11.3.11 Cladding
External claddings shall be suitable for their intended purpose, have suitable junctions and interfaces to resist the penetration of water and wind, be suitably durable and have an acceptable finished appearance. Issues to be taken into account include:
- junctions and interfaces between cladding types and adjoining units
- movement
- continuity of insulation, breather membranes and AVCLs
- tolerances
- finished appearance.
Masonry external cladding should be in accordance with Chapter 6.1 External masonry walls.
Lightweight external claddings, whether factory or site installed, should be:
- in accordance with Chapter 6.9 Curtain walling and cladding
- compatible with the framing system
- supported by systems assessed in accordance with Technical Requirement R3 which ensure that cladding design loads are effectively and safely transferred to the building structure.
Further guidance on render onto board backgrounds can be found in Clause 6.11.8.
The design and construction of cladding to external walls should consider:
- durability
- cavity drainage
- differential movement
- restraint
- performance in relation to fire.
Timber frame backing walls
Further guidance on the use of masonry and lightweight claddings with timber frame walls can be found in Chapter 6.2 External timber framed walls.
Light steel frame backing walls
Further guidance on the use of masonry and lightweight claddings with light steel frame walls can be found in Chapter 6.10 Light steel framed walls and floors.
11.3.11.1 Junctions and interfaces
Junctions and interfaces, including those between factory installed lightweight cladding systems to adjoining units, and those between lightweight cladding systems and other elements of the building, should be carefully designed and detailed to be weather resistant, and prevent moisture reaching parts of the wall it could adversely affect.
The design should take account of:
- differing profile characteristics
- movement
- design of suitable interfaces between differing cladding types
- tolerances and deviation
- the erection sequence.
For lightweight cladding finishes applied to an insulation backing, the use of small infill pieces at unit junctions or differing types of backing insulation (eg to form cavity barriers or fire-stopping at compartment lines) should be detailed in accordance with the manufacturer’s recommendations and within the scope of certification by an independent technical approvals authority acceptable to NHBC.
11.3.11.2 Movement
Movement joints to masonry cladding should be in accordance with Clause 6.1.3. Refer to Clause 6.2.8 for further guidance on accommodating movement in masonry cladding to timber frame structures, and Clause 6.10.20 for masonry cladding to light steel frame structures.
Lightweight claddings
Where lightweight or self-supporting cladding is used movement joints should be provided where required by the design.
Movement joints should be:
- formed in accordance with the cladding system manufacturers’ recommendations
- positioned to accommodate calculated movement
- continued through the depth of the cladding.
Accommodation of differential movement should be made at floor zones between lightweight cladding.
11.3.11.3 Continuity of insulation, breather membranes and AVCLs
Junctions and interfaces of adjoining units or units with surrounding construction should be carefully designed and detailed to ensure continuity of insulation, breather membranes and AVCLs.
The design should:
- ensure adequate laps of membranes or provision for suitable method of sealing in accordance with manufacturer’s recommendations
- make allowance for secure fixing of insulation, including at panel junctions, to the support frame or wall.
11.3.11.4 Tolerances
Where factory installed lightweight claddings extend to the edges of units, the cladding interfaces should meet the following tolerances unless specified otherwise by the design:
- be adequately straight in elevation, with a maximum ± 6mm deviation from nominal design width in any unit edge width or height up to 3m (see Figure 1)
- a maximum of 5mm from plumb or level in the overall interface joint between units (see Figure 2)
- a maximum deviation of 6mm in plan or section between faces of adjoining units (see Figure 3)
- a maximum deviation of 6mm in elevation between in-line edges across a transverse or cruciform interface joint (see Figure 4).
Figure 1: Straightness of interface joint widths
Figure 2: Taper of interface joints
Figure 3: Offset of cladding faces
Figure 4: Accuracy of cruciform interface joints
11.3.11.5 Finished appearance
Tolerances and finishes for factory installed external claddings should be in accordance with Chapter 9.1 A consistent approach to finishes.
Brick slip cladding
Factory installed brick slip claddings should be set out to co-ordinate with adjacent units and surrounding construction to avoid:
- cutting of brick slips, particularly in the storey heights, at corners, around openings, and at panel edges except when it is essential
- irregular or broken bonds of brick finishes, particularly at openings
- small cuts of brick finishes
- broken bond and out of line joints at junctions of panel and junctions with surrounding construction (eg substructure brickwork).
Care should be taken to ensure the finish specification of mortar used for site installed brickwork is the same as used for factory installed brick slip claddings to avoid variation in the texture, finish, and colour.
Weatherboard cladding
Factory installed weatherboard cladding should be set out to co-ordinate with adjacent units and surrounding construction to avoid:
- cutting and notching cladding boards around window and door openings
- misaligned cladding boards at panel junctions.
Last updated: 2nd January 2025