Architect Martin Goodfellow is milking SterlingOSB Zero for all it’s worth – which is plenty – in his conversion of a farm’s disused cowshed into a home for humans
When Martin Goodfellow set out to turn a cowshed on his dad’s farm into his new home, he wanted to root the building in the green rolling hills of the Dorset landscape.
Despite its idyllic location near Cerne Abbas, the cowshed that Goodfellow was hoping to transform was not big on pastoral charm. Far from it. This was a boxy, industrial style shed, built in the mid 1980s and based on a steel portal frame. It comprised a basic concrete floor which supported rough, half-height concrete block walls with a timber, Yorkshire-boarded upper.
This agricultural ensemble was topped by a grey, crinkly tin roof. ‘It wouldn’t have been my first choice of building to convert into a home,’ laughs Goodfellow. Goodfellow is director of Decent Goodfellow Architects. ‘I come from a farming background; my dad’s a farmer but I happen to be an architect,’ he says. In addition to being the project’s client and architect, Goodfellow is also undertaking most of the build himself.
The conversion of a former cowshed into a dwelling is allowed under Class Q permitted development, without the need for full planning permission.
However, Class Q does mean the building’s transformation is subject to certain conditions and limitations, including keeping the home within the external dimensions of the original building. ‘You have to use what you’ve got,’ Goodfellow says.
Decent Goodfellow Architects’ starting point in developing the design was to exploit views from the barn over the surrounding countryside. Goodfellow explains: ‘The shape and form of the barn is set because Class Q prevents any permanent add-ons outside the existing structure, so we developed the floor plates to frame the views – for example the Iron Age fort to the north and the view southwest over the rural landscape’.
Goodfellow (the builder) is working on the barn’s transformation. Externally, the building is now clad in an envelope of black corrugated metal sheets, which he says references ‘historical tin of industrial and agricultural buildings common in the area while helping blend the building into the darker patches of shadow that intersperse the verdant countryside.
To support the new ridged and grooved skin, Goodfellow has had to remove the original block and timber walls and infill voids in the existing steel portal frame with a timber framework.
This is braced by a skin of SterlingOSB Zero boards to both strengthen the structure and provide a backing on which to attach a layer of rigid insulation and a breather membrane. ‘I was told to add the SterlingOSB Zero boarding by the structural engineer because under the permitted development you are required to keep the existing structure without doing any substantial work to it,’ explains Goodfellow. ‘SterlingOSB Zero was the most cost effective solution and it was readily available,’ he adds.
SterlingOSB Zero has also been used to line the underside of the roof beneath the purlins to form what Goodfellow describes as ‘a strengthening diaphragm’. Class Q restrictions mean insulation could not be added on top of the roof so instead it had to be placed beneath its supporting structure. ‘Usually, you’d put SterlingOSB Zero on top of the purlins, but instead I’ve had to line the underside of the purlins with SterlingOSB Zero – after which I’ve still got to fit the rigid insulation and an inner skin of plasterboard,’ he says. ‘It’s an absolute nightmare having to build a cold roof.’
The building’s internal volume is high enough – just – to enable a first floor structure to be added. Decent Goodfellow Architects’ interior layout is based around two exposed blockwork boxes, a refined reference to the concrete blocks originally used to construct the outer wall. On the ground floor these boxes house the family bathroom and a bedroom. On the first floor, exposed untreated timber joists bridge the concrete boxes below to support the master bedroom and first-floor sitting area. ‘It’s in keeping with the idea of a barn; where there would have been a hay loft you will look up to see the doors and windows of the lounge and master bedroom,’ he explains.
SterlingOSB Zero has also been used to line the underside of the roof beneath the purlins
The exposed joists support a first- floor deck constructed using West Fraser CaberDek, tongue and grove moisture resistant particleboard. ‘I used CaberDek because it fits together well, it was cost effective and, as a self-builder working mostly on my own, it is easily manageable because of its smaller sheet size,’ he says. ‘Installing the CaberDek was one of the quickest and most satisfying jobs I’ve completed to date,’ he adds.
Hopefully, there are many more, equally satisfying, elements of construction still to come. Goodfellow estimates that he still has another 9 to 12 months’ work to complete the cowshed’s transformation.