How deep should a patio sub-base be?

Last checked 01-11-2026. A plain guide, not legal advice: check the official guidance below for your job.

For most domestic patios, paving makers give about 100 mm of compacted Type 1 sub-base, then a 30 to 40 mm full mortar bed for natural stone and porcelain, then the paving. Driveways need more, usually about 150 mm. Keep the finished paving at least 150 mm below the damp-proof course, and lay it to a fall away from the house.

Work it out with the free patio and paving slab calculator

The short answer

These figures are from paving makers' installation guides. They are for typical domestic work on firm ground; soft or poor ground needs more, and the makers say the design must suit the ground conditions and the loads.

Patio: Marshalls' porcelain and natural stone installation guides both say a sub-base of 100 mm should be enough for most domestic applications. Its short how-to guide for patios gives the same 100 mm, with a 40 mm bed on top.
Driveway: Marshalls' installation details for driveway setts say 150 mm for most domestic applications. The GOV.UK guidance on front gardens describes about 150 mm of sub-base, with 200 to 250 mm of construction in all under a drive.
Bedding for natural stone and porcelain: a full mortar bed 30 to 40 mm thick.
Finished level: at least 150 mm below the damp-proof course (DPC) where the paving meets the house.

Dig depth = paving thickness + bedding + sub-base. For 20 mm porcelain on a 40 mm bed and 100 mm of Type 1, that is 20 + 40 + 100 = 160 mm below the finished level.

Set the finished level from the damp-proof course

This sets everything else, so measure it first. Marshalls' guides say the finished surface of paving laid up to a building must be at least 150 mm below the DPC to prevent problems with rising damp.

That matches the building regulations guidance for walls. Approved Document C (England) says the DPC in an external wall should be at least 150 mm above the level of the adjoining ground, unless the design means part of the building protects the wall (paragraph 5.5). A patio that brings the ground up closer than that undoes it.

The Planning Portal says a new patio or drive does not generally need building regulations approval, but the work must not make access to the house less satisfactory than before. Its example is changing the level so that steps are needed where there were none.

If the existing ground is already close to the DPC, you will need to dig down further. Ask the designer or building control if you are unsure.

Type 1, laid and compacted in layers

Marshalls' guides specify a well graded Type 1 sub-base, 40 mm down to dust. Recycled crushed concrete or masonry can be used if it is well graded and compacts to a close finish. Do not use anything with organic matter in it.

Dig out soft spots and refill them with sub-base, as the GOV.UK guidance says.
If you are unsure about the ground, Marshalls recommends a geotextile membrane under the sub-base.
Lay it in layers no thicker than 75 mm, or twice the largest stone size, and fully compact each layer before the next. Marshalls' porcelain detail shows 100 mm laid in two layers of 50 mm.
Marshalls gives a tolerance of +5 to -10 mm on the sub-base level.
Form the falls in the sub-base, not by varying the bedding thickness.

Type 1 has a lot of fines, which is why it compacts so well. The GOV.UK guidance points out that it also stops water passing through easily. A permeable surface needs an open-graded sub-base, such as Type 3 or 4/20, instead.

Falls away from the house

Marshalls' guides give a minimum longitudinal fall of 1.25 percent (1 in 80) and a cross-fall of 2.5 percent (1 in 40), built into the sub-base so surface water runs off. Fall the patio away from the house.

The drop is the length divided by the fall ratio. Over 4 m at 1 in 80: 4,000 / 80 = 50 mm. At 1 in 40: 4,000 / 40 = 100 mm.
Check the falls with a level and straight-edge, or a string line, as you lay the sub-base.
The GOV.UK guidance says that if a drive slopes towards the house you should use a drainage channel to collect the water, not to direct water into soakaways close to buildings, and not to send it towards a neighbour's property.

Follow the installation guide for the product you are laying, as the makers' figures differ.

A full mortar bed for natural stone and porcelain

Natural stone and porcelain need a full bed of mortar, not dabs of mortar under the corners.

Porcelain: Marshalls says to lay it on a full, wet, workable bed of 1 part cement to 4 parts sharp sand, 30 to 40 mm thick, and never on a five-spot bed. Apply a priming slurry or primer to the back of every slab. Joints should be 3 to 5 mm, filled with a jointing compound or an exterior grout.
Natural stone: Marshalls says a full wet bed of 1 part cement to 3 or 4 parts sharp sand, laid 30 to 40 mm thick, which tamps down to about 25 mm. Prime the backs of the slabs. For joints it says a damp mix of 1 part cement to 4 parts building sand can be used where the joint is at least 10 mm and the slab at least 22 mm thick.
Both guides say never brush a dry or semi-dry sand and cement mix into the joints, because it stains and does not make a proper joint.
Cut with a water-fed saw to control dust, as Marshalls advises. Cutting stone and concrete paving makes silica dust.
Weather: Marshalls' natural stone guide says not to lay below 3 degrees C on a falling thermometer or below 1 degree C on a rising one.

Wet mortar is a cement product, so it needs the usual gloves, eye protection and washing facilities.

Driveways and front gardens

A drive carries cars, so the sub-base goes up to about 150 mm, as above, and the maker's guide for the block or sett you use applies to the bedding and jointing.

In England, paving a front garden can need planning permission. Under Class F of the permitted development rules, a hard surface between the principal elevation of the house (usually the front wall) and a highway that covers more than 5 m2 must either be made of porous materials or drain to a permeable area within the property, such as a lawn or border. A traditional impermeable surface over 5 m2 that drains to the road needs planning permission.

Patios and drives elsewhere round the house have no area limit, the Planning Portal says, though significant embanking or terracing may need planning permission.
The permitted development allowances do not apply to flats and maisonettes, some converted houses, or where a planning condition or Article 4 direction removes them. A listed building needs listed building consent for significant works.
Driving across a pavement needs a dropped kerb, which needs permission from the council.
Before you dig, check for underground services near the surface. The GOV.UK guidance names water pipes, cable TV and electricity cables.

Wales, Scotland and Northern Ireland have their own planning rules and building regulations, so check locally there.

Worked example: a porcelain patio at Wren Terrace

A porcelain patio behind a house on Wren Terrace, 6 m along the back wall and 4 m deep. The slabs are 20 mm thick. The DPC is 200 mm above the existing ground, which is level.

Area: 6 x 4 = 24 m2.
Construction depth: 20 mm slab + 40 mm bed + 100 mm Type 1 = 160 mm.
Finished level at the house: no higher than 200 - 150 = 50 mm above the existing ground.
Fall: taking the minimum 1 in 80 away from the house, 4,000 / 80 = 50 mm, so the outer edge finishes at 50 - 50 = 0 mm, level with the existing ground. If the paving maker asks for 1 in 40 in that direction, the drop is 100 mm and every dig depth below goes up accordingly.
Dig depth: 160 - 50 = 110 mm at the house, and 160 mm at the outer edge. The average is (110 + 160) / 2 = 135 mm.
Spoil: 24 x 0.135 = 3.24 m3 measured in the ground. It takes up more room once dug, so ask the skip or grab firm.
Type 1: 24 x 0.1 = 2.4 m3 compacted. At about 2.1 tonnes per m3, that is 2.4 x 2.1 = 5.04 t, and with 10 percent for waste 5.04 x 1.1 = about 5.5 t.
Compaction: two layers of 50 mm, each compacted.
Mortar: 24 x 0.04 = 0.96 m3 of wet mortar, laid at 40 mm. Ask your merchant how much sand and cement that takes.

Where the 2.1 comes from: Marshalls' sub-base guide works out tonnes by multiplying the compacted volume by 1.3 for compaction, 1.1 for waste and 1.6 tonnes per m3. That is 2.4 x 1.3 x 1.1 x 1.6 = 5.49 t, the same answer, and 1.3 x 1.6 = 2.08, which is the 2.1 used above. It is a rule of thumb, so check the figure with your supplier.

If the same area were a front drive, the sub-base would be 150 mm: 24 x 0.15 x 2.1 x 1.1 = about 8.3 t of Type 1, and the surface would need to be permeable or drain to a lawn or border to stay within permitted development.

How deep should a patio sub-base be?

The short answer

Set the finished level from the damp-proof course

Type 1, laid and compacted in layers

Falls away from the house

A full mortar bed for natural stone and porcelain

Driveways and front gardens

Worked example: a porcelain patio at Wren Terrace

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