COP v3.0:durability; clearances

4.16 Clearances 

To ensure the edge of the flashing does not mechanically remove protective coatings on the cladding, there must be enough clearance between the edge of a vertical flashing, or a notched flashing, and the cladding. Similarly, the edges of cladding running parallel to flashings, such as at a window head, should have clearance to avoid mechanical damage and allow drainage.

Having the lower edges of flashings apart from the surface they are covering helps to improve the cut edge durability of the flashing. Kick-out barge details are preferred to bird’s beak barge details for the same reason. The size of the clearance is not critical, but typically it is more than 5 mm.

 

 

4.16.1 Ground Clearance 

Clearance is required between the bottom of profiled metal cladding and large flat surfaces. For timber-framed dwellings, E2/AS1 requires a clearance of 35 mm to an adjacent roof, 100 mm to paved ground, and 175 mm to unpaved ground.

The clearance requirements for unlined buildings is less than that required for lined buildings, as the absence of lining enables the inner face of the cladding to dry more rapidly, and inspection and maintenance of the framing can be practically achieved.

4.16.1B Importance Levels from NZS 3604;2011 (Table 1.1)

Level 1Structures presenting a low degree of hazard to life and other property
Level 2Normal structures and structures not in other importance levels
Level 3Structures that may contain people in crowds or contents of high value to the community, or may prose risks to people in crowds.
Level 4Structures with special post-disaster functions.

4.16.1C Minimum Ground Clearance for Lined Buildings

Minimum Design Ground Clearance for
Profiled Metal Cladding on Lined Buildings of Importance Level 2.
 
Ground TypeMinimum Clearance
Garage door opening25 mm
Walls under canopies35 mm
Paved100 mm
Unpaved gravel125 mm
Unpaved lawn150 mm
Unpaved pasture175 mm

 

Importance level 1 buildings may have a lesser clearance provided occupant maintenance prevents the build-up of debris against the cladding.

Greater clearance may be required where gardens abut a wall, where lawn grasses are not grazed or maintained, or where soil spillage from adjacent banks may occur. Future landscaping effects on ground levels must also be considered.

4.16.2 Site Management 

The effectiveness of clearances in achieving durability requirements is subject to the occupant ensuring that vegetation, debris, and soil do not build up against the cladding surface. Design clearance from a surface is no guarantee of durability as effective clearances are subject to site development, occupant behaviour and building maintenance.

4.16.2A Cladding Open to Air
 

Cladding which is open to air will experience the normal wet/dry cycles for which it is designed.

4.16.2B Vegetation in Contact with Cladding

Vegetation or earth in contact with the cladding will increase the time of wetness and may contain corrosive compounds.

The separation of profiled metal claddings from corrosive surfaces such as wet timber or concrete is more critical at the bottom end of cladding, where high humidity levels may be experienced for extended periods. This may take the form of a 3 to 6 mm gap, an inert self-adhesive tape or a PVC vermin strip.

Internal environments are also important, ventilation must be adequate for the building use, and absorptive of corrosive substances must not be in prolonged contact with the external or internal face of the cladding or structure.

4.16.2C The Result of Debris Build-up Against Cladding

 
Allowing build-up of material against wall cladding can result in corrosion regardless of nominal ground clearance.