To better protect wood against rain, wind and the sun, usually it is impregnated. There are different wood treatment methods.
The traditional method is to dip the wood in a solution of water and copper-chrome-arsene. The wood will color green and gold, and it is bad for your health. This method is not eco-friendly and nowadays in most countries it is not an accepted method to treat building materials.
We usually use Tanalith-E or Boramon C-30. Tanalith is a European approved conservation chemical that is based on copper. Tanalith-E is pressed into the wood in the pressure-vacuum chamber. This treatment is effective, but expensive, actually very expensive.
Therefore we usually use Boramon C-30. This is also European approved, and based on boric acid. It is almost as effective as Tanalith-E but a lot easier to apply: just paint, spray or dip. We usually spray. Here is a wikipedia-link.
It is not always necessary to treat the entire house with Boramon C-30, usually the lower logs are the ones that are important. Sometimes treatment of the lower logs is enough, or we replace the lower log with a larch log.