Decking & Paving Pedestals: Complete Guide (spacing, load)

Adjustable pedestals let you create an accurately levelled deck or paved terrace — or a deliberately specified finished fall — over an uneven, sloping or waterproofed surface. They are normally installed without fixing through the roof membrane or structural slab.

They are widely used beneath porcelain paving, stone slabs, timber decking and composite decking on flat roofs, balconies, patios and roof terraces. By raising the finished surface, pedestals create a clear drainage and ventilation void while keeping roof outlets, services and the waterproofing accessible below.

Choosing the right pedestal is not only about height. The paving size, joist system, roof construction, waterproofing, insulation, point loads, wind exposure and intended use all affect the final layout.

Product information and prices checked: 28 September 2026. Always confirm the selected variant and current technical information before ordering.

Quick answer

What is an adjustable pedestal?

An adjustable pedestal is a screw-height support that holds paving slabs or a decking subframe above a structural surface. Rotating the threaded section changes the support height, allowing the installer to compensate for variations and falls in the substrate while setting the required finished level.

A correctly specified pedestal system can provide:

• An accurately levelled surface, or a designed finished fall, over an uneven or sloping substrate
• A drainage and ventilation void beneath paving or decking
• Installation without routinely penetrating GRP, EPDM or another compatible waterproofing membrane
• Access to roof outlets, services and the waterproofing beneath
• Dry installation without a traditional mortar bed
• Consistent paving joints when the correct spacer tabs are used
• Easier removal and replacement of individual slabs

MESA plastic supports are manufactured from 90% recycled polypropylene and are fully recyclable. Apex currently lists a 20-year limited warranty; check the warranty conditions and the terms that apply to residential or commercial use.

Paving pedestal, decking pedestal or steel pedestal?

The head or support fitted to the pedestal determines what it can carry. Do not select a pedestal by height alone.

See all available heights and variants in the adjustable pedestals collection.

What should you check before choosing a pedestal?

Pedestals are only one part of a raised terrace. Before selecting a model or calculating quantities, check the complete roof, balcony or patio construction.

Roof deck or slab condition

The supporting surface must be sound, stable and suitable for the intended loading. Pedestals cannot correct rotten or deflecting roof decks, loose concrete, wet insulation, damaged waterproofing, inadequate drainage or existing structural movement. Investigate and repair defects before covering the area.

Waterproofing and insulation

Confirm that the waterproofing manufacturer permits the proposed pedestal arrangement. GRP, EPDM and other roof membranes may require an approved protection pad or separation layer beneath each base.

The insulation must also have sufficient compressive strength for the concentrated load beneath the pedestal bases. A pedestal can be stronger than the insulation, membrane or roof deck supporting it.

Paving, decking and subframe

Record the paving dimensions and thickness, or the decking board and joist specifications. Check permitted joist centres, unsupported joist span, board direction, required paving-joint width, cut slabs, board-end joints and perimeter framing.

Porcelain or stone should be approved by its manufacturer for pedestal-supported installation. Thin, large-format or unusually shaped slabs may require mid-edge or centre support.

Finished height and thresholds

Measure the substrate at its highest and lowest points. Include door thresholds, waterproofing upstands, parapets, outlets, steps and the full paving or decking build-up. A sloping roof may require several neighbouring pedestal sizes across the same terrace.

Wind and perimeter restraint

Pedestal systems are usually loose-laid, but tall constructions, exposed roofs, open edges and high-wind locations may need perimeter restraint, bracing, ballast or a designed wind-uplift solution. Agree these details before ordering materials.

How much load can a pedestal support?

Apex's current MESA product information states a maximum load capacity of up to 1,000 kg per pedestal. That is a product capacity for the pedestal under the manufacturer's stated conditions. It is not the permitted load for the complete terrace or roof.

The assessment may need to include:

• The self-weight of paving, decking, joists and pedestals
• People using the area and its intended occupancy
• Furniture and moveable equipment
• Snow, wind and other environmental actions
• Planters, privacy screens and fixed features
• Concentrated point loads
• Maintenance access
• Local pressure on the insulation and waterproofing

Adding pedestals can distribute a load through more support points, but it does not increase the structural capacity of the roof beneath them.

What about planters and hot tubs?

Large planters, water features, outdoor kitchens and hot tubs require a project-specific structural assessment. Water is heavy, and the load is concentrated within a relatively small area. Do not assume that adding a few supports makes an existing roof suitable.

For public areas, commercial terraces, tall pedestal systems or any unusual loading, obtain a designed layout before purchasing materials.

Pedestal spacing and quantity

The paving slab, decking board and joist system determine the layout. The pedestal does not set the spacing on its own.

Spacing for paving slabs and porcelain

For a standard grid:

• Place one pedestal beneath every point where slab corners meet
• Provide support along open edges and perimeters
• Add support beneath cut or irregularly shaped slabs
• Follow the paving manufacturer's requirements for mid-edge or centre supports
• Keep bases clear of roof outlets and drainage channels

With 600 × 600 mm paving, the main grid is normally based on approximately 600 mm centres because each internal pedestal supports adjoining slab corners.

The often-used estimate of about 2.8 pedestals per m² describes only a large, uninterrupted field of 600 × 600 mm slabs. It does not include the extra supports required around the perimeter of a smaller terrace.

Simple paving quantity formula

For example, a 3.0 × 2.4 m terrace using full 600 × 600 mm slabs contains five slabs across and four slabs along:

• Six pedestal positions across
• Five pedestal positions along
• Basic grid: 6 × 5 = 30 pedestals

Add any supports required for cuts, steps, changes of direction, perimeter details and manufacturer-specified centre support. This is why ordering one pedestal per slab can underestimate the quantity.

Spacing for timber and composite decking

Decking is normally supported by joists, with pedestals positioned beneath each joist. The board manufacturer sets the maximum joist centres. Many composite systems use approximately 300–400 mm centres in a standard straight layout, but the actual product instructions always take priority. Diagonal board layouts commonly require closer centres.

The joist or subframe manufacturer determines the allowable distance between pedestals along each joist. It depends on the joist material, profile, depth, unsupported span, pedestal height and expected loading. Do not automatically use a generic 500–600 mm spacing unless the selected joist system confirms it.

Apex gives a broad planning estimate of approximately 3–7 decking pedestals per m². Small areas, double joists, steps and complicated perimeters can require more.

Simple decking quantity formula

Add further supports beneath joist ends, joist joints, doubled joists at board ends, steps, perimeter framing and any position identified by the subframe designer.

Height ranges and slope correction

MESA is a family of pedestal sizes and accessories. The full range is achieved by selecting the correct model and approved configuration; one individual pedestal does not adjust across the complete combined range.

How do you calculate pedestal height?

Measure from the local roof or slab level to the planned finished surface. Check whether the manufacturer's published height includes the selected head or accessory before finalising the order.

If the target finished level is 120 mm above the roof and the paving is 20 mm thick, the starting pedestal height is 100 mm.

If the target finished level is 160 mm above the roof, with a 50 mm joist and 22 mm decking board, the starting pedestal height is 88 mm.

Repeat the calculation at the highest and lowest points. Choose models that place the required settings comfortably within their adjustment ranges instead of designing every support at its extreme limit.

Slope correction and drainage

Pedestals must not remove or obstruct the drainage fall in the waterproofed roof. The membrane should continue to direct water towards clear, accessible outlets. The raised surface can then be adjusted independently to the required finished level or designed surface fall.

Selected MESA models accept slope-correcting accessories that help keep the head aligned over a sloping substrate. The available correction depends on the selected model.

Do not assume every paved or decked surface should finish completely level. Depending on the paving, decking, joints and exposure, the surface manufacturer or project designer may require a slight finished fall.

How do pedestals protect a GRP or EPDM roof?

Pedestal systems are normally positioned above the waterproofing without mechanical fixings passing through the membrane. This allows water to drain beneath the finish and keeps individual slabs removable for inspection.

Correct protection and compatibility are essential:

• Confirm that the membrane manufacturer approves the proposed pedestal system
• Use compatible protection pads or a separation layer where required
• Make sure the base cannot cut, abrade or chemically affect the membrane
• Clean the surface so no sharp debris is trapped beneath a base
• Keep supports away from outlets and unsupported roof areas
• Confirm that the insulation can resist the concentrated base load
• Preserve access to outlets for inspection and cleaning

If the waterproofing is being installed or renewed first, compare the Apex GRP roofing kits and EPDM roofing systems.

Basic installation sequence

This is a general overview rather than a substitute for the current instructions supplied with the pedestal, paving, decking, subframe and waterproofing systems.

1. Plan safe access. Arrange suitable access and edge protection before materials are taken onto the roof.
2. Inspect the substrate. Confirm that it is sound, clean, watertight and suitable for the proposed construction.
3. Check levels and drainage. Record high and low points, thresholds, upstands and outlet positions.
4. Plan the complete grid. Mark paving joints or joist lines, including perimeters, cuts, joints, steps and access points.
5. Position approved protection. Fit compatible pads or a separation layer where the membrane manufacturer requires them.
6. Set the first supports. Begin from a fixed reference point and adjust them with a laser or level line.
7. Complete the grid. Use the calculated centres and the correct height model in each area.
8. Install the finish. Ensure every required slab corner or joist is fully supported and no pedestal is outside its permitted range.
9. Inspect before use. Check edges, restraints, joints, movement allowances, drainage routes and outlet access.

For a more detailed walkthrough, read the Apex guide to installing adjustable decking pedestals.

Ongoing inspection and maintenance

Keep roof outlets and the drainage void clear. Investigate rocking slabs, movement, damaged edge restraint or changes in level rather than simply packing them with an unapproved material. Retain removable access where outlets or services require inspection, and avoid drilling through the finished roof without an approved detail.

Planning permission, Building Regulations and fire safety

Planning permission

In England, a new balcony, roof terrace or raised platform should not automatically be treated as permitted development. Planning permission is commonly required where the work changes how a flat roof is used, creates overlooking or materially alters the building's appearance. Listed buildings, flats, maisonettes and properties in designated areas can have additional restrictions.

Ground-level garden decking may fall within permitted development when it satisfies all relevant limits, including the 0.3 m platform-height rule. That does not mean an accessible roof terrace has the same status. Check the current GOV.UK permitted development guidance and ask the local planning authority where necessary.

Building Regulations

Depending on the project, the design may need to address:

• Structure and loading — Approved Document A
• Guarding and protection from falling — Approved Document K
• Fire safety — Approved Document B
• Waterproofing, drainage, thresholds and access where the relevant requirements apply
• Wind exposure and the restraint of the raised surface

Fire performance and metal supports

Reaction-to-fire requirements depend on the building type, height, terrace location and project fire strategy. Do not assume that a plastic pedestal is acceptable simply because a building is below a particular height, or that choosing a steel pedestal makes the complete terrace compliant.

Where the specification requires a metal or classified non-combustible support, the MESA steel range may be an appropriate starting point. Confirm the current fire-classification evidence, compatible head arrangement and performance of the complete build-up — including joists, paving, decking and other components — with the responsible designer or building control body.

How much do adjustable pedestals cost?

The price varies by height and configuration. These are current Apex guide prices, checked on 28 September 2026:

The lowest listed price may apply only to a particular height or variant. Allow separately for protection pads, slope correctors, joist cradles, edge restraint, bracing, paving or decking, joists, delivery and installation. Always check the live product page before calculating the final order value.

Which Apex pedestal should you choose?

Shop the MESA pedestal range

Choose the support type first, then select the height range and accessories required by the finished build-up.

Adjustable Paving Pedestals

• Approximately 11–740 mm
• Up to 1,000 kg per pedestal
• 2 mm, 3.5 mm and 5 mm spacer options

From £3.20 inc VAT

View paving pedestals

Adjustable Decking Pedestals

• Approximately 10–595 mm
• Up to 1,000 kg per pedestal
• Joist cradle and slope-corrector options

From £2.16 inc VAT

View decking pedestals

MESA Outdoor Steel Pedestal

• Approximately 25–500 mm
• Up to 1,000 kg per pedestal
• Metal option for a specified external build-up

From £4.51 inc VAT

View steel pedestals

Frequently asked questions

Can you install paving or decking on a flat roof using pedestals?

Yes, provided the roof structure, insulation and waterproofing are suitable. The supports normally sit above the membrane, create a drainage void and carry the raised finish without routinely penetrating the waterproofing.

What is the difference between paving and decking pedestals?

Paving pedestals have a flat head and spacer tabs that support slab corners and form consistent joints. Decking pedestals use a compatible cradle or head arrangement to support the joist subframe.

How much weight can a MESA pedestal hold?

The current product information states up to 1,000 kg per pedestal. This is not the load allowance for the complete roof. The deck, insulation, membrane, bases, layout and finished surface must all be suitable.

How far apart should paving pedestals be?

The grid follows the slab dimensions. With standard 600 × 600 mm slabs, the main grid is approximately 600 mm between centres, with support beneath every corner. Add supports around edges, cuts and wherever the paving manufacturer requires mid-edge or centre support.

How far apart should decking pedestals be?

The decking manufacturer determines joist centres, while the joist or subframe manufacturer determines the permitted support span along each joist. Apex gives a broad estimate of 3–7 pedestals per m², but the final quantity must come from the actual layout.

Do adjustable pedestals need fixing down?

They are generally installed as a loose-laid system without penetrating the waterproofing. Tall systems, exposed sites and open perimeters may require bracing, ballast, edge restraint or another approved wind-resistant detail.

What pedestal height do I need?

For paving, subtract the slab thickness from the distance between the local roof level and the planned finished level. For decking, also subtract the joist depth and decking-board thickness. Calculate this at both the highest and lowest parts of the substrate.

Are paving pedestals suitable for porcelain?

Yes, where the porcelain manufacturer approves pedestal-supported installation. Thin or large-format slabs may require additional support.

Can I place a hot tub on a pedestal-supported roof terrace?

Only after a project-specific structural assessment. Extra supports may distribute load through the raised surface, but they do not increase the capacity of the roof beneath it.

Can pedestals be placed directly on GRP or EPDM?

They can be used over compatible GRP and EPDM systems, but the waterproofing manufacturer may require an approved protection pad or separation layer. Confirm compatibility before installation.

Do I need planning permission for a roof terrace?

Potentially. In England, a new accessible roof terrace, balcony or raised platform should not automatically be treated as permitted development. Check with the local planning authority and building control before work starts. Different rules apply elsewhere in the UK.

Before you order

Prepare the following information:

• Overall length and width
• Paving dimensions and thickness, or decking and joist specifications
• Highest and lowest required support heights
• Type and condition of the roof, slab and waterproofing
• Locations of walls, thresholds, steps and outlets
• Details of planters, screens, equipment and other heavy loads
• Clear photographs of the full area and its perimeter details

With those details, Apex can help identify suitable starting products and estimate quantities. Structural suitability, wind restraint, fire performance and project-specific compliance must still be confirmed by the responsible designer where required.