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Fence Strip Foundation Calculator

Calculate concrete volume for fence strip foundations with integrated post holes. Features frost line depth checks and post displacement logic.

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Category Foundation & Concrete
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About

Installing a fence with a continuous concrete curb (strip foundation) provides superior durability and weed control compared to isolated post holes. However, calculating the concrete volume requires subtracting the displacement of the posts while adding the volume of the deep pilings that anchor the fence below the frost line. Failure to dig below the frost line in cold climates results in "heaving," where freezing soil pushes the foundation upwards, ruining the fence alignment. This tool handles the compound geometry of the strip plus the cylindrical post footings.

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Formulas

The total volume Vtotal is the sum of the strip volume Vstrip and the post footing volume Vpost.

Vstrip = (Lfence × Wstrip × Dstrip) − (Nposts × Apost × Dstrip)
Vpost = Nposts × πr2 × Dhole

Note: The calculator assumes the strip sits on top of, or integrates with, the post holes. The post displacement is subtracted from the strip to avoid double counting the intersection.

Reference Data

Climate ZoneTypical Frost DepthRecommended Footing Depth
Northern US / Canada40-60 in48-72 in
Midwest / Central EU25-40 in30-42 in
Southern US / South EU0-10 in12-24 in

Frequently Asked Questions

For the deep post holes, using cardboard forms (sonotubes) is recommended if the soil is sandy or loose to prevent collapse. For the strip itself, wooden formwork is required above grade.
The strip itself usually only needs to be 4-6 inches (10-15cm) deep for a fence, as it's not structural like a house foundation. Its main purpose is aesthetic and to hold the posts together. The *strength* comes from the deep post holes.