Concrete-free Passivhaus self build

The Old Woodyard self-build in Herefordshire, aiming for certification, avoided the use of concrete in its entire construction... And yes, that includes the foundations!

Herefordshire Passivhaus selfbuild

Passivhaus architects Polly Upton and Kirk Rusby, both architects with PHT Patron Architype, designed and project-managed their own self-build home in rural Herefordshire. The 3-bed house is designed ‘upside-down’ so that the bedrooms were on the ground floor and the living space above, to take advantage of the views. Clad in striking a red corrugated metal, the house is currently awaiting Passivhaus certification.

The project was in a slightly inaccessible plot close to a railway line. The challenges of getting materials to the site affected some of the building material choices made. It would have been impossible to bring a concrete-mixing lorry to the site, which was a strong contributing factor that led to the decision to have concrete-free foundations.

Low embodied carbon

The project has been modelled for 'whole life carbon' by Architype's Sonia Brookes. The upfront (embodied) carbon was found to have a 40% reduction and the whole life carbon a 60% reduction on LETI targets.

Embodied carbon at the Old Woodyard. Image credit: Sonia Brookes

Timber frame

Timber frame construction was chosen as a more familiar construction methodology and because it was more practical for delivering to site. Timber I-Joists and I-beams are used for the walls, roof and internal walls, insulated with 300mm recycled cellulose insulation. The timber frame was sheathed externally with a wood fibreboard, finished with an intelligent breather membrane and metal cladding. Internally, a vapour block board is used as the airtightness barrier.

The Old Woodyard self build during construction

Concrete-free foundations

The foundations comprise a footing of compacted recycled aggregate, with a bed of natural hydraulic lime mortar on top. A foam glass perimeter strip is used, which has the timber frame soleplate attached to it, on top of the Damp Proof Membrane (DPM) layer.

As well as reducing embodied carbon for the project, the use of concrete-free foundations avoided the stress of a concrete delivery due to the site’s difficult access.

Keeping costs down

A range of techniques developed to adjust to the constraints of the inaccessible site and to keep the self-build to financial & embodied carbon budgets:

How much space do you really need? The proposed floor area of the project was rigorously revised and found to be the most impactful way of sticking within budget.
The window openings were carefully considered and designed for simplicity and sightlines, with fixed windows being designed in to help minimise costs.
The project construction was undertaken by Polly's brother and was his first newbuild Passivhaus project.

Hear more from Polly in this webinar where she discusses the project in more detail, covering construction details and more:

Date for your Diary

Join the Trust on Wednesday 25 May 2022 to explore the relationship between Passivhaus and embodied carbon. This webinar will launch the Trust's Embodied Carbon paper, followed by presentations from key experts sharing their insights on addressing embodied carbon in Passivhaus buildings. And finally, PHribbon developer Tim Martel will be sharing how the plug-in for PHPP works.

Further information

Passivhaus & Embodied Carbon webinar

Passivhaus Primers: Net Zero, Retrofit, Embodied Carbon

Passivhaus goes Personal