NTR Wood Protection classes

Use class 1 and 2:
interior / under cover

Use class definitions (EN 335 service conditions)

Use class 1: Interior timbers in dry conditions.

Use class 2: Wood above ground and under cover and fully protected from the weather but where high environmental humidity can lead to occasional but not persistent wetting.

For a load bearing structures where personal safety, long service life, or difficult inspection/replacement requires integrity it can be required to use a higher NTR Class together with CE-marked construction timber.

Use class 3:
above ground exposed to weather or frequent wetting

Use class definition (EN 335 service conditions)

Use class 3: Wood above ground and either continually exposed to the weather or subject to frequent wetting; where there is relatively easy to replace damaged components and where the consequences of failure will be moderate.
When sub-divided:

3.1 limited wetting conditions,

3.2 prolonged wetting conditions

Use class 3.1:
limited wetting conditions (external – protected)

Corresponding NTR class	Description	Example use (typical products)	Penetration
NTR B	Above ground for finished exterior joinery, typically used where the component is protected and then coated/finished.	Windows and external doors (finished exterior joinery)	NP3
NTR B GL	Glulam of Pine and other permeable wood species for above-ground use with limited wetting conditions that are protected against precipitation, to ensure long service life.	Trusses, columns, beams, construction elements	NP3
NTR B mod	Modified wood classified for use class 3 (above ground) applications, typically where the product is used as finished exterior joinery	Windows and external doors Finished exterior joinery General UC3.2 applications or according to approval	NP3
NTR GRAN	Spruce products for above ground, partly protected exposure, restricted to specific products only.	Exterior cladding boards, bargeboards/fascia boards, counter battens/battens, nail battens	NP1

Use class 3.2:
prolonged wetting conditions (external – unprotected)

Corresponding NTR class	Description	Example use (typical products)	Penetration
NTR AB	For pine/permeable softwoods above ground where structures are unprotected against precipitation and moisture, to ensure long service life.	Fences and screens; trellis/pergolas; exterior cladding boards; bargeboards/fascia boards; roof battens; decking above ground	NP5
NTR AB GL	Glulam class for Use Class 3.2. Intended for above ground use that is unprotected against precipitation and moisture, to ensure long service life. Requires documented water/wet performance of glue coating or cover.	Trusses, columns, beams, construction elements	NP5
NTR AB GL2	Same as AB GL but treated with dual treatment. First treatment of lamells and second treatment of planed glulam.	Trusses, columns, beams, construction elements	NP5
NTR AB mod	Modified wood class intended for Use Class 3.2-type exposure.	General UC3.2 applications or according to approval	NP5

Use class 4:
ground contact, fresh water, or high moisture load

Use class definition (EN 335 service conditions)

“Wood in contact with the ground or fresh water or severely exposed to the weather; or if a wood component is inaccessible or where the consequences of failure will be particularly serious.”

Note: The wood preservative must have BPR approval for installation in or above water.

Corresponding NTR class	Description	Example use (typical products)	Penetration
NTR A	For pine/permeable softwoods with very good resistance in contact with soil or exposed to high moisture load, and for above-ground structures where personal safety, long service life, or difficult inspection/replacement requires integrity.	Posts; fencing posts; bridges; garden timber; external stairs; balconies; decking directly on ground; jetties/boardwalks above water; sills; joist structure under decking; playground/outdoor fitness equipment	NP5
NTR A pole	Dedicated class for poles and includes non destructive quality testing	Transmission, utility poles, round wood	NP5
NTR A GL	For glulam products exposed to high moisture load / soil contact, or demanding above-ground structures where integrity is critical.	High performance trusses, columns, beams, construction elements, fence posts, bridges	NP5
NTR A GL2	Same as A GL but treated with dual treatment. First treatment of lamells and second treatment of planed glulam.	High performance trusses, columns, beams, construction elements, fence posts, bridges	NP5
NTR A mod	Modified wood class intended for Use Class 4-type exposure.	General UC4 applications or according to approval	NP5

Information for jetties and waterside structures

Authorities in Europe have decided that wood treated with copper-based wood preservatives must not be used under water; occasional wetting from waves and splash is acceptable. All treated wood products must be used following approved use. Most preservative-treated wood can be used as usual for jetties/boardwalks above water.

Use class 5: sea water and extreme conditions

Use class definition (EN 335 service conditions)

“Wood constructions in sea water and constructions subject to extreme conditions or where there are special durability and strength requirements.”

Corresponding NTR class	Description	Example use (typical products)	Penetration
NTR M	Class intended for sea water exposure (marine structures and extreme conditions).	Marine structures	NP5
NTR M mod	Modified wood class intended for Use Class 5-type exposure.	General UC5 applications or according to approval	NP5