At this year’s Ecobuild, the Eco2h2ouse created such a stir that there was a constant crowd around it and a queue to go upstairs.

And what was attracting attention was not just the building’s timber frame, and its metal web joists and triple-glazed timber windows, but the water tanks placed in the ceiling to provide thermal mass – hence the brand name E CO2 H2O use.

Overheating is a common criticism aimed at timber frame buildings and it could become more of a problem if climate change turns up the heat, said Tim Fenn, the brains behind the building system and Eco2H2O Ltd.

“We have to take this into consideration,” he said. “We’re putting up timber frame buildings that will last 50 years, when we will have the same climate as the south of France.”

Based in Oxfordshire, Fenn’s other company, Oakwood Builders & Joinery, which he took over from his father, specialises in “eco reburbishments” and builds houses to the Canadian Super E standard. But it was his earlier work in community agriculture projects in Africa that got him thinking about how he could produce housing that didn’t rely on air-conditioning, or the thermal mass of energy-hungry concrete for cooling.

The answer was water. It has twice the thermal absorption potential of concrete, without its high embodied energy. And the tanks are cost-effective too, said Fenn.

Construction physics
In future, he maintains, architects and the building industry generally will have to think more about “construction physics”, how to heat and cool a building using construction techniques and materials rather than mechanical means.

“There’s going to be more of a focus on individual buildings because you won’t be able to build a housing estate with exactly the same house. You need a different design for each elevation,” said Fenn.

His answer – the Eco2ho2use – is a building system comprising a laminated veneer lumber (LVL) frame, CETRIS recycled wood and cement composite particleboard, triple-glazed windows, a range of insulation materials depending on the target energy performance, a continuous vapour barrier in the internal wall panels to maximise airtightness, mechanical heat recovery ventilation (MHRV) and the 200-litre water tanks.

Fenn chose timber for its renewability, and LVL specifically for its stability and the flexibility it gives to the design. “It has higher embodied energy than solid timber, but more strength and the durability,” he said. “If you write that off over 200 years it’s hardly any different. You have to look at the long term.”

LVL beams are also used for the roof, removing the need for trussed rafters. “If you have trusses you’re doubling up on the framing in that area,” said Fenn.

Topped out in a day
The roof structure provides the option to create living space in the loft, as well as room for the water tanks and the MHRV. The metal web joists also make running ducting and services easier and quicker. And all this means the roof can go on in a day.

“If you get the roof on in the first day, everything else can be done under cover,” said Fenn.
He is passionate about the airtightness of his buildings. He specifies Airflex to ‘wrap’ both his reburbishments and the Eco2ho2use, and in the latter has changed the make-up. “In most timber frame systems you have the stud work and then put the vapour barrier underneath the plasterboard. However, every time you make a hole for an electrical connection you’re breaking into the membrane, so we’ve moved the vapour barrier into the wall panel.” 

On the walls, the CETRIS board – which is denser than plasterboard – increases the internal thermal mass but it is the water tanks that do most of the work. Made in Australia and designed for rainwater harvesting, these are 500mm wide so they sit within the 600mm joist centres. The number and position depend on the building’s orientation and location.

“You’d expect to have more on the south side than the north. It really depends on the thermal modelling of the building,” said Fenn. “If you’re building in north-west Scotland it’s going to be different from building in Dover.”

Fenn is aware that some people may be apprehensive about living with several thousand litres of water above their heads but points out that it is no different from the hot water tanks, radiators and underfloor heating in most houses, “where you have water going everywhere”.

“But it is sealed; it’s in a tank and it’s not moving [flowing] so there’s less chance of leakage,” said Fenn. “And when you’re in a concrete building you don’t worry about the concrete collapsing.”

The ceiling void is a convenient place to house the tanks but they could also be positioned around the stairwell or in the walls. The house also has LED lights which average 15% of the energy consumption of an incandescent bulb and 50% of fluorescent tube lighting.

Like Super E, the Eco2ho2use – and an Eco2office and Eco2hotel are in development as well – is a building system, rather than a design, which any the architects or builder can use.

UK brand
Long term it could be the UK’s ecohouse brand, like the Canadians have Super E and the Germans Passivhaus. “We need a UK brand that demonstrates that a house is to a certain standard,” said Fenn. “All we have is the Code for Sustainable Homes which is about washing lines and all sorts of irrelevant stuff.”

Since Ecobuild he and his team have been kept busy costing the various enquiries generated by the show, and preparing to take centre stage at this month’s Grand Designs Live show at ExCel in London.

The market response so far has pleasantly surprised Fenn. “People [at Ecobuild] were interested in the technology; they were laughing about the simplicity of it [the system]. Most people got it, that’s what’s really important to me. It doesn’t have to be rocket science – you build a simple framing system that accommodates airtightness, insulation and ease of build,” he said.

And, he might have added, you just add water.