Introduction

External moisture - A guide to weathertightness remediation (the guide) provides an explanation of the process, documentation and project management needed to repair weathertightness defects successfully in timber-framed construction in New Zealand (refer to 'Building types covered').

Purpose
The purpose of this guide is to provide assistanceto consultants as they embark on weathertightness remediation work. It also aims to promote consistency in the way consultants assess weathertightness problems, make recommendations, detail and specify repairs, and implement remediation projects.

Building types covered
Although generally oriented towards housing, this guide will also prove useful for other types of timber-framed buildings (or parts of buildings). When the construction is appropriate, the guide should be useful for the following types of buildings.

• Housing - Communal residential buildings (as defined in NZBC clause A1)
• Communal non-residential Buildings
• Light commercial buildings 
• Industrial buildings

Limitations
This guide recommends the use of consultants as the most appropriate way to proceed with planning for and implementing remediation work.

Most remediation projects involve complex technical and contractual issues that are beyond the skills and experience of most building owners. If owners are considering undertaking the work, they should expect to have to exercise the functions and judgement of an experienced consultant, and must be aware of the potential risks that the work will not be properly diagnosed or repaired if professional advice is not sought.

The information provided in this guide does not replace professional advice. Guidance incorporated into remediation repair work must be reviewed by knowledgeable consultants, to ensure that the unique conditions and design of the particular building are reflected.

The use of the guide does not relieve consultants (or building owners) of their responsibility to comply with the Building Act 2004, the New Zealand Building Code, relevant New Zealand building Standards and other Acts, local bylaws and professional obligations. Issues relating to claims, litigation or similar matters that might be involved in some remediation projects are not addressed in this guide.

Other New Zealand Building Code issues
This guide focuses on moisture and associated durability issues.

It must be noted, however, that other Building Code issues (such as fire safety, structure and so on) need to be considered along with the moisture problems.

Audience
The primary intention of the guide is to provide guidance on the overall remediation process for:

• architects, engineers and other building professionals
• weathertightness building consultants.

The guide should also provide some useful background information for:

• building owners or managers
• builders involved in remediation work
• building specialists
• building officials
• legal advisors
• insurers and financiers.

Format of the guide

The guide identifies the general stages and the range of activities that must be carried out within a remediation project and decisions that must be explored. The stages are not neatly separated, instead they overlap, and include various 'feedback loops' when more information becomes available as the remediation project progresses.

Early in the remediation process it is important that building consultants use their experience to assess the likely extent of the repair work early so that owners can base their decisions on likely overall costs and repair options. As the project progresses, more information is gained on the underlying construction and condition of the building, which often results in the reassessment of earlier decisions.

This iterative (see glossary) process continues into the construction phase, when 'hidden' construction elements are finally revealed. The gradual decrease of uncertainty is particularly important in remediation work, because it can significantly affect budgets, schedules, consents and final construction.The unknowns that apply to various stages of the process must be taken into account during client consultations, budget preparation, when developing contract arrangements, when selecting contractors and when anticipating amendments to the consent documentation.

The broad stages of the remediation process are described in sequence within the guide, as shown in Figure 1. Additional detailed explanations, examples and reference information are provided in the appendices.

Boxes are used throughout the guide to provide further information, and the yellow boxes provide additional hints and warnings about possible pitfalls in remediation projects.

Terminology
The glossary at the end of this document explains many of the terms used throughout this guide. The following are frequently used abbreviated terms.

• Department - the Department of Building and Housing
• Building Act (or Act) - the Building Act 2004
• Building Code (or Code) - the New Zealand Building Code (NZBC)
• Consultant - the person advising a building owner on remediation contract work
• BCA - building consent authority (the local council that issues building consents, carries out inspections during construction and issues code compliance certificates, notices to fix and compliance schedules)

Companion documents
There are several companion documents (as shown in Figure 1) that should be read in conjunction with this guide and that provide useful information for surveyors and consultants on weathertightness remediation.

• External moisture - a guide to using the risk matrix provides additional information on weathertightness risk assessment. Its application to remediation projects is discussed further within this guide.
• Diagnosis of Buildings for Weathertightness is a more detailed report intended to be used by building experts who are commissionedby the Department of Building and Housing to investigate and diagnose the weathertightnessof a building for Determinations and Weathertight Homes Resolution Services. Diagnosis results can be used directly as the first step in remediation design, or indirectly by contributing to dispute resolution activities.
• External moisture - An introduction to weathertightness design principles explains the principles behind the E2/AS1 details inorder to provide a basis on which alternative weathertight details may be designed.

Background to the guide

The successful repair of weathertightness defects is developing into a specialist area within the inspection, design and construction sectors of the building industry.

Although steps have been taken to improve the weathertightness of new buildings, existing moisture-troubled buildings (or buildings that owners seek assurance about) still require attention.

The focus of this guide is on the remediation process, rather than 'rules' to be followed. Successful remediation design and construction is an iterative process that is shaped by the particular circumstances of each situation. Success also relies on the experience of the consultants and specialists who have been contracted to do the work.

Weathertightness and durability in the Building Code

Figure 2 shows how weathertightness and durability requirements fit within the Code.

The Department issues Compliance Documents that set out prescribed methods of complying with specific clauses of the Building Code. However, following these prescribed methods is optional.

Remediation work involves many situations outside of those covered by the E2/AS1 details. Performance-based alternative solutions for site-specific circumstances will need to be developed.

Alternative solutions are subject to acceptance by building consent authorities (BCAs). A remediation consultant must satisfy the BCA that the repair details will meet the requirements of the Building Code.

Understanding weathertightness and durability

Consultants involved in remediation work need to understand and use weathertightness and durability principles in all stages of the remediation process. This guide builds upon the background information provided in the companion document External Moisture - An introduction to weathertightness design principles, which is recommended for further guidance.

Weathertightness risk
At all stages of a successful remediation project, consultants must be able to recognise and assess the general and specific weathertightness and durability risks of a building. General risk factors must be understood and specific high-risk areas of the particular building must be identified.

Once the risks are identified and understood, the consultant can then pay particular attention to those areas that are known to have an increased likelihood of leaking.

Further detail
Table 5: Common weathertightness defects

The management of known weathertightness risks begins at the diagnosis stage (when potential sources of moisture penetration must be identified and investigated), and should extend through the design stage to the construction stage.

Common areas of weathertightness risk are shown in Figure 3.

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