All buildings will leak to some degree, either from imperfections in the design and construction, or subsequent actions such as adding an outside light or TV aerial, or raising garden levels too high.

Moisture can be retained behind the cladding by not being able to drain and dry out.

This moisture is hidden, usually on the back of the cladding so the owner or occupant can be quite unaware.

Retained moisture can lead to mould growth on building materials, decay of timber framing and rusting of steel fixings and framing.

With timber not treated against decay, the chance of decay occurring is very high. The nature of some of these decays is of great concern, e.g. dry rot.

NZS 3602, the Standard which permitted the use of kiln dried untreated pine was published in September 1995. The use of untreated timber would have started from 1996 onwards. Douglas fir has always been allowed without any treatment, however it is more durable than untreated kiln dried pine.

The only treatment requirement was for insect attack. After a field study, it was considered that kiln dried timber was unpalatable to borer. Issues of water ingress and fungal decay were not considered.

'Treated timber' means the addition of a chemical to prevent insect attack. Traditional wet framing used Boron which is an insecticide with the additional effect of also being an effective fungicide. Its presence certainly prevents a high incidence of early decay, especially dry rots.  NZS3602 has been revised.  This allows untreated pine for dry situations, H1.1 for insect risk, H1.2 (pink or blue)  for exterior framing including subfloors and H3 (H3.1 or H3.2) for balconies.

This is unknown. The low moisture levels that can cause certain decays mean it could take many years for the problem to surface. However, significant decay is being found in buildings built less than one year ago. Some decay has also been found inb uildings being constructed.

It all depends on how much moisture penetrates and accumulates behind the cladding. The biggest safety factor is the roof eave - the wider the better. However, any moisture entry is of great concern and there is no protection against decay.

Take advice from your own solicitor.

You need to look at your insurance policy. Most insurance policies do not cover gradual damage, though each policy is different. Take advice from your solicitor.

Try to bring the parties involved in the construction to account. Unfortunately this may mean expensive legal action. If those involved will not assist, money should first be spent on doing the repair and then you should try to recover costs.