Tradis Tardis

The pair of semi-detached homes are being built in Cherhill for the North Wiltshire Housing Association under the direction of the Integer Group. Room in the roof, near-instant build, and Integer’s green objectives are all being achieved through the use of Fillcrete Building Systems’ Tradis. Building Homes’ 1998 Innovation Award winner, Tradis delivers a house shell in a series of easy-to-assemble, factory-made closed structural panels.

Until now, Tradis has been commonly used for floors and walls, but the North Wiltshire project is the first to use the system for roof construction. Several more projects later this year will follow North Wiltshire’s innovation.

The housing association is a founding member of the Integer Group and this is its first experience of building ultra-green.

“We were attracted to the Masonite, Warmcel and Tradis system because it looked to us to be the best thought out solution on the market at the moment,” says John Llewellyn, architect team leader at North Wiltshire HA. “Quite apart from the excellent insulation standards achieved, we liked the fact that there was very little waste - even the offcuts end up being reprocessed as Masonite board.

“The scheme budget for these two three-bed units is £145 000: that’s around 35% more than we would expect to spend, but bear in mind that we are building to a much higher standard, including all kinds of elements that we don’t usually provide such as data cabling and intelligent white goods.

“Also, because we are using a room in the roof design, we have an internal floor area that is 110 m2, instead of the standard 85 m2.” Alan Juhlke, North Wiltshire HA’s quantity surveyor, reckons superstructural elements will cost around 30% more than on a typical brick and block house, but he adds that he would expect the differential to fall on subsequent projects.

“Using this system we get U-values down to 0.16, a much faster build programme, plus the extra floor space in the roof,” he says.

The plan is to build the superstructure of the pair of houses in just one day. At the end of the first day, the structure should be wind and water tight and fully insulated, enabling following trades to start installation on the second day.

The houses will use 200 mm Tradis wall panels, 300 mm roof plates and 350 mm floor cassettes. The roof cassettes are very similar in design to the walls. Each cassette runs the full width of the roof and is simply craned into place, each end resting on the gable walls.

Having extended Tradis to roof construction, Fillcrete Systems is looking at new ways of adding to the system. It is now developing techniques to enable render to be applied straight onto external boarding. This will produce walls no thicker than brick and block, but with U-values below 0.2.

What is Tradis?

All Tradis components have been in use for a number of years. Loadbearing Masonite I-beams are sandwiched between an external sheathing of Panelvent medium board and an internal sheathing of oil tempered medium board. In the factory, panels are machine-filled with Warmcel 500 insulation, which is made from recycled newsprint. Panels can be up to 12 m long and 3 m wide.

Masonite beam claims advantages over conventional timber framing:

• they are supplied at thicknesses between 150 mm and 550 mm, making it easy to build super-energy efficient walls

• they are available in lengths up to 12 m, making them suitable for creating open roof spaces and floors without supporting walls

• Masonite’s chemical structure eliminates vapour barriers and breather papers

• it is relatively clean. The amount of potentially toxic chemicals present in the finished structure is reduced. There is no need for timber treatments, negligible off-gassing and almost no formaldehyde.

• beams are lightweight, which makes them easy to handle and reduces the cold bridging effect of solid timber studding.

Masonite I-beams can be used to build open vaulted roofs:

Because the I-beams are capable of long spans, there is no need for supporting elements such as ridge beams or purlins. Opposite pairs of Masonite beam rafters receive plumb cuts at the apex and seat cuts at the base and are then simply nailed together and raised into place. There is no birdsmouthing involved; the end of the rafter beam sits plumb with the outside face of the walls and fascia and soffit details are nailed on afterwards.