Friday, 2 March 2012

Ventilation system [for] Low cost building in the tropics - Tropical Building

A few basic points

  • In the early 1930s a couple of guys with a bullock cart of supplies, a few stock horses and maybe a ton of corrugated iron trekked into what is now Litchfield National park and built this place. It was used as an outstation for a cattle property for about 8 months a year, the guys pulling out during the wet season.
  • The corrugated iron must have been a wonder material. Prior to [its] introduction they stripped the bark off trees for wall and roof covering.
  • So to make my point, the iron was light weight, easy to transport, quick and easy to use.
  • Most of the living and sleeping would have been on the verandah areas.
  • This place was abandoned in the 1950's, but it is still in remarkably good condition.
  • I took the photo of the termite mound say 5 miles from the homestead, termites are all over this area, they are a fact of life here and yet the timbers in the place are original. Untouched
  • It could be that the particular timber they cut for the place is resistant to termites. What I can say is that If I had to be building something like this today I would be asking the locals what is the best timber, and watching what they use and how they use it.
  • What I do know is that they would have used crushed termite mound material to make their floors. Ant bed floors were common in early Australian dwellings. When watered and compacted they gave as good or better surface than road base gravel.

Old steel Wesleyan church Darwin
A recently renovated old Wesleyan church in Darwin. Built in 1897 in Adelaide South Australia and shipped to Darwin.
  • This tropical building again uses lightweight, easily transported galv[anized] iron. The external wall sheeting is roll formed galv also to a different profile.
  • It also shows up the advantages of steel construction in a case like this. The old church was blown away in a cyclone, and this building that replaced it has survived many cyclones including the devastating Cyclone Tracy on Christmas Eve 1974.
  • The building is raised off the ground on short concrete stumps. A style very common in Queensland, but up here in the Territory we tend to put our elevated houses higher, say on 9ft [2.74m] high concrete or steel columns. This use of stumps gives a few advantages over the slab on ground house.
  • Easier to protect the house from termites. There are no hidden places that termites can enter unseen.
  • The concrete stumps would have steel hold down bolts cast into them, and then ant caps are fitted over the top of each column.
  • These are galvanised steel flashings that cover the column and have a say 1" slightly turned down lip all around. Because they used genuine galv. steel, not the modern equivalent of "Zincalume" it was possible to solder the the joint between the ant cap and the HD bolts, making a perfect and durable seal to stop the little sods.
  • Ant caps were also used in brick wall on concrete slab construction. After the first two courses of bricks were laid, the plumber would fix his ant caps. Mitred at the corners, with turn downs to the concrete floor at the door openings. All the joints were then soldered of course.
  • What makes this system effective, is that the termites can't or won't build their little mud passageways or tracks over and around these sharp edges.
Interior of the pre-fabricated church
Tropical building - This is the interior of the church, showing the main structural frame set apart from the wall, and the light weight components in the roof structure.
  • The raised floor levels of these tropical buildings gives a certain amount of cooling effect.
  • When concrete materials were expensive or hard to get, this was the only way to go, apart from the earth or paved floor.
  • The roof has a purpose built ridge vent. That is a vent that allows the rising hot air to escape, drawing in fresh air at the bottom. This is known as a passive vent, although when a wind blows over the ridge it can create a venturi that also sucks the air out.
  • Far more common today are rotary vents, some electrical but most wind powered. The one here in my backyard is industrial size 2ft dia.
  • The ceiling fans in this place conform to a maxim of an old mate of mine. He told me that it evolved from the British in India days. "12 ft under a fan and 4 ft over it". (3:1). They just work better if they have plenty space over them to suck from.


A traditional Malay house

Traditional Malay house Malacca
Traditional style Malay house in Malacca province.
Here's another interesting example of tropical building construction. A house I came across on a bike ride near Malacca last year.
  • Similar to the previous example, short stumps off the ground. This time it is sat on pre-cast pad footings.
  • Note the windows, timber shutters for bad weather, the lower section is an open timber balustrade, (there are curtains behind it), upper section wide open.
  • Above the windows under the protection of the eaves are fixed timber louvres.
  • The traditional roof cladding (woven palm matting?) has been replaced by corrugated iron. (I hope I am not beginning to sound repetitive here, I am a bit biased towards tin roofs).
  • The main feature of this type of house is the capacity for cross ventilation taking advantage of the slightest breeze. Look at the almost completely open gable ends, with the two huge woven mat louvres. They put some of our modern ones to shame. It is easy to see which one will react to the slightest breeze or air movement. There are no ceilings in the house.
  • The gable ends have generous overhangs. In both cases actually, more often gable end overhangs are about 18" and do little to protect the walls form heat or rain.
  • In the Malay house photo, note the more modern (modern not better) addition at the left, built when presumably other materials became available cheaply. (Concrete,glass louvres, sat TV).


Large ridge vent
A large ridge vent under construction in upmarket housing. Architects - Greg McNamara and Lena Yali - Troppo Architects Darwin.
Pressed metal purpose made gable end vent
The architect here has done a good job with this gable end vent. normally they are far smaller.
  • Provide ways for air to circulate, particularly in the roof space. Getting the air circulating not only cools the place down, but inhibits the growth of mildew and mould during the humid time of the year.
  • Ridge vents, gable end vents[gable vents], eaves vents, rotary vents. All of these work.
  • Provide generous wall openings, large doors and windows, that provide through ventilation. That is the breeze can go in one wall and out of the opposite wall. A continuous current of fresh air blowing through the house is a magic thing.
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