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Framing and building the treehouse

Once the floor is in place and you are convinced everything is secure, you can begin the building of the house itself on top. The treehouse should be entirely supported from the floor, with no contact with the rest of the tree. This prevents the build-up of stresses from parts of the tree moving in different directions. The supports should take care of all the tree movement. Occasionally this isn't practical, as will be discussed later.

The actual construction is similar to how you might make a ground based house or playhouse now that you have a solid wooden floor, so you can borrow techniques from other walks of architecture to make your design work. By now you should have a pretty clear idea of how the treehouse should look in the tree, with plans drawn up to guide the build and prepare materials.

Framing
Walls
Roof
Doors and windows
Finishing touches

Framing the structure

At this stage you should have a good set of plans to show all parts of the treehouse above floor level. Your plans need to show the height of the treehouse and where you are going to have to deal with obstructions like branches or a curving tree trunk.

It is definitely better to pre-fabricate the frame, or at least parts of it, on the ground. That way you can use vices and power tools in your workshop. I always find that pieces of wood that I cut and join together in the treehouse are not as square or accurate. It is much easier to work when you don't have to worry about falling out of a tree!

So long as the floor is big enough, you can make the frame any shape you like and then fasten it to the floor. I normally use brackets to screw the uprights of the frame to the floor. This forms a strong joint but it will still be able to move until you put your walls on. The walls add lots of bracing and will make the frame rigid when they are fitted. However, you may want to cut holes in the floor and attach the uprights of the frame directly to the floor supports. This creates a very strong and rigid frame before you have even added the walls.

Since the frame is built on a flat wooden surface, rules as to its construction are exactly the same as for any ground based wooden house. This lets you use a house building book to help with the design of your treehouse.

Walls

I use plywood for the walls because it is available in large sheets which can be cut to size with a jigsaw. It is also very strong due to the alternate direction of the veneers that it is made up of. Plywood does not normally look attractive, so wooden cladding boards may be better. These are simple to fit and cut, but the gaps between each board will close in winter and open in summer, due to the wood swelling in damp weather. This could let rain and wind into the treehouse. You can get round this by overlapping the boards, which also looks good. Boards do not have the same bracing effect as plywood because they can slide against themselves slightly, so you would need a rigid frame to begin with, possibly made of stronger materials.

Roof

The roof is what will make or break the treehouse over the long term. Clearly, wood will survive a lot longer if it is protected from running water or even occasional wetting. The roof is more than just a lid for your treehouse!

As mentioned above, a pitched roof looks better and is easier to waterproof than a flat roof , but it takes longer to make. To waterproof a sloped roof you can attach felt over a thin plywood base and cover it with shingles or boards. It is very important to keep water from spilling off the roof and onto the walls, because it will soak through and make everything inside damp and cold. This is especially true if you have a carpet which will hide damp and prevent the floor drying, leading to rot. A good idea is to design in a large overhang at the end of the roof, and by making the roof longer than the walls so it shelters them from rain.

A flat roof will need to have felt (tarred sheet material) securely fastened and sealed with a blowtorch. Any tiny hole can cause a leak, and this will be worse if puddles collect on the roof. You can paint the felt with thick sealing paint or you could make the roof very slightly sloped. This helps water run off the roof, but still be flat enough to stand on top.

Doors and windows

If you are putting a door in a wall make sure that the frame cannot twist. On a ground based house this isn't usually a problem, but the limited size of most treehouses means that the weight of the door may twist the frame slightly, letting the door rub on the floor and possibly stick. An alternative is a trapdoor in the floor, but it can be difficult to climb in through a trapdoor. If you choose this idea, you could put a counterweight on string over a pulley to make the door really easy to open (if it is on hinges) as shown in the diagram below.

A lock is recommended to keep intruders out - make sure it cannot be broken easily. See the security page for more details.

Windows are one of the key features of a completed treehouse, allowing you to gaze out from your new hideaway through the branches and beyond. If the conditions allow it, put lots of windows in your treehouse so you never forget how close you are to the natural beauty of the tree.

Windows are quite easy to fit, and they can be hinged, but I suggest that you fit them into a suitable frame on the ground and attach this to the treehouse. Try and put them on a side of the treehouse that is difficult to get to from the outside, to reduce the chance of people breaking in that way. Glass is easy to clean and is traditional, but if the treehouse twisted badly it could shatter. Perspex or safety glass (as used in car windscreens) is safer, but Perspex scratches easily, and squeaks if it rubs against any wood. This happens in my treehouse because I have some corrugated Perspex lying on wooden beams, and it is very annoying! There is more information on securing windows on the security page.

Finishing touches

Carpet transforms the inside of a treehouse, as does a coat of paint. Use soft carpet for sitting on, and light shades of paint so that the treehouse is not dark inside. If you find that the treehouse is cold, you could panel the inside of the frame, filling the gap with insulation (eg, glass wool). Many treehouse builders who stay overnight in their buildings like to add a wood burning stove. These can be very safe if fitted with care - you need to ensure the stove is solidly bolted to the floor and that you surround the base with fire resisting materials in case embers fall onto the floor. I fitted a fireplace in my treehouse and had a small tiled area in front to catch any sparks. As with a fire in a ground house, you should keep either a fire extinguisher or bucket of water handy at all times.

It is now relatively inexpensive to purchase solar panel kits that come with a battery and light for garden use. If you wire a few of these together you could easily collect enough electricity to illuminate the house at night time. A more serious approach would use a car or truck battery and large panels or even a small wind generator with a charging regulator. This will provide plenty of energy for light and music and could even be wired to a transformer to convert the supply to mains voltage. Devices to do this are quite cheap, but bear in mind that a standard lead acid car battery will drain fast when used with appliances more used to an unlimited mains supply.

After that, it's up to you what else you want to include to make your treehouse into a home. Everything from loft beds, cookers and fitted bathrooms to zip lines, rope ladders and relaxation nets have been built into treehouses, so the possibilities are endless!