Here are a few definitions with extracts from the NF EN 335 and FD P 20-651 standards:
- Use class 1
A situation where the timber is indoors, completely protected from bad weather conditions and not exposed to humidity. Under these circumstances the wood generally has an average balanced humidity of around 6 to 12%. Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depend mostly on geographical location (1). Attacks from discolouring and wood-destroying fungi are minor and always accidental.
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- Use class 2
A situation where the wood is indoors or under a shelter, protected from bad weather conditions, with an occasionally higher surrounding humidity with the potential to cause non-persistent humidification (condensation). The wood dries very quickly. Under these circumstances the wood generally has an average balanced humidity of around 12 to 20 %. Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depends mostly on geographical location (1). In this use class, condensation may begin to form around the surface of timber and timber-based products. Attacks by discolouring and wood-destroying fungi may occur.
- Use class 3.1
A situation where the wood is placed outdoors in contact with the ground, and is subject to frequent humidity over short periods of time (several days). The wood becomes completely dry before a new humidity period begins. The wood is directly exposed to bad weather conditions and the building is designed to quickly evacuate water.
NOTE: certain draining designs that are partly protected from bad weather conditions, with occasional humidity from rain, are assigned use class 2.
Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depends mostly on geographical location (1).
Attacks by discolouring and wood-destroying fungi may occur.
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NOTE: the risk of the wood being affected by fungi depends on the weather conditions and the conditions of use (temperature, relative humidity, driving rain, structural conditions, design details and maintenance provisions).
- Use class 3.2
A situation where the wood is placed outdoors, not in contact with the ground, and is subject to very frequent humidity over long periods of time (several weeks). The wood becomes completely dry before a new humidity period begins. The wood is directly exposed to bad weather conditions and the building is not designed to quickly evacuate water. Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depend mostly on geographical location (1). Attacks by discolouring and wood-destroying fungi may occur.
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NOTE: the risk of the wood being affected by fungi depends on the weather conditions and the conditions of use (temperature, relative humidity, driving rain, structural conditions, design details and maintenance provisions).
- Use class 4
A situation where the wood is:
– either in contact with the ground or a surface subjected to recurring humidity (capillary rise, waterlogged surfaces…) ; – or in contact with, and partially immersed in, soft water (lake, river, pond) ; – or exposed to bad weather conditions or other forms of regular humidity, with a design conducive to significant water retention (e.g. horizontal upper surface, non-draining structure…) ; – or exposed to very significant induced humidity, either due to the overall unique design of the building (e.g. saturated air humidity causing condensation), or due to an accident (burst pipes).
Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depend mostly on geographical location (1).
Attacks by discolouring and wood-destroying fungi may occur.
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NOTE: timber and timber-based products permanently submerged and saturated in water are not susceptible to fungi attacks, but they are vulnerable to attacks from bacteria.
- Use class 5
A situation where the wood is submerged or partially submerged in salted water (marine environment and natural brackish water).
The main problem is attacks by small marine invertebrates, particularly in hot water, where organisms such as Limnoria spp., Teredo spp. and pholadidae can cause significant damage.
Attacks by wood-destroying fungi, and the development of surface mould and blue stain fungi are also possible.
Sections of certain parts of a structure situated above the water – wood stakes used in ports, for example – may be exposed to wood-eating insects.
GENERAL NOTE: in certain cases, parts of wooden structures may be affected by specific humidity conditions despite being sheltered from direct bad weather. This could require the wood to be reassigned from use class 3.1 to use class 4.
(1) If the national standards do not specify the risk of attacks from insects, it is worth consulting local or national experts for advice on the insect attack risks.
Catégorie : Looking to use pine wood outdoors ?
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