Timber is treated according to the hazards to which it will be exposed
Before we launch into treated timber, I would like you to be aware that there are naturally durable timbers available which do not require toxic timber treatment.
A word of advice: I believe that treating non durable timber is essential, you are protecting your investment, it is a fact, borers eat some types of timber, however, we can successfully treat using Borates, which do not present a health hazard to us. We treat timber to give it a longer lifespan. There are effective and non-toxic ways to protect your log home, and give it more value, all of which is covered in detail on the course.
Some timber needs protection from wood boring beetles and rot. This depends on the circumstances, where and how the timber is used, species, location, climate, etc.
My favorite Eucalyptus timber heartwood is naturally beetle resistant, therefore, none of the sawn board timber (floor boards, etc.) in my home requires treatment.
We call this 'hazard class'. Click here for a hazard class chart
Let me very briefly explain:
If the timber is to be used indoors, not in ground contact, it is considered as a low hazard and and would fall into hazard class 1, or H1.
If it is outdoors, in ground contact (fence poles, etc), this is a higher hazard, the treatment is more 'heavy duty' is referred to as hazard class 4, or H4.
The most hectic environment for timber is the ocean, the marine borers are very active, this is considered the highest hazard class - H6.
It is not necessary to treat your log home to H6 - unless of course you are building Noah's ark.
Some timber does not require any treatment, this is discussed in class.
Personally, I do not believe in exposing myself or my family to any potentially harmful chemicals. I prefer to take a precautionary approach and I urge you to do the same.
In South Africa, construction timber must be treated according SANS 10005 'The preservative treatment of timber'.
The copper which is impregnated into the timber with several of the preservative treatments has a galvanic reaction with galvanized metal fasteners, (screws, nails, brackets, etc), this causes them to corrode rapidly. If your house is built out CCA or ACQ treated timber, you may have a problem in the future when your house falls apart due to failure of the fasteners.
How long will it last? A galvanic reaction occurs between the copper in CCA treated timber and the zinc plating on the screw (you have created an approximately 0.8 volt battery). When this occurs, the copper in the timber always wins and the fastener always loses.
Get the full tech here.
Moisture is required and acts as an electrolyte. (readily available on an exposed deck each time it rains) CCA treatment is being phased out in many places and is often replaced by ACQ, it is less toxic but has a severe corrosion problem.