-hoc ways of working to a ‘whole-building’ approach, whereby multiple measures are considered simultaneously to achieve a better overall result and improve cost efficiency.

The PAS 2035:2019 document was compiled following a government commissioned review called, ‘Each Home Counts’ which was designed to identify and tackle the high level of failure present in retrofit of energy efficiency and renewable energy measures.

The document includes best practice guidance for implementing energy measures including:

• How to assess dwellings for retrofit
• Identifying the most beneficial improvements
• Design and specification of energy efficiency measures
• Monitoring of retrofit projects.

In October 2023, PAS 2035 was reviewed and an update, which is included several key changes, was released. Due to come into effect on 30 March 2025, one of the key updates concerns airtightness testing.

What is airtightness testing?

The ‘whole-building’ approach to reviewing a dwelling considers multiple factors including insulation, heating and cooling systems, lighting, monitoring systems and airtightness.

Airtightness testing (sometimes referred to as air pressure testing), measures how much air is escaping from your building. Air can leak through gaps around windows, doors, sockets, skirting boards, pipes, spotlights and where external walls meet the floor, as well as other areas. Inefficiency can cause cold draughts which lead to heat loss and impact energy-efficiency, potentially causing higher heating bills.

Following an airtightness review, which will be compulsory as part of PAS 2035, areas identified as problematic can be improved through measures such as:

• Ensuring gaps around windows and door frames are sealed
• Draught strips applied to areas such as loft hatches and on existing windows and doors
• Sealing holes around services pipes which pass through external walls or suspended timber floors
• Sealing joins between the ceiling and external wall
• Sealing joins between drylining and skirting boards.

Is an airtightness test required on all buildings?

While airtightness testing has been mandatory for all new builds in England, Wales and Northern Ireland since 2006 and since 2010 in Scotland, until the formation of PAS 2035 in 2019, there was no guidance for assessing airtightness in existing buildings.

Under the PAS 2035 retrofit standard, an airtightness test is only mandatory for Path C (high) risk levels. However, is also advises that testing of the air permeability of the building envelope may be useful irrespective of the level of risk and should be carried out at the discretion of the Retrofit Coordinator.

The 2023 review of the PAS 2035 guidance included updates to the design criteria for airtightness strategy which states that, where EEMs improve the building fabric, an airtightness/leakage strategy is required. Should an airtightness target be set in this strategy, compliance must be proved by means of a test.

How do you test airtightness efficiency?

There are two main methods used for testing airtightness. These are:

• PAS 2035 blower door test
• PAS 20235 pulse test

Both methods require the following preparation before undertaking a test:

• All external windows and doors should be properly closed
• All internal doors should be open for the duration of the test
• All devices taking air from or rejecting air to the outside should be switched off
• All purpose provided ventilation temporarily sealed i.e. cooker extractor, chimneys, fans etc.
• Drainage traps in toilets, sinks, showers and wet rooms should be filled with water.

How can we help assess your buildings?

We have a fully qualified and experienced in-house Retrofit Coordinator who provides support to your retrofit schemes to help you achieve maximum energy-efficiency to your existing estate.

A Retrofit Coordinator is mandatory role for PAS 2035 projects and includes the overseeing of assessments, as well as the subsequent specification, monitoring and evaluation of energy-efficiency measures.

Our qualified Retrofit Coordinator is on hand to help you:

• Complete a retrofit risk assessment for each building within the retrofit project
• Create a comprehensive retrofit project plan
• Develop an improvement plan for every dwelling, for implementation over a number of years
• Document the project progress, including any information that is supplied by building owners and other retrofit stakeholders involved in the delivery of the project.

Ready to improve the energy-efficiency of your estate? You can read more about our dedicated Retrofit Coordinator, Gary Adams, by visiting his biography or contact us today to get started with your PAS 2023 retrofit project.