How the two differ in kind
The same pavers can be laid two entirely different ways, and on a roof terrace or a balcony the choice is close to made for you.
BEDDED construction is the familiar one: a compacted aggregate base, a screeded bedding layer, the pavers laid on it, and the joints filled. On the ground it is the right answer — it is cheap, it is stable, it spreads load into the subgrade, and every trade knows how to do it.
Over a waterproofed structure it has three problems. It puts a continuous mass of aggregate and sand directly on the membrane, which is a substantial dead load on a structure that has to carry it. It buries the membrane, so any leak has to be found and reached by excavating the build-up. And it obstructs drainage across the roof, so water has to find its way through or around the build-up to the outlets.
PEDESTALS solve all three. The pavers sit on adjustable supports at their corners, leaving an open VOID beneath: water falls straight through the joints and runs across the waterproofing to the outlets unobstructed; any paver can be lifted by hand to reach the membrane below; and the load is a fraction of a bedded build-up's, being pavers and supports rather than pavers and a volume of stone.
The second capability is what makes them the standard for terraces: the supports are ADJUSTABLE, so a level walking surface can be built over a roof that falls to its outlets. A roof must slope and a terrace should not, and pedestals reconcile the two by varying in height across the area. A bedded build-up can only do the same by varying the depth of aggregate, which adds still more load exactly where the roof is lowest.
At ground level the comparison reverses, and pedestals are for the specific case where a level surface is wanted over something that must drain or stay reachable.
The factors that actually differ
Show
| Pedestal-mounted pavers | Pavers bedded on aggregate | |
|---|---|---|
| What is beneath the pavers | An open void. Water drains freely across the structure below. | A continuous compacted base and bedding layer. |
| Load on the structure | Low — pavers and supports only. | High — the full depth of aggregate and bedding over the whole area. |
| Access to what is underneath | Lift a paver. This is why they are used over waterproofing and over services. | Excavate the build-up. |
| Level surface over a falling substrate | Straightforward — the supports are adjustable and that is their second purpose. | Only by varying the aggregate depth, which adds load where the fall is deepest. |
| Drainage | Through the open joints and across the membrane beneath, unobstructed. | Across the surface to a gully, or through the joints into the base if it is permeable. |
| Paver requirements | Must span between supports and resist point loading at its corners — so thickness and strength are specified, and not every paver qualifies. | Fully supported, so thinner and weaker units are acceptable. |
| Edges and wind | A real design item. Pavers on pedestals are not restrained by mass alone, so edges, upstands and wind uplift need addressing on an exposed roof. | Restrained by the surrounding construction and by the mass of the build-up. |
| Feel underfoot | Slightly hollow, and a poorly adjusted support produces a rocking paver — adjustment is the finishing operation. | Solid. |
| Cost | Higher per square metre for the supports, lower for the absent aggregate and its handling. | Cheaper in material, and at height the cost of craning aggregate is what changes the comparison. |
| Where it belongs | Roof terraces, balconies, podiums, and over anything that must drain or stay accessible. | The ground, where the base does useful structural work. |
Which one, and when
Choose pedestal-mounted pavers when…
- It is a roof terrace, balcony or podium over occupied space — this is what pedestals are for.
- A level walking surface is needed over a substrate that has to fall to its outlets.
- The waterproofing must remain accessible without demolishing the surface.
- The structure's load capacity will not take a bedded build-up, which at height it frequently will not.
Choose pavers bedded on aggregate when…
- It is at ground level on a prepared subgrade, where the base carries and spreads load.
- The surface has to take vehicles, which a pedestal system generally is not designed for.
- Cost governs and there is nothing beneath that needs draining or reaching.
- A solid feel underfoot matters, or the area is small enough that the pedestal system's benefits do not apply.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Why do roof terraces use pedestals rather than bedding?
- Because a roof has three requirements a bedded build-up fights. It must drain, and a continuous aggregate base obstructs water crossing the membrane to the outlets. Its waterproofing must be reachable, and burying it under a build-up means any leak is found and repaired by excavating. And it has a load capacity, which a full depth of aggregate and sand across the whole terrace consumes a large share of. Pedestals answer all three at once: the void beneath drains freely, any paver lifts by hand, and the dead load is a fraction. The fourth reason is levels — a roof falls to its outlets and a terrace should be level, and adjustable supports reconcile those two geometries directly, whereas a bedded system would have to vary its depth and add load exactly where the roof is lowest.
- Can any paver go on pedestals?
- No, and using an unsuitable one is how they break. On pedestals a paver is a slab spanning between point supports at its corners, so it has to resist bending across that span and concentrated loading at the support points — which is a structural requirement its manufacturer states, in terms of a minimum thickness and a strength or a permitted span. Thin units intended to be fully bedded will crack, sometimes under a foot and sometimes later under a table leg. Porcelain pavers for pedestal use are made thicker than their bedded equivalents for exactly this reason, and many systems require a reinforcing tray or mesh backing for additional safety in case a unit does break. The other requirement is dimensional consistency: pavers with variable size sit unevenly on a grid of fixed supports.
- How is wind uplift handled?
- Deliberately, because it is the failure mode a pedestal system introduces. Pavers on supports are held down by their own weight and nothing else, and on an exposed roof — particularly at corners, edges and parapets, where local wind pressures are highest — that can be insufficient. The responses are established: heavier or thicker units in the high-pressure zones, mechanical restraint clips tying pavers to their supports or to each other, a perimeter restraint detail, and in severe cases a ballast or a solid edge course. Which of those is required comes from a wind load assessment for that building, that height and that exposure, rather than from a general rule. The corollary is that a system specified for a sheltered courtyard is not automatically suitable on an exposed roof twelve storeys up.
- Does the roof still need a fall?
- Yes, and the pavers do not change it. The waterproofing beneath must still slope to its outlets so water runs off rather than standing — the pedestal system is simply a walking surface above, and the roof beneath it is designed as a roof. What pedestals allow is for that fall to exist without being felt: the supports are adjusted to different heights across the area so the paver surface is level while the membrane below slopes. A common error is assuming that because the water passes through the joints and drains beneath, a level substrate would do — which produces standing water across the whole membrane under a terrace nobody can see into. The outlets also have to remain accessible and be protected, usually by an inspection unit that can be reached by lifting a paver.
- What stops the pavers rocking?
- Adjustment, and it is the finishing operation rather than an afterthought. Each support is set to the height the level surface requires, and any variation in paver thickness or in support height leaves a unit bearing on three points and rocking on the fourth — which is unpleasant underfoot, stresses the paver, and eventually cracks it. Systems provide adjustment in the support itself, usually by a threaded mechanism, plus thin shims for fine correction, and the installation sequence is to set out, lay, and then walk the whole area correcting anything that moves. Self-levelling support heads, which tilt to follow the substrate's slope while keeping the paver level, remove most of the problem on a sloping roof and are worth specifying where the fall is significant.
- What maintenance does the void need?
- Enough that access to it should be designed in rather than assumed. The void collects what falls through the joints: leaves, grit, moss, and anything the wind brings, and over years that accumulates on the membrane and around the outlets. A blocked outlet under a paved terrace is a serious problem, because the water has nowhere to go and nobody can see it happening. The practices that keep it manageable are an inspection unit at every outlet — a paver or hatch that lifts to reach it — a periodic check at a stated interval, and keeping the perimeter details free. This is one of the system's genuine advantages over bedding, since the inspection is a matter of lifting a slab; it only counts if somebody actually does it.
- Is a pedestal system suitable at ground level?
- It can be, for a specific reason rather than as a default. On the ground, a bedded base does useful work — it spreads load into the subgrade, it is cheap, and it is what the pavement needs. Pedestals over a ground-level slab make sense where a level surface is wanted over something that falls, where services or drainage must remain accessible beneath, where a level threshold to a building has to be achieved without a step, or where a deck-like surface is wanted without timber. What they do not do is substitute for a base on soil: pedestals need a firm, stable, load-bearing surface beneath them, so on the ground they sit on a slab or on a properly prepared and compacted base, and setting them straight onto soil produces a terrace that settles unevenly.
- How is the pedestal height worked out?
- From the finished level you want minus the substrate level at each point, less the paver thickness — which on a falling roof means the height varies across the area and the calculation is done on a grid rather than once. The inputs are the target finished floor level, usually set by a threshold or a door, the substrate's level at each support position including its fall to the outlets, and the paver thickness. The output is a range, and that range has to sit within the adjustment the chosen support system provides, with extenders where it does not. Two things to allow for: the minimum height of the support at the roof's high point, which sets how much the threshold has to be raised, and the maximum at the low point, which can become tall enough to need bracing or a different product.