Welsh lessons - Millers Place
A developer is rolling out Passivhaus social housing schemes in Wales at no extra upfront costs, thanks to considered construction at design and delivery stages. Its approach is exemplified in the 40 apartment Millers Place project in Newtown for Barcud Housing Association, 32 of which are due to be Passivhaus certified in early 2026.
PHT member MWP is a property developer in mid-Wales that works closely with PHT member Hiraeth Architecture to deliver affordable Passivhaus social housing. Their ambition is to deliver social housing that targets and prioritises the Passivhaus standard and they have developed a formula for achieving this within the structure of the Welsh Government social housing grant.
The Millers Place project is the team's second and largest scheme targeting the Passivhaus standard. 32 of the 40 apartments are targeting Passivhaus certification. The Passivhaus apartments are fully contained within the larger building on site, with a further 8 flats in a two storey detached building that is not going through certification but have been constructed to the same specification. The early design revisions were modelled for building performance to ensure that all proposals would meet Passivhaus standard. PHT member MEAD Consulting is Passivhaus Certifier on the scheme.
Key stats
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MWP was involved in the innovative housing programme in Wales and became aware of the wide extent of fuel poverty. Passivhaus seemed an obvious solution – a no-brainer. Once you know what Passivhaus delivers, it is hard to revert to anything else. On a personal level, pushing ourselves to deliver to the Passivhaus standard is an interesting and engaging challenge. It's about wanting to do a better job for everyone involved. We’re seeing the effects of climate breakdown already and delivering homes with climate resilience is becoming more and more important. Harry Bowen, MWP Developments |
Construction
The Millers Place site was situated close to several Grade II listed buildings. The apartment design referenced the architecture of local woollen mills, using ornate brickwork to soften their appearance. Each MWP development has a bespoke design but uses standardised construction. The standardised system helps keep costs down and streamlines a consistent approach on-site.
Key elements
- Twin wall timber frame, often referred to as a form of Larson Truss, is the chosen construction method. In this case, both timber studs are of a consistent section and are structurally load bearing as opposed to alternative forms where the internal stud is the principle load-bearing element. The wall thickness can be altered to accommodate insulation requirements however the specified thickness has been generally consistent across MWP recent projects.
- Open panels with external sheathing boards and windtight membrane are assembled off site. Onsite the panels are craned into position fixed to the sole or intermediate plates and lined internally with airtight OSB and appropriate tapes.
- The airtight timber panels are filled with mineral wool insulation blown in on site.
- Exterior finishes are an external cavity with a masonry rain screen.
- Platform frame construction is used, with the panels assembled storey by storey.
- At the intermediate floor detail, floors are hung from the interior of the panel, rather than the typical platform frame approach of bearing on to the top of the lower panel. Detailing like this is key to achieving good airtightness and minimal thermal bridging.
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Using PHPP, you're able to micromanage the cost to an impressive level. A key benefit of the data available from the PHPP is that we can review the results throughout the design process to ensure that all elements of the design and specification are contributing effectively to the performance of the building. Armed with this data we can accurately reflect on the benefit and cost of all sorts of factors; from the contribution of windows, to the availability of alternative insulations, and refine the project accordingly. Rob Thomas, Hiraeth Architecture |
U-values |
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Roof: 0.095 W/m2K Truss rafter with airtightness board below and mineral wool insulation |
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Wall: 0.120 W/m2K Twin wall timber frame with mineral wool insulation |
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Floor: 0.067 W/m2K Insulated concrete slab. |
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Building performance
Designed energy performance |
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Airtightness n50 (≤ 0.6ACH @ 50 Pa)
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0.6 @ 50 Pa
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Space Heating Demand (≤ 15 kWh/m².a)
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3 kWh/m².a
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Heating Load (≤ 10 W/m²)
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5 W/m²
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Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)
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60 kWh/m².a
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Primary Energy Renewable Generation
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58 kWh/m².a
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*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.
Heating & hot water: The apartments at Millers Place are heated using all electric heating, provided via electric panel heaters and hot water via water cylinder. Air source heat pumps (ASHP) were not utilised, in accordance with the clients' and developer's preference.
Renewables: 200+ solar PV panels were installed on the roofs. The PV array provides 1.2-1.7kW per flat.
Ventilation: Each flat has an individual MVHR (mechanical ventilation with heat recovery) system.
Summer comfort: The modelled risk of overheating is very low, therefore summer comfort is managed via the MVHR with additional night ventilation provided by openable windows.
Challenges & lessons learned
Repeat supply chain: MWP has worked to build and develop a consistent knowledgeable local supply-chain alongside their tight-knit project team.
Training & site culture: The contractor teams have been trained in-house so that they understood how to install the products and the sequences that must be followed to achieve the outcomes required. An open door policy is in operation encouraging the contractors to suggest modifications that benefit all without compromising quality.
Simplified M&E strategy: The construction team has been trained in MVHR installation and commissioning, which has helped keep costs down. Similarly, the repeat construction specification means that M&E design can also be undertaken in-house.
Repeat thermal bridging details: Using standardised construction techniques helps ensure robust continuity of technical detailing.The project team has undertaken some detailed thermal bridge analysis of the construction detailing, so they can input exact thermal bridge PSI values into PHPP instead of just including conservative guesstimate values. This can really help to deliver some big wins within the PHPP modelling and makes achieving Passivhaus certification more possible.
Incremental refinement of construction detailing: Inevitably, there is a steep learning curve when adopting Passivhaus and the company probably sacrificed quite a bit of profit on its first Passivhaus project . Over time, the MWP construction details have simplified, increasing buildability and reducing room for error. An example might be the airtightness strategy, which has become more robust to reduce any risk of damage during construction.
Standardised construction: The project team’s approach has been to use exactly the same U values and specification and construction on each job. This makes construction easier as you are working with the same widths of wall etc. This approach usually means that apartments will perform a lot better than other building types, thanks to their better form factor. It can also allow a good ‘margin of error’ within the PHPP modelling, de-risking projects. It can also help if orientation is not optimal. This has been helpful for MWP’s Miller’s Place apartments, which are sited in a constrained stepped site, with high levels of shading on one side of the building.
PHPP in value engineering & early-stage design: Using PHPP as a design and value engineering tool is also a way the project team helps keep costs down. The team will develop a fenestration design and then realise through PHPP modelling that a window design with 2 casement arrangement instead of a single casement arrangement is increasing costs by 60% and is not performing as well.
Passivhaus certification: Targeting Passivhaus certification is a prerequisite of MWP social housing projects, but, to keep certification costs down, currently only a proportion of properties on developments are certified, though all homes are built to the same standard. The team hopes to increase this proportion, as certification costs become more streamlined.
Resource efficiency: Another cost saving for the MWP developments is the efficient approach to ordering materials. A software ordering system has been developed to order materials for the site as needed.
Business model: MWP undertakes social housing developments using a ‘self-delivery’ model that contributes to the overall effectiveness of its delivery. The company tends to purchase land itself and then work with a housing association to deliver homes on their behalf. It is very different to the usual delivery model of speculatively bidding for tendering as a contractor.
Key team
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The Millers Place project is an inspiring example of what is possible in terms of delivering affordable Passivhaus social housing in Wales, and across the UK. The project's lessons learned offer great insights as to how to ensure large scale Passivhaus social housing projects can be cost-effective and be delivered within housing grant budgets. The project is due to achieve Passivhaus certification in early 2026.
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Further information
Passivhaus Benefits Guide & costs research
Previous PHT story: Mid and North Wales site visit to Y Wern - 20 September 2025
Previous PHT story: Local networking kicks off in Wales - 20 June 2025
Previous PHT story: Passivhaus now 1% of all new UK housing projects - 20 February 2025
Previous PHT story: Welsh Passivhaus social housing takes off – 1 February 2025
Previous PHT story: Welsh social housing blazing a trail - NEW Welsh social housing pattern book - 15 January 2025
Previous PHT story: ‘Fabric first’ alternative option for Welsh social housing - 15 January 2025
“ MWP was involved in the innovative housing programme in Wales and became aware of the wide extent of fuel poverty. Passivhaus seemed an obvious solution – a no-brainer. Once you know what Passivhaus delivers, it is hard to revert to anything else. On a personal level, pushing ourselves to deliver to the Passivhaus standard is an interesting and engaging challenge. It's about wanting to do a better job for everyone involved. We’re seeing the effects of climate breakdown already and delivering homes with climate resilience is becoming more and more important.”
Harry Bowen, MWP Developments1st December 2025
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