A sub-base (typically MOT Type 1) is the critical load-bearing foundation for any driveway or patio. Use our calculator to estimate the required tonnes and bulk bags, including a 20% compaction factor to ensure your project remains stable and level.
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Volume Needed:0.00 m³
Weight Required:0.00 Tonnes (0 kg)
Delivery & Buying Options
Compare the most cost-effective ways to order your sub-base:
Option A
25kg Small Bags
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Individual Bags
Est: £0
Option B
Bulk Bags
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~850kg Bags
Est: £0
Option C
Loose Tipper
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Total Tonnes
Est: £0
Estimated Labour:0.0 hrs
Expert Note: Result includes the 20% structural compaction factor. Loose tipper loads are generally 40% cheaper for projects over 10 tonnes.
A patio or driveway is only as good as the foundation beneath it. If your sub-base isn't deep enough, or if you haven't ordered enough material to properly compact it, your finished surface will eventually sink or crack.
The 20% Compaction Rule
When calculating MOT Type 1, the most common mistake DIYers make is failing to account for compaction. A loose pile of sub-base contains a lot of air. When you run a wacker plate (compactor) over it, the smaller dust particles fill the voids between the larger stones, locking them together to form a solid mass. Because of this, MOT Type 1 reduces in volume by approximately 20% to 25% when properly compacted.
Our calculator accounts for this by letting you input a compaction and waste allowance, ensuring you order enough loose material to achieve your final, compacted depth.
Converting Volume to Tonnage
Different materials have different densities. MOT Type 1 is very dense, typically weighing around 2 tonnes per cubic metre. This means even a small domestic patio can quickly require several tonnes of material. To prevent overloading a standard car, it's highly recommended to have bulk bags delivered directly to your door.
Frequently Asked Questions
How much sub-base do I need?
To calculate sub-base, multiply the length and width of the area by the required depth. For a standard domestic patio, a depth of 100mm (0.1m) is usually recommended. Remember that sub-base will compact by approximately 20% once vibrated, so it is best to order slightly more than the "loose" volume calculation.
What is the best sub-base for a driveway?
MOT Type 1 is the industry standard sub-base for driveways. It consists of crushed concrete or granite (graded from 40mm down to dust). The "fines" (dust) allow the material to lock together when compacted, creating a solid, load-bearing surface that won't shift under the weight of vehicles.
How deep should sub-base be for a patio?
For a standard garden patio with foot traffic, a sub-base depth of 100mm (4 inches) is sufficient. If the ground is particularly soft or prone to waterlogging, you may want to increase this to 150mm and use a geotextile membrane underneath.
Can I use ballast as a sub-base?
While ballast can be used for very light-duty projects, it is not a direct substitute for MOT Type 1. Ballast is a mix of sand and gravel and does not provide the same structural integrity or "interlocking" strength as graded Type 1 aggregate.
What is the difference between Type 1 and Type 3 sub-base?
The main difference is the amount of "fines" (dust). Type 1 contains fines to help it compact into a solid mass. Type 3 has fewer fines, making it more permeable. Type 3 is often required for SuDS-compliant (Sustainable Drainage Systems) projects like resin-bound driveways to allow water to drain through the sub-base.
Do different materials have different compaction factors?
Yes. MOT Type 1 and Crushed Concrete typically require a 20-25% volume allowance for compaction because they contain "fines" (dust) that fill the gaps between stones. MOT Type 3 has significantly fewer fines, meaning there is less "void space" to fill, so it often requires a lower compaction allowance of around 15%.
What is a SuDS compliant sub-base?
SuDS (Sustainable Drainage Systems) compliance requires a sub-base that allows water to infiltrate into the ground rather than running off into sewers. For these projects, MOT Type 3 is the standard choice. Unlike Type 1, which compacts into a solid mass, Type 3 has reduced "fines" (dust), leaving small voids that allow water to pass through. This is essential for resin-bound driveways and permeable block paving.
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Building Regulations & British Standards
The structural integrity of your project depends on following established UK construction standards and regulations:
Part H (Drainage): Building Regulations REQUIRE that any new driveway over 5m² must be permeable or drain to a natural soakaway within the property boundary.
BS 7533-13: The British Standard for the design of permeable pavements. It specifies the use of 'reduced fines' aggregates (like MOT Type 3) for the sub-base and laying course.
BS 8000-0: The standard for basic workmanship on construction sites. It emphasizes the importance of layer-by-layer compaction to prevent future settlement or 'rutting'.
Sewerage Sector Guidance: If you are connecting a new surface to a public sewer, you must obtain a Section 106 agreement from your local water authority.