Designing the Whole Home Retrofit of 1930s Solid Wall Semis


Understanding stock condition is the fundamental challenge for zero carbon retrofit programmes for social housing. Knowledge must be sufficiently detailed to allow housing providers and their partners to design the optimum blend of retrofit technologies for each property.

How does this process look in action? Osborne Carbon Neutral SOLUTIONS, working in collaboration with the London Borough of Enfield (LBE) and the Greater London Authority (GLA) has been engaged to carry out a programme of whole house retrofits to properties built during the 1930s.

LBE identified a number of semi-detached solid brick-built properties that had an Energy Performance Certificate of D or below. Condensation was an issue because of the solid wall design. Vents installed in some of the properties to combat condensation caused draughts and made them harder to heat.

The solid wall construction of the properties and their history of issues with damp has a major impact on the programme of work.


Osborne and specialist partners Bow Tie Construction are responsible for the design and retrofit coordination.

The solution includes external wall insulation that will create a thermally efficient envelope and to house new high performing windows and doors. Loft insulation completes the continuous thermal envelope around each building.

Controlling air flow into and around the property was a critical consideration, particularly given the history of the properties. We carried out an air tightness test to identify the existing air flow rate and identified all areas that needed to be sealed.

The solution includes Mechanical Ventilation with Heat Recovery (MVHR) and AirEx smart vents that provide a secondary source of passive ventilation for the floor void.

Heating and hot water are supplied by air source heat pumps linked to a solar PV system and batteries to minimse the overall energy consumption and cost. The installations include an unvented hot water cylinder to store enough hot water for continuous use for 40 minutes.

The system can heat 140 litres of water to a temperature of 45oC within an hour. By engaging a single M&E provider we reduced the size and number of the system components while maintaining the performance targets.


The London Borough of Enfield has an established and practical retrofit archetype that can be applied to multiple similar properties to deliver carbon reduction, lower energy bills and a more pleasant internal environment for residents of the retrofitted properties.

The results of the project will enable future programmes to be accelerated at every stage including resident engagement, planning approval and delivery.

For large scale retrofit programmes Osborne Carbon Neutral SOLUTIONS is partnering with group members Innovaré to develop the offsite Flexihomes Retrofit System (FRS). This is a panelised solution for external wall insulation, designed to be delivered fully constructed and lifted onto pre-installed brackets.

For ideas about how to increase the rate of progress towards net zero carbon social housing visit our resource centre. Or contact Nick Davidge ([email protected]).