The Harper House

Terry and Liesl Harper, after replanting the cleared land they had purchased at Eumundi on Queensland's Sunshine Coast, decided to build a state of the art environment friendly house on it. To achieve this, they hired the professional assistanceof a building designer, Graeme Rickard. The home had to have as little impact on the environment as possible. It had to capture its own water, recycle as much of it as possible, and produce as few greenhouse gases as possible. To achieve the latter, solar energy and energy efficiency were of paramount importance.

As Mr Rickard had never designed an energy efficient home before this brief, he and the Harpers spent many hours poring over many books on the matter, and then put pen to paper. A concept was arrived at, and architectural drawings were commissioned. Because the Harpers were very keen on promoting this project to the general public after its completion, they felt the need to have the design energy rated to be important. To do this, they approached the Brisbane college of TAFE’s Renewable Energy Faculty, who hired the services of GREENhouse design.

At first glance, the concept looked well thought out. However, to the Harpers' utter disappointment, when the design data was first entered in BERS, it proved to be quite ordinary, rating just 2 stars.

So what was the problem?

It took many hours of analysis to establish why this concept did not live up to its expectations.

Initially, the building envelope was too complex. If the perimeter of a building is too great with respect to its floor area, then much more energy can enter/leave the building through the walls.
The initial design also incorporated no fewer than 5 rows of clerestory windows. Too much glass simply weakens the building envelope, and far too much ambient external heat was entering the house, causing it to overheat in summer. So this was reduced to just one row.

Using BERS, other window sizes were also fine tuned to achieve the Harpers’ requirement

Another obvious error was the total lack of thermal mass. This is no easy site to design for: sloping steeply to the southwest, it was impossible to build this house on a concrete slab over its entire floor plan; however, it was decided to introduce one underneath the higher section of the house where the wet areas were sited. This also allowed the use of massive walls (as seen opposite), this time built of earth to fulfill the client’s environmental commitment. It was suggested that the eastern and western louvres be fitted with timber rather than glass slats to minimise solar gain during summer mornings and afternoon.

Whilst GREENhouse design was not the originator of this design, our input had a major impact on the final results, and particularly the house's thermal performance.