(1) When stresses and dimensions of timber poles are calculated, the extreme fiber-stress under maximum design forces shall not exceed 27 per centum of the average modulus of rupture for the species concerned, determined on clear specimens of maturity equivalent to that of the timber being used.

(2) The stresses and dimensions in regard to steel poles shall be calculated in accordance with the requirements of the provisions of Chapter 3.

(3) Unstayed aerial poles and flagpoles of dimensions other than those set out in this section, and all built-up masts, shall be permitted only after the necessary calculations and drawings have been submitted to the local authority and the construction has been approved by it.

(4) Unstayed flagpoles and aerial poles having n inclination not exceeding one horizontal to four verticals shall be permitted, provided that they comply with the requirements set out in Table I or Table II, and, if such poles are permitted by the local authority to project over a street or public place, they shall, in addition, comply with paragraphs (c) and (d) of section 8.

(5) If the minimum diameter of a natural timber pole—

a) Does not exceed 125 millimeters, the diameter of such pole shall be 20 millimeters greater than as specified in Table II;

b) Exceeds 125 millimeters, the diameter of such pole shall be 25 millimeters greater than as specified in Table II.