A wide enough roof overhang prevents direct contact with rain and is more effective than treatments. Old, wooden buildings always have a wide roof overhang to protect external walls and cladding.
1. Protect the building materials and construction from rain and moisture. Avoid lengthy exposure to the weather and finish the roof quickly.
(Use well-seasoned Timber / Wood)
It would be worth writing a whole book specifically about proper construction methods. Here are some worthwhile recommendations which should be followed by you, the architect, biological building officer and trades people.
The conclusion is, no fungus can grow under 20% moisture content. If we dry wood properly, there is no need to use chemicals to protect it from fungi and insects.
The two things which we need to adhere to are:
Furthermore, it is very rare that even wood with 20-25% wood moisture content is infested by destructive fungi.
(The proper storage and drying of wood is an important step to prevent it from rot and decay.)
Indoors, wood in a heated room ends up containing around 6-10% moisture. Basically any wood in the building industry (apart from balconies and terraces) which is protected by a roof is just not moist enough for fungi to exist and grow.
When further processed, no matter whether it turns into a piece of furniture, floor, walls or roof, the wood dries out even more.
The moisture content of external wall cladding is around 12-18% (depending on the atmospheric conditions).
When boards, squared timber or slabs are being stacked, covered and stored outside for air drying, the wood ends up with a moisture content of approximately 12-20% (depending on the climatic conditions).
Like all living organisms, fungi too look for the best possible conditions and prefer to take the way of least resistance. These optimum living conditions however are not around 20% but rather around 30% moisture content.
Natural wood preservation to prevent fungi
In this table, you can see the ideal moisture content which fungi need to grow to decompose wood.
(Table: Bernhard Leisse: Treating Timber Naturally, Heidelberg 1994)
The key to those specialized fungi and insects lies in the moisture content of the wood. Building constructively allows us to use naturally dried wood in specific ways so even beetles and fungi will not cause any harm.
Insects are of no real threat to good quality wood either. Only very few are able and interested in feeding on dried wood. If we manage to handle this small group of insects naturally, we don't need to treat wood.
When exactly is wood breaking down? 99% of the breakdown occurs in the forest, under the open sky and exposure to the weather. Our houses all have a protective roof which means that when we cover our build with a roof, the wood stays dry, unlike in a forest.
Understanding natural organisms would help us find simple ways to keep them from breaking down our buildings and furniture. If we use common sense, we don't need to poison our surroundings.
The next generation of trees is metabolizing the energy of the old trees and keeps the cycle going.
Is it wise to replace natural organisms with chemicals and fight them with poisonous sprays? Or is it more productive to investigate and study the life of fungi and insects?
When a tree dies, falls and begins to decay, insects, fungi and micro-organisms are there to help break down the bark, wood, leaves and needles to return it to the soil where it came from. A healthy forest recycles and reuses everything by turning it into fertile mulch.
The homeowner could have saved a lot of money had he used natural wood preservation methods along with good quality wood.
What actually do we need to protect our wood from?
In addition, this brief went on to prescribe the demolition and the expensive disposal of the toxic waste. The newly erected balconies were made of alpine larch which has been harvested at the right season and moon phase.
The main reason is the disregard of constructive measures to protect the wood. It also suggests that chemical wood preservatives do not effectively protect external wood, however, it does turn wood into toxic waste."
Here is an excerpt from a tender brief from an engineer's office:
"The existing wooden balconies have, despite consistent maintenance and treatment with commercial chemical wood preservatives, fully rotted away.
Natural Wood Protection
Working only with natural wood protection has several advantages. Natural wood will provide a healthy and long-lasting usage of buildings and also eliminates expensive and complicated products.
Before you embark on this, you need to discuss with a professional as working with green wood requires particular skills.
If in doubt, the best solution is to dry building wood naturally to about 20% moisture content before building with it.
When properly used, building wood sometimes can finish its drying process after installation. For example, if it is guaranteed that the beams are aerated from all sides and the build is being protected from rain and snow, beams for a timber ceiling can be used a few months after they have been cut in the saw mill.
Recommended times for storage and air drying of wood
Building wood, depending on what it is being used for: 1-5 years
Floors, cladding from coniferous wood: 1-2 years
Floors from leaf trees like oak needs longer storage and drying time: 2-4 years
Furniture Wood: 1 year per 1 cm wood thickness
My tip for building wood is the waning moon, close to new moon in Capricorn which falls in the middle of winter, usually around Christmas and New Year.