Superstructure (excluding roofs)

6.9Curtain walling and cladding

This chapter gives guidance on meeting the Technical Requirements for curtain walling and cladding.


This chapter gives guidance on the forms of curtain walling and cladding acceptable to NHBC. Curtain walling and cladding systems that do not conform to the descriptions in this chapter will not generally be acceptable. Conservatories are not covered by this chapter.

Guidance on the use of other types of cladding, including brickwork, rendered masonry, vertical tile and slate cladding and timber cladding, is given in Chapter 6.1 ‘External masonry walls’ and Chapter 6.2 ‘External timber framed walls’.

Curtain walling

Comprising a prefabricated or site assembled support framework with infill panels and/or wall sections with glazing systems which include:

  • structural silicone glazing
  • mechanically fixed structural glazing
  • slope glazing, excluding patent glazing
  • coupled door and window frame assemblies (including spandrel panels) which are one storey or more in height, or not contained between a floor and ceiling.

Rainscreen cladding


  • an outer skin of panels which have unsealed, open, baffled or labyrinth (rebated) joints
  • a minimum 50mm pressure equalised air gap between the insulation and the panels
  • an insulated and airtight backing wall.

Insulated render

Comprising insulated render systems fixed to a backing wall.

Brick slip cladding

Comprising brick slip cladding fixed to a backing wall.

Stone and precast concrete cladding

Stone and precast units should be designed as curtain walling or rainscreen cladding in accordance with this chapter.

Definitions for this chapter

Air barrier A continuous layer that limits air leakage through the backing wall.
Air cushionBalancing external and internal air pressure to create a cushion within the air gap.
Air gap The space between the back of the cladding panels and the external face of the insulation in a rainscreen system.
Backing wall A framed or masonry wall to which the system is fixed.
Brick slip cladding system A brick slip system fixed to masonry or framed backing walls, generally supported by a proprietary carrier.
Cavity The space between the cladding system and the backing wall. The cavity should be adequately drained, and ventilated where required.
Cladding panels The outer units of a rainscreen cladding system which provide some protection.
Compartmentation The provision of baffles and cavity closers to form compartments within the air gap of a rainscreen cladding system to equalise pressure.
Curtain walling A form of enclosure that supports no load other than its own weight and the environmental forces that act upon it, e.g. wind, water and solar.
Curtain walling system The vertical building enclosure system, including frames, brackets, fixings, flashings, gutters, copings, glass, panels, gaskets and sealant, that forms the assembly.
CWCTThe Centre for Window and Cladding Technology at Bath University.
CWCT Standard The current Centre for Window and Cladding Technology Standard for systemised building envelopes.
Design life The period for which materials, products and systems should be designed to be durable, assuming routine inspection and maintenance.
DPC/DPM Prevents the passage of moisture. In curtain walling terminology, a DPC is often referred to as a DPM.
Façade The external facing part of the building envelope.
Fire and smoke
Prevention of the transmission of fire and smoke through voids or cavities.
Fixing Componentry used to attach or secure other components, e.g. curtain walling or a cladding system, to the structure.
Gasket A compressible material used to form an airtight and/or watertight seal.
In-service performance The manner or quality of functioning of a material, product or system.
Insulated render
A cladding system applied externally to an insulating layer which is fixed to a backing wall.
Condensation caused by vapour from within the building condensing on colder surfaces within the wall construction, often occurring due to a cold bridge.
Negative pressure Where the air pressure on the internal face of the system is greater than that on the external face.
Positive pressure Where the air pressure on the external face of the system is greater than that on the internal face.
Primary components Components and parts of the system that are not easily replaceable. These may include:
■ cladding panels
■ fixings
■ framing
■ insulation
■ vapour control layers
■ weathering components.
Pressure equalisation The creation of an air cushion within the cavity to reduce the amount of water passing through the joints of a rainscreen. Compartmentation and adequately large joints are required to achieve pressure equalisation.
Rainscreen The part of the assembly, generally the outermost, that prevents the majority of rain from penetrating the wall. Some water may pass through the joints of a rainscreen, but this should be limited by appropriate detailing of open joints or the provision of baffled or labyrinth joints.
Rainscreen cladding system A façade that provides a barrier to wind and rain and which typically includes a vapour control layer, air barrier, supporting framework and fixings, insulation, breather membrane, cavity/air gap and cladding panels. Traditional tile hanging and timber cladding are not classed as rainscreen cladding systems under the definitions of this chapter.
Those which are readily replaceable without compromising the design and durability of the building or the need for progressive dismantling of the envelope. Where this cannot be achieved, components should be designed as primary components. A method statement should be provided to demonstrate how components will be replaced with specific reference to accessibility as detailed in this chapter.
Secondary componentsComponents and parts of the system that are easily replaceable. These may include:
■ cladding panels
■ external finishes
■ glazing and gaskets
■ internal linings
■ seals and sealant
■ window and door furniture.
Separating floors
and walls
Floors and walls designed to provide separation between homes.
Slope glazing A drained and ventilated sloped roofing system.
SystemsFor the purposes of this chapter, this term refers to acceptable forms of curtain walling, rainscreen cladding, insulated render systems and brick slip cladding systems.
Spandrel panelA panel used in place of glazing units to hide the edges of floor slabs, ceiling details, insulation, and other building elements.
Test pressureThe pressure at which testing is conducted.
Vapour control layerA layer used to restrict the passage of water vapour into the construction to reduce the risk of interstitial condensation.