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What are sheerlegs?


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Click here to see a diagram of some sheer legs; this should be helpful.

The erection of a timber framed building involves the lifting of large components into place. The oak trusses on our house weigh about half a ton. They must be assembled and then lifted 12' from ground level and placed on top of the supporting posts. It would be easy to do this with a crane but cranes are very expensive to hire so we used sheerlegs. These comprise a triangular structure made of 5" X 5" timber, each side of which is about 22' long. One side is rested on the ground and the other two sides are elevated until they are at an angle of 70° to 80° to the horizontal. They are secured in this position with a block and tackle attached to the top of the triangle and then lead to a strong point some 30' away. The angle of the sheerlegs to the horizontal can be varied by shortening or lengthening on the block and tackle. The top of the triangle can thus be moved over a limited distance at a height of about 20' above the ground.

Another block and tackle is attached at the top of the triangle and this hangs down vertically to take the load to be lifted. This (e.g. a truss) can be lifted on this second block and tackle and then moved horizontally until it is over the posts and lowered into position. Unlike a crane, sheerlegs cost almost nothing as the wood they are made of is subsequently incorporated into the building.

Originally horses would have been used to provide the lift but we employed a hand winch attached to the back of a Range Rover (see photographs).

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