Portsmouth, Wilmcote House EnerPHit

Residents benefi t from reduced energy costs and fuel poverty after refurbishment to Passivhaus principles

Working with Portsmouth City Council, the University of Southampton engaged with residents of Wilmcote House to assess their living conditions and the effects it was having on their well-being. It was agreed that due to the size of Wilmcote House, and the number of resident’s homes which would have been disrupted, its demolition would have been complicated and expensive; however, by retaining the existing building, it would provide an opportunity to improve the estate’s image and encourage the longevity of the present community. A case study was also conducted by the Building Research Establishment (BRE) and Wilmcote House was selected as a residential building within Europe that was ideal to be retrofitted to Passivhaus principles. ENGIE was one of only two contractors who had the resources to tender this project. We successfully refurbished Wilmcote House, making the building more sustainable and energy efficient, whilst also providing cost savings for Portsmouth City Council, and benefitting residents by reducing their energy costs and fuel poverty.

Following design consultation between ENGIE, ECD Architects and Portsmouth CC, the proposed Passivhaus strategy was agreed.


The 11-storey development of three linked blocks, situated within the Somerstown Housing Estate in the south of Portsmouth, was built in 1968 using a prefabricated reinforced large concrete panel system, ‘Bilson REMMA’, which was designed in the late 1940s, and was still in use well into the 1960s, but now major elements had come to the end of their serviceable life. The concrete reinforced panels incorporated only about 25mm of insulation, which, combined with all electric heating, means staying warm in the building was expensive; with many residents experiencing fuel poverty.

The building consisted of 107 properties comprising seven, one-bedroom apartments, Portsmouth City Council housing office at ground floor level and 100 three-bedroom maisonettes on the floors above. The linked blocks also comprised of maisonettes, and ground floor apartments, a communal lounge, laundry, drying room, concierge and offices. 11 new apartments were earmarked for construction within the existing office space on the ground floor. 

Passivhaus Strategy
Following design consultation between ENGIE, ECD Architects and Portsmouth CC, the proposed Passivhaus strategy was agreed for quality building components, superior insulation, ventilation with heat recovery, thermal bridge free design and airtight construction to reach levels of energy efficiency of one or less per hour and comfort for buildings that are compliant to the EnerPHit standard. To make the building more energy efficient, we constructed a new external façade and roof covering by installing a separate structural steel frame around Wilmcote House. This was to enable the wrapping of the entire building in 300/400mm ROCKWOOL external insulation which would reduce draughts, condensation and mould growth.

The steel frame included enclosing the landings within the facades and extended the recessed areas within the upper area of each maisonette to meet the line of the new building envelope, which extended the building footprint by up to 1m. The access deck below was included in the demolition and alterations to the concrete walls and slabs.

The new facade and frame required new piled foundations. Structural fixings were secured from the outside of the building, at high levels, through each maisonette kitchen and lounge party walls. We replaced windows and doors to all external openings and various internal openings that were either in common areas, or bordered the access decks.

Associated works were undertaken within the maisonettes which included:


The over-clad design to the whole of Wilmcote House meant the installation of the ROCKPANEL cladding façade system and ROCKWOOL External Wall Insulation had to be done very carefully to avoid damage to the existing LPS (Large Panel System) as these type of buildings are subject to disproportionate collapse if damage is caused and a load bearing element damaged or removed. The roadside wall was over-clad with insulated render, supported by a hot rolled galvanised frame with cold formed secondary members. The frame was fixed 100mm away from the face of the building where the windows were to be installed within the frame. It was not possible to make any load bearing fixings into the panels on this elevation, so therefore, we had to support the cladding with brackets connected to the main cross wall foundations at ground level. Upon commencement of the roof works, seagulls were discovered nesting on the roof. All species of gull are protected under the Wildlife and Countryside Act, therefore, we had to delay roofing works until nests became inactive, so we re-programmed work accordingly.

For the new fully suspended roof structure, the steelwork had to span from cross wall to cross wall and not bear on the existing roof structure except at these points. Therefore, we did not bolt the upstand posts into the joint at the head of the cross wall between the adjoining planks. Instead, we connected the post to the framing beams in each direction so that it created a rigid moment connection for the lateral shears to be transferred into the concrete roof. We also provided fixing points to each elevation of the roof frame for suitable anchorages of the mansafe equipment so that specialist abseilers could make connections for rope.

Relationships and Communication

We primarily minimised disruption through extensive consultation, undertaken by a team of four dedicated Resident Liaison Officers (RLOs) who managed residents’ expectations, explained the works and detailed the programme timetable. While works were undertaken, we erected Isoclad panels to protect residents during works. These panels not only prevented residents from gaining access to the open façade, but insulated them from the elements. Each living room was then extended to the new façade and a drying
room installed, increasing the footprint of the flats and providing more habitable space for residents.

We also provided an integrated email server for the client, subcontractors, and suppliers so that everyone was kept informed of progress.

Health and Safety

ENGIE attaches the highest importance to health and safety, with  the protection of individuals and all stakeholders being deeply embedded and guided by our collective objective, "No Life at Risk”.

We are pleased to say there were no reportable injuries during the whole of this project.


We carried out on-site workshops with mock-ups to practice installation sequence (below)/complex steel junctions/taping / insulation continuity.

Responsible Business

We carried out an extensive social value plan of events on this high profile project, including:


The excellence achieved on this project was recognised by the multi-awards received:

Award Winner:

Furthermore, the site has positive assessments from Considerate Constructor Scheme (CCS) visits, receiving a Bronze Award 2016 and a CCS certificate of Performance Beyond Compliance, scoring an ‘Excellent’standard in the Appearance, Community, Safety and Environment categories for achieving a high score of 39/50.

Making Zero Carbon Happen
In harmony with ENGIE’s drive to be the world leader in the Transition to Zero Carbon, the improvements help Portsmouth City Council to generate CO2 emissions savings of 10,765.28 tonnes over the lifetime of the measures installed, and support their progress towards achieving ambitious government targets to reduce carbon emissions by 57% by 2030.

The Outcome
Fuel Poverty and wellbeing: Throughout the works and after completion, the BRE and the University of Southampton undertook studies on the thermal modelling, energy use and social studies associated with the provision of better accommodation and the material effect this will have on the wellbeing of the occupants.  Southampton University results for winter and summer seasons have shown that the building provides thermal comfort in winter with little or no active heating whilst reducing the risk of overheating in the summer.

Resident health and wellbeing is also improving because there is less damp, mould and condensation. The introduction of heat recovery units and triple glazed windows drastically reduce residents heating bills by up to 90%. Portsmouth City Council also benefit from the significant reduction in ongoing maintenance costs and increased ability of residents to pay their rent. 

Fire safety and antisocial behaviour: The new EWI performs to the new enhanced fire regulations and as part of the project, we also installed new fire doors and door entry systems, thus increasing fire safety and security. Furthermore, the new door entry system has helped to combat the levels of antisocial behaviour within the blocks and reduce the number of rough sleepers that were previously able to access the building. Additionally, the external works have significantly improved the aesthetic of the blocks and overall appearance of the estate.