Clients often arrive with a foundation type already decided, usually because a neighbour used it. It is worth understanding what each one is doing, because picking the wrong one is expensive in both directions — you either underbuild and crack, or overbuild and pay for concrete that is doing nothing.
Strip foundations
A continuous reinforced strip running under the loadbearing walls, spreading a line load over a wider bearing area. It suits single-storey and light G+1 loadbearing masonry on firm, uniform soil with reasonable bearing capacity — a lot of the red laterite ground around Kampala, Mukono and Wakiso qualifies.
Where it fails is on variable ground. A strip is stiff along its length but has no way to bridge a soft pocket. If half the strip sits on murram and half on a filled hollow, the wall above cracks at the transition.
Pad foundations with ground beams
Individual pads under each column, tied together by reinforced ground beams. This is our default for framed buildings — commercial units, warehouses, anything G+1 and above.
The pads take the point loads down to a competent stratum. The ground beams do two jobs people underestimate: they carry the ground-floor walls so the walls are not sitting on unreinforced fill, and they lock the pads into a single frame so that differential movement between pads is resisted rather than transmitted upwards. On expansive clay this is not optional.
Pads also let you found at different depths where the ground varies without redesigning the whole substructure — you deepen one pad, not the entire perimeter.
Raft foundations
A single reinforced slab under the whole footprint, sometimes thickened into beams beneath the column lines. A raft spreads the total building load over the entire area, so the pressure on any square metre of soil is low.
Rafts earn their keep in three situations: weak or highly variable soil where no shallow layer can be trusted with concentrated loads; sites where the water table is high and deep excavation is impractical; and small footprints where the pad excavations would nearly meet anyway, so a raft is cheaper to build than a set of pads.
The trade-off is reinforcement. A raft uses considerably more steel than pads for the same building, and steel is the volatile line in every bill of quantities we price.
How we actually choose
The decision comes out of the trial pit logs and the column loads, in that order:
- Competent stratum within reach and loads modest and line-based → strip.
- Competent stratum within reach and loads concentrated at columns → pads with ground beams.
- No competent stratum within economical excavation depth, or highly variable ground, or high water table → raft, or pads taken deeper with a piled option priced alongside.
We price two options on most jobs and show the client both. It is a more honest conversation than presenting one number.
The mistake we see most
Strip foundations built on backfilled ground because the plot was levelled before anyone thought about the structure. The fill was never compacted in layers, nobody tested it, and the strip is founded on material with no reliable bearing capacity. The building settles unevenly within two rainy seasons.
If your plot has been cut and filled, that history matters more than the foundation type on the drawing. Say so early.
OK Estate Construction and Supply Limited designs and builds foundations across Uganda and South Sudan. Talk to our team about your project.