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Last year’s AYA judges were impressed by the work of PRP Architects, which was a finalist in two awards including Public and Social Housing Architect of the Year.
In this series, we take a look at one of the team’s introductory projects and ask the company’s associate director, Sarah Campbell, to break down some of the biggest spec challenges to overcome.
What are the main requirements for a client profile? How do you meet these requirements through design and specifications?
In February 2020, Salford City Council appointed PRP to conduct capacity studies for five brownfield sites in Salford, Greater Manchester, to deliver more than 200 new affordable homes. Following planning approval, PRP changed its name to Seddon Construction. The five sites are divided into two phases, with the first now completed and the second due to be handed over by summer 2024.
The initial mission was to provide low-energy housing. However, after planning approval was granted, the brief was changed to Passive House. While we considered a structure-first approach to creating deeper facades, the home was positioned without optimizing its orientation and without considering glazing proportions or architectural form. The sites are designed to maximize capacity to ensure feasibility.
PRP has an in-house Passivhaus designer so we can quickly assess whether Passivhaus is a realistic goal. To test the design, we decided to complete the first part of the Passive House Planning Package (PHPP) on each of the homes that we expected would perform poorly due to poor orientation.
This gives clients and contractors the reassurance that we can achieve Passivhaus in every home. PHPP assisted in testing the exterior envelope specifications and evaluating the size and location of the Phase 3 window aperture dimensions. Slight adjustments were made to the size of the northern and southern windows to minimize heat loss or maximize solar gain.
What was the biggest specification challenge for this project?
As with every project, the most important issue is cost. Tender price increases aside, high-performance insulation and triple-glazed windows do come at a cost, but unlike other housing schemes we cannot downplay the specification of these key components which are vital to achieving overall certification .
We found that the word “Passivhaus” has the same effect as the word “wedding”, an opportunity to inflate costs to cover perceived risks. As Passivhaus becomes more familiar with the industry, we expect to see tender prices come down and a larger, more mature supply chain with more choice and competition.
While there are advantages to using Passive House certified products, we demonstrate that this can be achieved using standard building components. This is achieved through the use of capable supply partners who can provide the required technical data for inclusion in PHPP to demonstrate compliance.
What are the three biggest specification considerations for the type of project? How does this apply specifically to your project?
Passivhaus relies on building a thermally efficient airtight envelope, which means it is beneficial to use a Passivhaus certified building system such as Beattie Passivhaus. The system is designed to be virtually thermal-bridge-free and fully tested to provide extremely low U-values and airtightness. It was deemed unaffordable, so SFS was specified for the main structural frame load-bearing of the apartment, while traditional timber framing was specified for the house.
Given that both systems rely on membranes to provide airtightness, their installation is critical, so we ensured that market-leading products were specified. Pro Clima is applied to the interior surface of the timber frame and completely adhered and sealed with Pro Clima airtight tape. Since the structural SFS is panelized, this means we cannot wrap the membrane continuously where the partition wall meets the exterior wall. This forced us to move the airtight wire to the exterior sheathing panels. Without this continuation, the Passive House Certification Agency would not have certified the building.
SFS framing subcontractor Mansells proposed a solution that included the use of a self-adhesive air barrier on the outer surface of the sheathing panels. Proctor Wraptite proved to be the only way we could provide a continuous airtight barrier using the Metframe system.
What do you think is the biggest success of this project?
We manage to deliver affordable Passive Houses at scale with inexperienced project teams and contractors. We successfully utilized most standard building systems and traditional details. We managed to build something that we as a team are very proud of.
Passive houses are the gold standard in energy-efficient design. They are strong and durable and have huge health and wellbeing benefits, but providing homes for Greater Manchester’s most vulnerable people that tackle fuel poverty is in my view the greatest success.
Project details
architect PRP Architects
client salford city council
main contractor Seddon Architecture
Employer’s Agent Identity consultation
Ministry of Environmental Protection Engineering Design Partner
structural engineer Ritchie Partners LLP
Building control salford city council
passive house designer PRP Architects
Passive House Certification zero energy
Load-bearing SFS (apartment) Mansell Metframe and Metsec
Timber frame (house) framework technology
Exterior windows and doors subcontractor New look windows, product REHAU GENEO
curtain wall brayton construction ltd.
structural concrete floor bobcat prefab
roofing subcontractor The fuel cell
airtight vapor control layer Pro Clima Intello Plus
outer airtight layer Proctor Wraptite Exterior Air Barrier
insulation Jinkuan K112
External Juliet balcony MAB metal factory
Wooden stairs stair craft
kitchen morse
lift nose
AOV Louvre Seltus
Our What Makes This Project series highlights the outstanding work of the Architect of the Year finalists. To keep up to date with the Architect of the Year Awards, visit here.
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