Remediation of leaky buildings

By - , Build 131

Designing solutions for weathertightness problems is a growth sector of the industry, yet it is an area many designers are unfamiliar with. What are the factors that need to be considered for this type of work?

Understanding why and how weathertightness failure occurs and then how to remedy the situation is essential for designers undertaking leaky building remediation design. Remediating leaky buildings is a complex task that also requires expert input from building surveyors, engineers, remediation specialists and builders.

The goal of a weathertightness remediation project is a cost-effective solution that remediates the situation, reduces future risk and restores the confidence of the building owner.

It is important to determine how the defect(s) allow water entry. The way defects trigger leaks can be unexpected and depend on circumstances such as siting, orientation, construction and maintenance. Combinations of defects can also work together, so fixing one defect may mean that others resurface later.

Design inputs

While the key design issue for remediation is the diagnosis – the diagnostic report – other factors to consider include:

  • performance improvements the owner may wish to make during the repair
  • the budget
  • building-related faults not identified as part of the weathertightness assessment but that may be uncovered later.

Uncertainty is part of the process

Weathertightness remediation has design uncertainties that will affect the final scope of the work. Because most building assessments are carried out before any cladding is removed, the full extent of damage and the necessary remediation, particularly to untreated framing, may not be determined until after construction starts.

As knowledge of the underlying construction increases and damage is exposed, the level of uncertainty reduces. A rough estimate is that the unknown factor is around 30% of the work.

Alongside the usual considerations, designers should have a clear understanding of the:

  • stresses the owner may be under
  • budget available, including allowance for contingencies and unknown factors
  • building consent process for remediation.

Start with comprehensive report by expert

Buildings being remediated should have a report on their condition carried out by a recognised specialist with specific relevant training and the necessary equipment.

Any report from a registered building surveyor or Weathertight Homes Resolution Service assessor should be comprehensive, but there is always the risk something has been overlooked.

While house checks and prepurchase inspections may identify potential problems, more extensive investigations will usually be required. House checks are generally limited in scope, and prepurchase inspectors would rarely have been allowed to carry out invasive investigations such as drilling holes for moisture meter readings or cutting inspection holes through claddings.

The remediation designer needs to be satisfied that any report provides sufficient information to base a design on. A good building assessment report should cover:

  • the causes and locations of water entry
  • areas of elevated moisture content in timber framing
  • the extent of the weathertightness failure
  • the likely level of framing timber treatment – confirmed once the framing is exposed
  • the likely extent, whether minor, localised or widespread, and the type of damage, such as to cladding, framing, insulation and lining
  • whether the failure is systemic and the likelihood and extent of future damage
  • changes made during the building process from the consent documents
  • remediation recommendations
  • cost estimate, including contingencies.

If no report, get one

Some owners wishing to evaluate and repair a building may approach a designer directly. In these cases, it’s recommended that the designer have the owner commission a report by an experienced remediation specialist. It’s unlikely that most designers will have the experience and equipment of a recognised specialist.

Three repair options

Remediation design options, which must be based on and supported by the assessment report on the building, are:

  • full reclad
  • partial reclad
  • localised repairs.


As a general rule, if the building has untreated timber framing or timber framing with little or no treatment, extensive leaks and decay (particularly with direct-fixed monolithic claddings), all the cladding must be removed to:

  • assess timber damage
  • facilitate replacement of decayed timber
  • treat any remaining sound timber
  • remove any hazardous mould spores
  • allow the building to meet Building Code requirements.

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A localised repair that only addresses a specific failure may be a valid option, provided there is a clear isolation of the specific weathertightness issue and non-systemic failure of the building elements. Advice from a specialist remediation expert should be sought when considering whether a localised repair is appropriate.

Designers proposing these options need to ensure their client is aware of the risk that further damage may be found during repairs, necessitating a substantial redesign and a significant increase in the costs to the owner.

Also, any defects not identified and repaired during the remediation process will continue to cause deterioration and require further remediation in the future. Unless these risks are carefully managed, the designer could become involved in further claims made by the owner.

Other options besides remediation

Some owners do not want to undertake repairs or may not be able to afford them and may choose another option:

  • Make temporary repairs to slow or limit further damage until a decision can be made on the remediation option. This shows a proactive response by an owner where a claim is being made for repair costs. However, temporary repairs can be problematic, and the repair work may not comply with the Building Code.
  • Demolish the building. This may be a cost-effective solution where there is significant and widespread damage.
  • Sell as is with full disclosure of the weathertightness issues.
  • Do nothing. The building’s condition is likely to continue to deteriorate, and it may become unsafe. If it is eventually declared unsafe by the local authority, work or demolition may be required at the owner’s cost. There is also the potential of health risks for occupants from a damp, mouldy environment.

Designers and remediation design

As part of a remediation design, the designer has several responsibilities:

  • They should visit the site to review the findings of the diagnostic report and understand the building, consider design options, note areas requiring details and consider landscaping issues such as abutting fences, planting and ground levels.
  • They should discuss with the owner the available repair and upgrading options and agree which approach will be followed. The remediation design must deal with any durability concerns or structural elements that no longer comply with the Building Code or were incorrectly designed or installed originally and constitute a safety risk.
  • They must address all of the points of water entry. Details that are not yet leaking but are likely to do so within the required minimum durability periods must also be considered.
  • They should consider removing very complex design elements or adding features such as eaves to lower weathertightness risk.
  • They must work within the limitations of the original building and still achieve a design that delivers weathertightness. Think of the 4Ds – deflection, drainage, drying and durability – when considering design options.
  • They should assemble a team to cover all aspects of the work: the remediation expert, a quantity surveyor (depending on the complexity and scale of the project), a structural engineer and, if possible, the BCA and builder. Where the building is being repaired under the government’s financial assistance package, both the Ministry of Business, Innovation and Employment – Building and Housing Group and the BCA will have to agree with the proposed remediation solution.
  • They should also keep good records during the design, documentation and construction phases of the project.

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