D
oc # 472818
Page 1 of 4 Sheet PS-04.1E
Weathertightness risk matrix
Supporting information for building consent application
V
ersion: 5
Date: December 2019
Code: PS-04.1E
Project location:
D
escription of work:
Establishing the risk
A risk assessment of the proposed design shall be carried out, using a building envelope risk matrix. This allows the risks
related to various features to be aggregated, resulting in a risk score for the design.
Figure 1 shows the process that shall be followed in order to assess the risk.
FIGURE 1
How to assess risk
(paragraph 3.1)
Applicant checklist
Item
Step One:
Detailed drawings.
Suitably detailed drawings are required to assess weathertightness risk. This documentation may
include a site plan, floor plans, elevations, details of junctions and penetrations, and the presence of
features like decks and pergolas.
S
tep Two:
Assess each external face against risk factors.
Assess the drawings for each external face to determine the risk score for each risk factor. These are:
Wind zone
Number of storeys
Roof/wall intersection design
Eaves width
Envelope complexity
Deck design
(Table 1)
Step Three:
Complete the building envelope risk matrix table.
Complete the “Building envelope risk matrix” (Table 2) for each face of the building.
Note : It is possible for different elevations to have different risk scores.
Step Four:
Determine suitable cladding.
To determine what cladding types are recommended with the risk score for each face. (Table 3)
The cladding selected must be appropriate for the score on that face, but can be beyond the
minimum required (ie cladding suitable for a higher score can be used).
Wall claddings - the following wall cladding systems are covered in the Acceptable Solution (E2/AS1)
a) Masonry Veneer Paragraph 9.2
b) Stucco Paragraph 9.3
c) Timber Weatherboards Paragraph 9.4
d) Fibre Cement Weatherboards Paragraph 9.5
e) Profiled Metal Wall Claddings Paragraph 9.6
f) Fibre Cement Sheet Paragraph 9.7
g) Plywood Sheet Paragraph 9.8
h) EIFS Paragraph 9.9
Other wall claddings are beyond the scope of the Acceptable Solution.
Doc # 472818
Page 2 of 4 Sheet PS-04.1E
Definitions of risk
Table 1 sets out the definitions of risk levels relating to the location and design features of the building.
TABLE 1
Definitions of risk
(paragraph 3.1.1, figure 1)
A. Wind zone
Low risk
Low wind zone as described by NZS 3604
Medium risk Medium wind zone as described by NZS 3604
High risk High wind zone as described by NZS 3604
Very high risk Very high wind zone as described by NZS 3604
B. Number of
storeys
Low risk One storey
Medium risk Two storeys in part
High risk Two storeys
Very high risk More than two storeys
C. Roof / wall
intersection
design
Low risk Roof-to-wall intersection fully protected (eg hip and gable roof with eaves)
Medium risk
Roof-to-wall intersection partly exposed (eg hip and gable roof with no eaves)
High risk Roof-to-wall intersection fully exposed (eg parapets, enclosed balustrades or
eaves at greater than 90º to vertical with soffit lining)
Very high risk Roof elements finishing within the boundaries formed by the exterior walls (eg
lower ends of aprons, chimneys, dormers etc)
D. Eaves width (1)
(2)
Low risk
Greater than 600mm for single storey
Medium risk 451-600mm for single storey, or over 600mm for two storey
High risk 101-450mm for single storey, or 451-600mm for two storey, or greater than
600mm above two storey
Very high risk 0-100mm for single storey, or 0-450mm for two storey, or less than 600mm
above two storey
E. Envelope
complexity
Low risk Simple rectangular, L, T or boomerang shape, with single cladding type
Medium risk More complex, angular or curved shapes (eg Y or arrowhead) with no more
than two cladding types
High risk Complex, angular or curved shapes (eg Y or arrowhead) with multiple cladding
types
Very high risk As for High risk, but with junctions not covered in C or F of this table (eg box
windows, pergolas, multi-storey re-entrant shapes etc)
F. Deck design (3)
Low risk None, timber slat deck or porch at ground level
Medium risk
Fully covered in plan by roof, or timber slat deck attached at first or second
floor level
High risk Enclosed deck exposed in plan or cantilevered at first floor level
Very high risk Enclosed deck exposed in plan or cantilevered at second floor level or above
Notes:
(1) Eaves width measured horizontally from external face of wall cladding to outer edge of overhang, including gutters
and fascias.
(2) Balustrades and parapets count as 0mm eaves.
(3) The term deck includes balconies, as described in the Definitions.
Doc # 472818
Page 3 of 4 Sheet PS-04.1E
The risk score
Table 2 sets out the risk matrix that shall be used to define the risk score for a building within the scope of the Acceptable
Solution. A risk score is calculated for each elevation of the building. Claddings are then selected from Table 3 according to
the risk scores, or the highest risk score may be used for all walls.
TABLE 2
Building envelope risk matrix
(paragraph 3.1.2, figure 1)
Elevation or wall
Risk factor Low Score Medium Score High Score Very high Score
Subtotal for
each risk factor
Wind zone (per NZS 3604)
0 0 1 2
Number of storeys
0 1 2 4
Roof / wall intersection design
0 1 3 5
Eaves width
0
1
2
5
Envelope complexity
0 1 3 6
Deck design
0 2 4 6
[Enter the appropriate risk severity score for each risk factor in the score columns. Transfer these figures across to the right-
hand column. Finally, add up the figures in the right-hand column to get the total risk score.]
Total risk score:
Elevation or wall
Risk factor Low Score Medium Score High Score Very high Score
Subtotal for
each risk factor
Wind zone (per NZS 3604)
0 0 1 2
Number of storeys
0 1 2 4
Roof / wall intersection design
0 1 3 5
Eaves width
0
1
2
5
Envelope complexity
0 1 3 6
Deck design
0 2 4 6
[Enter the appropriate risk severity score for each risk factor in the score columns. Transfer these figures across to the right-
hand column. Finally, add up the figures in the right-hand column to get the total risk score.]
Total risk score:
Elevation or wall
Risk factor Low Score Medium Score High Score Very high Score
Subtotal for
each risk factor
Wind zone (per NZS 3604)
0 0 1 2
Number of storeys
0 1 2 4
Roof / wall intersection design
0 1 3 5
Eaves width
0
1
2
5
Envelope complexity
0 1 3 6
Deck design
0 2 4 6
[Enter the appropriate risk severity score for each risk factor in the score columns. Transfer these figures across to the right-
hand column. Finally, add up the figures in the right-hand column to get the total risk score.]
Total risk score:
Elevation or wall
Risk factor Low Score Medium Score High Score Very high Score
Subtotal for
each risk factor
Wind zone (per NZS 3604)
0 0 1 2
Number of storeys
0 1 2 4
Roof / wall intersection design
0 1 3 5
Eaves width
0
1
2
5
Envelope complexity
0 1 3 6
Deck design
0 2 4 6
[Enter the appropriate risk severity score for each risk factor in the score columns. Transfer these figures across to the right-
hand column. Finally, add up the figures in the right-hand column to get the total risk score.]
Total risk score:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Doc # 472818
Page 4 of 4 Sheet PS-04.1E
TABLE 3
Suitable wall claddings
(paragraphs 3.1.2, 3.4.1.1, 3.4.2.1, 3.4.2.2, 3.4.3.2, 9.1.1, 9.4.1.2, 9.4.1.3, 9.6, figure 1 (E2/AS1))
Risk score Suitable wall claddings
Direct fixed to framing
Over 20mm minimum drained cavity
0 - 6
a) Timber weatherboards - all types
b) Fibre cement weatherboards
c) Vertical profiled metal (3) - corrugated and
symmetrical trapezoidal (3)
d) Fibre cement sheet (4) (Jointed finish)
e) Plywood sheet
a) Masonry veneer (2)
b) Stucco
c) Horizontal profiled metal (3) - corrugated and
trapezoidal only
d) Fibre cement flush-finished
e) EIFS
7 - 12
a) Bevel-back weatherboards
b) Vertical timber board and batten
c) Vertical profiled metal (3) - corrugated
only(3)(6)
a) Masonry veneer (2)
b) Stucco
c) Horizontal profiled metal - corrugated and
trapezoidal only
d) Rusticated weatherboards
e) Fibre cement weatherboards
f) Fibre cement sheetflush and jointed finish
g) Plywood sheet
a) EIFS
13-20
a) Vertical profiled metal - corrugated only (3)
(6)
a) Masonry veneer (2)
b) Stucco
c) Horizontal profiled metal - corrugated and
trapezoidal only
d) Rusticated weatherboards
e) Fibre cement weatherboards
f) Fibre cement sheetflush and jointed finish
g) Plywood sheet
h) EIFS
i) Bevel-back weatherboards
Over 20
a) Redesign the building to achieve a lower score, or
b) Specific design
The design may need changing to reduce the risk
The building consent authority may require more comprehensive details and documentation
providing evidence of weathertightness
The building consent authority, designer or owner may require more inspections
A third party audit of the design may be required.
Notes:
1) The wall claddings in this table are limited to those covered in this Acceptable Solution.
2) Traditional masonry veneer as per SNZ HB 4236, with minimum 40mm cavity.
3) Refer Figure 38 for profiles.
4) Except stucco over a fibre cement backing.
5) Claddings in Extra High wind zones require rigid underlays
6) Direct fix vertical corrugated steel is included as cavity construction.
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