August 21, 2003
Height and Its Townplanning Impact
Height, or a reasonable height for building, has become a townplanning negative.
Nearly all town plans try and prescribe the height of buildings to be to minimums. There is a phobia about heights being higher or much higher in room spaces than that allowed for by the Building Code of Australia, ie 2400mm in many cases, and 2700mm in others. Most plans seem to base what is allowed upon the achievement of these minimums.
In the Brisbane City Plan 8.5 metres is declared as the sacred height. This is taken as a height above the “natural fall of the land”. This is ridiculous when you take into account sloping ground and the consequences that has on building and design.
It is conspicuous in observing the offspring of people that they are all substantially taller than their parents in 90% of cases. This is an unresearched statement, but I know few people whose children are not taller than them.
If we continue in the present vein, the houses and residential stock constructed will be found wanting as far as the height of the citizens will be in a hundred years time. This will mean that what we build will be totally and utterly waste— 100% discardable in a few generations—the worst environmental outcome. Older buildings of course were constructed with higher floor-to-ceiling heights because of lack of mechanical services and limited artificial lighting. This makes them much more reusable than any modern building.
Floor-to-ceiling heights.
The desire to try and fit underneath the 8.5 metre height limit often results in maintaining minimum floor-to-ceiling heights. The floor-to-ceiling height that should apply in Queensland is 2700mm at a minimum. The BCA should have an amendment to take this into account.
As we all know, it costs much more to build to a greater height, so townplanners should have nothing to fear in having a plan which encourages places of a higher floor-to-ceiling height.
Instead of living in fear of higher buildings, the City Plan should allow that somebody wishing to build with floor-to-ceiling heights above the minimum of 2700, gets an increase on the 8.5 metres by the amount required, up to a maximum of 3.6 metres for floor-to- ceiling height. The positive nature of this is that it puts out the challenge to the developers to build higher floor-to-ceiling heights rather than being able to say “oh well, we’re just complying with the standards that we have to build”.
Height related to setbacks
The setback from the side boundary regulated by the Building Act works even if buildings become taller. For example, 1.5 to 4.5 metres high, 2 metres to 7.5 and 2.5 to 10.5 metres high. This height setback has been around for a long time and could continue to be used. Penetration of overhangs into this should be incorporated to enable people to build environmentally sensible design without being penalised by setbacks.
Site cover and height
The City Plan is really remiss in this area, especially in relation to small lots. Height limitations are the major cause of people building long thin houses on small blocks. The Brisbane City Council is now trying to stop this by restricting the length of construction, the height at the side and increasing side setbacks.
If they allowed a greater number of storeys at the same time as reducing the site cover allowable, they would encourage the release of a lot of land for gardens and outdoor activities
There should be a formula which says if you go to 2 storeys you are allowed to cover 50% of the site, if you go to 3 storeys you are allowed to cover 40% of the site, if you go to 4 storeys you can cover 33% of the site.
As you go higher, they should reward the person constructing with a greater Gross Floor Area allowance. There is a disadvantage in going higher of course, in that the circulation space is consumed by stairs etc. However there should be an encouragement of taller buildings with less site cover.
Height in relationship to climate
On a long site where you have a long northern boundary to the side, you can successfully design a single storey or a long two storey house which will gain the best of the climate. However, if you have a site which has the long boundary side to the east and the west, you are in an environmentally difficult situation--the shortest elevation to the ideal sun orientation.
In such a circumstance it would be much better to have a taller, thinner building. This should be incorporated in the City Plan.
The whole paranoia about tall thin buildings has to be stopped. It is unlikely that many people will choose to build them as a first-up choice because of the costs involved.
Environmental damage by restricted height
The restrictive height requirements of the City Plan cause people to excavate in order to fit their houses under the height requirement. This is especially so on sloping blocks of land. The results of these excavations are:
° the excavated material is usually removed from the site and dumped somewhere else at great cost.
° the dumping process puts more large trucks on the roads – increasing fumes and traffic holdups.
° the construction then requires retaining walls. If these retaining walls are to abut habitable rooms they require tanking. Tanking ALWAYS fails eventually, making the habitable room uninhabitable.
Add together the sheer cost of taking away the fill, the construction of the wall, tanking, backfilling, sub-soil drainage, and the costs are unnecessarily escalated.
These consequences could all be avoided by allowing people to build to a greater height. At some time in the future, if people did insist, they could always choose to excavate underneath for further expansion, as is now commonly done, but at the initial point it could be avoided.
Height in relation to the fall of the land.
On a falling block it is sensible that the height of the floor allowed be, say, 300-600 above the edge of the road reserve at that point. This height is selected as a means to get the run-off water from roofs to enter the curb. Additionally, it provides the major floor level to be a little higher than the road reserve rather than lower.
The other advantage is that as you descend the hill you can get underneath and park the cars. The current situation where a lower level below the kerb line is possible but the plan declares the building 3 storeys instead of 2 is a disaster.
For land rising from the road reserve it is a little more difficult to come to conclusion as to what is the most sensible. My thoughts are that you pick a height back from where a residence would start and declare that as the point to spring the 8.5 metres. I don’t accept 8.5 metres to start with, but if we live within what the City Plan starts with that is a starting point.
