A young couple have got to grips with unusual galvanised steel foundations, a barrel vaulted roof and geothermal heating in building a low carbon footprint bungalow in Kent, under the glare of television cameras.
Back breaking endeavour from a husband and wife construction team has culminated in completion of a bespoke bungalow, built using precast components and novel techniques never previously used together on one project. The property features a striking precast concrete barrel vaulted roof, is supported on foundation beams made from galvanised steel and sits astride concrete piles incorporating heat transfer tubes designed to draw warmth from the ground.
Nine months of hard labour from Paul and Jo Tarling of Chatham, complementing the work of building specialists, was captured by a television crew for the Grand Designs programme and transmitted to millions of viewers this month (April). The enthusiastic novices gave up their day jobs to work full time on the build, after enlisting revered architect Richard Paxton, who since sadly passed away, to design the new home. Their aim was to build a distinctive bungalow for Jo’s parents, to make use of a renewable source of energy to heat the property and incorporate wheelchair access to accommodate the needs of her father.
The barrel vaulted roof, galvanised steel foundations and geothermal installations came from the specialist contractor and manufacturer Roger Bullivant Ltd (RBL). The company helped the Tarlings in order to demonstrate how a series of emerging construction techniques can be used in unison.
RBL project manager Paul Emblin explains: “This is an architecturally innovative project and it seemed appropriate to try out a series of new engineering ideas. We are taking advantage of new geothermal heating technology, have specified a lightweight variety of house foundation that we have never previously used and designed a special roof that conceals cable runs and pipes.”
Groundworks began last July with the creation of 46 piles to a depth of 10m. Sections of augered flight measuring 1.5m long and 300mm in diameter were installed using a 12t piling rig and connected to one another. Removal of the augured flights brought material to the surface. The presence of heavy clay in the soil allowed the 300mm diameter voids in the ground to remain open long enough for reinforcing cages to be inserted.
Harnessing the warmth of the ground to heat the property involved use of heat transfer tubes, which were secured to each reinforcing cage and inserted to full pile depth. Warm air is drawn through the pipes to serve a reversible heating and cooling system, installed by the clients beneath the floor.
Self builder Paul Tarling said: “There is enough stable temperature at a depth of 10m to provide sufficient warmth for a building of this size. I would hope that this development proves to be carbon neutral. It made good sense for us to attach the heat transfer tubes to the pile reinforcing cages, which were being installed in any case to provide a durable foundation.”
Each pile was later filled with ready mixed concrete and completed with a 760mm diameter circular pile cap.
Delivery to site of over 50 lightweight galvanised steel foundation beams followed, and a pair of operatives placed 20 different lengths of the ‘SystemFirst Homes’ foundation by hand. Each beam spans between a pair of pile caps and is shot fired to each cap to provide a secure connection. The longest span was 3.3m and the shortest was 0.9m.
Clear labelling on each beam avoided the potential for confusion over which section belonged where. “This is one of the first projects on which we have installed the galvanised steel version of the SystemFirst Homes foundation,” says RBL’s Paul Emblin. “It is cheaper to manufacture and proved to be lighter and quicker to install than a previous version of the foundation made from stainless steel.”
Additional steel cross members – known as ‘ladder racks’ – were installed between the main foundation beams to provide added support, before square panels of polystyrene were dropped into place to offer insulation. The bungalow’s floor was completed with the installation of underfloor heating and a 100mm thick concrete screed.
Each main beam features a pair of troughs to receive a pour of concrete and the completed foundations support a single course of 365mm thick ‘Ziegel’ blocks, which form the perimeter and internal walls of the bungalow.
Use of a single leaf of the Ziegel blockwork to build the perimeter walls removed the need for cavity brickwork and installation of wall ties. Blockwork assembly, rendering and plastering took less than three weeks.
Next came installation of the bungalow’s barrel vaulted roof, which spans a width of 5.6m, has a headroom clearance of 3.5m in the centre and 2.5m at each edge. The roof is formed of 23 ‘dual skin’ precast concrete sections, each of which is supported by a reinforced truss.
Roof sections were manufactured by RBL’s Concrete Products division and contain a central core of polyurethane foam insulation. Five conduits installed inside each roof segment during manufacture – and which now run the length of the bungalow – are designed either to hide cables for interior lighting or keep heat transfer pipes from view.
A mobile crane lowered each 2.5t roof section into position and panels were slotted into one another in a tongue and groove fashion. Installation of the roof took just two days during December. The vaulted roof covers the length of the main body of the bungalow, with a flat roof shielding an annex that houses a master bedroom.
Paul’s wife Jo Tarling remarks that she thoroughly enjoyed the experience of building a property with her husband, but is relieved that the project is over. “There was a vicious learning curve for both of us to get to grips with. We bought an excavator and dumper off the Internet, and got stuck in.
“It has been both a stressful and exciting experience, but most importantly it has been great to do something worthwhile for my parents.”
