Since Richard Sewell and his family moved into their five-bedroom house in Yorkshire in early January they have had to keep tweaking the heat pump – to lower the inside temperature.
The new house, situated on the edge of the village of Fangfoss, was built using Kingspan TEK’s structural insulated panels (SIPs) which have an enviable U-value of 0.2W/m2/K, resulting in the cost of heating being virtually negligible.
In the past, property developer Sewell, a partner in RM Developments, had used ‘traditional’ block and brick and cavity wall construction, but he had always wanted to do something that was “a bit more sustainable”. “I wanted it to be timber frame because I wanted the U-values to be down; SIPs seemed to be the one with the lowest U-value. There are other products on the market, such as polystyrene blocks filled with concrete, but they didn’t reach the U-values I wanted.”
He had previously been discouraged by the cost, but building a house for himself provided the perfect opportunity to experiment. “After the build I could look at the cost, look at the speed of build and determine whether that’s the way I would go in the future,” he said. Having done the sums, he’s a convert and another five-bedroom house for a client is going up in Wetherby.
Chris Davis of Chris Davis Architecture was also a SIPs novice when he designed Sewell’s house and he is also using the system again. “It’s been quite a revelation,” he said.
For both men it was the speed of construction and the low U-value that impressed them most: the house was up and watertight in just 13 days. “As soon as the timber frame people had the ground floor up and started to move down towards the garage, they waterproofed it and we started on the brickwork. The first floor was starting to go up with about 0.5m of brickwork going up,” said Sewell. Half way through the 13-day build, bricklayers were working on the outside while underfloor heating was being fitted inside.
The process requires good site co-ordination, said Sewell, but the overwhelming advantage is that it cuts construction time – reducing the length of bank loans. To build a similar house in brick and block would take two to three months longer.
Davis is equally enthusiastic. “I was impressed by the speed of the package as much as anything, and the accuracy. I was sceptical to start with but it exceeded expectations.”
The Kingspan TEK SIPs, supplied by Skipton-based SIPS@Clays, comprise a core of rigid urethane insulation between two structural skins of OSB3 and form the walls and roof of the Kingspan system. Andy Porter, managing director of Clays, said it supplied a lot of self-builders so he was interested to get developer Sewell’s perspective. “He could see you might pay a little bit more for SIPs but that there’s a cost saving because the building goes up quickly.”
Much of Clay’s business is one-offs, dispelling perceptions that “SIPs are for building estates of standard boxes”.
The panels arrived on two artics, with each cut to size and window and door apertures already formed. “Everything is cut to the millimetre so when it comes to site everything is straightforward,” said Sewell.
He was also impressed with the clean site working. “You don’t have any waste. All we had was the materials you need for timber frame, a crane for a day for the roof, and a teleporter to move things around.”
The roof panels are insulated and supported by glulam beams, providing a useable roof space. “The house wasn’t built to go up into the loft but when we saw this huge space, we put another staircase in,” he said. “This is the thing you can do with SIPs; they give you flexibility.”
In SIPs construction, the floor joists – in this case, 335 linear metres of engineered I-joists – provide rigidity for the building. Because of this, said Paul Amphlett, executive director of engineered timber products at the I-joist supplier CR Taylor, rather than running the joists over internal load-bearing walls, they stop at the wall and are put on hangers.
Such is the airtightness of a SIPs house that some Clays homes require nothing more than a wood-burning stove to provide heat. “We supply people who are almost trying to build to PassivHaus standards,” said Porter.
In addition to a stove, Sewell opted for underfloor heating – a wet system which is fed by the heat pump. The site was not large enough to run piping so, instead, two 85m bore holes were sunk to circulate water in 40mm pipes back to the pump.
“For every kilowatt of power used to run the pump, 4.5kW is gained,” said Sewell. “All the hot water requirements to run the underfloor heating and hot water system come from this.” The system’s efficiency was proven when the pump was turned off to cool the floor while tiles were being laid. “A week later I ran the taps and the stored water was still warm,” he said.
Because of the airtightness, a heat recovery system (MVHR) has also been installed. The warm, moist air from the kitchen, the two ground floor toilets, two en suites and the bathroom is sucked into a unit in the loft, which extracts stale air and filters new air coming in, heating it to 95% of the warmth of the stale. This is then fed, through 150mm ducts, into the living areas. On the lowest setting there is a full air change every two hours.
“You don’t need trickle vents, and you don’t run fans taking moisture out of the bathroom and showers and throwing all that hot air outside,” said Sewell, adding that the MVHR also filters out dust, pollen and other impurities in the air.
Thermal efficiency also extends to the windows where cold bridging is reduced by using plastic spacing bars, rather than aluminium, and the windows are fitted right across the cavity. Even the garage door has 45mm insulation.
Completing the whole house approach is a sound and audio system that is connected to every room and wired for the future. “Any technology that comes out in the next 10 years can be wired into the system,” said Sewell.
Moving from a 1930s house with little insulation to a 21st century SIPS house has been quite a change for the family. “it’s a warm place to be,” said Sewell. “It’s a different way of living.”
|
BEcause the I-joists do not run over internal load-bearing walls, they are placed on hangars |
Keywords: Kingspan TEK SIPS@Clays
