Block Paving: Sub-Base Depths, Edge Restraints, Patterns & Permeable Options

Summary

Block paving is one of the most durable and versatile forms of hard landscaping, but it's also one of the most demanding to install correctly. The difference between a block-paved driveway that lasts 20+ years and one that sinks and becomes uneven within 3–5 years is almost always in the sub-base depth, material quality, and compaction. Skimping on the sub-base to reduce cost is the single most common mistake.

The planning permission issue for front driveways in England is a genuine constraint that has been in force since 2008 but is still regularly ignored. If a client wants a new impermeable front drive over 5m², they either need planning permission (which takes 8–12 weeks and costs £206 for a householder application) or need to use permeable paving. Permeable concrete block paving and permeable resin-bound gravel both avoid the planning requirement and can look excellent.

For tradespeople, understanding the difference between a standard block paving installation and a permeable paving installation is increasingly important — permeable installations require a different sub-base specification (open-graded aggregate rather than MOT Type 1) and different jointing material.

Key Facts

• Sub-base depth (standard residential) — 100mm compacted MOT Type 1 aggregate
• Sub-base depth (clay soils, driveways, large areas) — 150mm compacted MOT Type 1
• Bedding layer — 50mm sharp sand (Zone 2 to BS EN 13139); not building sand, not mortar
• Block thickness (pedestrian) — 60mm standard; 50mm minimum for lightly used paths
• Block thickness (driveways, vehicles) — 80mm minimum; 100mm for commercial vehicles
• Edge restraints — all block paving must be contained; typically concrete haunching (semi-dry 1:8 mix) or proprietary plastic edge restraint; without edge restraint, blocks migrate laterally
• Jointing sand — kiln-dried sand brushed into joints after compaction; re-applied annually; 2–3 applications at installation
• Plate compactor — vibrating plate compactor used to consolidate blocks into bedding sand and drive jointing sand; minimum 75kg plate weight for driveways; fit rubber plate to protect surface finish
• Permeable block paving — concrete blocks with larger joint width (typically 5–6mm) filled with permeable grit; requires open-graded sub-base (not MOT Type 1)
• Permeable sub-base — 4/20mm clean single-size aggregate (no fines); allows water to drain through to soil below; soakaway function within sub-base
• Planning permission — GPDO 2015, Schedule 2, Part 1, Class F.2: impermeable front garden paving over 5m² requires planning permission in England (not Wales — different rules)
• Laying patterns — herringbone (most stable for driveways), basket weave, stretcher bond; herringbone 45° to traffic direction is the strongest pattern
• Cutting — always needed at edges; use a disc cutter (angle grinder with block-cutting diamond blade) or block splitter; cut dry; wear FFP2 mask for silica dust
• Falls — minimum 1:80 fall away from buildings; toward a gully, channel drain, or permeable area
• Cleaning — pressure wash annually; apply block paving sealant every 2–3 years to reduce weed growth in joints and staining

Quick Reference Table

Detailed Guidance

Sub-Base Installation

The sub-base is the foundation of all block paving. Failure here means failure everywhere, and it can't be rectified without lifting all the blocks.

MOT Type 1 (Clause 803 material, also known as DTp Type 1): crushed angular aggregate, well-graded from 40mm down to fines. Compacts to form a dense, stable, load-spreading layer. Do not substitute soft core (mixed demolition waste) — it lacks long-term bearing capacity.

Laying and compacting:

1. Excavate to formation level — allow for block thickness + 50mm sand + sub-base depth + any geotextile
2. Compact the subgrade with at least 3 passes of the plate compactor
3. Lay geotextile membrane (woven polypropylene, 100g/m² minimum) across the formation level — this prevents fines migration from subgrade into sub-base
4. Lay Type 1 in maximum 75mm compacted lifts; each lift minimum 3 plate compactor passes
5. Check level with a string line; final surface should be accurate to ±10mm

For driveways, the total excavation from finished surface is typically 280–300mm (100 + 50 + 80 + margins). Plan this carefully against existing levels at the road and house entrance.

Bedding Sand

Sharp sand (coarse angular sand, Zone 2 to BS EN 13139) is the correct bedding material. Never use:

• Building sand (too fine, washes away, doesn't compact)
• Mortar (blocks become permanently fixed; no settlement correction possible)
• Wet sand (will be squeezed out under compaction)

Application: screed to 60–65mm depth (it will compact to 50mm under the blocks). Use parallel screed rails set at the correct level and a screed board to level. Do not walk on screeded sand before laying — footprints make low spots that show in the finished surface.

Note: the screed sand is the last precise level control before blocks go down. Get this right and the rest of the job is straightforward.

Laying Pattern and Starting Point

Herringbone pattern (45° to traffic direction): the strongest pattern for driveways because the interlocking action of blocks is maximised. Blocks do not align in any single direction, so vehicular turning loads are distributed effectively.

Starting point: always start from a fixed right angle (a straight wall, a straight edge restraint). Use a string line at 45° to establish the herringbone direction. Lay the first course of blocks along the string line, then build out from there.

Cut blocks: leave cutting until the area is fully laid. Mark cuts with a pencil or chalk, cut using a disc cutter, fit cut pieces last. Cut blocks should always be at the perimeter — never in the middle of the pattern.

Edge Restraints

Edge restraints are non-negotiable. Without them, the sand bedding layer is unconfined at the edge, blocks migrate outward under load, and the whole installation opens up.

Concrete haunching: semi-dry concrete (1:8 OPC:sharp sand), mixed stiff, haunched at 45° against the outside face of the edge block, extending below the sand to the top of the sub-base. Allow 24–48 hours to cure before plate compacting adjacent to haunched edges.

Proprietary edge restraints (plastic channel edging, e.g., Brett Martin Align, Marshalls Edge): L-shaped plastic fixed with 300mm ground pegs at 600mm centres. Quicker than concrete haunching but less robust for driveways with vehicles.

Existing kerb or wall: if a wall or kerb already exists, use this as the edge restraint on that side.

Compaction and Jointing

After laying all blocks (including edge cuts):

1. First pass with rubber-footed plate compactor — this sets blocks into sand, equalises levels
2. Brush first application of kiln-dried jointing sand across the surface; use a stiff broom to push into joints
3. Second and third passes with plate compactor, brushing additional sand in between passes
4. Final inspection: joints should be fully packed with sand; no hollow spots audible when tapped

The plate compactor should NOT be used within 1m of an unsupported edge until haunching has cured.

Permeable Block Paving for Planning Compliance

Permeable block paving uses blocks with wider joint widths (5–6mm typically) and permeable jointing material (permeable grit or angular grit), combined with an open-graded (single-size, no fines) aggregate sub-base that holds water and allows it to infiltrate slowly.

Sub-base for permeable systems:

• Bottom layer: 100–150mm 40mm clean single-size aggregate
• Middle layer: 50mm 20mm clean single-size aggregate
• Bedding: 50mm 6–10mm permeable grit (not sand — sand would wash into the open-graded sub-base)
• Geotextile between subgrade and sub-base (do NOT use geotextile between layers — it blocks drainage)

Jointing: permeable grit (4–8mm rounded) brushed into joints. Do not use kiln-dried sand — it washes out and blocks drainage.

Soakaway or infiltration: the sub-base stores water temporarily and releases it to the ground below. On clay soils this may not be fast enough — a perforated drain at the base of the sub-base may be needed to discharge to a soakaway or surface water outlet.

Brands: Tobermore Hydropave, Marshalls Priora, Cemex Aquaflow — all tested to BS 7533-13 and CIRIA guidance.

Frequently Asked Questions

How deep does the sub-base need to be for a car to park on the drive?

Minimum 100mm for a standard domestic car. For clay soils or where the driveway is subject to heavy or frequent vehicle use, 150mm is better practice and significantly reduces the risk of differential settlement. The 100mm minimum assumes good subgrade — if you encounter soft or waterlogged soil, excavate further and lay a geotextile membrane before the sub-base.

Can I seal block paving to stop weeds?

Yes — block paving sealer (gloss or matt finish) applied every 2–3 years hardens the jointing sand and significantly reduces weed germination in joints. However, it reduces permeability (an issue if the drive is permeable paving for planning compliance) and must be re-applied periodically. An alternative is polymeric jointing sand (Romex Pave Set, Techniseal HP), which bonds when wetted and prevents weed growth and ant activity without sealing the surface.

My client wants a herringbone pattern — does the direction matter?

For driveways, lay herringbone with the V-point in the direction of the main traffic flow (pointing toward or away from the road, not across it). This maximises the interlock under braking and turning loads. For decorative patios, direction is a visual choice.

What's the minimum block thickness I can use?

60mm for pedestrian areas; 80mm for driveways used by cars; 100mm for areas used by vans, lorries, or commercial vehicles. Thinner blocks (50mm) are available but only suitable for decorative pedestrian areas.

Regulations & Standards

• Town and Country Planning (GPDO) 2015 — Schedule 2, Part 1, Class F.2: front garden paving planning permission

• BS 7533-1 — guide for the structural design of pavements constructed with clay, natural stone or concrete pavers

• BS 7533-4 — code of practice for the construction of pavements of precast concrete flags, natural stone slabs and clay pavers (vehicular)

• BS 7533-13 — guide to the design of permeable pavements constructed with concrete, clay or natural stone

• CIRIA C753 — SUDS Manual; permeable paving design

• BS EN 1338/1339/1340 — concrete block/flag paving product standards

• Planning Portal — Paving Your Front Garden

• Marshalls — Technical Information

• Tobermore — Installation Guides

• Brett Landscaping Technical

• patio laying — related laying techniques for flags and natural stone

• drainage landscaping — drainage solutions for driveways and hard landscaping

• artificial grass — comparison of permeable options for front gardens