5..The roof and house design

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Have you driven around the newer residential areas of Cairns? Notice the roofs?
Take a look at the photo to your left, this is McFarlane Drive, Kanimbla, where many of the roofs of the houses are dark in colour, making them warm in summer.
The owner and the builder usually prefer the roof to be dark rather than a highly reflective white because its reflection may annoy neighbours, hides the mould, and dark colours tend to blend in better with the nearby vegetation. The last reason, especially, may be true for housing on the hillslopes that surround Cairns for example, however, we must face the generally accepted fact that painting the roof white will significantly cool a building. One study estimates that energy savings ranging from 7% to 15% of the total cooling costs are possible if the roof is painted white. (Please also read this ReNew Magazine article.)


So therefore, is there a way around all this, such that the building is cooler in summer but not have its roof standing out like a sore white thumb when looked at it from a distance?



Perhaps there is, if we take a closer look at the design of the latest commercial buildings.



On your right are two buildings. You will notice a parapet at the top of these buildings that surrounds most of the roof. These buildings are in Aumuller Street, Westcourt and along Mulgrave Road where the original WOW (now Pillow Talk) building stands.

 

Below is a description of a residential version of those commercial buildings. Also shown are drawings of the side elevation as well as floor plans:


Cladding
Notice in the elevation drawing shown below, that the exterior walls extend up above the ceiling by well over a metre, creating a parapet around the roof of the building. It is intended that these external walls will be made up of autoclaved aerated concrete (AAC) panels, partly because its thermal mass performance is suitable for hot and humid climates, but also because AAC has the advantage of being very light, thus making the relocation of the house easier, if in the distant future, the house has to be transported elsewhere. An example of its use in housing construction for the Cairns region can be seen here. For a third party analysis of this product, see Ecospecifier.


Ventilation
If you look at the wind roses for Cairns, you will notice that, as a general rule, the prominent wind directions, especially during the cooler months, are from the south and southeast. However when the seasons warm, the much-appreciated cooling breezes come in from the sea during mid-afternoon. Therefore, to control all these breezes effectively, shutters (or louvres) would be essential. To assist this ventilation, shutters are placed above all doors (including bedroom doors) to assist the breeze to flow throughout the house during the hotter months.
The design of the windows is part glass, part shutter and is described in more detail in the next section called "Window design". Up on the roof is a solar chimney and heat exhaust fan combination. During extreme heat the thermostatically controlled electric fan will kick in. The shutters at the other end of the roof cavity are adjustable so that they can be opened during dry weather and shut during rainy periods.


Roof Drainage
The "roof drain" (or a larger than standard size gutter) is shown to the right of the drawing. The gutter's steeper than normal slope as well as the easy access to the roof, would make it easier to be keep the gutter leaf and litter free. Also, by having the gutter on the outside of the external walls will mean that excess water from exceptionally heavy rains will flow out safely onto the yard area.


The side elevation of the proposed building is shown below:


Floor Plan
The floor plan, shown below, is of a three bedroom house. This floor plan has no ensuite (there is a composting toilet as an extra, if one is desired). A landscaped carport is fenced off from the rest of the house - the fence is provided for reasons of child safety.

Water Control
The bathroom is to have a shower and washing basin combination that will not only save water but it will lessen stress upon the solar hot water system. A diagram showing how it works is shown here. The bathroom is to have all its walls and ceiling reinforced so that it can withstand a category five cyclone and will act as a shelter for residents during such storms.The floor plan also shows a water tank which will provide irrigation for a proposed permaculture style garden nearby. The outer wall of the laundry will have shutters. This will allow the breeze to dry the washing hanging on clothes lines inside the laundry.

More Floor Plans
To see alternative floor plan designs, taking into account different locality conditions, click here and here. Also please look at the floor plan below which is of a house that can be expanded in stages from one having a single bedroom to one that has five. The extra rooms would be built when the owners can afford to do so.

Reasons to favour this building style over the standard design would be:
1.. The owner can easily access the roof - with little risk of slipping off the house.
2.. These days numerous items are placed on the roof. Those items such as PV, solar HWS and TV antennae/dish etc would not be visible to passers-by because of the parapet.
3.. Having these items hidden from view would allow the resident the freedom to place them, particularly the PV & solar HWS panels, more correctly so as to obtain their maximum effectiveness.
4.. The parapet around the roof would help protect these roof items from strong winds.
5.. The easy access to the roof would make regular cleaning, maintenance and adjustment of the above items a possibility.
6.. Having a large gutter with a pronounced slope, would help reduce its leaf and soil build-up.
7.. The roof cavity would have excellent ventilation because of a thermostatically controlled solar chimney that would help cool the building during the hotter periods as well as reduce any mould in the roof cavity.
8.. Construction costs should be less than that of standard style housing because of the simple shape of the roof.
9.. Awnings can be more flexible than eaves and therefore offers the opportunity to better control the heating of the walls by the sun.
10.. During cyclones, because of the building's parapet configuration, there would be no lift forces exerted on the roof, thus minimising the risk of the roof flying off the house.
11.. On the subject of cyclones, the structure of the bathroom will be reinforced to withstand a category five cyclone. The bathroom will have its own roof, separate from the building.
12.. And of course, the owner can paint the roof white.


Housing with a parapet in the Cairns region is rare but two examples are shown below. They are close to each other and are situated in one of the most exclusive areas in Cairns at Summer Hill Drive, upper Mooroobool. Both photos show the western side of the house. Notice, however, the lack of awnings. The architects must be from down south do you think?

 

For clarification of the window design suggested above, go to the next section.

 

 

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