Case Study

Ventilation Assessment in Cavity Wall Insulation

When installing measures that could reduce the infiltration of air into a house it is important to carefully consider whether additional ventilation is required to provide a healthy internal environment. Airtightness measurements using Pulse are a useful tool to make informed decisions on whether additional ventilation is required.

Cavity Wall Insulation Ventilation Assessment
Semi-detached bungalow where Pulse was used to provide ventilation guidance when cavity wall insulation was installed

The Project

Dyson Energy Services were tasked with installing cavity wall insulation in a semi-detached bungalow, following a PAS 2035 compliant process. Because cavity wall insulation can reduce the air permeability of a building, it is important to consider whether there will be sufficient ventilation to provide adequate fresh air after the insulation is installed.

What you don't measure, you can't manage; so in order to make an informed decision on what additional ventilation requirements Dyson undertook airtightness measurement before and after the retrofit using Pulse having undertaken training provided by the Insulation Assurance Authority (IAA).

Prior to the retrofit, the bungalow has intermittent extract fans in the wet rooms but no trickle vents installed in the windows and no undercuts on the internal doors. No evidence of mould or condensation was observed, but the residents reported that they often opened windows to provide additional ventilation. Without carrying out airtightness measurements it would be necessary to install trickle vents and undercut the doors to comply with the risk management protocols of PAS2035.

The Results

Before the retrofit, the air permeability for the whole house was 1.69 ACH@4Pa (1/h). After the retrofit the air permeability of the house was significantly reduced to 1.15 ACH@4Pa (1/h), demonstrating that even for a single measure it's important to consider the effect on ventilation for the building.

Despite the reduction in air permeability, the post-retrofit measurement was above the threshold of 1 ACH@4Pa (1/h) under which additional ventilation measures are required by the IAA Background Ventilation Competency Scheme.

Room-by-room air permeability measurement was also undertaken using Pulse, as although the whole building may have adequate ventilation it's possible that individual spaces within the building may not, and therefore be at risk of condensation or mould growth. The measured air permeability was above 1.5 ACH@4Pa (1/h) for each room, indicating that each room has sufficient ventilation as well as the whole building.

The Outcomes

Pulse measurements allowed the insulation installer, Dyson, to carry out the installation of the cavity wall insulation in an informed manner with due consideration to the risks of a reduction in ventilation and in compliance with PAS2035:2019.

The measurements demonstrated that after the installation of the single measure of cavity wall insulation there was still sufficient fresh air provision to the building and the rooms within it via infiltration. This meant that additional ventilation measures such as the installation of trickle vents and undercutting internal doors were not required.


Luke Smith

Luke Smith

Managing Director

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Rooms tested in one go

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