MOT Type 1 (SHW Clause 803)
Last reviewed: 9 September 2026
What it covers
MOT Type 1 is a well-graded crushed stone, typically limestone or granite, from 40mm down to dust. The fines (dust) fill the gaps between the larger stones, so it locks together tightly when compacted, giving a dense, strong, load-bearing layer with limited drainage. It's the default sub-base choice for driveways, paths and patios, and what most UK merchants mean when they just say "MOT" or "hardcore" informally.
The Specification for Highway Works guidance behind Clause 803 also specifies how it should be laid: compacted in layers of no more than 100mm at a time, not dumped in and compacted all at once, or the bottom of a thicker layer won't compact properly no matter how many passes you make over the top.
What it does not cover
Clause 803 is a grading and compaction specification - it defines what the material is and how to lay it, not how to convert a job's area and depth into tonnes to order. That conversion needs a bulk density figure, which isn't part of the grading spec itself. Our calculators use 1,920 kg/m³ at compacted density for this - sourced independently, not read off the clause - and are explicit that this is the compacted figure, not the loose (as-delivered) density, since the two differ by roughly 7% and conflating them is a common source of under-ordering.
"Crusher run" is a related but distinct term worth not confusing with this: it's crushed stone graded similarly to Type 1, but not necessarily certified to the Clause 803 specification. Worth checking with your supplier whether theirs meets Type 1 spec if that matters for your job.
Which of our calculators rely on it
- Sub-Base Calculator - MOT Type 1 is the default material option, with compacted volume, loose volume to order and tonnage all built around the 1,920 kg/m³ figure.
- Paving Slab Calculator and Patio Calculator - both use the same 1,920 kg/m³ figure for their own sub-base tonnage line, matching the sub-base calculator exactly rather than using an independently-guessed number.
- Shed Base Calculator - MOT Type 1 sub-base sits beneath both the concrete slab and paving-slab base types.
- Gravel Calculator - offers MOT Type 1 as one of its selectable material densities, for the (less common, but real) case of ordering it loose rather than as a sub-base layer.