When winds reach up to 140 kilometres per hour during cyclones, there are some vital considerations to make when designing a treehouse in the tropics. Unlike normal buildings, treehouse’s are more subject to the forces of nature, and the safety element gets reduced depending on a few things like the tree’s size, shape and strength. Likewise the size of the structure itself also affects how safe the treehouse is; I mean, if you try and build a three-story treehouse in a lemon tree it’s probably not going to be so safe.
Last year in Tamil Nadu there was a small cyclone which lasted a few days. As the storm hit the city of Chennai waves as high as 20ft were recorded near the coast. The monster cyclone ripped through the city uprooting trees and power lines. Cars were literally picked up and dumped onto the ground and many houses and buildings were smashed up. Only four people were killed, but much damage was done. Even during this small cyclone winds got as high as 140kph. Somehow, both of the two treehouse’s we built in Chennai were undamaged except for a little bit of water leakage. Check out how lush and bushy the tree was before and then how it looked after the cyclone (treehouse still intact):
Although we were happy to see two of our treehouse’s survive the storm last year, it doesn’t always go this well… 2012 marked the year in which Cyclone Nilam laid waste to southern India & Sri Lanka. Nilam is known as the 50-year storm, for storms that big only come once every 50 years. One of the treehouse’s which was built at the youth centre in Auroville was brutally blown down as the tree was torn out of the earth, roots and all. It must have seemed pretty miraculous but most of the house was more or less intact. Instead of clearing up the waste where the tree lay on it’s side with the house tangled and smashed in it’s branches, the guys managed to rotate the treehouse into an upright position. They made some quick repairs and built a new roof. It’s now known as ‘the fallen treehouse’. In place of a staircase you jump onto the the roots and walk along the trunk to enter, people have lived in it ever since:
A well designed treehouse becomes a part of the tree – it moves, sways and flexes with it – and as in stormy conditions trees often fall down, putting a house up high needs some prior thought.
As we talked about in part 1 of treehouse design the first consideration is the tree. Ideally it’s growing strong, directly upwards and the branches spread out in all directions allowing you to place the structure’s weight in a central position. If the tree is leaning, or the branches are growing more on one side than the other, you could build more to the opposite side to help offset the tree’s centre of mass away in the opposite direction to where it’s leaning. It’s pretty vital that the treehouse does not cause the tree to sag, bend or twist, as the heavy forces acting on the tree could damage the tree or worse, bring it down. The trick is to recognise the opportunities that the tree is offering us in terms of construction and work within its limits.
So what do you do when facing cyclone winds? A tree can be analogised to a sail, each individual branch containing a spread of leaves reaching out as far as they can to get sunlight. All of these leaves and branches make up the canopy which just like a sail, catches the wind. When this happens the branch tips bend and have the potential to crack if they reach their breaking point. Furthermore the breaking point is much less when the branch has extra weight on it. A real easy way to reduce the forces acting upon the branches is to prune the tips thereby reducing the area which can catch wind. Basically you give the tree a haircut, and make the sail smaller. Reducing the overall size of the canopy like this is really essential when building a treehouse, and as a rule of thumb – the equivalent weight which you put up into the tree should be removed by pruning. Within reason of course… Pruning and removing leaves reduces the tree’s ability to photosynthesise and produce energy, so you can’t just cut everything off.
Going more into this idea of a tree being like a sail on a boat; the treehouse also creates it’s own sail effect which adds to the bending motions acting upon the branches. Sometimes it’s necessary to find solutions which minimise this effect, especially with a large treehouse. One simple method is to build many windows and ventilation. Any large walls which are going to be a major wind catch can be designed to have sections which you can open up during high winds allowing the air to pass through. Alternatively if you knew which direction the winds come from, you could design walls into shapes which deflect the wind, like the bow of a boat which cuts through water.
Coming soon: how to design a shuttered ventilation system from old solar panels which can help to save your treehouse during them dark and stormy conditions.