Wondering if anybody else has come up with this one.

When designing a simple timber rafter, the requirements for strength are based on the vertical load and span dimension on plan. However, when it comes to deflection the calculation based on the span on plan dimension will be incorrect. If I have got this right, to obtain the correct value of deflection normal to the rafter, one needs to take the value calculated from the span on plan dimension and divide this by cos? of the pitch angle. In the case of a 45 degree pitch roof this will double the value of deflection calculated from span on plan. Hope this makes sense.

If there is agreement it would seem to be a useful addition to SuperBeam if this modification could be incorporated.

When designing a simple timber rafter, the requirements for strength are based on the vertical load and span dimension on plan. However, when it comes to deflection the calculation based on the span on plan dimension will be incorrect. If I have got this right, to obtain the correct value of deflection normal to the rafter, one needs to take the value calculated from the span on plan dimension and divide this by cos? of the pitch angle. In the case of a 45 degree pitch roof this will double the value of deflection calculated from span on plan. Hope this makes sense.

If there is agreement it would seem to be a useful addition to SuperBeam if this modification could be incorporated.

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