04 / Selection and limits
How the five foundation paths are measured
The gravel path expands the shed footprint by the entered overhang on all sides, multiplies that pad area by compacted depth, then applies your loose-order factor. Slab mode uses plan area times entered thickness and reports mesh area, optionally converting it to sheets from entered product coverage, or grid-line rebar length. Piers and blocks form a rectangular point grid by rounding each span up to the entered maximum spacing; pier concrete adds the volume of a cylinder at every point. Skid mode draws parallel unspliced runs and checks each against the stock length. These are five different material questions, not five interchangeable structural designs.
Worked choices
The loaded gravel-pad example enters a 10 × 12 ft shed, 1 ft pad overhang on each side, 6 in compacted depth, and 1.2 loose-order factor. Expect a 12 × 14 ft pad, 84 ft³ compacted volume, and 100.8 ft³ loose delivery allowance before any supplier conversion. Those numbers describe the example pad only, not whether gravel is an approved support for this shed.
The same 10 by 12 ft shed with pier points no farther than 5 ft apart needs three columns and four rows, or 12 modeled positions. A 12 in diameter by 3 ft deep cylindrical shaft is about 0.067 m³ each, approximately 0.80 m³ for 12 shafts before enlarged footings or waste.
Choose, measure, and check the support path
Obtain the shed manufacturer's permitted support and anchoring details first. For a pad, measure footprint overhang and finished compacted depth; for points, mark every row and column on the actual site; for skids, verify each unspliced length against available stock. Match the resulting sketch to drainage, frost, soil, and access conditions before asking for a supplier quote.
Field decisions before ordering
- Check whether the shed maker permits the chosen support and how the floor is anchored.
- Confirm bearing ground, frost exposure, drainage away from the site, and a level bearing surface before interpreting the sketch.
- Do not treat mesh area or a rebar line count as reinforcement design; slab edges, laps, and cover require a separate specification.
- Never splice a short skid solely to satisfy this stock count without a suitable connection detail.
Shed foundation questions
Does the cheapest tier identify the right base?
No. The tier is a relative planning prompt. A shed with a slab floor, a raised framed floor, or a manufacturer-required anchor can rule out an otherwise inexpensive choice.
Why can the pier count jump when spacing changes slightly?
The sketch needs a whole number of intervals on both axes. Crossing an interval threshold adds a full row or column of points rather than a fraction of a pier.
Is the gravel pad volume also the excavation volume?
Only when the excavated area and depth actually match that modeled pad. Subgrade removal, edge treatment, and local grading have to be measured separately.
Source and planning boundary
Tuff Shed's site preparation guidance describes a firm, level, dry base and directs buyers to check local requirements. QUIKRETE's concrete calculator likewise treats volume as a geometry and yield question. Sources reviewed September 24, 2026. MaterialNest cannot select a foundation for your soil, shed load, wind exposure, frost depth, or permit. Have the actual support and anchoring details checked against the shed manufacturer and the local authority before construction.