Innovative Riverside Passivhaus Self Build with a Spectacular Cantilever

Navigating the sloping riverside plot

Having worked as a consultant with Beattie Passive, Kerry knew that the company’s offsite manufactured structural system was the one for this build. “I liked their approach and that they train builders to use their system,” she says. “Our contractors, led by Rob Shaw, were brilliant – plus we had Tim from Habitat+ project managing.”

As the plot has a steep slope up from the river (almost 6m in height difference from the river to the road) careful attention was needed for the building stage. The upper level sits at road height, with half of the lower floor below ground. “We commissioned a flood risk assessment and found that when the river floods it spills out onto the other bank. The house is well above the one-in-a-hundred-year flood risk level, so the risk of flooding is very low,” says Kerry.

The sloped plot means you enter the upper storey from steet level

With a highly skilled team behind them, they deciphered how to best work with their tricky plot. “The roadside wall was formed as a U-shape to be both the house wall and retaining wall rather than needing two separate elevations,” says Kerry. “There’s not a huge distance between the road and the river, plus the excavation of the house occupied just about the whole width of the land. We wondered at one point about transporting materials to site via boat on the river, but the builders carefully managed the construction so this wasn’t necessary.”

The living areas have fantastic riverside views

Piling wasn’t suitable because of the proximity to historic buildings on both sides, so their architect suggested the Isoquick insulated raft foundation system. The structural engineer then recommended incorporating a sheer key. “It’s like the keel of a boat; it’s built down into the ground and will stop the building from sliding down towards the river,” says Frank. “It uses pre-cut

Lego-brick style blocks filled with rebar, then concrete with waterproofing underneath. But we had torrential rain at the point, so it was the second time we’ve had polystyrene blocks floating in a basement area – the last time being 1994!”

Working on the tight site meant there was very little space to store all the welfare, materials and equipment needed for the construction, which was a challenge. “Many builders would not have managed with this space, but ours were brilliant,” says Kerry. They shored up the east side with some big I-beams because they were building close to a historic boundary wall.

Closer look Passivhaus-standard bifold doors

A span of bifold glazed doors opens the kitchen-dining area onto the balcony. Frank and Kerry struggled to find a Passivhaus-compliant product. “Everyone wanted to sell us something different, but in the end we found Danish-based Lacuna.

These doors were great because the system could be delivered in components, meaning the glass panels and frames arrived separately. This meant that we could carry them through the building to their position, as having to lift them over the top of the house with a crane would have been another significant expense. And the size and weight of finished doors would have required that,” says Kerry. “Our builder put the bifolds together, meaning we didn’t need a special installation company involved.”

guide to bifold doors

Drainage complications

The drains were another big challenge. “Usually when you build underground you need to pump wastewater up from the lower floor, but the main sewers on the street were positioned 4.7m down. So we thought, great, we can drain by gravity straight out from our downstairs, which is 4m below street level,” says Kerry.

Rob and his team did all the underground pipework at the right depth and it was just the last manhole that needed an accredited contractor to make the connection to the main sewer, followed by repairs the road. Kerry and Frank found someone suitable and paid them an £8,000 (50%) deposit, but the contactor disappeared and become uncontactable. In the end, it transpired this contractor hadn’t even submitted the documentation to get the permissions from Highways. Sadly, after months of chasing, they needed to find another way.

The house has an upside-down layout, with the living spaces upstairs and the bedrooms below. Both floors benefit from big windows that frame views of the river and outside seating areas

At this point, the couple had moved out from their rented accommodation and into the house, but with no proper drainage connections, they got through it by using a washing up bowl, the builders’ loo and took showers at the gym. “We were really living in a building site through the whole of that period,” says Kerry.

In the end they found a local company who had done drainage connections along this riverside. “There was a two-week period where we had to partly close the road for the works,” says Kerry. “It was a hot June, so the ground was dry and the team were brilliant. I would say the reinstatement of that road was one of the best I’ve ever seen in my career.”

Completing the Passivhaus self build

Despite the setbacks, Kerry and Frank have achieved a house full of special details with exceptional sustainability credentials. “Some things were a challenge, but we really wanted to make them happen, such as finding a Passivhaus compliant bifold,” says Kerry. “Another was the staircase that we were originally quoted £25,000 for but managed to achieve it for much less by drawing it up in CAD, having the builder create the framework and using kitchen worktop for the treads.” The wrought iron balustrade on the balcony was made by a local blacksmith, designed to echo the bulrushes in the river. The couple are also very happy with the pivot door in the sitting room; “It makes a special feature in the house,” says Kerry.

With their house now finished, Frank and Kerry have enjoyed hosting some Passivhaus open days and, ever-curious about how things can be improved, are enjoying keeping track of how their home is performing. “We’re monitoring our humidity levels and temperature – we bit the bullet in not having a wet heating system, but the solar gain is working really well,” say Kerry.

We learned

• Pay tradesmen promptly to get a reputation as a good client. People will come willingly to do work for you if you cherish your team and treat them well.
• Some products marketed as Passivhaus don’t have the data required to go into the PHPP (Passivhaus Planning Package) tool. For example, for a window you don’t just put the U-value of the unit. You have to have every single element of the product: the individual frame and anything else as separate data to go into that. So it’s quite a chore!
• We bit the bullet with having no heating, as we rely on the MVHR and the natural warmth of the sun in the Passivhaus design. In winter we don’t generate enough casual heat to keep the temperature up, and we like mid 20s, not high teens. We have found that the MVHR does not lead to the same temperature throughout the house so we have installed additional heaters to warm individual rooms when necessary. All heaters are Trust electric radiators so we don’t store heat unnecessarily.