Home External Moisture Risk Matrix

This Risk Matrix is based on the DBH publication "External moisture - a guide to using the risk matrix". It should be used in conjunction with the Guide, which can be downloaded from the Ministry of Business, Innovation and Employment website.

This program is distributed in the hope that it will be useful, but without any warranty and the author is under no circumstances liable for any building failures arising from the use of this site. The matrix does not cover every situation. Each design should be assessed independently for sound building practice. The main purpose of the Risk Matrix is to highlight those factors which should be addressed by careful design.

Philosophy of the Risk Assessment Matrix

The development of the risk assessment approach taken in E2/AS1 is based on a simple concept called "the 4Ds" to describe the basic principles of water management in buildings. The 4Ds are:

Deflection: Keeping water away from potential entry points.
Drainage: Providing means of removing water that does enter.
Drying: Allowing any remaining moisture to be removed by ventilation or diffusion.
Durability: Providing materials with appropriate durability.

Ideally, a design incorporates and balances all 4Ds.

How to Use this Matrix

Complete the risk factors for each external face in your design. At the bottom of the table your total risk score will be shown together with suitable cladding types. Clicking on the -buttons shows a more detailed description of the options.

Project Name / Facade ID:
Wall type: Parapet or enclosed balustrade

Risk Scores Low Medium High Very High
A. Wind Zone: Low = 0
NZS 3604 limit 32m/s
Medium = 0
NZS 3604 limit 37m/s
High = 1
NZS 3604 limit 44m/s
Very High = 2
NZS 3604 limit 50m/s

Extra High = 2
NZS 3604 limit 55m/s
B. Number of Storeys: show details Low = 0
1 storey
Medium = 1
2 storeys in part
High = 2
2 storeys
Very High = 4
more than 2 storeys
C. Roof/Wall Intersection Design: show details Low = 0
Roof-to-wall intersection fully protected (eg, hip and gable roof with eaves)
Medium = 1
Roof-to-wall intersection partly exposed (eg, hip and gable roof with no eaves)
High = 3
Roof-to-wall intersection fully exposed (eg, parapets, enclosed balustrades or eaves at greater than 90o to vertical with soffit lining)
Very High = 5
Roof elements finishing within the boundaries formed by the exterior walls(eg, lower ends of aprons, chimneys, dormers etc.)
D. Eaves Width: show details Low = 0
Greater than 600 mm for single storey
Medium = 1
451-600 mm for single storey, or over 600 mm for two storey
High = 2
101-450 mm for single storey, or 451-600 mm for two storey, or greater than 600 mm above two storey
Very High = 5
0-100 mm for single storey, or 0-450 mm for two storey, or less than 600 mm above two storey
E. Envelope Complexity: show details Low = 0
Simple rectangular, L, T or boomerang shape, with single cladding type
Medium = 1
Moderately complex, angular or curved shapes (eg, Y or arrowhead) with no more than two cladding types
High = 3
Complex, angular or curved shapes (eg, Y or arrowhead) shapes with multiple cladding types
Very High = 6
As for High risk, but with junctions not covered in C or F (eg, box windows, pergolas, multi-storey re-entrant shapes etc)
F. Deck Design: show details Low = 0
None, timber slat deck or porch at ground-floor level
Medium = 2
Fully covered in plan by roof, or timber slat deck attached at first- or second-floor level
High = 4
Enclosed deck exposed in plan or cantilevered at first-floor level
Very High = 6
Enclosed deck exposed in plan or cantilevered at second-floor level or above

Total Risk Score:

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This wall can use any of the wall cladding types which have a green tick . Claddings with red crosses are not permitted under the Acceptable Solution E2/AS1.

The risk score of this wall is above 20. Redesign the building to achieve a better score or demonstrate Specific Design compliance!
Claddings in Extra High wind zones shall be installed over drained cavities and require rigid underlays (ref. Paragraph in E2/AS1).
Claddings on parapets and enclosed balustrades shall be installed over drained cavities.
Direct fixed to framing
Timber weatherboard - all types
Timber weatherboard - bevel backed
Fibre cement weatherboards
Vertical profiled metal - corrugated and symmetrical trapezoidal
Vertical profiled metal - corrugated only
Vertical timber board and batten
Fibre cement sheet jointed finish (except stucco over fibre cement backing)
Plywood sheet
Over nominal 20 mm drained cavity
Masonry veneer
Horizontal profiled metal - corrugated and trapezoidal only
Rusticated weatherboards
Fibre cement weatherboards
Fibre cement sheet - flush finish
Fibre cement sheet - jointed finish
Plywood sheet
Bevel backed weatherboards
This table is based on Table 3 of E2/AS1. The claddings which have not received a green tick should not be used in this situation.

Changes to the Risk Matrix will be introduced on 2 August 2011.

This calculator includes these changes, but still needs to be peer reviewed.

Please confirm the risk scores and corresponding cladding types by refering to E2/AS1.