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Building envelope

External Wall Build-Up Systems

Read a wall from outside to inside and two answers appear. The first is where water is stopped — at the outer face, in a drained cavity, or somewhere within the depth of the construction. The second is which way the wall dries once it inevitably gets wet. A cavity wall, a solid wall, a masonry veneer over a framed backup and an insulated timber or light steel frame wall answer that pair of questions in genuinely different ways.

Retrofit build-ups belong here too, because adding insulation to an existing wall changes both answers at once and is a different problem from building new. The outer skins carried on an already-complete wall are described under facade and cladding systems, and the continuous planes running through any of these walls are described under control layers. Nothing here states a thermal value or judges a wall adequate for a given exposure.

7 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.

  • New-build external walls in masonry, timber frame and light steel frame
  • Where the water line sits in the wall thickness and which way the wall is allowed to dry
  • Retrofit insulation build-ups that change how an existing wall handles moisture
  • Not covered: thermal values, condensation risk analysis, exposure assessment or insulation thickness

All entries

Every external wall build-ups entry

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

Twin-Leaf Cavity Wall →An external wall of twin masonry leaves separated by a tied cavity, in which the outer leaf sheds most water and the void is there to interrupt the path across the wall and route it back out.Timber Frame Wall →A layered external wall of timber studs, sheathing and insulation, closed outside by a breather membrane and inside by an air and vapour control layer, with cladding beyond a drained void.Solid Wall →An external wall built as one continuous masonry thickness with no drained void, which takes moisture in, holds it within its mass and gives it back again by evaporation.Masonry Veneer Wall →An external wall whose visible face is a single non-loadbearing masonry leaf, anchored back across a drained void to a sheathed framed wall that carries the building behind it.Light Steel Frame Wall →An external wall framed in cold-formed steel sections, sheathed and layered as a stud wall, commonly built as infill between the floors of a primary structure and carrying a separate cladding.Internal Wall Insulation →A retrofit insulating layer applied to the room face of an existing external wall, together with the control, fixing and finish layers that have to accompany it.Retrofit Cavity Fill →The insulation of an existing masonry cavity by introducing fill into it from outside, converting a clear drained void into a filled one within a wall that is already built and closed.

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.

Cavity and solid wall questions →Establishing what an existing wall actually is.Exterior wall materials →The choosing-and-comparing side of external wall materials.Internal wall insulation questions →Preparation before an internal insulation retrofit discussion.

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.

Masonry & Blocks →Reference entries for unit masonry — clay and concrete bricks, blockwork, mortars, and the ties, lintels and accessories that hold masonry construction together.Insulation →Reference entries for thermal insulation materials — mineral and glass wool, rigid foam boards, natural-fibre insulations, blown and sprayed products and reflective systems.Exterior Cladding →Reference entries for external wall finishes — fibre cement, timber and composite cladding, vinyl siding, metal and laminate panels, terracotta rainscreens and the render families.Wall Finishes & Linings →Reference entries for internal wall and ceiling materials — plasterboard, gypsum, lime and clay plasters, polished plaster, paints, primers, wallpaper, panelling and acoustic linings.

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.

Browse all building systems →