Timber treatment testing

Recently a client called for a pre-purchase inspection. His special requirement is to cut a hole through GIB lining and take a timer sample to determine the timber treatment. As he mentioned, he has obtained an approval to do so from the owner.
We tried our best to tell him why this is not appropriate for a pre-purchase inspection and why this does not help him with decision-making.
In another situation, a client has entered into an purchase agreement subject to an innovative condition: timber treatment.
Here is the summary of our opinion regarding timber treatment testing:

Scope of timber treatment
We can not give an Yes or No answer regarding the timber treatment of a regular house. We must define the timber treatment type, retention, distribution and location within a building.

• Type: Even for framing timber only, there are different types of treatments required for different framing parts. It is common that timber treated to H1.2, H1, H3.1, H3.2 are all found within timber framing of one house. 
• Retention: One piece of timber may be treated to a certain level, say H1.2. But due to constant exposure to moisture, its preservative is largely diluted and the actual preservative left inside the timber may be far away from H1.2.
• Distribution: Preservative inside timber frame is never evenly distributed. It is common that a piece of timber specified to a certain level of treatment is found to be under-treated or untreated at all.
• Location: When legally different treatments required for different areas such as wet area, exterior framing, eave framing, low pitch truss, high pitch truss, high wind zone vs. low wind zone and etc, the on site reality is often different when builders making their own mind.

So, without clarification of the above mentioned scope of timber treatment, we can not answer the question even enough samples are obtained.

How many samples are required and how big samples should be?
If you are lucky, you may get consent from the owner to take a timber sample. But where do you make your cut? bottom plate, top plate, wet area, internal framing? risky area, control point, foundation framing, flat roof framing? What about if a core sample is required to define the treatment in the middle of a piece of timber? How can you take a timber core sample without affect the actual framing integrity?

Who can give you the right answer?
So, if somehow you have got enough timber samples for framing in almost all areas, don't think that a pre-purchase inspector will give you a clear answer straight on site.
So far, base on current technology, the only reliable way to determine timber treatment of timber samples is to through lab testing.
Are you ready to pay for this laboratory test? Are you ready to interpret the complicated test result? Any idea how long you need to wait before the test result can be ready for you?

Why do you need to find out the timber treatment?
Will the result of the timber treatment answer your question: is the house a leaky house? If the timber is treated, will the house be safe? If the timber is treated, will that mean there are no rots? So, if timber treatment is not the answer for the above raised questions, why you are so particular about timber treatment at all?

Within our building industry, sometimes we do need to be precise in terms of timber treatment, for instance, we need detailed timber treatment information for leaky building remediation design work. In that situation, taking samples and making cut-outs through cladding are not a issue. But back to pre-purchase inspections, we can not see any point at all for timber treatment testing.