A Low Impact Self-build by the Thames

It must have been a comic scene when a quiet party around a bonfire suddenly turned into a bucket-brigade firefight, as Julia Kendell and her partner, Andrew Hughes-Hallett, strove to contain the flames consuming the remains of the shack that had been their home for the previous few months before it spread out of control.

Having pulled the place down to make way for their new self-build home, Andrew had thought that a bonfire party with a few friends would be a simple and fun way to mark the occasion, but the centuryold timber was far more flammable than anticipated and went up like a tinderbox, putting the neighbours in fear for the safety of their homes. Fortunately, a plentiful supply of water was on hand to control the flames, because running along the bottom of their garden is a picturesque stretch of the River Thames.

Apart from the obvious fun of it, the motive for burning the old house down was well intended. Julia and Andrew’s ethos for their whole project was to design and build a new home with as little impact on the environment as possible, including the creation of almost no landfill. “Just three skip loads of waste left the site to go to landfill during the entire build,” explains Julia, who juggled her involvement with the project with her TV work as the interior designer on BBC1’s DIY SOS.

“The waste that did leave the site was almost entirely packaging for materials,” claims Andrew, who ran the nine-month build with help from his nephew, a general builder, and a pair of Polish carpenters.

“We dug no foundations so there was no spoil, used almost no concrete, and all of the offcuts from the timber building have been cut up and stored in bags, and are gradually being used up as firewood for our woodburning stove.” For a new house that measures 350m2 plus a large garage, this is quite an achievement.

The couple say their inspiration for the project was a prototype eco house built further down the River Thames undertaken by their friend and architect, Chris Tapp. Chris had devised a simple post and beam frame system using glulam timber: small sections of Douglas fir, laminated together to form structural beams and columns that are immensely strong, dimensionally stable and also highly ecological. Bolted together on a regular grid pattern, designed around standard sheet panel sizes to minimise waste, they can form a structural post and beam frame, within which almost any configuration of room layout is possible.

The structural skeleton, which Julia likens to a giant Meccano set, takes little skill to assemble, and can be clad in interlocking structural insulated panels (SIPs) to form walls and a roof, and panels of double-glazed low-E glass windows and doors, to create an incredibly airtight and energy-efficient building envelope.

The really clever part, however, is the foundation system. Instead of digging out trenches and filling the ground with tons of concrete, the house is supported by a series of helical steel piles which are literally screwed into the ground until they have sufficient friction bearing to support the required load: in this case they go down 8.5m. The piles are capped with a metal plate, which can be adjusted to level, and the frame is built off these. The posts are braced with stainless steel ties to give the whole structure rigidity. As there is no excavation, there is no spoil to remove from site. “What little ground we did dig up for the dry dock and septic tank, we used to repair the eroded riverbank,” explains Andrew.

“As well as being a highly ecological building system, it also lends itself perfectly to building within the floodplain,” says Andrew. “This site floods every year and the Environment Agency rules dictate that the ground floor of any new house in a floodplain has to be at least 300mm above the level of the highest flood expected in the next 100 years. With a post and beam system you can build above the flood line or on a sloping site very cost-effectively.”

“The foundation and build system means there is almost no impact on the existing landscape at all,” says Julia. “And to blend in with the wooded setting we chose to clad the building in western redcedar, which has been left untreated to weather naturally.”

“The whole exterior is designed to be zero maintenance,” adds Andrew, “with Spanish roof slates and untreated Siberian larch around the edges forming box gutters, powder-coated window frames of recycled aluminium, and aluminium downpipes.”

Julia and Andrew’s brief to their architect was to create a five bedroom home that related closely to its beautiful surroundings. The design also had to work within the constraints of the Environment Agency’s policy for new buildings within the floodplain, which as well as dictating height above flood level, limited both the footprint and volume of the house. These constraints gave rise to the space-efficient one-and-a-half storey design.

The architect’s ingenious solution to raising the garage above the floodline, without having unsightly ramps, was to build the entire structure on mechanical jacks, which are operated by float switches. When the river bursts its banks, as it does every year, the entire garage, complete with cars, rises up above the waterline.

The self-raising garage is far from the only technology in this new property. The energy-efficient, airtight envelope has a very low heat requirement, making it ideally suited to an underfloor heating system powered by a water-to-water, closed-loop heat pump system which extracts energy from the wet dock, constructed in the riverbank. The couple claim a Coefficient of Performance (CoP) of 1:5, which means they get 5kW of usable heat out of every 1kW of electricity they put in.

“We have no gas supply here, or sewer or water, so apart from electricity we are completely autonomous,” says Julia. “Heat pumps are at their most efficient when the coils are in a body of water, and the Thames rarely drops below 10°C, even in winter. We draw our own water from an aquifer via a borehole we installed to the side of the house. We have also fitted a mechanical whole-house heat-recovery ventilation system to control ventilation and heat loss.”

One of the few problems we had was installing the mini sewage treatment plant. “Even in the summer, the water table is only 1m down and we needed to go down just over 2m to get the right fall and to be below ground,” says Andrew. “We had to put in sheet piling and excavate within this, with a pump going constantly to keep it dry so we could cast a level concrete base.”

Although the building’s form is dynamic and contemporary, the use of natural materials softens it and helps it blend in well within its riverside setting.

Internally Julia has kept the same theme, using largely natural materials. “I wanted to keep the interiors quite simple to let the house and environment speak for itself. The oak floor sits well against the Douglas fir structure and cedar cladding on the ceilings, and is the right backdrop for the house.

“Lighting is key to any design, and we have gone for lots of discreet light sources all controlled by a Lutron mood lighting system.” As well as programmed settings for different times of day, inside and out, the system has a holiday setting which emulates the daily pattern of lighting even when the family are away.

The ground floor layout is centred around a spacious open plan kitchen, dining and living space that occupies much of this level, and has magnificent views down the garden and over the river.

Julia wanted to create a double-height space somewhere in the property “to connect the upstairs and down”, and this inspired the open gallery above the kitchen which mirrors the adjacent stairwell.

“Living here is very serene and relaxed and we could happily stay for ever,” says Julia. “But we want to push the eco technologies further and so we plan to build all over again just up the river, and we have already found the site and put this place up for sale.”

An Innovative Flood Protection Solution

Set on the river bank, Julia and Andrew’s picturesque site does occasionally flood, so the house is raised on timber posts, permanently out of harm’s reach. However, an entirely different solution has been employed for the garage, as architect Chris Tapp explains: “Normally on floodplains the solution is to make holes in the walls to let the water out, but that means everything gets wet. So I came up with the idea to simply lift the whole garage up, and designed a system that uses mechanical screw jacks, powered by an electric motor. The technology itself is actually pretty old, but I only know of one other instance of a property utilising it in this area — a home office.”

Chris explains the system in more detail: “Piled foundations support a grid of steelwork on the ground. Inside the grid, there’s a floor frame which the jacks are connected to. When you suspect flooding will occur, you turn on the system with a remote and the jacks raise the frame up to one-and-a-half metres off the ground, where it will stay until you decide to move it again — there’s no power involved in holding it up. As the building is built on top of the floor, it can be built in any style, and the power, water supply and drainage are all connected by a long flexible pipe.

“This garage measures around 60m² and the cost of putting in a system like this is around £50,000 over and above the normal cost of building a garage of that size.”

Further reading:

• A Super-E Airtight Kit house
• A Boat House on the Thames
• A Low Impact Eco House