A Greenhaus for a Greater Manchester!

Greenhaus, the largest Passivhaus affordable housing development in the North West, is now Passivhaus certified and residents have started to move in. The nine-storey development on Chapel Street in Salford, comprises 96 homes, The one and two-bedroom homes are available in a mix of tenures including social rent, affordable rent and rent-to-buy.

Salford is the 18^th most deprived area in the UK and the majority of Salix Homes customers are in receipt of welfare benefits. The new homes at Greenhaus will help reduce fuel poverty for residents, with the monthly cost of heating and hot water expected to be around £40, compared to £95 for a similar-sized new-build home with a gas boiler. Greenhaus is predicted to give a 68% reduction in annual heating demand and a 57% reduction in overall energy usage, compared to current building regulations.

Greenhaus was delivered in partnership with the English Cities Fund (ECF) – a joint venture between Muse, Legal & General, and Homes England, supported by Salford City Council. Salix Homes is the housing association partner and is financing the project after securing funding with its banking partner NatWest. Grants were also secured from Homes England and Greater Manchester Combined Authority (GMCA).

Launch of Greenhaus Salford. Image credit: John Parker Lee

Key stats

Construction: SFS (steel frame system) within concrete frame
Number of homes: 96
TFA: 5825 m²
Form factor: 1.04
Build start date: 2022
Completed: 2024
Certified: Passivhaus, 2024

With the rising cost of living, a shortage in the supply of affordable and social housing, and a need to address the challenges posed by the climate crisis, Greenhaus demonstrates what can be achieved through effective partnership working, and a shared desire to create cleaner, greener, and healthier homes that are fit for the future and won’t need retrofitting.

Sue Sutton, CEO, Salix Home

The building was orientated to optimise solar gain, as far as was possible within a complex urban context that had shading from adjacent buildings. Airtightness measures included minimising penetrations of the thermal envelope, for example using automatic air admittance valves so that soil and vent pipes vent at the head of the drainage run. An external airtightness membrane was used, and all junctions were carefully detailed.

Greenhaus, Salford I Image © Aeroflair

To achieve Passivhaus standards within a budget, the design team created a compact build form and simplify the thermal envelope, reducing the exposed surface area for heat loss. The design team avoided complex details such as overhangs and inset balconies and, as a result, the building has a low form factor of 1.04. Simplifying the architectural detailing helped pre-empt potential junction issues, improving airtightness and minimising thermal bridging on the project. Unheated spaces were grouped together to keep the thermal line as compact as possible.

Measures to reduce thermal bridging included:

The positioning of windows within the insulation zone
Use of aluminium reveals to reduce thermal bridging
Use of reduced height parapets to minimise the thermal line
Avoidance of high gauge masonry supports and ties in the walls
Use of insulated internal rainwater pipes
Location of MVHR units on external walls, keeping the length of the intake and exhaust ductwork under 2 metres.

Glazing was designed to achieve a 20% glazing to wall ratio on all elevations. Wider, shorter windows were specified to improve daylight distribution and moderate overheating risk. The curtain walling system utilises spandrel panels and textured brickwork, to help achieve a vertical appearance and a balance of solid to apparent void.

Greenhaus. Image © Jon Lee Parker. I New resident Harriette quote: When I got the call to say I had a place at Greenhaus, I just couldn’t believe it - I feel so lucky. I know all about Passivhaus as I’d seen it on Grand Designs, and I always said to myself that when I get my own place, I want it to be a Passivhaus, and now I’m living in one - it couldn’t be more perfect.

Construction

The Design & Build Contractor was appointed on a pre-contract services agreement. The scheme utilises a SFS (steel frame) system within a concrete frame, with a masonry external envelope. The construction method was chosen as a commercially viable build-up for industry-wide application. SFS was deemed to have a faster installation than the concrete block commonly used on apartment schemes. SFS imposes less weight on the main structure and can be used in conjunction with Mast Climbers, so significantly reduced the time required for the construction programme.

Greenhaus under construction. Image © Buttress

U-values
Floor: 0.152 W/m²K	Wall: 0.256 W/m²K	Roof: 0.174 W/m²K

While the initial cost of building Passivhaus standard homes might be higher, Salix Homes has considered the long-term savings to be made on repairs and maintenance or complex and expensive retrofit solutions, as well as the financial and health benefits for residents.

Jim Battle, Chair, Salix Homes

Building performance

Designed energy performance

Airtightness n₅₀ (≤ 0.6ACH @ 50 Pa)

0.5 @ 50 Pa

Space Heating Demand (≤ 15 kWh/m².a)

14 kWh/m².a

Heating Load (≤ 10 W/m²)

9 W/m²

Primary Energy Demand (≤ 120 kWh/m².a)

64.8 kWh/m².a

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Services

The majority of heat demand in the building is met by internal gains from people and equipment and as a result, there is a smaller heating plant requirement for the project, resulting in project cost savings that could be spent elsewhere on the project. Space heating is provided by local electric wall-mounted panel heaters. Domestic hot water is supplied to each dwelling via an ASHP (air source heat pump) hot water cylinder with integrated electric immersion heater and radial microbore. Each apartment has an individual MVHR (mechanical ventilation with heat recovery unit).

Challenges & lessons learned

Start with Passivhaus: Passivhaus was introduced later in the design, when the project was at RIBA Stage 3, so design revisions were necessary.
Glazing design: The streetscape & prominent adjacent cathedral drove a vertical emphasis to the elevations. The optimal approach to meet Passivhaus would be to have wider and shorter windows, sized to balance heat loss and gain. This would improve the daylight distribution in the rooms and is typically easier to moderate the overheating risk by shading. However, there were concerns that this would result in an unaesthetic design that would not fit local context, unsympathetic & inconsistent with neighbouring buildings. To address this, architectural features such as spandrel panels and textured brickwork were introduced to achieve a balance of solid to ‘apparent’ void, to retain the original vertical design intent.
Simple detailing: The early stage design phase was key to the project's success, in which the design team aimed to simplify the architectural detailing to pre-empt potential site interface issues and worked very closely with contractors and their supply chain.
Collaborative working: The design team worked closely with contractors to ensure installation quality. A mock-up rig was used to test airtightness. The rig helped avoid costly defects by highlighting areas that needed addressing before work started on the main build.

Key team

Client: Salix Homes/ Muse
Architect: Buttress
Passivhaus Consultant: Max Fordham
Contractor: Eric Wright Construction
Structural engineer: Alan Johnston Partnership Ltd
M&E consultant: Hannan Associates
Passivhaus Certifier: ZE Passivhaus

Handover & monitoring

Salix Homes has planned a careful education and monitoring process for new residents. All residents will receive a detailed user guide and instructional videos to help them understand their new home and ensure it continually performs as it was designed to. Salix Homes has set up a specialist support team for its Passivhaus customers and has installed technology to remotely monitor the air quality and energy usage.

All data will be monitored, along with repairs and maintenance expenditure, and compared with non-Passivhaus developments to help track the long-term benefits and identify lessons learned. Salix Homes is also working in partnership with Salford University to track the health of new residents, to further understand the health benefits of living in Passivhaus property.

Next steps

A second Passivhaus development is already in the pipeline in Salford, to the same specification as Greenhaus, and undertaken by the same team. The 100 homes planned are to be 100% affordable, and 100% Passivhaus certified!