What is weathertightness?
Weathertightness refers to the resistance of a building to the natural weather elements. In New Zealand the issue of building weathertightness (or ‘leaky building syndrome’) has affected many houses where the poor design and use of building materials resulted in severe building damage. The problem occurs when water and moisture penetrates the building, accumulating behind the cladding. The water build-up is prevented from evaporating, providing a perfect environment for mould to grow, and eventually rotting the timber framing. The mould also presents a health risk to occupants. Untreated timber framing is especially susceptible to rot, and was commonly used as framing in residential houses built during the early 1990’s.
Building a New Weathertight Home
During the design phase of building a new home, ensure that the design, materials and construction methods used present a low weathertight risk. Many factors such as location and weather effects, materials, building shape and style will impact on.
It is advisable to discuss the weathertight building options with your designer in the early stages of the design process. It is important that you, the home owner, understand what the minimum standards set out in the New Zealand Building Code are for a weathertight home.
The Building Code sets out the minimum performance standards that must be met. The Acceptable Solution E2 / AS1, provides solutions that can be used to minimise and manage the risk of leaky building problems. It also provides ways to address compliance with the Building Code and risk scores to each risk factor of a building.
The acceptable solution is used by designers and engineers to assess potential weathertightness risks, and whether any specific design features need to be used. Your designer should be familiar with this matrix and you should discuss this with them.
Risk factors include:
- Wind zone
- Number of storeys
- Roof / wall intersection design
- Eaves width
- Envelope complexity
- Deck design
Your designer should be considering information in the following two documents, as risk scores need to be provided along with the building plans as part of the Building Consent application. Buildings with high risk scores may be required to supply further information to Council.
- Acceptable solution to E2/AS1: There are some easy to understand information about assessing risk (Figure 1 on page 28), and definitions of risk levels (Table 1 on page 29), Building envelope risk scores (Table 2 – page 30) plus much more.
- External Moisture guide to E2/AS1 risk matrix.
Buying an Existing Home
There are specific design and installation methods used in the past that contribute to leaky buildings, some of which you can easily identify. If you are planning to purchase an existing home it is highly advisable to have an inspection undertaken by an independent qualified and experienced inspector prior to purchasing, to identify any risk areas of weathertightness. If the property was built in the 1990’s or is built with monolithic cladding systems it would be important to get an inspection undertaken, as these homes are more susceptible to weathertightness problems. Ask the inspector to look for indications of water damage or potential leaks, especially in the high-risk areas. Refer to MBIE’s Guide on Diagnosis of Leaky Buildings and refer to the risk factors and scores above.
Qualified independent building inspectors can be found in the Yellow Pages. Further information is available from the Consumer website. As the potential property owner, it is in your best interest to assess the building prior to purchase. A Land Information Memorandum may provide information any weather tightness issues. You can request a LIM through your local Council.
Maintaining your Home
If you own a property that has issues with weathertightness it is highly advisable to complete regular maintenance checks to help identify any further potential leaks. Information about what to look for is available online:
- Consumer website
- Maintaining Your Home publication available from BRANZ.
- MBIE information sheets on general maintenance, and maintenance and repairs for leaky homes.
If you do observe any potential leaks it is important to engage a weathertightness consultant to assess the area, and then to follow with repairs as soon as possible. Visit the New Zealand Institute of Building Surveyors (NZIBS) website where you can find your local surveyor member.
Addressing Leaky Home Problems
If you suspect your home may be affected by weathertightness problems, get it checked immediately. Leaky homes need to be repaired promptly once the problem becomes apparent. If a leak remains, this may lead to extensive damage, and therefore more costly repairs. Other areas of the building will need to be inspected to check if there are any further potential problems. Refer to the Building Performance (MBIE) documents:
- Guide to the Diagnosis of Leaky Buildings [PDF 797 KB, 72 pages]
- Guide to Remediation Design [PDF 4.43 MB, 60 pages]
The repair must comply with a weathertightness standard of the New Zealand Building Code. You may be able to make a claim under the Weathertight Homes Resolution Services Act 2006, through the Weathertight Homes Tribunal, if your home was built or altered within the last ten years (from the date of lodging the claim). The Weathertight Homes Resolution Services (WHRS) Act provides owners of leaky homes with a low-cost assessment of the weathertightness problems, and access to dispute resolution services. Further booklets and information about the WHRS and Weathertight Services for homeowners are available from the Building System Performance website (MBIE). It is also advisable to seek legal advice from your lawyer.