Water pooling on horizontal wooden surface, halves its life expectancy.
The screw heads often rip into the wooden fibers at the surface and cause small puddles of water. These boards will rot twice as fast. Ideally it is best to screw from underneath.
Whereas a deck built with alpine Spruce that was harvested at the right time and installed constructively, lasts for 30 years or longer. The same decking made with sapwood free oak is more expensive but will last 50 years or longer!
Here are some examples:
A wooden deck outdoors built with fast grown Spruce and Pine (harvested in spring or summer) and with water pooling on it, can easily break down after just three years.
Some woods like Douglas fir and Larch, disintegrate much slower than other species such as Spruce and Pine. Additionally to carefully selecting weatherproof and long lasting woods, we can use particular building techniques which further delay the decaying process.
It is an illusion to think it could last forever when exposed to wind and weather on a daily basis. Nevertheless, there are natural ways we can use to make wood last considerably longer.
The oldest preserved dwellings are solely built with stone and untreated wood and have survived for millenia.
Timber constructions outdoors
Nature intended wood to weather and finally break down into mulch to close the natural cycle.
Infested roof trusses and wooden houses can be treated with hot air by specialized companies for the same effect. A re-infestation in older wood is practically impossible.
If we choose appropriately, harvest at the right time, season wood properly and use constructive building methods, chemical treatments become redundant.
If you heat up the infested parts (right into the core of the wood) for more than three hours and above 55'C, all insect life dies! Smaller pieces like furniture can be put into the sauna or a kiln for treatment.
Risk of infestation by Longhorn Beetles in context to the age of the wood:
The table shows that the older the Timber/Wood, the less likely it will be attacked by the Longhorn Beetle.
Should the Longhorn Beetle have established itself, there is still no need to panic!
Nutrients are attractive to insects and when wood is aging, protein and carbohydrates are broken down, leaving 30-50 year old buildings immune to infestation. It is important therefore to allow wood to season slowly and naturally before working with it.
It is best to use wood which has been harvested at the right time. Treat all wooden components before installing them with a boric salt preparation. Boric salt is a naturally occurring substance and is classed as harmless in the ecological building industry.
It only attacks conifers and not hardwood and needs small cracks and tears to deposit its eggs. Dressed beams make it very hard for it to breed. It is very territorial and in towns where it is unknown, it is unlikely to just appear. Speak to local carpenters and wood workers to find out if there are any known infestations in your area.
The Longhorn Beetle is the most significant of all the damaging insects. If we use reasonable caution and constructive measures when building with wood, it does not pose a real danger to our buildings.
In case treatment is necessary, heat treatment is very successful (look at the House Longhorn Beetle).
House Longhorn Beetle
It mostly spreads when damp or infected wood has been used. By thoroughly drying and aerating stored wood and only using wood free of infestations, you can reduce the danger of the House Borer or Knock Beetle to just about zero.
Common House Borer and Knock Beetle
These beetles are able to survive in wood with moisture content as low as 12%, their optimum however lies around 30%. In heated rooms with a wood moisture around 6% to 12%, it simply cannot exist.
You can treat a contaminated piece of furniture effectively by putting it outside on a frosty night and all beetles and eggs will be destroyed. Therefore, this exotic creature does not really pose any threat to buildings and furniture made of spruce, pine, fir, or larch.
It doesn't like conifers at all and only the light colored types of leafy trees (like maple) or the periphery of some trunks are edible. In the northern hemisphere, this tropical migrant can't fly from one home to the next; therefore, new infestation is hardly possible.
The Common Powderpost Beetle is not native to Europe; most likely it was introduced with imported wood from the tropics. Even though it is able to infest dry wood in our cold climate, it doesn't feel at ease here. It doesn't enjoy the European species of trees.
At first this appears as a danger to anything made with wood. But only at first glance! Let us have a closer look at why constructive building methods have defied this trio for hundreds of years:
Common Powderpost Beetle
Natural wood protection against insects
Here the situation is similar, a dry and protected build doesn't offer any chances of survival to most insects. There are only three specialists for dry wood:
Only those three species are able to live in dry conditions.
Realistically, in all the years of our professional building work, we never came across any dry rot in wood which has been dried, stored and worked with properly.
Living conditions for the most common and destructive wood insects:
(Table: Bernhard Leisse: Treating wood naturally, Heidelberg 1994)
When restoring the building, all infested wooden components should be generously removed and any existing strands of fungi should be eliminated from the masonry, brick and stone work with a blowtorch.
How to prevent dry rot? If the house has been built in a constructive and proper way, it usually is enough to make sure there are no rotting piles of wood, old building parts or off cuts which provide feeding and breeding ground anywhere close to the building.
The true dry rot needs damp wood (more than 20%) to grow, however, once established it can grow several meters long in up to one centimeter thick strands. These strands transport water to neighbouring, dry areas and dampen these for the infestation to spread.