Denby Dale Passivhaus

Location: Denby Dale, West Yorkshire
Completion Status: Completed	Occupancy: Occupied
Architect: Derrie O'Sullivan Architects	Consultant: Peter Warm
Contractor: Green Building Company	Client: Geoff & Kate Tunstall
Certification: April 2010	Certifier: WARM
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The Denby Dale Passivhaus is the first certified Passivhaus in the UK to be built using cavity wall construction. To achieve Passivhaus performance in cavity wall construction, the Green Building Store team developed a number of original design details. These details have been freely disseminated to the wider construction industry through technical briefings, blogs and films, including BUILDING's Passivhaus Diaries.

The Denby Dale Passivhaus was designed and built by an inter-disciplinary team led by Green Building Store’s Bill Butcher as a cost-effective and ultra energy-efficient home for a retired couple. The clients’ desire for a conservatory was incorporated into the building envelope as an integral solar space on the south elevation, with exterior blinds to minimise overheating.

The project’s pioneering approach has subsequently been adopted by a number of large scale projects and has demonstrated that cavity wall construction is a serious and cost effective option for Passivhaus projects.

Denby Dale Passivhaus Image credit: Green Building Store

Building performance monitoring

Leeds Beckett University undertook extensive post-occupancy monitoring of the project which concluded that that space heating during the monitoring period could be estimated to be in the range 9 – 20.7 kWh/m2/year, in line with Passivhaus certification criteria of 15 kWh/m2/year, while total primary energy requirement was also within the certification criteria.

Key facts

Total floor area: 118m2
Treated floor area: 104.4m2
Heating requirement/ year: 15 kWh/m2/year
Heat load: 10 W/m2
Primary energy requirement: 87 kWh/m2/year
Airtightness: 0.33 ach @ 50 Pa (to Passivhaus and Euronorm standard)

Denby Dale Passivhaus. Image credit: Green Building Store

Lessons learnt

The team had to develop construction detailing for cavity wall construction that would address the Passivhaus requirements for minimal thermal bridging and high levels of airtightness. Examples of detailing developed for the project included:

Use of 300mm insulation in the cavity going right down to the strip foundation, so that any heat lost from the concrete floor slab will have a longer thermal transfer path.
Use of lightweight aerated block below ground level, which does not transfer heat as readily as standard concrete block.
Use of basalt resin cavity wall ties (instead of the usual steel ties).
Positioning of windows and doors at the centre line of the insulation layer.
Concrete floor slab is carried across the top of the blockwork of the inner leaf of the wall to minimize shrinkage cracking between the wall and the floor.
To improve airtightness around the window opening, a plywood box was set into the wall. An adhesive-backed airtightness tape was then attached to the plywood with a fleece wrapped into the wet plaster, making the junction between the plywood and plaster airtight. Another airtightness tape was used to seal the gap between the window and the plywood box.

Subsequent Passivhaus cavity wall projects undertaken by the same team included iterations and developments on construction detailing include Golcar Passivhaus & Kirkburton Passivhaus.

U values

Exterior wall: 0.113W/m2K
Roof: 0.096 W/m2K
Ground floor: 0.104 W/m2K
Windows/ average: 0.8 W/m2K

Embodied carbon

In 2022 the project team undertook some research looking at the embodied carbon of cavity wall construction in comparison with other possible construction types using the PHribbon tool.

The team concluded that although the timber frame construction options modelled had lower embodied carbon there might still be a role for masonry cavity wall construction, due to buildability and practical considerations. The research illustrated that it was important to address operational energy (building to the Passivhaus standard), low carbon heating (installing a heat pump) as well as addressing the embodied carbon of building materials.

Given the modest difference in the embodied carbon between the 6 construction types examined, at this point, the priority must be to adopt Passivhaus standards of new build operational efficiency combined with heat pumps starting right now.

Green Building Store

A quantum jump in quality and major change in methodology for builders is required to deliver high-quality Passivhaus cavity wall that does not suffer the performance gap. This may be more alien than a largescale move to timber frame.