Location And Excavation


Before the exact location of the house on the site is decided, it is important to check with the municipality or township for minimum setback and side yard requirements, because these can be determining factors in placing the house.

Always check with local utility companies prior to digging to ensure that the excavation will not interfere with buried services. Inadvertently

cutting telephone, gas or power lines can prove costly and can result in personal injury.

After the site is cleared, the perimeter of the house is marked using the exact location of the corners of the lot as a reference. These are usually determined by a certified survey. The corners of the house are marked by small wooden stakes, accurately located at each corner, with nails driven into their tops indicating the outside line of the foundation walls.

Because these stakes will be eventually lost during excavation, additional markings are needed. Offset markings may be located by extending the lines of the foundation walls from the established corners, and fixing these offset markings either with stakes on the ground or marks on surrounding, but permanent, objects. These markings are used after the excavation to set up an arrangement of batter boards (Fig. 5B). However, if the foundation shape is simple, the site area unconstrained and the excavation carefully done, the batter boards can be erected at this point.

The area to be excavated is staked out usually 24 to 28 in. (600 to 700 mm) wider than the corners of the house. This extra width is needed for easy handling and erection of the formwork, placement of the drain tile, application of dampproofing, and placement of the exterior insulation, if applicable. Allow for a slope on the sides of the excavation where the depth exceeds 4 ft. (1.2 m). This creates stability of the slope and the safety of the workers.

An alternative approach to marking the perimeter of the excavation, especially when the foundation shape is not a simple rectangle, is to spray fluorescent paint directly on the ground.


In most case, the quickest and least expensive way to excavate is to use a bulldozer or power shovel. Before this is done, however, all topsoil should be stripped and stored for reuse. The subsoil from the excavation is usually carried away for disposal unless grading requirements allow its use on the site. The depth of the excavation and, consequently, the elevation of the foundation usually depend on the elevation of the street, sewer and water services, the profile of the lot, and the level of finished grade around the perimeter of the house. The elevation of adjoining houses and surface drainage patterns must also be considered.

The basement headroom and the elevation of the floor above grade also affect the depth of the excavation. Basement headroom should be at least 6 ft. 5 in. (1.95 m) to the underside of beams or joists, but a headroom of 6 ft. 7 in. (2 m) is preferable. If the basement is to be used as a living space, however, the minimum headroom should be 7 ft. 7 in. (2.3 m), the same height as the other finished floor areas. The elevation of the first floor should allow for a minimum distance from finished grade to the beginning of exterior finishing (normally starting at the foundation top) of 6 in. (150 mm) for masonry and metal siding, and 8 in. (200 mm) for wood siding, plywood, hardboard and stucco (Fig. 6). This is intended to minimize damage to siding caused by melting snow and rainwater bouncing off the ground.

At times, the depth of the excavation will also be affected by the type of soil encountered. The excavation may be deepened until suitable soil is encountered. Similarly, the depth of the water table or encountering bedrock can affect the depth of the excavation.

The rough grade around the house should be kept at least 4 in. (ioo mm) below the line established for the finished grade to allow for subsequent placing of topsoil or paving material.

If a granular base is to be used under the basement floor slab, the excavation should be made deep

Finish grade sloped for drainage.

enough to accommodate this base. Normally, this depth is also sufficient to accommodate the thickness of the footings. If the site is well-drained and only a dampproofing membrane is used without the granular base underneath, the excavation is stopped at the elevation established for 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 beside the footing.

The steepness of the excavation's back slope is determined by the type of subsoil encountered. With clay or other stable soils and depending on the depth of the excavation, the back slope can be nearly vertical. When sand is encountered, the banks must be cut back.

Be sure that the excavation does

8" (200 mm) minimum for wood-based siding and stucco

6" (150 mm) minimum for masonry or metal siding slope for drainage (5% slope recommended)

finish grade foundation

8" (200 mm) minimum for wood-based siding and stucco

6" (150 mm) minimum for masonry or metal siding slope for drainage (5% slope recommended)

finish grade foundation

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