Standard Armco corrugated beams have an overall length of 3.5m, but because they overlap at the joints, they provide an effective coverage length of 3.2m.
To calculate your required materials:
(1) Divide your total required length by 3.2m to get the number of beams (round up).
(2) For post spacing, the standard is 3.2m centres (one post per beam lap) for general use, or 1.6m centres (two posts per beam) for high-impact areas requiring double the structural strength.
(3) Always add one extra post to finish the end of the final run.
