Insulation: Board and lodging

It takes grit and determination to manage the design and construction of your own home. But it takes an extra level of confidence to have the whole process filmed and then broadcast to the British public. Nonetheless, architect Richard Hawkes agreed to let Channel 4’s Grand Designs and presenter Kevin McCloud film construction of his new family home in the Kent countryside.

Crossway is an ambitious eco experiment that incorporates a plethora of technologies and materials aimed at improving thermal performance and reducing its carbon footprint. In fact, Hawkes claims the building would achieve level 7 on the Code for Sustainable Homes – if such a level existed.

One product that Grand Designs will introduce to the nation is a phase-change insulation board called Energain manufactured by Dupont. It modifies the internal temperatures by absorbing heat when rooms become hot and then releasing it when they cool down. It’s particularly well suited to timber- framed buildings which need extra thermal mass.

Crossway is, in fact, a timber and masonry hybrid, with a brick vault structure giving the house its distinctive arched profile. The Energain panels have been fitted to interior walls in two south-facing rooms with large windows that don’t come into contact with the masonry. ‘The house has been highly insulated to keep it warm in the winter, but we needed Energain to increase thermal mass in these rooms in the summer without having to build a brick wall,’ says Hawkes.

The 5mm-thick aluminium-coated boards are filled with a compound of paraffin wax and a stabilising copolymer. When the room temperature exceeds 22ºC during the day the wax melts, absorbing heat from the room, and when temperatures drop below 18ºC at night it re-solidifies, returning heat to the room. ‘Dupont created a thermal model of the rooms, which showed that the boards should reduce heat by up to 7 ºC,’ says Hawkes.

Using Energain alone will not prevent the rooms from overheating in summer and at Crossways the panels work in conjunction with a heat recovery ventilation system to stabilise changes in temperature.

Other insulation techniques include the use of recycled newspaper, which was transformed into papier mâché, combined with inorganic salts and stuffed in the cavities of the timber-panelled external walls. Hawkes says it’s the cheapest means of achieving the highest U-value of 0.12 in a wall 300mm thick. Straw bale insulation, for instance, would have eaten up living space due to its 600mm thickness.

Papier mâché is a lot cheaper than Energain, which, at around £32/m2, stretches the purse strings. But Hawkes says the expense is justified as, combined with other insulation technologies, it meant he didn’t have to purchase an air conditioning system or pay the associated running costs.

He’s also convinced that using a paraffin-based product does not increase fire safety risks. ‘The panels go under a layer of plasterboard, so it already has 30 minutes of fire protection, followed by the enclosing layer of aluminium. The wax is also stabilised by the copolymer, so even when the paraffin melts it won’t slump to the base of the panel. Basically the whole house could burn down and the paraffin wax panels would still be fine,’ he adds.

Stewart Delgarno, director of product development at developer Stuart Milne Group, also trialled the product in the Code 5 Sigma Home at the BRE Innovation Park in Watford. ‘We used it in some smaller rooms to prevent overheating and we would consider using Energain in a development-scale test. There’s work to do on installation and performance. The panels still have to be fitted behind plasterboard, and operatives have to be careful when cutting the board’s edges to fit between studs. Fire integrity is still an issue. But it’s only through test projects like this that technical innovations ever get to market.’

Hawkes tends to agree: ‘People in construction are very fickle and it can be like trying to get an oil tanker to change directions. But luckily by building my own house I get to just try these things out!’ And by inviting the Grand Designs team into his house, Hawkes has ensured that innovative ideas such as Energain reach 4m TV sets – and helped to nudge the tanker on a new course. cm