Article 6

‘Why do architect designed houses cost so much?'
Article # 6 - Roof Costs (in a series of 9)


Roof Costs

The additional roof costs in our typical sample architect designed house are shown in the chart below.

This article will deal with roof structural costs as well as roof area, cladding systems and roof drainage.


Roof Structure

The lowest cost roof framing system in a house is a timber truss roof supported by simple load-bearing timber external (and perhaps some internal) wall framing, deliberately designed to reduce or eliminate structural steel.

Most volume builders tailor their designs towards achieving these simple and low cost structural systems.

The more complex building forms sometimes found in architect designed houses (such as the one used as our sample project) often require more complex structures. In some instances, this may include a full structural steel frame with the timber wall framing being non-loadbearing infill panels only.

Roof Area

Volume builder's houses often have minimal eaves and verandahs. Some even have no eaves at all with the eaves gutters places on the outside face of the external walls.

Typically, architect designed houses have a higher proportion of eaves, verandahs, pergolas, etc. It should be noted that this is not always the case, and is very much dependant on the particular roof design.

In our sample projects indicated in the chart above, the roof area in the volume builder's house is 115% of the floor area, whereas in the architect's designed house it is 120%.

Roof Cladding Materials

Most volume builder's houses use either Colorbond steel, concrete tiles or terra cotta tiles. These materials respond to the general market expectations and also are from the lower cost range of the options available.

These materials are also used extensively in architect designed houses, however in some instances higher cost finishes such as copper, zinc, slate, membrane systems, green roof systems etc are used and these have a significant impact on the cost of the roof cladding.

Roof Drainage

The most economical roof drainage system is eaves gutters feeding into external downpipes. Box gutters and internal downpipes are more expensive options. In particular, box gutters may have an impact on the roof structural design and cost as well as being a more expensive roof plumbing option.

Optimising the value for money in the roof costs requires a careful balance of design, roof area, structural systems, cladding materials and roof drainage systems.

In Article # 6 we will discuss the differences in internal fitout and finishes costs between volume builder's houses and architect designed houses.