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Envelope and protection

Sealants & Membranes

These are the least visible materials in a building and among the most consequential. A vapour control layer, a damp-proof course, a breather membrane and a bead of sealant all do one job: they control where moisture and air are allowed to go. When they are placed on the wrong side of an assembly, or interrupted, the assembly can behave quite differently from the intent.

These entries describe what each product family is and what the decision depends on. They contain no waterproofing specifications, no condensation risk analysis and no instruction on where a given layer should sit in a given build-up — that is assembly design, and it belongs with a qualified professional.

10 reference entries · educational materials reference · suitability always depends on the complete assembly and qualified professional review

Scope

What this category covers

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

  • Joint sealants and the movement joints they occupy
  • Damp-proofing, tanking and below-ground moisture control products
  • Vapour control, air-tightness and breather layers and their tapes
  • Not covered: which layer belongs where in an assembly, waterproofing design, condensation analysis

Start here

Frequently referenced entries

A starting point, not a ranking — these are simply the entries most people arrive looking for.

Silicone sealant →A flexible cured-rubber jointing sealant associated with sanitaryware, glazing and wet junctions, water-tolerant but in most grades not paintable.Vapour control layer →A membrane intended to restrict water vapour passing into a construction, close to opposite in intent from a breather membrane and routinely swapped with one.Breather membrane →A membrane that resists liquid water arriving from outside while staying relatively open to vapour passing outwards, and frequently confused with a vapour control layer.

All entries

Every sealants & membranes entry

The complete set for this category, in reference order.

Silicone sealant →A flexible cured-rubber jointing sealant associated with sanitaryware, glazing and wet junctions, water-tolerant but in most grades not paintable.Polyurethane sealant →A tougher and usually paintable elastic jointing sealant associated with construction joints where movement is combined with abrasion or contact wear.Acrylic frame sealant →A paintable water-based filler for small static gaps at skirtings, architraves and frames, which is neither a movement-joint nor a wet-area material.Damp-proof membrane →A continuous sheet or liquid-applied moisture-control layer associated with floors and slabs, and a different product from the course built into walling.Damp-proof course →A moisture-resisting strip or course built into walling as it is constructed, distinct from the continuous area membrane associated with floors and slabs.Vapour control layer →A membrane intended to restrict water vapour passing into a construction, close to opposite in intent from a breather membrane and routinely swapped with one.Breather membrane →A membrane that resists liquid water arriving from outside while staying relatively open to vapour passing outwards, and frequently confused with a vapour control layer.Cementitious tanking slurry →A rigid cement-based coating bonded to masonry or concrete, used only as one element of a scheme designed by a suitably qualified waterproofing specialist.Air-tightness tape →Adhesive tape used to join membranes, boards and junctions so a control layer stays continuous, with performance decided by the substrate and by the sequencing.Expanding foam →A canister-dispensed polyurethane that expands as it cures to fill irregular voids, where the expansion itself is the main thing to understand about the material.

Browse by role

By the role the material plays

The same entries, clustered by what they typically do in an assembly. A material can appear in more than one cluster because it genuinely plays more than one role.

Substrate and base

Backgrounds and bases that other materials are fixed or applied to.

Weather barrier

Layers that shed or resist rain, wind and weather.

Internal surface

The visible inner face people see, touch and walk on.

Jointing and fixing

Materials that bond, seal, support or connect other materials.

Where they appear

Parts of a building this category touches

An orientation aid only — it does not imply that any entry is suitable for that part of a particular building.

  • Foundations and groundworks · 3
  • External walls · 7
  • Roofs · 3
  • Internal walls and ceilings · 6
  • Floors · 3
  • Wet areas · 2
  • External works and landscape · 1

Elsewhere on Build Design Hub

Planning guidance for this subject

This library explains what materials are. These sections help with choosing between them and preparing for the conversation.

Materials planning guides →Planning and comparison guidance for material choices.Building envelope checklists →Preparation before envelope conversations.Material maintenance guides →Planning upkeep for sealed and jointed surfaces.

Materials & Systems Encyclopedia

Reference entries for building materials, product formats and system components — what they are, what their behaviour depends on and what to ask about them.

Browse the full Materials Library →