Roofs
Truss and Purlins
Roof trusses and purlins are normally quite expensive items requiring high-end timber or metal profiles to meet the structural reliability. These components can easily be replaced by low-cost bamboo elements with their high tensile capacity, trimmed to a dimensional standard and combined with an efficient back-to-back gusset joint design.
Steel plate gusset material can be sourced from scrapyards at very low cost. The 2 mm steel plate covering “white goods” like washing machines, refrigerators etc is perfect. That surface has a high-quality corrosion resistant coat and cuts can be bevelled and quickly recoated. If CNC equipment is available cutting can be efficiently organized for large scale production.
When mounting the bamboo culm halves with the steel gusset placed in position, drill right through all parts with bits for metals. (See cross section, note importance of changing bit size) Small pieces of wood placed on the protruding screw on the other side, creates pressure and anvil.
Purlins can be made using the same recomposed bamboo culm halves, hence the same section as for the truss. Mounting the purlins is then simply done by inserting a sufficiently long wooden screw. Let it first enter between the purlin halves and then reach through the truss culm halves.
With a common roof pitch of 27 degrees this method should be enough. For a steeper roof pitch, it might necessary to support the purlin with a small piece of wood or bamboo also stuck in between the truss culm halves . The center-to-center distance for the purlins is of course a matter of roof cover weight, wind pressure and structural design.
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