Prefab Foundation Calculator (Light Loads)

A PCC plinth is a full slab cast over the entire footprint — typically 75–125 mm thick — and is the simplest option for very light prefab houses on relatively level, well-drained ground. A strip footing is a perimeter ribbon cast under the load-bearing walls only — typically 75 mm thick by 300–600 mm wide — and saves concrete on larger footprints. As a rule of thumb, use the plinth for footprints under about 30 m² and strip footings for larger plans.

Soft soils need wider strip footings (600 mm) and a thicker plinth slab (+50 mm bump) to spread the building load over more bearing area. Medium soils sit in the middle (450 mm strip, +25 mm plinth bump). Hard soils are forgiving — 300 mm strip footings and a base 75 mm plinth slab usually suffice. If you don't know the soil class, assume medium and have it verified by a local geotechnical test before pouring concrete.

The PCC volume is the as-cast concrete itself. Excavation needs additional working space for compacted sand/aggregate underneath (typically 50–75 mm), side clearance for shuttering and access, and a small over-cut at the top to handle uneven ground. The 1.5× multiplier matches the rule used by the project's main excavation calculator and is conservative — actual excavation can range from 1.3× to 1.7× depending on soil stability and worker safety setbacks.

No. This calculator is sized for low-load prefab structures: single-storey Korean panel houses, light steel-frame cabins, modular site offices, and similar. The PCC thicknesses and strip widths used here would not be enough to support an RCC building with cast columns and slabs. For RCC houses, use the RCC Footing Calculator (isolated, combined, or raft footing) instead — those calculations include reinforcement, depth-of-bearing, and structural design checks.

PCC stands for Plain Cement Concrete and is, by definition, unreinforced. For light prefab loads on well-drained ground, plain concrete works fine. If the soil is expansive, the slab is over 4 m in any dimension, or the slab will support a heavier structure than this calculator targets, switch to RCC (reinforced) and add at least an 8 mm bar mesh at 300 mm spacing in both directions, top and bottom. That changes both the cost and the structural calculation — use the RCC Slab calculator for that case.

This calculator only outputs the concrete and excavation volumes. Always plan for an anti-termite chemical pour over the prepared sub-grade before casting (typically 5–7.5 litres of chlorpyrifos solution per m²) and a damp-proof course (DPC) layer at plinth level — usually a 25–40 mm cement screed with an integral waterproofing admix, sometimes with a polythene sheet between sub-grade and PCC. These add a few percent to the total foundation cost and are non-negotiable in monsoon-prone areas.