EMMA CULLINANjoined the party atmosphere near Frankfurt to watch a pre-prepared 'passive house', which needs little heating, being assembled in a day

THERE WAS a party atmosphere despite the early hour of 8am. The sun was shining, helium balloons were bobbing against the blue sky and people were already gathered on the grass to watch the first walls of a house go up. This was home construction as a performance, with the workmen carrying out the carefully choreographed build.

We were here, one hour east of Frankfurt, to see a house being built in a day. May 17th was a day dedicated to the building of prefabricated houses in Germany and the Hanse Haus company, which has, for 80 years, built prefabs and now specialises in "passive houses", took the opportunity to show people what they could do and how fast they could do it.

All that had been pre-prepared were the concrete foundations, which had taken a few weeks to set, and we then witnessed how cranes and builders carry panels and slot them in. Whole walls, stairs, ceilings, dormers and gables were lifted piece-by-piece from a lorry and guided into position.

External walls are put in first, followed by internal walls, all sliding in along a 'male/female' tongue-and-groove system. While the ground floor was being constructed we were taken on a tour of the on-site factory, in Oberleichtersbach. This is truly housing as a production line, where teams of people compile structures bit-by-bit as each house, to a specific design, makes its way from one end of the factory to the other.

Being the large products they are, there is no storage space so each home is made-to-order. Lorries wait at the far end of the factory to take the buildings to site, Europe-wide. The company, which also has offices in Tullamore, Co Offaly, has honed this product so that you can have any style you wish, from American Colonial, with all its twiddly bits, through a simple dormer heaven home, to a stark black box designed by a company architect and which has won a design award.

Should you wish to seek inspiration you can stroll around the company's site, on which these various styles of houses have been built. Also on site is a showroom where people come and choose absolutely all of their finishes in the one place, from sanitaryware, tiles, roofing fabric, kitchen, flooring and so on. They come for two days and, admits Giles Hirst of Hanse Haus, by the end of it they are brain dead (the company has now set up an internet site to help people hone decisions before they arrive on site).

So all of those difficult decisions about finishes and the hunt from showroom to internet, which people who build their own homes experience, are compacted here both spatially and timewise.

In the house-making factory the obsession with the airtightness that is the raison d'être of passive houses is apparent. This feels akin to car production.

Passive houses are designed to be so heavily insulated and airtight that they require little or no heating - in fact many of the heating systems sold with these homes involves taking heat from people and cookers and turning it into home heating. The house is ventilated through filtered air brought in from the outside.

So carefully is the ventilation controlled that when tiresome householders want cosy extras, such as wood-burning stoves, it upsets the system and has the ventilator working overtime. The suggestion that you could counter this by opening a window is met with an incredulous "but then you would let dirty air and pollen into the house".

Such is the need for airtightness and balance that they won't use folding doors between interior and exterior and letter boxes and cat flaps are also frowned on - sorry tiddles. It will take a mindset adjustment for many of us to live such a sealed existence but there are degrees of energy efficiency and Hanse Haus will also build highly insulated homes - and there are more than 30 of them in Ireland - that aren't totally passive.

All of the house details have been honed here, from proper sealing at windows and doors to stop "cold bridges" and air escape; even the window shutters are built-in to make sure no one whacks in holes while installing them later, and there are special holders that hug electrical wires so closely that no air escapes.

The panels made in the factory also include tightly embedded and connected plumbing pipes - the idea is that as little as possible is left to the builders: about 80 per cent of these structures are created in the factory and 20 per cent on site. Standard walls comprise layers of 2mm of plaster, 3mm reinforced plaster and fibreglass mesh, 15cm of polystyrene, 8mm of particle board, 12.5cm timber frame structure with mineral wool infill, 8mm OSB (oriented strand board) panels and 12.5mm plasterboard - no wonder these houses are warm. Standard windows are in PVC.

Passive houses do cost more to build - with sums ranging from €1,000 a sq m to €2,000 a sq m being quoted - although they are obviously cheaper to run. Should you want a more eco-friendly spec, - such as timber windows and sheep's wool instead of polystyrene and PVC - then the cost is higher.

The message is that you can have anything you want, and that includes solar panels, wind-turbines, wood-chip boilers and so on.

Back on site the German builders show how easy a house build can be, although there are awkward moments when final ceiling panels and a dormer window takes a while to fit.

But the delays here last for 10 minutes, in stark contrast to the couple of weeks it can take to fix problems when things go wrong on a normal house build.

It is still early as we watch the staircase being lowered in and by 10.22am the ceiling is on over the ground floor and at 10.34am the gables are being lowered into place. By this time the frankfurter and chips stall is doing brisk business as locals and Hanse Haus staff and their families come to join the fête. As each stage is finished a bagpipe player (or "dudelsack" in the local parlance) heralds the event and just after 4pm two men dressed in traditional roofers' outfits - reminiscent of the film Witness - are performing the topping out ceremony with the aid of a local-radio reporter.

Now the form of the house is up that's the end - materials such as roof tiles and the external rendering, and internal fit-out will be added later and the actual house will be finished in September.

We are still impressed, although to Hanse Haus staff this is pretty normal: it usually takes two days to get to this stage and typical homes are finished in six weeks.