Pedestal-Supported Terrace Paving System

Pedestal paving turns a sloping structural deck into a level terrace without burying it. Adjustable supports of differing extension stand on the deck and take up its falls, slabs or boards or trays rest on those supports, and the joints between units are left open. Nothing is bedded, bonded or grouted, which is what makes the rest of the arrangement possible.

Water arriving on the surface passes straight through the open joints into the space beneath and runs down the deck falls to the outlets. The trafficked layer is therefore not the layer that resists water at all; it is a wearing surface and a shading layer over the real one. That separation is what lets the surface be walked on, cleaned, lifted and replaced without disturbing what keeps water out of the building.

This is the pedestal instance of the trafficked roof deck assembly, which covers bedded and bearer-supported surfacings in the same position. The test is simple enough to apply while standing on the terrace: can a single unit be lifted by hand? Here it can, because units are loose-laid and held by their own weight and the perimeter. Rigid paving is bedded in mortar onto a bound base, so lifting a unit means breaking it, and there is no open void beneath to drain, ventilate or inspect.

Because this is a surfacing method rather than a build-up, it does not determine what lies beneath. The same arrangement is found over warm decks and over inverted roofs, and it is not the same entity as the adjustable support component on its own. The system is the relationship between supports, units, void and deck, which no component description contains.

Pedestals and deck falls solve opposite problems and depend on each other to do it. The deck must keep falling so water reaches the outlets; the terrace must be level so it can be used. Every pedestal resolves that difference locally, which makes the support layer the place where an error in deck level shows up, and the place where a change of deck level after the fact cannot be absorbed.

Because units are loose, load does not spread the way it does through a bedded surface. A point load on a slab corner arrives at a pedestal head and then at a small patch of whatever lies below, so the protection layer, the insulation where present and the water-resisting layer are all loaded through a concentrated area. How that stack behaves is a property of the assembly and is assessed by the designer using the manufacturers' information.

The open joint and the drained void are a single mechanism, not separate features. Water leaves the surface only as fast as the void lets it, and the void works only while it stays connected to the outlets. Debris falls through the joints and collects where nobody looks, and the first sign of a blocked outlet is often water appearing somewhere that has nothing to do with where the blockage is.

Losing the ability to lift a unit removes the reason for building this way. Bonding units, filling joints, bedding a course at the edge or standing a heavy fixed object on the terrace all convert part of the assembly into something that must be broken to reach the deck. Guarding posts taken down through the paving to structure do the same locally, so their route has to be planned rather than discovered.