The exterior of a typical modern leaky building often belies the damage within. It only takes a few judicial digs with a crowbar to reveal the true extent of mouldy horror.

That soggy mess might as well be piles of wet $20 notes. Like a heritage building in need of renovation, what is hidden below the surface of a leaky building can be a devastating shock to the owner.

Official estimates put the number of leaky buildings dating from 1992 onwards certainly in the tens of thousands and possible as many as 90,000. The true extent may be even higher. What's clear is they will cost billions to fix.

In each case, an expert quantity surveyor (QS) is a huge asset in ensuring any rescue mission is costed correctly from the start. A leaky building owner often feels helpless and their anguish is compounded if the cost of repairs balloons unexpectedly.

Because it is such a big financial commitment to go through a dispute resolution process such as adjudication, building owners need to weigh up those likely costs of the process versus selling the building as it is, with appropriate disclosures.

A QS will help provide sound cost benefit analysis to aid the decision.

Now that their skills are being more widely recognised, QS professionals are becoming more involved in New Zealand's weathertight remediation process. Specialised consultants provide cost estimation retrospective and back-costing analysis, and expert quantum evidence during a dispute resolution process.

A QS who specialises in this field will work alongside the building surveyor to develop a comprehensive cost estimate which details the items identified in the repair recommendations. A good QS is aware of the myriad unknowns which are likely to read their ugly head.

No matter the size of the project, it is critical for all parties to know the costs of what is involved, and the potential pitfalls and benefits of all the options. Only then can a well-informed decision be made to proceed or not.

If a leaky building owner decides to have the problem fixed, it is important a QS is involved throughout the process. A good QS is indispensible, helping to weigh up options and provide lateral solutions to problems along the way, and amending the project budget accordingly. If expenditure is to be increased in one area, savings need to be made elsewhere. For leaky building projects, a QS provides a breakdown of all labour and material costs and ongoing financial management of cists during the repair process to ensure payment claims are fair and reasonable.

A true professional should help make the process as stress-free as possible. People who are unfortunate enough to own a leaky building should select a project team which has their best interests at heart.

It is almost inevitable that a leaky building project will be an emotional rollercoaster for the owner. An expert QS should show empathy along the way, rather than simply sending through a series of invoices.

In most leaky building situations, the first step should be obtaining legal advice which establishes whether the owner has a legal remedy. Next, a building surveyor should thoroughly assess the state of the building - a QS should come on boards during the building surveyor's preliminary specialised area of the profession, with expert knowledge required to deal with mould, fungi, and different types of timber, and to collect evidence and data necessary to move forward to some sort of dispute resolution process.

Usually the biggest unknown is how much timber damage and decay there is going to be. Often, a closer look reveals other examples of poor workmanship around structure, drainage or fire ratings, which can be a surprise. Builders, building surveyors and the QS can work together during this stage to fully quantify the extent of the damage.

Leaky buildings present many opportunities for the building industry and quantity surveyors to work together. Rather than an 'us and them' situation, a close alliance should be promoted.

Being involved from start to finish is the optimum way a QS can guide an owner through the leaky building minefield, and help keep the lid on costs.