This post we will focus on how to construct a simple platform.
Assuming you’ve read the first post in the treehouse design series: Picking a tree – Treehouse Design Part 1 and have found a tree, now where do you start?
The foundations of course! As your foundation is the tree itself, you need to figure out the strongest points which can take the load of your structure.
First, look at the point where the trunk first branches out. Follow those branches along to where they split out again. These initial branch forks on all the major branches are the best points to try and lay your main beams. To make a basic square or rectangular shaped platform, Ideally you’d have four branch forks – all at similar heights – to make up the corners of your platform. Lay one beam between two forks, and another between the other two. If you only have two forks available, you can make hanging connections from the upper branches instead. The general idea is to get the two beams laying level and more or less parallel to each other (like image on the right bellow) with a span between them which you will lay your secondary beams across. Think about the span between your two main beams and consider the strength of your secondary beams. The span should not be so big that your secondary beams bounce or sag in the middle.
Work with the natural shape of the tree, if your support points seem to make your platform a funny shape it doesn’t matter, what’s important is making the foundations strong and well placed so as not to damage the tree by putting too much weight on a weak point. If none of your fork’s are at the same height (because they aren’t going to be) make blocks to place underneath your connection points so that your beams lie level to each other.
Remember that your foundations for the house – the branches – are constantly growing. Undertaking a lengthy construction project for example, 3 months down the line you may have branches growing into the house, a floor becoming un-level or other parts of your house coming under stress as the tree adjusts.
Tree’s transfer nutrients through the layer just underneath the bark, so It’s essential that this layer is not harmed. The best way to do this is to use thick rubber -from old car tyres – at any point of connection between house and tree. Nail the rubber into your beams at the points where the beam touches the tree. It is possible to connect beams by putting bolts through the branches; if done correctly the tree can grow around the bolt and no harm or hindrance to growth is caused. It’s kind of like a piercing, but then again it’s not necessary and there’s a few reasons why it’s not good to build treehouses like this: Firstly, fastening doesn’t allow movement – over time as the tree grows the pieces that are fastened may start to get pulled or twisted, or the tree itself may incur some problems. Secondly, tree’s aren’t punks – they don’t like piercings.
Instead, securing foundation beams can be achieved simply by making a groove which fits the forking, an upside down U-shape will stop any sideways movement, and once there is weight loaded you don’t have to worry about the beam popping out (see above). If the beam is not sitting well or the connection is weak, then you can make clamping systems out of blocks of wood, rubber and metal threaded rod. Displayed bellow: a vertical structural piece fastened to a branch with a block on the other side. Clamping the pieces together with rubber buffers like this is an extremely effective way to secure the structure to the tree without causing any damage to the tree.
*It’s worth noting that care must be taken when tightening the bolts, the branch shouldn’t be too constricted, otherwise you may cause growth problems.
You should now be thinking about laying your secondary beams. This will determine the shape of your floor. Depending on the kind of wood and thickness of the beams you’re using you can generally allow the secondary beams to overhang your main ones by 1m. Likewise the main beams should not overhang the support points too much, otherwise the extremities of the platform will flex – not a nice sensation for somebody walking to the edge. Typically your secondary beams should be spaced at 50-60cm. Lay them out in your square, triangle or whatever shape your platform is and secure them to the foundation beams.
When checking the level of your secondary structure, if some of the beams are too high you can carve out a groove and inlay them into the primary beams, if they are too low you can make wooden spacers to raise them. Now it’s time to prepare your floor planks and start laying them by joining two planks at a beam. Once it’s finished you can relax up on your new platform and think about what to do next… Possibly a staircase is a good Idea.