Council offices get EnerPHit uplift

Eden District Council is undertaking a deep retrofit of an office building in Penrith in Cumbria aiming for the EnerPHit (Passivhaus retrofit) standard. The 1950-60s municipal offices retrofit involves wrapping the building in external wall insulation and offers valuable lessons for commercial upgrades.

Voreda House is being developed for Eden District Council to replace its current inefficient offices, with the building purchased from the NHS specifically for this purpose. Following a recent announcement on Local Government Reorganisation, the building may also be used as public service hub for the new Westmorland and Furness unitary authority. Eden District Council has received £850K grant funding from the Government to make the project net zero carbon. Salix Finance, a non-departmental public body owned wholly by Government, managed the transfer of these funds to the Council.

The proposed design is considered to make a positive contribution to the environment in all senses, improving an existing building to meet the challenge of climate emergency, enhancing its immediate environment, creating a healthy workplace, and creating a landmark building that Eden District Councll can be proud of.

Eden District Council

Key Facts Number of occupants: up to 140 Treated Floor Area: 1400 m2   Construction status: On site   Completion: Early 2023  Construction type: Original building is concrete frame with pre-cast concrete panels making up the facades. The concrete panels are to be replaced with steel frame and dry cassette external wall insulation system Aiming for: EnerPHit

 

I’m delighted that the long-held aim of Eden District Council for a single site is now a reality. All the more so because, firstly Penrith can offer state of the art facilities to house increased local government jobs and services - just in time for the new unitary authority, and secondly because the building will lead the way in reducing carbon emissions.

Councillor Virginia Taylor, Leader of Eden District Council

 

Design approach

The building is mostly being wrapped in insulation externally to improve the offices thermal performance and comfort. The pre-cast concrete roof was overlaid with insulation and the concrete panelling on the outside of the building is being removed and replaced with a steel frame system (familiar to the contractors) which holds a carrying panel with  stone wool insulation to insulate the building externally. External wall insulation (EWI) was extended down into the ground to minimise thermal bridging at the building’s foundations. Externally, the building will be clad with a lightweight dry-cassette cladding system which will maintain the colour of sandstone to retain the stone character of the conservation area.

We are very pleased to have contributed to the collaborative team effort which has taken this challenging, but unique Net Zero Carbon project from an initial concept through to a start on site. We hope that many more commercial buildings can aspire to achieving Net Zero Carbon operation and use Passivhaus as the design process to inform any refurbishment.

Rod Hughes, Director, 2030 Architects Ltd

The building had an undercroft (an open ground level area which is covered by the building above) and it quickly became clear to the team that it would be important to bring this space within the thermal envelope to improve the building’s treated floor area and simplify its form factor. The ground floor area was therefore extended to match upper floors.

 

Retrofit projects are always a challenge. They need to be designed to achieve realistic levels of efficiency within the limitations of the existing structure. Not every retrofit can achieve Passivhaus or EnerPHit levels of performance, but when the opportunity presents itself, it just makes sense.

Paul Smith, Associate Director, Greengauge

Challenges 

As is often the case with retrofits the design team have had to work around a number of challenges on the existing building.

• The stairwell and lift shaft on the building could not be moved as were important structurally; so they were wrapped with internal wall insulation to minimise thermal bridging.
• The floor to ceiling height was constrained which meant that adding ground floor insulation was difficult. Aerogel space-saving insulation (at a thickness of 11mm) was used for the floor of the existing building floor as a result. The location of ventilation ducting in low ceilings was also a challenge for the design team.
• There were limited options for penetrations for services, such as ventilation, and penetrations through the existing roof were structurally not possible. The roof could not be altered as it was deemed that any changes to the structural elements that tied the concrete frame together could alter how the frame transfers the loading stresses and impact its structural integrity. To address this an external service zone was created and the ductwork drops were run external to the thermal envelope.
• Using a steel frame system to hold the EWI system created its own challenges: Steel frame was familiar to the contractors but increases thermal bridging issues and is harder to model in PHPP. In PHPP the steel U value error factor is >10% so had to be carefully interrogated by the design team. The use of metal fastenings also contributed to a lower wall U value.

Ventilation strategy

Ventilation design at Voreda House - groundfloor (left) and first floor (right). Image credit: Greengauge

The design team has spent a lot of effort in designing a ventilation system that will cope with the building’s varying occupancy rate and different room layouts (cellular on ground floor and more open plan on upper floors). In response to the COVID pandemic, efforts were made to minimise the mixing and cross-flow of air in the building. Displacement ventilation strategies were used, with air supplied at low levels and extracted at higher levels to address this.

Greengauge are very pleased to be part of the team bringing Voreda House up to an exceptional energy efficiency standard. The Passivhaus standards are a demonstration of exceptional quality and energy efficiency.

Hannah Jones, Director, Greengauge

Key Team Client: Eden District Council Architect: 2030 Architects Passivhaus consultant & M&E Design: Greengauge Passivhaus certifier: Etude Contractor: Collinson Construction

Greengauge presented this project at the 2022 Passivhaus Retrofit Masterclass on Non-Domestic Buildings - where details about the ventilation strategy and steel frame challenges are elaborated upon. All sessions from the mini-series have been recorded and still available to purchase to watch online.

 

Further information

Voreda House

Passivhaus Retrofit

Passivhaus Retrofit Masterclass series on demand

Passivhaus Commercial

Voreda House transformation begins - 25 March 2022

7th June 2022

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