Specialty Timbers New ZealandE2 External moisture - wall claddings
Building code Acceptable solution E2/AS1 External moisture provisions for timber-framed buildings up to 10 m in height provides acceptable solutions for timber weatherboards "to ensure buildings shall be constructed to provide adequate resistance to penetration by, and the accumulation of, moisture from the outside".
Wall cladding types are deemed suitable according to a risk score totalled by adding up risk severity scores for each risk factor below:
| Risk severity | ||||
| Risk factor | LOW | MEDIUM | HIGH | VERY HIGH |
| Wind zone | 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 |
Table 3.1.2.1 below defines risk levels.
For risk scores of 0-6, all types of timber weatherboards are allowed to be fixed directly to framing.
For risk scores of 7-12, only bevel-back timber weatherboards and vertical timber board and batten weatherboards are allowed to be fixed directly to framing as the Acceptable Solution. Rusticated weatherboards are also allowed, provided they are fixed over a nominal 20mm drained cavity.
For risk scores of 13-20, bevel back weatherboards and rusticated weatherboards are allowed, provided they are fixed over a nominal 20mm drained cavity.
Table 3.1.2.1: Definitions of risk levels
Notes:
- Eaves width measured horizontally from external face of wall cladding to outer edge of overhang, including fascias and external gutters/spoutings.
- Balustrades and parapets count as 0 mm eaves.
- The term deck includes balconies, as described in Appendix B. Definitions.
- Buildings in Extra High wind zones require rigid underlays and drained cavities, refer to Table 3.1.3.2. (5) Refer also to Table 3.1.3.1.
See Acceptable Solution E2/AS1 External moisture (4th edition July 2025).
Disclaimer: While every effort is made to ensure the accuracy of the information provided on this site, Specialty Timbers New Zealand inc. do not accept liability for any consequences arising from reliance on the information published. If readers have any doubts about acting on any articles they should seek confirming, professional advice.