Water and external systems

Decks, Paving and Hard Landscape Systems

An external surface is judged by what is under it. A paved area is a small pavement, with a subgrade, a base and a laying course; a timber deck is a frame with boards over it; a pedestal terrace is a surface floating clear of a waterproofed roof beneath. In every case the visible material is the last decision made and the least likely to explain why the surface later moves, ponds, lifts or stains.

Balconies and their guarding are included because they are the same problem carried on a building rather than on the ground, with a connection back through the envelope that has to be resolved. Paving and decking materials themselves belong in the materials library, and the drainage a surface hands its water to has its own family. No entry states a gradient, a layer thickness, a loading, a slip classification or a guarding requirement.

15 system entries · educational assemblies reference · how a system performs always depends on the whole building and qualified professional design

Scope

What this category covers

Where the boundary of this part of the encyclopedia sits, including what it deliberately leaves to qualified professionals.

Timber decks, pedestal terraces and the balcony structures carried on a building
Paving read from the subgrade up: foundation layers, then flexible, rigid, permeable or cellular
Edges, guarding, trafficked deck membranes and the planted openings that interrupt a surface
Not covered: gradients, layer thicknesses, loading, slip classifications or guarding requirements

All entries

Every decks & paving entry

The complete set for this category. Frequently referenced entries come first — a starting point, not a ranking.

How the parts relate

Timber Deck Framing →A framed external platform in which ground supports, beams and joists carry a spaced board surface over a ventilated, freely draining void beneath.

Permeable Paving →A paving build-up that admits water through its surface into a coarse storage layer beneath, so the pavement is at once a trafficked surface and a working part of the site's drainage.

Guarding System →The edge assembly at a change of level: infill, supporting posts or frame, top rail or handrail, and the anchorage carrying all of it back into a supporting structure.

Freestanding Wall →An external wall that encloses or divides without retaining ground or carrying a building, combining a foundation, a damp-proof course, a wall body with piers, movement joints and a coping.

Pedestal Terrace Paving →Paving units, boards or trays laid loose on adjustable supports above a structural deck, forming a level trafficked surface over an open, drained and ventilated void.

Cantilevered Balcony →A balcony projecting from the building's own floor structure, considered together with the crossing where that structure passes through the insulated, sealed and water-shedding envelope.

Bracket Supported Balcony →A balcony platform carried on brackets, hangers or columns outside the wall, so the load is taken outside the envelope and the fixings become discrete penetrations of it.

Trafficked Deck Membrane →A seamless site-applied external deck surface in which the layer resisting water is also the wearing surface, built from a prepared substrate, a bond coat, a reinforced base and a wear layer.

Pavement Foundation →The construction between natural ground and any external surface - prepared subgrade, separation, capping where the ground is weak, and a load-spreading sub-base - treated as one foundation.

Flexible Paving →A field of separate units seated on a loose laying course over a sub-base, sharing load through filled joints and held from spreading by a continuous restraint rather than by any bond.

Rigid Paving →A surface bedded in mortar or cast as a slab on a bound base, where surface and base act largely as one stiff element and movement is directed into joints rather than absorbed by loose confinement.

Cellular Confinement Surfacing →A surface in which a cellular grid over a prepared permeable foundation confines a loose or living fill, holding it against displacement under traffic while water continues to pass through.

Tree Pit System →Below-paving construction giving a tree an uncompacted rooting volume while still carrying the surface above, using load-bearing cells or structural soil with aeration, irrigation and root guidance.

Bituminous Surfacing →An external surface of bitumen-bound courses laid loose and compacted in place, continuous and unjointed, bound enough to spread load yet able to deform instead of fracturing.

Fence and Gate →A boundary line of posts, rails and infill resisting wind at its post bases, together with a gate whose hanging and closing posts are loaded by a swinging leaf instead.

Elsewhere on Build Design Hub

Planning guidance for this subject

This encyclopedia explains how these assemblies are organised. These sections help with choosing between them and preparing for the conversation.

Deck and patio materials →The choosing-and-comparing side of external surfaces.Paving material decisions →Preparation before a paving conversation.Deck planning preparation →Questions to settle before a deck is designed.

Materials Library

What these assemblies are built from

A systems entry explains how an assembly is organised. These materials sections describe the substances themselves — what they are, how they behave and what governs their use.

Tiles & Stone →Reference entries for tile and stone surfacing — porcelain and ceramic tile, natural stones, engineered quartz and sintered surfaces, mosaics, backer boards, adhesives and grouts.

Building Systems Encyclopedia

Reference entries for building assemblies — how each is organised, what role every component plays, how the parts interact and which junctions matter.

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