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Building envelope

Envelope Control Layers and Continuity

A control layer is only worth as much as the line you can trace with a finger around the whole building without lifting it. Air, vapour, water and heat are each governed by a plane intended to be continuous, and this family holds those planes together with the two things that break them: thermal bridging, where the insulating line is interrupted by something conductive, and thermal bypass, where air loops behind insulation that is otherwise perfectly intact.

These entries describe the idea of each layer and what its behaviour depends on, not where a layer should sit inside a particular wall or roof. That placement is assembly design and belongs with a qualified professional working on the actual build-up. The junctions where these planes meet, turn or are pierced are described under envelope junctions, and the complete walls and roofs they run through have families of their own.

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.

  • The air, vapour, water and thermal control planes treated as continuous ideas, not products
  • Thermal bridging and thermal bypass as the interruptions that decide whether continuity is real
  • Structural thermal breaks, where a load path has to cross the insulated line
  • Not covered: where a layer belongs in a given build-up, condensation analysis or thermal values

All entries

Every control layers entry

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

Air Barrier System →The connected set of planes, joints, seals and transitions that resists uncontrolled air movement through a building enclosure, defined by its continuity rather than by any one product.Vapour Control System →The ordered arrangement of layer resistances that governs how water vapour moves through an assembly, together with the directions in which that assembly is able to dry again.Thermal Bridging Control →The arrangements by which conduction paths that cross an insulating layer or run around outside it, at junctions, fixings, frames and changes of geometry, are interrupted or reduced.Water Control Layer →The drained plane sitting behind an outer surface that receives whatever water passes that surface, with the shingled laps, flashings and exits that return it to the outside.Damp-Proof Continuity →The linked horizontal and vertical damp-proof layers at and below ground floor level, read as one barrier through the laps, upstands, thresholds and service entries that connect them.Thermal Bypass Control →The closures, linings and baffles by which an insulating layer is enclosed, so that air is resisted from circulating around, behind or through it and carrying heat past it.Structural Thermal Break →A connection in which a structural element crosses the insulation line through a lower-conductivity body placed within the load path, so that load stays continuous while conduction is interrupted.

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.

Air barrier planning →How an air control strategy is approached at planning stage.Vapour barrier and vapour retarder planning →The distinction that governs which layer does what.Airtightness conversation preparation →Questions to prepare before an airtightness 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.

Insulation →Reference entries for thermal insulation materials — mineral and glass wool, rigid foam boards, natural-fibre insulations, blown and sprayed products and reflective systems.Sealants & Membranes →Reference entries for the thin control layers — joint sealants, damp-proof courses and membranes, vapour control layers, breather membranes, tanking systems, tapes and foams.

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 →