MOT Type 3 (SHW Clause 805)
Last reviewed: 9 September 2026
What it covers
MOT Type 3 uses the same stone sizes as Type 1, but with the fines (dust) screened out. Removing the fines means the stones can't lock together as densely, which is the point: it makes the material free-draining rather than dense, so water passes through it instead of sitting on top or running off. It's used under permeable block paving and in SuDS (sustainable drainage) schemes, wherever the design intent is for water to soak away through the sub-base rather than be shed off the surface.
What it does not cover
Like Clause 803, Clause 805 is a grading specification - it defines the stone sizing and fines content that makes the material free-draining, not a materials-buying guide. It doesn't compact as densely as Type 1 by design, so a tonnage figure for Type 1 should never be reused for Type 3 on the same job without adjusting the density assumption. Our sub-base calculator treats it as a distinct material option with its own compacted density, not a variant of the Type 1 figure.
Which of our calculators rely on it
- Sub-Base Calculator - MOT Type 3 is offered as a distinct material option alongside Type 1, crusher run, recycled aggregate and hardcore, with its own compacted density rather than an adjusted Type 1 figure.