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of 150 mm (6 in.) for masonry and metal siding, and 200 mm (8 in.) for wood siding, plywood, hardboard and stucco (Figure 29). This is intended to minimize damage to framing and cladding from melting snow and rainwater deflected from the ground and to protect the wood from insects and pests. Poor soil conditions may require the excavation to be deepened until suitable soil is encountered. The foundation depth can also be affected by the water table or bedrock elevation. Ensure that excavation does not affect the foundations of adjacent buildings. Contact your local building department when these situations are encountered. Ensure the excavation is deep enough to accommodate the granular base under the basement floor slab. This depth is usually
sufficient for accommodating the thickness of the footings. If a site is well drained and only a dampproofing membrane is used without the granular base underneath, the main excavation need only extend to the elevation of the top surface of the footings. When this is done, the footings are formed by trenching. Adequate space must be provided for the drainage pipe outside the footing. Insulate the excavation in the winter to prevent frost penetration. Building on frozen soils can cause problems that are difficult and costly to remedy. The rough grade around the house should be kept at least 100 mm (4 in.) below the line established for the finished grade to allow for subsequent placing of topsoil or paving material.
29 Finish grade sloped for drainage
200 mm (8 in.) minimum for wood-based siding and stucco 150 mm (6 in.) minimum for masonry or metal siding slope for drainage finish grade foundation