Fire-resistance and maintenance:
durability, impregnability and types of use.

1

Fire-resistance

“Wood burns, but only on the surface, and it can do so slowly and preserving some properties that make it ideal for construction purposes in the event of fire” (from Fire performance of wood and by-products – Luis Miguel Elvira, Doctorate in Forestry from the INIA wood and cork department).

Difference between structure and material

A building structure hardly contributes to the development of a fire at all, although it is usually affected by it. The building’s accessory materials (decorative features, claddings, etc.) are usually what contribute to the spreading of fires..

Fire performance.

Timber in structures performs well in the event of a fire, and it can also be improved by using the right products, treatments and construction solution. Wood can be made fire-resistant for longer through:

• Increased cross section of structural elements.
• Low thermal conductivity and superficial carbonisation which prevents the outside temperature from reaching the inside of the structural elements quickly.
• Insignificant thermal dilation.
• Non-toxic combustion gases.

Moreover, the ever-evolving timber conversion technology allows its features and properties to be optimised. Holtza, S.A. produces glued laminated timber structural elements in accordance with the requirements established by OTTO-GRAF INSTITUT, F.M.P.A. Bandenwürttemberg, Pfaffenwaldring-4. 7000 STUTTGART 80, Germany. This Institute certifies that our production processes comply with Standard DIN 1052.

The following Standard is applied to the engineering, manufacturing and installation of laminated timber structures as regards fire resistance: DIN 4102 Fire performance of construction materials.

The following Basic Building Standards are used to calculate structures: Fire Safety Basic Document (DB-SI)..

2

Maintenance.

Wood is one of the longest-lasting materials in the right conditions (even in adverse conditions for other materials), especially with the ideal level of humidity and ventilation.

Preventive wood protection includes: types of use, construction methods, treatment, choice of protection type and protective treatment quality control. Wood protection is ensured by the designer, responsible for choosing the type of wood to be used, the type of use and the construction details, and the company responsible for adding the protection in accordance with requirements and selecting the most appropriate treatment.

Hence the importance of structure design (construction protection to prevent changes in wood humidity content and direct exposure to sun and rain) and material quality (choice of material and chemical protection in accordance with the type of use). Construction protection is another alternative to chemical protection and allows the use of chemical products on a natural product like wood to be reduced or avoided altogether.

The aim is to prevent (with the right choice of wood type, treatment, such as fungicides, insecticides, water repellents, etc., the construction solution and handling until the works are completed) rather than cure. There are however a number of recommended maintenance procedures broken down into Types of Use.

Durability and impregnability.

These are wood protection properties IMPREGNABILITY refers to the wood’s ability to absorb a product and how deep it penetrates into the wood. DURABILITY refers to the wood’s ability to withstand an attack from xylophagous insects without having undergone any chemical treatment. The structural elements must be protected in accordance with their risk type. Wood that provides enough natural durability for the type of use can be used an alternative to applying a protective treatment.

Types of use.

• TYPE OF USE 1
  Situation whereby wood is under a roof, completely protected from the elements and not in contact with the ground, and not exposed to humidity or direct sunlight. Wood reaches an equilibrium moisture content of less than 20%. There is no risk of fungal decay and the possibility of insect attack is insignificant.
  
  Chemical protection: Non required
  Construction protection: The roof must be sealed properly.
  Maintenance: The roof must be sealed properly. Under normal conditions no maintenance is necessary.
  
  
• TYPE OF USE 2
  Situation whereby the wood is under a roof, not in contact with the ground and protected from the elements, but with the possibility of occasional damp. In this case, moisture content occasionally exceeds 20%.
  There is the risk of attack from chromogenic fungi. The risk of insect attack is similar to Type of Use 1.
  
  Chemical protection: Surface protection is necessary, applied by brush, spray or brief immersion.
  Construction protection: The structure’s sides and top, which are occasionally affected by rain or direct sun exposure, will be protected using copper or zinc sheets or other materials, as described in the “protection details” section. The roof must be sealed properly.
  Maintenance: Once the construction measures have been applied, a fungicide and insecticide top-up should be applied every 10 years. The roof must be sealed properly.
  
  
• TYPE OF USE 3
  Situation whereby wood is exposed to the elements but not in contact with the ground. The wood is constantly exposed to the elements. Dampness caused by rain is frequent. This type of use is subcategorised into Type of Use 3.1. and Type of Use 3.2.

  TYPE OF USE 3.1:

  The wood is on the outside, above ground level, but protected with a design or construction solution that prevents excessive direct exposure to the elements. There is a significant risk of attack from chromogenic or xylophagous fungi.
  
  Chemical protection: Medium protection (at least 3mm on the alburnum on each side of the element) is required, using pressure treatment or prolonged immersion (for elements with a small cross section).
  Construction protection: Depending on the wood element and its location, the construction detail with the right protection will be designed.
  Maintenance: Due to the structure’s complete exposure to sun and rain, topping up the chemical protection is recommended by brushing on a decorative protection layer. This should be applied every 3 years if the wood faces South and every 5 if it faces North.

  TYPE OF USE 3.2:

  The wood is exposed to the elements, above the ground and with no construction protection. There is a significant risk of attack from chromogenic or xylophagous fungi.
  Protección química: Es necesaria una protección media (al menos 6mm en la albura de todas las caras de la pieza), mediante el tratamiento en autoclave o inmersión prolongada (para piezas de secciones pequeñas).
  Chemical protection: Medium protection (at least 6mm on the alburnum on each side of the element) is required, using pressure treatment or prolonged immersion (for elements with a small cross section).
  Construction protection: A design and construction solution that prevents water from stagnating or accumulating in the element is recommended.
  Maintenance: Due to the structure’s complete exposure to sun and rain, topping up the chemical protection is recommended by brushing on a decorative protection layer. This should be applied every 3 years if the wood faces South and every 5 years if it faces North.
  
  
• TYPE OF USE 4
  The structural element is in contact with freshwater on the ground and is therefore constantly exposed to a moisture content of more than 20%.
  
  Chemical protection: Deep protection is required. For circular wood elements, it must penetrate at least 25mm on each side. For rectangular elements, it must completely penetrate the alburnum.
  Maintenance: No maintenance is necessary, although visual inspections to confirm that the structure is aging properly are recommended.
  
  
• TYPE OF USE 5
  Situation whereby the structure element is constantly in contact with salt water. In this case, the wood’s moisture content is always more than 20%.
  
  Chemical protection: Total protection is necessary in the alburnum and at least 6mm in the exposed duramen.
  Maintenance: No maintenance is necessary, although visual inspections to confirm that the structure is aging properly are recommended.
  
  

There is also a classification in accordance with TYPES OF SERVICE. There are three types of service that match the types of use. Type of service 3 would include types of use 3, 4, and 5. TYPES OF USE refer mostly to installation while TYPES OF SERVICE refer to resistance values and the calculation of deformation under specific environmental conditions.