Extended in Four Weeks

Hallam Funke's weatherboarded cottage in a pretty Kentish village was built in 1840, and lived in originally by a shepherd who was employed by the nearby manor house. With its two-up, two-down layout and downstairs bathroom, Hallam, 36, and his partner Merle, 28, soon found they needed more living space in the cottage, and to achieve this they needed to make major changes.

They waited for two years before starting work, and considered various different ways of altering and adding to the layout before finally asking a local architect to draw up plans. Hallam was in a better position than most to cost out the building materials for the project, as by this time he was sales director (he is now Managing Director) of Styro Build, a well-known brand in Europe for the past 30 years.

The company manufactures and markets a revolutionary lost-shuttering system consisting of an inner and an outer layer of polystyrene blocks that slot together like children's building blocks, thanks to the castellation of their upper and lower edges. The two layers are erected 150mm apart and separated using plastic spacers or ties which form a cavity, or shutter, for concrete to be pumped into. This combination provides walls with excellent heat and sound insulation.

The great advantage of the system is that its very quick and relatively easy to put together - but when Hallam first started working for the company he'd seen resistance from builders and electricians, who were sceptical about the unusual new method of construction. If he'd needed any convincing himself about the benefits, though, the enthusiasm of these same people once they started working with the system - and their willingness to extol its virtues when potential customers were being shown around would have persuaded him that he should practise what he preached and use it to build his own extension.

"As well as being involved with Styro Build, I'm also a director of Build It Supplies, a broker for self-builders that shares the same warehouse and depot, so I had all the relevant information to hand and was easily able to compare the different options available to me. I quickly realised that, even on a relatively small project like my extension, it would be far less costly to use Styro Build than it would be to achieve a build of the same quality using traditional construction methods," says Hallam. "In fact, the potential cost saving allowed me to go back to the architect and ask him to draw up new plans for a larger extension than I'd originally envisaged, and we were able to maximise the internal floor space because the good insulation properties of Styro Build meant the wall construction could be fairly narrow. Obviously it was going to be good publicity for us if I could say I'd used Styro Build on my own home, but even setting that aside, it was an obvious choice right from the start."

The key saving is on labour, because the construction process is so quick. And, as anyone who's ever been involved with building work themselves knows, delays can cause a huge amount of frustration - as well as unexpected additional costs - when one element isn't finished in the planned timescale, thus holding up the next stage.

"The speed of construction was almost as important as the cost saving in this case as we were fast heading towards winter and I was keen to get everything done before the weather got really bad," says Hallam.

In the event, he was ready to start construction at the end of November, right in the middle of a storm that rumbled on for several days. Despite having to battle with the weather, he and one other person were able to put up the basic framework in just two and a half days. "We started by setting out the first layer of blocks to the architects plan. By mid-morning on the first day, the walls were well on their way up and, by lunchtime, we were ready to put in the preformed lintels for the windows and doors. At teatime, concrete was pumped in. First thing the next day I was walking around in what was to be the master bedroom upstairs."

"For the flooring, we decided to use the V-Tec system, which is a precast concrete beam into which a lattice of steel is cast. I have to say, we found the beams were quite manageable for two of us, even on long spans."

"That just left the roof, which was on by the end of the week," he says. "I knew in theory that it should be possible to build the extension so quickly, but actually seeing it happening on my own property was still a revelation."

The internal walls were plastered straight over the blocks and, by Christmas, work was finished - the new rooms felt as though they had been there forever.

The extension is in the shape of an L on its side, and has added a bathroom and a master bedroom with en suite shower room upstairs, with a new kitchen below and a large living room stretching out from the back, where French doors open onto a wide area of decking. Overall, the extension has increased the size of the cottage by 125 per cent - and almost doubled its value.

Hallam found that he was able to get planning permission for the extension relatively easily, the only stipulation being that the exterior should match the traditional features of the existing building exactly, with weatherboarding at the front, and the rear part tile-hung and part rendered. In fact, it is now impossible to distinguish between the new and old sections of the house.

"If we had used traditional construction methods, the extension would have cost a total of around £55,000," says Hallam. "But by using Styro Build, we were able to reduce that by about £15,000." What's more, because the system is so energy efficient, the extension stays nice and cool in the summer and warm in the winter, and that has a knock-on effect on the original rooms too. "We only have to have the heating on when its bitterly cold and I reckon we save literally hundreds of pounds each year on fuel bills. The sound-proofing is excellent too, so we don't have to worry about the neighbours if we want to have music playing at full volume, either! All in all, its been a huge success."

Further reading:

• A DIY Self-build
• SIPs: Faster, Greener, Warmer?