A building located on a slope can offer spectacular views combined with major engineering problems. The task centers on creating a flat foundation that is dug into the slope and rests on vertical supports. The biggest challenge is coping with water drainage. The need for retaining walls, higher grade foundation slabs and earthworks increases the construction costs for all buildings on sloping ground. Specialist engineers and building contractors are needed at every stage.
Things You'll Need
- Batter boards
- Steel reinforcement bars
- ¼-inch thick plastic sheet
- House frame, fittings and roofing
- Damp proof course
- Plumbing and utility lines
Determine the slope gradient and check local building codes. Albermarle County, Virginia urges "extreme care" when building on slopes of 25 percent (1 unit vertically against 4 units horizontally).
Hire a geotechnical engineer to examine the soil characteristics by taking soil samples from boreholes around the site. Determine the depths of the water table and bedrock. Discuss methods of digging trenches for land drains to divert runoff water from the building site, away from neighboring properties and into a natural water course or public drainage system. Dig a drainage system.
Hire a structural engineer to help design the building you have in mind. A sloping site will require a walkout basement or crawl space bounded by a foundation wall on the uphill site. Submit the final plans to local authorities and apply for necessary building permits.
Hire building contractors to excavate a wedge for the foundation area out of the slope. Start at the lowest point on your site and excavate into the hillside. Remove all organic matter from the excavated area.
Instruct the builder to construct a retaining wall on the uphill side of the house. Ensure that soil above bedrock at this point dips away from the house. Leave sufficient distance between the retaining wall and the house for natural light to enter the house.
Follow Repairhome instructions and hire a surveyor to mark out the corners of the house with batter boards. Excavate the strip foundation footings with the backhoe to a depth of at least one foot. Ensure that the foundations are level and the bottom is undisturbed soil or bedrock.
Set steel reinforcement bars (rebars) in the footings and pour in concrete. Leave to harden for three days. Install drainage and utility lines. Erect foundation walls on the footings.
Backfill the bottom space with gravel and compact until it lies one brick below the top of the foundation wall. Cover with ¼-inch thick plastic sheet. Pour over concrete for the foundation slab until its surface is flush with the top of the foundation wall. Smooth out the concrete and leave to harden for three days.
Install the house frame. Place a damp proof course under all walls. Brick all walls simultaneously. Install windows and doors followed by roof structure and tiles. Install house plumbing and utility lines. Complete plasterwork, ceilings and floor fittings.
Tips & Warnings
- Visit your site during heavy rainfall to see where the water flows.
- Check all gas, water, electricity and communication lines with local utilities.
- Supervise all concrete pouring to ensure that your contractors don't take short cuts.
- Allow time for local building authority inspections. These includ a foundation inspection before concrete placement, a framing inspection before exterior and interior wall cover, and final building inspection.
- Excavate footings down to the bedrock if your budget can accommodate the extra cost. This improves the building stability.
- Design a floor plan that mimics the contours or the land and reduces excavation costs.
- Avoid retaining walls higher than two feet. Build two or more stepped retaining walls if necessary.
- Make sure there is no water build up behind the retaining walls.
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