A 19th-century, locally-listed manor house in Egham, Surrey, is being retrofitted into a collection of nine unique family homes. Respecting the history of the existing building, the new designs will add value and increase sustainability.

Having bought the property with planning permission to create six apartments and two new townhouses, developer Yellow Brick Capital (YBCAP) asked airc.design and airc.digital to review the initial proposals.

Recognising several challenges and missed opportunities, airc presented new plans that would use the existing space better and would preserve many more of the house’s original features, including staircases, timber ceilings, chimneys and cornices as part of a heritage-led design.

Moreover, the project would deliver nine units in total instead of eight. In addition to the seven apartments created in the original building, the project includes an extension to create two new townhouses. This extension incorporates many of the design features of the original manor house but with a clear distinction between the two buildings.

Throughout the project, airc.design and airc.digital modelled to the level of detail that was needed at the time. For example, for the planning application, the team was able to show the original and historical features that needed to be preserved for the listed building protection, all within the Archicad model.

Considering the building’s wider impact

Throughout the project, the team aims to reuse as much material as possible. Everything that is removed from the site will either be reused as part of the project or elsewhere.

“This can prove difficult,” says Jaime Ingram, BIM Lead and Co-Founder of airc.digital. “For example, there are some fluorescent lights that are in a perfect state and could be used in another building. If we can’t reuse them, we will recycle; the ultimate aim is to avoid all waste.”

In addition, there were bats living in the roof that needed to be relocated to the back of the existing building. This has to be done at specific times of the year to minimise disruption and must be completed before building work commences on the existing building.

With the help of the BIM model, airc was able to demonstrate to the council that the new space available for the bats is appropriate.

Pierre Saunal, Architect and Co-Founder of airc.design, explains: “At the planning committee, the proposal was unanimously approved by the council. The planners agreed that the proposal ‘makes the best use of the building’. It’s simple – but that’s what you want to hear when you work on retrofit. You want to have the feeling that you have maximised the potential of the building.”

Collaboration is key

airc started working at a very early stage with the contractor Harlequin Brickwork and effectively combined RIBA Stages 3 and 4 of the design. By bringing together the contractor, structural engineers, MEP and landscaping teams early on, the Archicad model helped to communicate the design with all those involved in the project.

Pierre continues: “By working closely together, there is a real understanding of the value of the design process; the contractor and subcontractors, led by Michael Leonard, embraced and welcomed straight away the creation of the BIM model because it helped them to understand the design intentions and the construction elements.

“Moreover, the model helped us work collaboratively on the design. For example, when we were looking at the best way to preserve the original chimney structures, the contractor was able to input into the process.

“Another solution we found during these meetings was the addition of a dormer window to one of the roofs. This idea came directly from Michael looking at the 3D model.”

When sustainability and heritage align

To improve the energy efficiency of the original building, extra insulation was necessary, but this couldn’t be applied to the external walls as the building is listed.

Internal insulation was, therefore, added but needed careful consideration to keep the building’s internal original features. The approach airc took was to model the existing features in Archicad, digitally remove them from the model, add the internal insulation and then add the features back in.

Jaime says: “Previously, this would have been very difficult and time consuming to do. However, with the Archicad model, coordination is much easier. For example, we are able to take out existing cornices, insulate underneath and put them back. The ability to accurately model this process comes directly from using the point cloud from the start, which also help reduce survey costs by at least half.”

The project includes several sustainability improvements including roof and wall insulation, rainwater management and permeable surfaces, air-source heat pumps, EV charging points and protected trees within the landscape.

Further planning applications are underway to increase the sustainability and desirability of the site with an exclusive entrance and discreet solar panels.

Overall, the new designs will add value and increase sustainability while respecting the history of the existing building.

Work on site started in March 2024 with an expected completion date of September 2025.