Pools on a slope.

What the soils report decides

Almost every jurisdiction we work in asks for a geotechnical report on a sloped parcel, and even where one is not required, we commission one, because it is the document that decides the structure. It tells the engineer the bearing capacity, the depth to competent material, whether the soil is expansive, whether the lot carries uncertified fill, how the slope is expected to behave, and where the setbacks from the top and toe of slope must fall. Everything that follows is drawn from it.

Caissons, grade beams and retaining

On a slope, the downhill side of a pool sits over ground that may be fill, may be shallow, or may simply be too steep to bear a shell full of water. The conventional answer is drilled caissons: deep concrete piers taken down to competent material and tied together by a grade beam that the pool wall bears on. The shell is then a structure on piers rather than a shell on soil. Where the uphill side is cut, a retaining condition is engineered into the pool wall or built separately, and where the cut is significant the drainage behind it is designed as carefully as the wall.

Access is the other half of the plan. A hillside lot often has no path for a conventional excavator, so the dig is done with a smaller machine walked down, a conveyor, or on the steepest sites a crane. Spoils leave the same way. We plan the access route and the staging before we price, because it is a real line in the estimate.

Setbacks from the slope

The building code sets a pool back from the top and toe of a slope so that the shell neither surcharges the slope below nor sits under one that could move. The City of Los Angeles applies one quarter of the slope height on an ascending slope and one sixth on a descending slope, and requires the site plan to show them; the City of Ventura asks for both dimensions measured from the water line. Other jurisdictions apply the same code with their own drafting standards. Those distances often determine whether the shell can be dug conventionally or must move onto caissons, which is why a survey comes before a drawing.

Drainage

Water is the enemy of a slope. Surface water is directed away from the shell and the walls, subdrains carry it from behind retaining conditions, deck drains keep it off the slope below, and the pool's own overflow and backwash are piped to an approved discharge. On a hillside, drainage is part of the structural design, not the landscaping.

The review hillside parcels can trigger

Slopes bring review. In the City of Santa Barbara, exterior permits in the Hillside Design District, grading over 50 cubic yards there, and retaining walls over six feet or on slopes of 15 percent or more can trigger the Single Family Design Board. Santa Barbara County applies Hillside and Ridgeline Guidelines and Critical Viewshed Corridors on many foothill parcels, though a pool alone is exempt from Board of Architectural Review. Malibu adds geology and coastal engineering clearances on bluff lots. We tell you which of these your parcel carries before we draw, and our permits guide sets them out.

What it costs

A hillside pool costs more than the same pool on a flat lot: the soils report, the engineering, the caissons and grade beam, the retaining and drainage, and the access all add real scope. It is also where the most extraordinary pools we build sit, and where a vanishing edge stops being a feature and becomes the reason for the pool. In our recent projects, hillside work runs from the generous band into the estate band on our cost page. Every project is unique and custom to its environment.