Fireproofing, water repellency and antisepsis of wood used in construction; regulations

Wood has a lot of qualities, but also weaknesses such as low resistance to fire, moisture, insects, fungi and mould. When we use it to make furniture and other objects, it is protected from the factory with different materials, and if it happens to be damaged by water, mould or insects, even if the damage is total, the consequences are not dramatic. But what happens when it is used to build wooden houses, when the planks, beams and posts are building materials on whose resistance to fire, water and insects the whole house and even the lives of those in it depend? In this case special treatments are needed to increase its strength.

Do we apply treatments only if we want or are there regulations and obligations?

Before we look at the treatments that apply to wood used in construction, let's first see if there are regulations and what they are. I don't think anyone believes that you can build anything, that anyone who wants to build a house can start tomorrow and use anything and everything to build it. Of course there are regulations, which are known to both builders and those who sell or produce building materials.

At European Community level there is the EN 1995, i.e. Eurocode 5: Design of timber structures, called E5 for short. It is a comprehensive and complex document that covers the properties of wood and wood-based materials used in construction, their durability, behaviour in extreme situations, joints with metal and other such information.

In addition to this European standard, there are national standards and regulations, because each country has its own specificities. These too must be respected, and if the EC requirements are more lenient, national ones take precedence, which take much better account of local hazards.

Moisture resistance regulations

In our country, in terms of moisture resistance, wood is divided into 5 risk classes:

• Class 1 - wood that does not come into contact with the weather or environmental moisture
• Class 2 - wood that may occasionally come into contact with an environment that creates a non-persistent moisture content
• Class 3 - wood outdoors, subject to frequent weathering and wetting, but not in contact with the ground
• Class 4 - wood outdoors, in contact with soil or fresh water, permanently exposed to moisture
• Class 5 - wood permanently exposed to salt water

If for wood in the first risk classes, resistance is solved with simpler treatments that can be applied on site after installation, the last classes require wood with superior properties, impregnated in autoclaves.

Regulations on resistance to biodegradation

Resistance to fungi and moulds is also regulated, with 4 degrees of biodegradation risk:

• Grade 1 - wood used indoors where moisture cannot cause xylophagous (wood-loving) fungi to grow and develop
• Grade 2 - wood used indoors in areas with minimal risk of xylophagous fungi (rafters, battens, interior walls)
• Grade 3 - wood used outdoors where there is a risk of wood-boring insects and humidity can reach 30% (outdoor stairs, balconies, railings, wood for exterior cladding)
• Grade 4 - wood permanently in contact with the ground or permanently exposed to the weather (posts, house soles, shingles)

I will explain in a moment about the insect-fungicidal substances with which the wood is treated to resist these degrees of risk.

Fire resistance regulations

The regulations in this area are very complex and it would take a long time to talk about each one. First of all it should be known that the fireproofing processes to which the wood is subjected do not make it immune to fire but much more resistant. Basically all these treatments should slow the spread of the fire and make it easier to extinguish the fire.

It is good to know that a house made with modern building materials such as glulam or CLT are highly fire resistant and are used in countries such as Finland, England and the Netherlands for the construction of multi-storey buildings. They are even better than steel for structural strength because steel, unlike glulam, loses its load-bearing capacity at temperatures above 700ºC.

The regulations are, as I said, very many. Decision 2000/367/EC lays down the performance classes of materials for fire performance. There are product standards that require a certain level of fire resistance. There are also regulations that say that if products meet the requirements of the standards, they do not need further testing (EC Delegated Regulation No 1291/2014).

In our country the regulations on fire protection are: Law no. 307/2006, Law no. 212/1997, OG no. 114/2000. Failure to comply with them can lead to very serious consequences. There are also regulations on the use of fireproofing materials and the testing of the fireproofed product:

• Technical standard C58-96 - on fireproofing of combustible materials
• SR 652-98 - verification of flame retardant effectiveness
• SR 7248-99 - method for determining flame propagation on the surface of materials
• SR ISO 4828 parts 1-6 - General conditions for paints
• Standard for quality control and acceptance of construction and related works C56-85

This may scare you, but these are regulations that must be followed for everyone's safety and should not be ignored. Now let's see what protective treatments are applied to wood used in construction.

Fireproofing

It is the process of treating wood with flame retardants to increase its fire resistance, slow the spread of fire and make the fire easier to extinguish. It should be noted that it is not a way of protecting wood from burning at all.

The substances used are generally sodium, calcium or potassium silicates. Treatment can be done before the wood is used in construction or after the construction has been completed. Pre-treatment is done in special factories, by impregnation in autoclaves, under vacuum or pressure. In this case the substance penetrates much deeper into the wood and makes it more resistant.

Before that, impregnation by immersion can also be done. It is more difficult because tubs have to be made in which the substance is placed and where the wood will be immersed. As the wood used in construction is large, this operation is not easy. The wood stays in this solution for several hours, during which time it must be turned over to soak in on all sides.

It is easier to treat the wood after construction by brushing or spraying. However, this type of wood is less resistant and the treatment must be repeated after 3 years. If the wood is not visible, it does not need to be treated. We only need to make sure that the materials covering it are fire-resistant or fireproof.

For fireproofing to be effective the wood must not have a moisture content higher than 15%. There are sources that say 18%, but The recommendation of 15% I found from companies that deal with fireproofing and are recognized by ISU. Fireproofing is not performed if the ambient temperature is below 10ºC and the humidity is above 70%.

Flame retardant substances are diverse. There are impregnating solutions, primers, varnishes, paints. Flame retardant finishes should be applied in min. 3 coats and the total amount of material left on the wood should be min. 450 g/m². If such a quantity is applied in 1 or 2 coats there is a high risk that the film will crack and the protection will be compromised.

There are, as I said, also wood derivatives with very high fire resistance, such as lamellar beams (glulam) and CLT panels. In this case, the glue used to glue the solid wood layers together plays a role in blocking the spread of fire. The fire acts on the outer layer and when it reaches the first layer of glue it is extinguished and the strength structure remains intact.

Moisture protection

I have written about moisture and water protection before. All the finishes used to coat wood protect it primarily from moisture. The natural state of wood is to absorb water because that was its way of feeding itself. Absorbing nutrient-laden water has ensured its growth and development. The channels through which water enters the wood remain after the wood is cut. Moisture exchange with the environment continues after the cut wood reaches equilibrium. Absorption is strongest at the ends of the fibre, i.e. through the cuts perpendicular to the trunk axis. Therefore, if effective protection is desired, those are the places where it must be insisted upon.

When we talk about wooden houses or wood as a building material then the main problem is rotting when in contact with the ground or areas with permanent moisture. The area is much more affected compared to wood immersed in water because oxidation (oxygen from the air) and UV radiation in the case of unprotected wood from outside come into contact.

Resistance to decay is different depending on the species. In general, hardwoods are more resistant, but there are also species of resinous wood that are very resistant and recommended for construction (larch, pine, molid). Very resistant is acacia wood, oak, frasin, nuc, tec.

Oil is a very good material for moisture protection. Unfortunately it is washed out in the weather and sometimes needs to be refinished even after only a year. Moisture resistant varnishes and paints are often more effective and more resistant over time, but they are not natural. Varnishes and paints are effective if the application technology and quantities recommended in the manufacturer's data sheet are followed.

Treatment against insects, fungi and mould, i.e. antisepsis of wood

Wood is a material loved by insects, fungi and moulds, especially if its humidity exceeds 18-20%. They feed on wood and over time end up grinding it. Especially if the wood is in less visible areas - attic, cellar, areas covered with parquet or thermal or sound insulation. This can dramatically affect the strength structure.

Insects can even come from "live" wood. They usually stay between the bark and the trunk, but can penetrate the wood to lay their eggs. To avoid starting work on wood that is already infested, wood used in construction is treated beforehand by heating to 60ºC or steam treatment. At these temperatures the insects, their eggs and larvae die.

Insecticide treatments are also very varied. Wood can be impregnated in autoclaves, substances can be sprayed or applied with a brush or trafalette or injected. Another method of eliminating insects (koi) is gassing or fumigation. However, this is a dangerous procedure that must be carried out by specialists. If you decide to apply such substances with a pump, you should be aware that you will need a mask and a special suit and that the substances are very aggressive.

The most used substances for insect fungicide treatment are copper sulphate (bluestone) and sodium borate (borax). Both are familiar to you. Bruise stone is used to make solutions to sprinkle on vines and fruit trees. In combination with lime milk it forms bordeaux juice, also used against pests of vines and fruit trees.

Borax is also used to make solutions with which sprains can be treated. Despite appearing harmless it is a very good insecticide and is also used by manufacturers of natural insulation (hemp, jute) against rodents.

In conclusion

Wood used in construction needs to be treated for strength. Even in a self-made house, building materials that have been subjected to impregnation, heating or steaming treatments should be used so that insects and their larvae are removed and strengths are greatly increased.

Don't try to save money by eliminating fire, moisture or insect resistance treatments. The consequences can be really significant. And never overdo the recommendations of firefighters or building officials. It's better to take extra measures than not enough. You know what they say - good guard over bad danger.

Good luck!