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 Other
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:
Low = 0
1 storey
Medium = 1
2 storeys in part
High = 2
2 storeys
Very High = 4
more than 2 storeys
Move the cursor over the sketches to see the risk factors for the shown walls.
C. Roof/Wall Intersection Design:
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.)
Low risk
other examples in E2/AS1 Paragraph 8.0:
Figure 25: Timber fascia eaves for masonry tile
Figure 36: Eaves and barge for metal tile
Figure 45 (a): Eaves for profiled metal
Medium risk
other examples in E2/AS1 Paragraph 8.0:
Figure 28: Roof/wall ridge for masonry tile
Figure 45 (b): Roof/wall ridge for profiled metal
Figure 61: Verges in membrane
High risk
other examples in E2/AS1 Paragraph 6.0 and 7.4:
Figure 9: General capping joints for parapets and enclosed balustrades
Figure 10: General construction of parapet and enclosed balustrade
Figures 11 to 13: Parapet/balustrade junctions with walls
Figure 18: Enclosed balustrade - bottom of cladding
Very high risk
other examples in E2/AS1 Paragraph 5.0:
Figure 7: Basic apron flashing
Figure 8 (a): Gutter/wall junction
Figure 30: Abutment at framed penetration for masonry tile
Figure 37: Hidden gutter flashing for metal tiles
Figure 48: Parallel apron flashings for profiled metal
Figure 50: Parallel hidden gutter for profiled metal
Figure 62: Junctions with walls for membrane
Graphics: Ministry of Bussiness, Innovation and Employment, "External moisture - a guide to using the risk matrix"
D. Eaves Width:
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
(1) Eaves width measured horizontally from external face of wall cladding to outer edge of overhang, including facias and and external gutters/spouting.
(2) Balustrades and parapets count as 0mm eaves.
Graphic: Ministry of Business, Innovation and Employment, "External moisture - a guide to using the risk matrix"
E. Envelope Complexity:
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)
Low risk
Low-risk building envelopes tend to have the following features: The floor plan is simple, with limited and straightforward corners. This limits the number and complexity of corner junctions, and hence the number of potentially vulnerable points. They have a single wall cladding, there are no inter-cladding junctions vulnerable to water entry. Window and door joinery is simple in design. There are no complex windows such
as box, bay or conservatory-type glazing that may be difficult to weatherproof. There are no exposed attachments such as pergolas, with fixings that penetrate wall claddings.
Medium risk
These building envelopes tend to have the following features: The floor plan is complex, with more corner junctions, and possibly curved walls. Corners may be at acute angles. The number and complexity of corner junctions is increased, and hence the number of potentially vulnerable points. Walls have no more than two different wall claddings, there are limited inter-cladding junctions vulnerable to water entry. Window and door joinery is reasonably simple in design, without complex windows such as box, bay or conservatory-type glazing that may be difficult to weatherproof. There are no exposed attachments such as pergolas, with fixings that penetrate wall claddings.
High risk
These building envelopes tend to have the following features: Complex floor plan, with many corner junctions, and possibly curved walls. Corners may be at acute angles. The number and complexity of vulnerable corner junctions is increased. Wall tend to have multiple wall claddings with inter-cladding junctions vulnerable to water entry. Window and door units are conventional in design, without specialised windows such as box, bay or conservatory-type glazing. There are no exposed attachments such as pergolas, with fixings that penetratewall claddings.
Very high risk
Very high-risk building envelopes tend to have the following features: The floor plan is very complex, with multi-levels, many corner junctions, and possibly curved walls. Corners may be at acute angles. The number and complexity of corner junctions is increased, hence the number of potentially vulnerable points.Wall have multiple wall claddings with inter-cladding junctions vulnerable to water entry. Window and door joinery may be non-standard in design, with complex windows such as box, bay, dormer or specialised conservatory-type glazing that lead to complex window-to-wall junctions. There are exposed attachments such as pergolas, with fixings that penetrate wall claddings.
Graphics: Ministry of Business, Innovation and Employment, "External moisture - a guide to using the risk matrix"
F. Deck Design:
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
Timber Slat Decks
The most vulnerable areas for timber slat decks are the connections of the deck structure to the exterior wall.
Deck connection details are covered in E2/AS1 paragraph 7.0:
Figure 14 (b) and (c): Threshold separations
Figure 15: Junction with wall for non-cantilevered timber deck
Figure 16: Junction with wall for cantilevered timber deck.
Enclosed Decks
The areas most vulnerable to moisture penetration are solid balustrades and deck-to-wall junctions.
Covering the deck with a roof overhang helps to protect the junctions of the deck to the exterior walls and decreases the risk, while cantilevering the deck joists increases vulnerable penetrations and increases the risk.
In E2/AS1 Paragraph 8.5, enclosed deck details are covered by:
Figure 56: Fall in membrane roofs and decks
Figure 62: Junctions with walls for membrane.
Graphics: Ministry of Business, Innovation and Employment, "External moisture - a guide to using the risk matrix"
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 9.1.7.2 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
External Moisture Risk Matrix
-buttons shows a more detailed description of the options.
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. Claddings with red crosses 
are not permitted under the Acceptable Solution E2/AS1.