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Umbrellable roofing truss

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I have, of late, been building a barn*. It's not huge - about the equivalent of three one-car garages side by side. It came as a kit - sort of a giant oak Jenga.

The roof is fairly straightforward - it has a ridge shorter than the building, and hips (ie slopey bits) at each end, as well as sloping front and back. Putting it up single-handed** has been a bit of a faff.

A bit of thought suggests that there's a better way. Provide fixings which attach the rafters, at their top ends, to the ridge, with hinges***. In this way, the whole roof would be sort of like a rectangular umbrella. The bottom ends of opposite pairs of rafters would be tied together (temporarily) to stop them spreading out more than intended.

Then - gadulka! Assemble the roof on the floor of the building, then lift the ridgepole up (higher than its normal position). Open out the rafters, drop the roof down onto the walls, fix down the ends of the rafters, remove the tethers and you are good to go.

Yes, I know you can buy ready-assembled single roof trusses, but this isn't that kind of roof.

(*You have to do something over the Christmas break.)

(**Yes, I know I should use two hands.)

(***The hinge would be at the bottom end of the rafter, where it meets the bottom edge of the ridge. Hinges are not necessarily very strong, but this joint is in heavy compression when the roof is finished. For added strength, spikes on the end of the rafter would bite into the ridge when the joint is closed.)

MaxwellBuchanan, Dec 28 2014


       At it's inevitable conclusion skyscrapers would be put up in this manner. You might need a rocket or two to lift them.
normzone, Dec 28 2014

       Are the ceiling joists, which tie the two sides of the structure together, part of the mechanism?
EnochLives, Dec 28 2014

       //ceiling joists// This particular roof has no joists. There are 4 big tie-beams that run from front to back (one at each end of the building, and two at the 1/3rd and 2/3rds points) so, they are effectively very big joists, but they're part of the main structure rather than the roof. The roof itself, viewed in section from front to back, consists of a series of inverted V's, rather than A's. The bottom ends of the inverted V's are notched to sit on the oak beams that run left-to-right.   

       (The hipped ends are basically the same idea.)
MaxwellBuchanan, Dec 28 2014

       Rockets were also my first thought. A tethered drone could provide hours of amusement for the neighbours. (hmm).
FlyingToaster, Dec 28 2014

       I was thinking about helium balloons. But the weight isn't really an issue. I lifted the horizontal oak beams (some of which weigh maybe 500lb) with a mini- digger. The whole roof (minus tiles and battens) weighs maybe 500-800lb. I think I could lift it either with the minidigger (which might not reach high enough), or by the cunning use of ratchet-straps (which I used to lift some of the bigger components).
MaxwellBuchanan, Dec 28 2014

       A couple of drones, attached to the ridge of the umbrella'd roof, powered by a groundbound genset. Fly the ridge up, incidentally clearing the concrete dust out of the building, set to "hover", and start tacking the beams to the top of the walls.   

       Or mess about with telephone poles and pulleys.
FlyingToaster, Dec 28 2014


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