Energy-led retrofitting of solid wall dwellings: technical and user perspectives on airtightness

Purpose – Mechanical ventilation with heat recovery (MVHR) is increasingly being promoted in the
UK as a means of reducing the CO2 emissions from dwellings, and installers report growing activity in
the retrofit market. However, the airtightness of a dwelling is a crucially important factor governing
the achievement of CO2 reductions, and the purpose of this paper is to understand the technical
implications of airtightness levels in an experimental dwelling, purpose built to typical 1930s
standards, at the same time as gaining the users’ perspectives on airtightness and ventilation in their
homes.
Design/methodology/approach – In-depth interviews were carried out with 20 households to
collect information on their retrofit and improvement strategies, attitudes to energy saving and their
living practices as they impinge on ventilation. The experimental house was sealed in a series
of interventions, leading to successive reductions in the air permeability as measured by a 50 Pa
pressurisation test. The behaviour of a whole-house MVHR system installed in the experimental
house, was simulated using IES Virtual Environment, using a range of air permeability values
corresponding to those achieved in the retrofit upgrading process.
Findings – In the house considered, air permeability must be reduced below 5m3/m2h for MVHR to
make an overall energy and CO2 saving. However, to achieve this required a level of disruption that, on
the basis of the views expressed, would be unlikely to be tolerated by owners of solid wall dwellings.
Originality/value – The paper is the first to combine results from a user-centred approach to
exploring the existing practices of householders with a simulation of the energy and CO2 performance
at different levels of airtightness of an experimental house in which MVHR has been installed.