Protect the wood from parasites means above all protecting it from humidity. Well seasoned wood used and stored in dry environments is almost never attacked by insects, fungi or even parasites, except in cases of really serious infestation. If the humidity is under control, the wood does not require special protective treatments. But what is the attention threshold?
Let's start by saying that for protect the wood you first need to know which wood you are talking about. Insects prefer woods that have an internal humidity higher than 10% while mushrooms need a higher humidity, higher than 20 percent. Now: since the humidity of the wood depends on the relative humidity of the air and that in (healthy) living environments the latter is generally quite low, the risk of infestation is limited.
The above means that in a living environment where there is a correct thermohygrometric balance it is not necessary protect the wood from parasites. Surely there is no need for aggressive treatments with chemicals that would have the only result of polluting the air of the house to the detriment of the occupants' health.
A set of rules for protect the wood from parasites without treatments could be the following: use only seasoned and planed woods; make sure that the humidity of the wood corresponds to that of the rooms; protect the wood from rain, condensation, capillary humidity, infiltrations from the roof; ensure sufficient ventilation; use anti-intrusion nets to prevent insects from entering the eaves or ridge of the roof; mount mosquito nets on the windows.
You can avoid having to protect the wood from parasites also by learning about wood. Infestations are more frequent in sapwood and much less in heartwood, so it is advisable to use only heartwood for all the elements most at risk, such as roof beams and windows. Obviously also the resistance of the heartwood varies according to the essences.
In the case of fungal infestations, the woods that the DIN 68364 standard considers very resistant (class 1) are: teak, robinia, doussiè. Resistant (class 2): mahogany, oak, red cedar. Mediocre (class 3): douglas, larch, meranti. Not very resistant (class 4): spruce, silver fir, pine. Not resistant (class 5): maple, birch, beech, ash.