(1) Hollow glass blocks used in masonry walls shall be regarded as forming non-load bearing panels in such walls, which, for the purposes of section 1 shall be regarded as openings, and shall comply with the requirements of the following subsections.

(2) If the panel of hollow glass blocks exceed six metres in height or breadth, or 12 square metres in area, then intermediate stiffeners, in accordance with the requirements if subsections (11) and (12), shall be provided so as to limit the area of blocks between the supports afforded by such stiffeners or by the edges of the panel to not more than 12 square metres.

(3) The distance apart of such parallel support shall not exceed sic metres.

(4) In exterior walls, the panels shall be accommodated in masonry or other recesses, and, in interior walls, in recesses or rebates at the head and jambs of the opening, and, on these three sides, clearance joints not less than 12 millimetres in width shall be provided in order to keep the panel free of the surrounding wall.

(5) The clearance joints shall be filled with non-hardening compound or with glass fibre pointed with a non-hardening compound.

(6) Horizontal reinforcement for the panel shall be provided in the form of corrosion-resistant metal strips or mesh not less than 25 millimetres and not more than 65 millimetres in width, which shall be built into the horizontal mortar joints as follows-

a) for panels not longer than 4,5 metres, every fifth course;

b) for panels not longer than 5,1 metres, every fourth course;

c) for panels not longer than 6 metres, every third course;

but the vertical interval between reinforcements shall not exceed 1 metre.

(7) Where of steel, reinforcing strips shall be not less than i millimetre, and steel reinforcing mesh shall consist of not less than two longitudinal wires, each not less than 3,55 millimetres, welded into the longitudinal wires at interval not exceeding 200 millimetres.

(8) Where other shapes or metals are used, the tensile strength shall not be less than that of such steel reinforcement.

(9) Where the reinforcing-strips are of steel-wire mesh, they shall continue throughout the length of the horizontal mortar joints, and be turned up in the expansion joints not less than 75 millimetres, and be secured to the frame of the building or to a stiffener by means of nails, bolts or wire located at least 40 millimetres above the horizontal joint.

(10) The fastening shall be capable of developing the full strength of such reinforcing-strip.

(11) Stiffeners.-Stiffeners shall be of sufficient strength to withstand the bending moments and shearing forces which may be caused by dead loads and wind forces on the glass-block panel at stresses not exceeding 20 per centum of the minimum specified tensile strength of the materials concerned.

(12) stiffeners of steel shall be protected against corrosion by painting or by some other method of an efficiency satisfactory to the local authority.

(13) Mortar for glass blocks.- Mortar used with glass blocks shall mixed in the proportions of 1 part of cement to 1 part of hydrated lime or lime-putty, to not less than 4 and not more than 6 parts of sands by volume.