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Building envelope

Envelope Junctions, Interfaces and Terminations

Assemblies rarely fail in the middle. They fail where one thing meets another: at a window reveal, a door threshold, an eaves, a parapet, a roof-to-wall abutment, a rooflight kerb, or wherever a pipe or a bracket passes through. At each of those places the water line, the air line, the insulated line and the structure all have to be resolved together, usually by different trades, often on different days.

This family exists so that those junctions are treated as systems with named parts and stated dependencies rather than left to prose. It does not contain the continuous layers themselves, which are described under control layers, nor the walls and roofs a junction joins. No entry gives an installation sequence, a lap or upstand dimension, a fall, or a sealant specification — those are design and manufacturer matters.

9 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.

  • Transitions where one control layer hands over to another and continuity has to be maintained
  • Openings and thresholds, where a wall is deliberately interrupted by a window or a door
  • Roof terminations and penetrations: eaves, abutments, parapets, kerbs and pierced layers
  • Not covered: installation sequence, lap and upstand dimensions, falls or sealant specification

All entries

Every junctions & terminations entry

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

Window Opening Interface →The perimeter assembly around a window, where a wall's structure, control layers and finishes meet a manufactured frame at head, jambs and sill. It is the opening, not the unit.Abutment Detail →The layered weathering where a roof plane meets a wall, chimney or adjoining building that continues above it, combining a roof-side upstand with flashings and a concealed tray.Cavity Trays →The trays, upstands, stop ends and drainage openings that collect water travelling inside a wall cavity wherever that cavity is interrupted, and return it to the outer face of the wall.Control Layer Transition →The junction at which a control layer on one plane is carried onto a different plane or a different material, with the arrangement that keeps that barrier continuous across the change.Penetration Sealing →The assembly that restores the continuity of interrupted control layers wherever a pipe, duct, cable, fixing or structural member passes through the building envelope.Door Threshold Interface →The horizontal junction at an external doorway where wall and floor control layers, external drainage, the walking surface and a door's own weather seals all have to be resolved in one line.Eaves System →The termination where a roof plane passes over the wall head, gathering underlay discharge, insulation continuity, ventilation inlet, fascia, soffit and gutter support into a single junction.Parapet System →A perimeter wall standing above the roof surface, with the coping, concealed damp-proofing, insulation return and waterproofing turn-up that terminate the roof against its inner face.Rooflight Kerb →The upstand framing an opening cut in a roof deck to receive a rooflight, and the way the roof's waterproofing, insulation and vapour control turn up and stop against it.

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.

Envelope detailing review preparation →Questions to prepare before reviewing junction details.Window flashing planning →How the water line around an opening is planned.Flashing materials →The material side of terminations and weatherings.

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.

Roofing →Reference entries for roof coverings and roof waterproofing — tiles and slates, shingles, sheet and standing-seam metal, single-ply and built-up membranes, liquid systems and green roofs.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.Glass & Glazing →Reference entries for glass and glazing products — float, toughened and laminated glass, insulated glass units, low-emissivity coatings, obscured glass, glass block and polycarbonate.

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 →