Milltir - a selfbuild work of art
A modest selfbuild project, Milltir has been built by its owners Simon & Violet Greaves in a challenging plot in Llangollen on the banks of the river Dee. The house also serves as a gallery of the work of Simon's father, artist Derrick Greaves, and lays claim to being Denbighshire’s first Passivhaus.
The owners purchased a plot with planning permission for a modern house but wanted to see if the existing design could be adapted to achieve Passivhaus certification. A PHPP model was made of the pre-existing design which identified a considerable number of challenges with the existing design which would not only compromise certification but would also result in significant discomfort caused by overheating. The project was constructed on a challenging east/west facing site, that also involved a significant level change underneath the house.
A resubmitted design to achieve Passivhaus certification was granted planning permission. The river location, with a nearby tailrace for a neighbouring hydroelectric scheme, meant that onerous flood protection requirements were needed for the house.
Adapted and redesigned by PHT member Mark Siddall, certified by PHT member MEAD Consulting, the house has been built by the selfbuilder clients themselves.
Key stats
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Construction
The house was constructed in masonry cavity wall construction, having taken inspiration from a visit to the Steel Farm Passivhaus.
U-values |
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Roof: 0.141 W/m2K Flat roof hybrid cold roof with 300mm timber I-beams and insulation |
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Wall: 0.102 W/m2K Masonry cavity wall with 300mm full fill insulation |
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Floor: 0.068 W/m2K Screed on 300mm insulation, on suspended concrete floor |
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Building performance
Designed energy performance |
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Airtightness n50 (≤ 0.6ACH @ 50 Pa)
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0.4 @ 50 Pa
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Heating Load (≤ 10 W/m²)
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10 W/m²
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Primary Energy Demand (≤ 120 kWh/m².a)
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87 kWh/m².a
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Overheating %
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6% |
*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.
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Services
The services strategy included the use of a gas boiler for hot water and heating. Minimising overheating was a key element of Milltir's design. The project's shading strategy included the specification of deep window reveals and seasonal demountable shading.
Challenges & lessons learned
- Summer comfort: One of the key challenges was adapting the original design to achieve the Passivhaus standard. This is because analysis confirmed that the highly glazed east and west facing facades lead to considerable overheating (30% exceedance of 25C). Following a redesign, which was informed by daylighting calculations, overheating risks were reduced to less than 6% exceedance and therefore within the scope of the Passivhaus criteria. At the time, no overheating assessment existed in Building Regulations. An amended planning permission to achieve the Passivhaus standard was subsequently granted.
- Selfbuild knowledge: The owner-builders received training from their Passivhaus Architect Mark Siddall during the course of the project. Fully equipped with the appropriate knowledge and skills, they were able to advise the Building Control Officer (BCO) about the design, what was being done differently, and why it was appropriate. Following these discussions, the BCO was satisfied with the specification and construction work. The blower door test results confirmed the success of the specification and workmanship. The project subsequently received a North Wales LABC Building Excellence Awards 2023
- Post-occupancy monitoring: To assess the as-built energy use and the delivered standard of comfort, the house is currently undergoing a 36-month building performance evaluation process. The results will be made public so that lessons can be learned and shared.
Architects view
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Picking up the project after initial planning permission had been granted required an extensive redesign to minimise overheating and achieve the Passivhaus criteria. There was a process of further rationalisation that not only transformed tight, gloomy stair and lift wells into well-lit circulation but also simplified the construction process, reduced capital costs, and created a highly buildable design. During this process, thermal bridges were designed out, a robust airtightness strategy was developed and every room was redesigned to accommodate a functional services strategy – which includes mechanical ventilation with heat recovery. The construction details were prepared to identify and subsequently reduce site risk whilst enabling the project to be completed successfully. As such, once the project was out of the ground, few problems arose on site. Mark Siddall, Architect & Passivhaus Designer |
Key team
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Congratulations to the hands-on selfbuilders for managing to build this Passivhaus themselves, achieving impressive levels of airtightness. For more selfbuild inspiration, join the Passivhaus Open Days and Passivhaus workshop at the National Self Build & Renovation Centre in Swindon.
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Further information
Technical guidance - Keeping cool: Avoiding overheating risks
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Overlooked by the ruins of Dinas Bran, a 13th Century castle, nestled in a valley and sandwiched between the River Dee and the busy A5, Milltir is a surprising Passivhaus. Not just a Passivhaus home but because it is living gallery, a testament to the work of Simon’s father, Derrick Greaves, an artist who first gained acclaim in the 1950’s and worked tirelessly into his 90’s.
Built by owner/occupiers Simon and Violet Greaves this modest self-build dwelling is Denbighshire’s first Passivhaus. The house reduces energy demand without compromising comfort or indoor air quality and demonstrates what can be done to reduce energy use and in-use carbon emissions.
Constructed on a challenging east/west facing site with a significant level change underneath the house, onerous flood protection requirements and a tailrace for a neighbouring hydroelectric scheme, completion was delayed by the Covid 19 pandemic, and subsequent material shortages.
To assess the as-built energy use and the delivered standard of comfort, the house is currently undergoing a 36-month building performance evaluation process. The results will be made public so that lessons can be learned and shared.
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18th October 2024
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