Sub Bases For Patios

Sub Bases for patios

In this article, we’ll explore key questions surrounding the construction and maintenance of patio bases, providing insights into the necessity of base layers, optimal thicknesses, and the use of various materials. Whether you’re planning a new patio, a walkway, or any hardscaping project, our concise yet thorough guide, complete with detailed tables and guidelines, will equip you with the knowledge to build a durable and stable foundation for your outdoor spaces.

Do Patios Need a Base Layer?

Patios will require a base layer if vehicles are driving on top of the however, base layers are optional for foot traffic only.

Base needs depend on the surfacing type. Interlocking concrete pavers require a base while materials like stamped concrete may perform fine without, but could benefit from one. See Table 1.

Remember that bases spread loads and provide critical support. Omit only with good reason.

Compacting base gravel with plate compactor

Table 1: Base Guidelines by Surface Type

Surface Material Base? Depth Notes
Paving Stones Always 4-6 inches Essential in most cases
Concrete Pavers Usually 4-9 inches Also helps level
Asphalt Often 3-5 inches Depends on traffic load
Gravel Sometimes 4-8 inches Depth varies with usage
Brick Generally 2-4 inches Best with a sturdy base
Natural Stone Varies 3-6 inches Dependent on stone type
Rubber Tiles Rarely 2-3 inches Mostly for play areas
Wood Chips No 2-4 inches Commonly used in gardens
Sand No 2-3 inches Good for drainage
Composite Decking Usually 3-5 inches Requires solid support

General Patio Sub base Cross Section Shown Below

patio cross section with sub base

What Thickness Should a Patio Sub  Base Be?

For patios, a 4-6 inch base of packed gravel is typical. Driveways often use 6 inches minimum depth. Commercial projects may exceed 9 inches base thickness.

There’s a general rule to make base layers at least twice the maximum rock size to prevent pressure points.

So if the largest rocks are 1 inch, the minimum depth should be 2 inches. See diagram:

Thus, for 1.5 inch road base stone, the formula gives 1.5 x 2 = 3 inch minimum. Round up to the nearest inch.

If the existing base will be 4 inches, the maximum rock size should be 4 / 2 = 2 inches.

Table 2: Recommended Base Depth

Table 1: Requirements for Sub-base and Recommended Thicknesses
Type of Paving Sub-base Required? Thickness (mm) Remarks
Flexible Block Paving Always 75-150 Minimum 75mm for pedestrian areas, 100-150mm for driveways, over 150mm for commercial use
Rigid Block Paving Typically 100-225 Can be positioned under the base layer
Patio Flags Sometimes 75-100 Optional, but beneficial for elevating levels
Indian Sandstones Sometimes 75-100 Optional, but advantageous for raising levels
Yorkstone Flags Sometimes 75-150 Not required for pedestrian areas, suggested for driveways
BS Flags Generally 75-150 Unnecessary for patios, advised for driveways, commonly specified for commercial projects
Gravel Generally 75-150 Skippable in ornamental areas, essential for trafficked zones
Setts/Cubes Generally 75-150 Optional for rigid construction, crucial for flexible construction
Cobbles Sometimes 75-150 Potential use under base layer
Tarmac Always 100-150 100mm for footpaths and light driveways
Concrete - PIC Typically 100-150 Frequently excluded beneath PIC on driveways, though this may not be ideal
Resin Systems Typically 75-150 Varies based on the underlying surface type

Can I Use Salvaged Materials as Base?

Base layers provide critical support, so durability matters. Scrimping with low-grade fill risks problems.

The issue with repurposed masonry and concrete is random sizes/shapes and gaps. The same for “hardcore” rubble.

Over time, backfill trickles into voids, allowing settling. Jagged pieces telegraph through, causing instability.

Avoid using whole bricks. Halved is better, but crushed masonry blended with clean gravel makes the best DIY base option. Topping this stabilized layer with 4-6 inches of road base stone completes a durable patio foundation able to withstand seasonal movement.

Cutting corners on base build shortchanges overall longevity. Proper base materials make sound, long-term investments.

shows concrete sub base for patio.

What Base is Ideal for Sandstone Pavers?

The optimal base for sandstone pavers is crushed stone or limestone, known for its compaction and high-traffic endurance. Sand is also favoured for its drainage capabilities.

Which Sub-Base Material is Best for Paving Slabs?

MOT Type 1, comprising crushed limestone, concrete, or granite without fines, is the preferred sub-base for paving slabs due to its superior quality and stability.

What Sub-Base is Needed for a Porcelain Patio?

For a porcelain patio, a Type 1 MOT or General Sub-Base (GSB) aggregate is essential for providing strength and stability. It should be raked out to create an even layer, approximately 30mm below the string line.

What Should be Placed Under Porcelain Pavers?

According to Best Practices for Porcelain Pavers a sand base is suitable for small patios or walkways over concrete or level ground, especially in dryer climates. This involves installing porcelain pavers over a compacted sand base.

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