The bold, angular looks of architect Adrian James’s home belie a low-impact timber-frame house that optimises solar gain, is zero carbon in use and aims to offset its embodied carbon within 30 years. What was the thinking behind the form?
The copper cladding makes the home extremely conspicuous. Was it difficult to get planning permission?
Strangely, given its adjacency to protected meadowland and the green belt, it was relatively easy. The site is at the very end of a lane and was formerly the lower garden of the next-door property. When they sold us the land, it was on the understanding that there would be a height restriction and no windows looking north to their property. This was fine by us, since the key view is to the east; and south was green belt land. The planners were concerned with the perception of the house from the public rights of way to east and south, while the landowner was happy with our design’s clerestory windows, which preserved their privacy.
Can you explain the reasoning for Copper Bottom’s angular form?
The 235m2 home’s diagram is simple. We wanted it to be two-storey for compactness, with living spaces and bedrooms facing south – so the parameter of a cuboid was there from the start. The aim was also to make it net zero, generating more energy than we used, so we sloped the roof to the south to use as much PV on it as we could. On-site energy generation is at 134 per cent.
Given the south-, east- and west-facing aspects, we needed to protect all the windows on these sides. We could have created a cube and attached brise soleils onto the building to do this, but this would have involved a lot of metal, embodied energy and potential cold bridges when fixing it back to the structure. So we decided to embody the brise soleil within the form of the house using angled timber trusses on the wall attached to a simple box-like superstructure of highly insulated SIPs panels, delivering an overall U-value of 0.261W/m2K.
The shading concept may have been influenced by Marcel Breuer’s 1970 offices for IBM in Boca Raton, Florida, but there’s a hint of Mario Botta, even Shin Takamatsu, in there. I was struck by Philippe Starck’s 1989, copper-clad Nani Nani building in Tokyo at the time, though I also used copper on my previous home. I worked at John Outram’s office earlier in my career, so a ‘strong’ form didn’t bother me.
The upshot is that the copper cladding becomes a drape for the formed timber frame, so once we created the necessary 900-1200mm ‘prows’ to protect the windows set into the SIPs structure from solar gain, the sculptural form really just evidenced itself.
What about the use of copper – isn’t it high in embodied carbon?
Most carbon-capture calculations you download have a very high rating for copper as it’s smelted, but the reality is that isn’t the case. Most copper used for cladding is recycled wiring; this is 100 per cent recycled and recyclable. We went for a pre-patinated copper finish since I wasn’t convinced the inevitable weathering differentials on different faces and facets of the building would ultimately look satisfactory. It also gave a monolithic form, which we liked. The actual copper finish is a mere 0.6mm thick, which means very little of the material is used, despite its covering all four sides of the house. We considered using Corten, but panels would have been at least 5mm thick – a lot heavier – and we would have had to use interface fixings. As it was, we used the same guys who clad our first home years ago – real craftsmen, who have done a great job with the standing-seam cladding here.
What about the foundations?
The ground quality was so good that we only needed shallow 600mm concrete strip foundations, and very little concrete was used. Had we needed more, we would have opted for screw piles. We used standard concrete as GGBS would have meant either mixing a full mixer batch – or mixing it on site, which the engineers weren’t happy with. As it is, it makes up just a small proportion of the home’s 217kgCO2/m2 carbon footprint.
Can you explain the heating, cooling and PV strategy?
Despite a skin of of highly insulated SIPs panels, the floors are concrete and we have a solid brick wall at the centre of the home. That introduces a lot of thermal mass, helping steady the internal temperature. The house has a low form factor, triple glazing and the commensurate insulation to be Passivhaus. We have one air-source heat pump for hot water and the underfloor heating. If the house overheats during the day, we open the clerestory glazing for nighttime purging – and most of the time, this suffices.
We installed a Zehnder MVHR system in the plant room, which does the air handling and, most of the year, works as it should. We have found that for about two weeks in summer, if heat builds up during a particularly warm period, there is no scope to cool the house sufficiently despite all these measures. So we introduced a small air conditioner, which we can use at this time. Its controversial, I know, but it was important to be pragmatic about future-proofing the home.
The plant room also has a PV battery and inverter to convert it to AC power. A typical house will have five or six solar panels on the roof – we have 37! That means we are massively overproviding electricity. Our annual CO2 emission is -3.36kgCO2/m2 and we aim to offset the embodied carbon used in the home’s construction within 30 years.
You said you weren’t quite Passivhaus?
Not quite – we achieved 2.95m3/h.m2 – but it was a driving aspiration. For instance, we achieved the recommended 50 per cent glass ratio on the south side to promote solar gain in winter, though we were compromised by having a double-height space in the centre of the home, meaning the Passivhaus floor-to-volume algorithm worked against us. We also would have needed greater levels of airtightness, which, while gained with the tilt-and-turn triple-glazed aluminium windows we specified throughout, wasn’t achieved with the sliding doors in the ground-floor living spaces. Sliding doors can be problematic if you’re looking to achieve stringent airtightness, since they tend to involve a brush rather than a silicone seal at the more affordable end. You can just feel a little air coming through if you put your hand to the tiny gap between the frame sections, and that’s where we fell short.
How did you deal with roof access?
There is no dedicated roof access per se. We’ll need to access the roof every couple of years to maintain the PV panels and gutter, which at 300mm wide and with a 180mm fall, is large enough to deal with the run-off from a 10-degree roof slope, as well as leaf accumulation in this rural location. Set behind the top prow, it has a 160mm-diameter outlet that runs down within the SIPs panels to a low-level stainless steel hopper. Leaves from the roof wash down to here and can be removed by hand. This avoids the need for regular roof access and is helped by an occasional drone inspection.
How has the design been received?
Local residents and passers-by like it, but reactions from architects are mixed. The thing they seem concerned about is the void between the ‘skin’ and structure, which is seen as non-functional. But that’s not the case; it is, in fact, an embodied brise soleil that performs an essential role in dealing with solar gain as our climate gets hotter and wetter. The home is designed to last 100 years – every building erected now should have blinkers around its windows!
Client Adrian James and Sarah Shekleton
Architect Adrian James Architects
Structural engineer SOLID Engineering
Services engineer CBG Consultants
Principal designer Adrian James Architects
Approved building inspector Vale of White Horse District Council
Main contractor GC Interiors