Palomar court pilots Passivhaus prefab

An 8-unit block of Passivhaus-certified apartments, the Palomar Court project in the Gascoigne neighbourhood of East London was constructed using an offsite light gauge steel frame system. The project, commissioned by Barking and Dagenham Council, aimed to be a pilot study using off-site construction on Passivhaus projects, exploring how prefab may apply to future phases.

Palomar Court consists of two separate blocks connected by a communal core. The core is external to the thermal envelope envelope, and the two blocks, North & South, were submitted for Passivhaus certification separately. Based on energy modelling, the Passivhaus consultant estimates that residents will experience typical energy bills that are just an eighth of the national average. The homes are to be marketed at either London Affordable Rent or Affordable Rent levels.

The cost of people heating their homes is a serious cause for concern to so many households across the country in recent times. Delivering these low carbon, affordable, and energy efficient homes will help reduce our residents’ energy bills in a neighbourhood that fosters a sense of community and social wellbeing. Cllr Darren Rodwell, quote

Key stats

Construction: Light gauge steel frame
Number of homes: 8
GIFA: 816 m²
Build start date: 2021
Completed: 2023
Certified: Passivhaus, 2024

Construction

Light gauge steel panels & frame (LGSF) were specified. Offsite manufacture and assembly helped to increase efficiency as well as reduce waste. A foundation design was used that could be joined together on site like LEGO, using prefabricated XPS modules. The design team stipulated the necessity for a fully non-combustible through-wall construction, which helped the project meet Passivhaus and fire protection requirements.

Adapting the Passivhaus requirements to the use of LGSF involved detailing the airtightness line on the external face of the wall. This was challenging as it was penetrated by the brick slip cladding.

Careful assessment of the spacing and gauge of the LGSF studs minimised the thermal bridging & ensured the robustness of this detail in PHPP (Passivhaus Planning Package).

Building on our previous work, we completed the thermal bridging and condensation risk calculations for Passivhaus certification. The next project is likely to need fewer calculations as we build a pattern-book of typical details. Nick Devlin Quote.

Embodied carbon

The specification of LGSF provided significant embodied carbon reduction. Further embodied carbon was removed from the project by eliminating avoidable waste and reusing demolition waste. The project is estimated to have around 50% lower embodied carbon emissions over its lifetime and achieved beyond LETI benchmarks for embodied carbon.

U-values

Floor: 0.106 W/m²K

300mm concrete over 300mm XPS insulation

Wall contruction build up at Palomar Court Gascoigne Estate. Image credit: Collida/ Willmott Dixon

Wall: 0.148 W/m²K

100mm light gauge steel frame stud with 240mm mineral wool and brick slip cladding

Roof: 0.075 W/m²K

300mm XPS insulation.

Palomar Court Passivhaus project. Quote:

Building performance

Designed energy performance

	North block	South block
Airtightness n₅₀ (≤ 0.6ACH @ 50 Pa)	0.4 @ 50 Pa	0.4 @ 50 Pa
Heating Load (≤ 10 W/m²)	10 W/m²	10 W/m²
Primary Energy Demand (≤ 135 kWh/m².a)	124 kWh/m².a	120 kWh/m².a
Primary Energy Renewable Generation	0 kWh/m².a	28 kWh/m².a
Overheating %	0	1

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

Services

The scheme is connected to a district heat network, which meant no air source heat pumps were required,. Each apartment in Palomar Court has a dedicated MVHR (mechanical ventilation with heat recovery) system. Rooftop solar PV panels supply electricity on the south block of the apartments.

Solar panels at F2 Palomar Court. Image credit: Collida Willmott Dixon

Challenges

Applying Passivhaus after planning approval: The decision to aim for Passivhaus certification came after RIBA Stage 4 (Technical Design) when the client wanted to pursue a more ambitious sustainability target. The design originally featured a traditional beam and block construction with Mechanical Extract Ventilation (MEV) system. RIBA Stage 4 needed to be revisited to refine the building's design to target Passivhaus certification.

Redesign: Navigating this change of specification posed challenges, given the existing planning permissions, which constrained design modifications. The project team collaborated closely with planners to ensure that all revisions fell within the scope of non-material amendments. Through this redesign process, several significant thermal bridges were successfully eliminated, and Psi values were optimised. Additional shading was removed from the design, as overheating was no longer a problem.

Certification: Due to the substantial glazing in the core, and the evolving ventilation strategy, it was not feasible to certify the entire block as one entity as had been originally planned.Certifying the two blocks individually incurred additional air tests and reduced the overall treated area.

Steel frame: Incorporating steel frames into Passivhaus buildings involved a significant learning curve, as Passivhaus Trust guidance on the subject had not been issued when the project commenced.

District heat network: The district heat network created some challenges for the Passivhaus Certified Designer to model, as the consumption, energy source and distribution losses of the network needed to be captured and evidenced for certification.

Palomar Court Passivhaus. Image credit: Collida/ Willmott Dixon

The success of such projects necessitates the involvement and education of a collaborative supply chain partner, a Stage 5 set of detailing and sequencing to be complete prior to commencing works, and a robust quality management audit on site.

Lorna Taverner, Head of Collida Design, Willmott Dixon

Lessons learned

The project acts as a useful template for how to deliver Passivhaus using a LGSF system. Passivhaus projects constructed using LGSF or steel frame systems (SFS) are likely to be adopted more widely, due to fire regulations and the increased adoption of Modern Methods of Construction (MMC).

For similar future projects, the design team would hope to simplify the design to ensure that Passivhaus certification could be undertaken for one entity, rather than being broken down into parts.