13 4.4.4 Internal Conduit Drain Where the open backyard area of each intermediate terraced development is not linked to the front yard
by a corridor at ground level, a conduit drain for conveying surface runoff may run beneath the building itself. The conduit drain shall beat least 300 mm in diameter. The conduit drain shall be laid straight without any bend or sag in its alignment. At both the inlet and outlet
ends of the conduit drain, maintenance sumps shall be provided with invert level drops of at least 150 mm deep. The conduit drain shall be fully supported along its entire length by (and not attached to) the ground beams of the building and shall form as part of the permanent structure of the building to ensure against settlement.
4.4.5 Drainage for Air Wells Courtyards Conduit drains serving the air wells or courtyards shall be designed to cater for the runoff and shall beat least 150 mm in diameter. Maintenance sumps) should also be provided. If the drainage of the air wells runs
through more than one premises, the size of the conduit drain shall comply with the requirements of the common drain as stipulated in Clause 4.5.1.
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