{"id":842,"date":"2026-02-03T15:50:10","date_gmt":"2026-02-03T14:50:10","guid":{"rendered":"https:\/\/www.ntr-nwpc.com\/?page_id=842"},"modified":"2026-02-09T13:20:15","modified_gmt":"2026-02-09T12:20:15","slug":"ntr-wood-protection-classes","status":"publish","type":"page","link":"https:\/\/www.nwpc.eu\/index.php\/finding-the-right-timber\/ntr-wood-protection-classes\/","title":{"rendered":"NTR Wood Protection classes"},"content":{"rendered":"\n

Find the right NTR wood protection class<\/h2>\n\n\n\n

NTR classes are related to the EN 335 use classes. Start by choosing the exposure (use class)<\/strong>, then select the relevant NTR class<\/strong> for the product type (sawn\/round timber, glulam, modified wood, spruce cladding products).<\/p>\n\n\n\n

\u201cNTR wood protection classes are defined to ensure that wood and wood products meet the required performance in their intended service conditions (use classes).\u201d<\/p>\n\n\n\n

<\/p>\n\n\n\n

\n

Use class 1 and 2:
interior \/ under cover <\/h2>\n\n\n\n

Use class definitions (EN 335 service conditions)<\/h3>\n\n\n\n
\n

Use class 1: Interior timbers in dry conditions.<\/p>\n\n\n\n

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.<\/p>\n<\/blockquote>\n\n\n\n

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.<\/p>\n<\/div>\n\n\n\n

\n

Use class 3:
above ground exposed to weather or frequent wetting<\/h2>\n\n\n\n
\n

Use class definition (EN 335 service conditions)<\/h3>\n\n\n\n

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: <\/p>\n\n\n\n

3.1 limited wetting conditions, <\/p>\n\n\n\n

3.2 prolonged wetting conditions<\/p>\n<\/blockquote>\n\n\n\n

\n

Use class 3.1:
limited wetting conditions (external \u2013 protected)<\/h2>\n\n\n\n
Corresponding NTR class<\/th>Description<\/th>Example use (typical products)<\/th>Penetration<\/th><\/tr><\/thead>
\"\"
NTR B<\/td>		Above ground for finished exterior joinery, typically used where the component is protected and then coated\/finished.<\/td>Windows and external doors (finished exterior joinery)<\/td>\"\"
NP3<\/td><\/tr>
\"\"
NTR B GL<\/td>		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.<\/td>Trusses, columns, beams, construction elements<\/td>\"\"
NP3<\/td><\/tr>
\"\"
NTR B mod<\/td>		Modified wood classified for use class 3 (above ground) applications, typically where the product is used as finished exterior joinery<\/td>Windows and external doors
Finished exterior joinery
General UC3.2 applications or according to approval<\/td>		\"\"
NP3<\/td><\/tr>
\"\"
NTR GRAN<\/td>		Spruce products for above ground, partly protected exposure, restricted to specific products only.<\/td>Exterior cladding boards, bargeboards\/fascia boards, counter battens\/battens, nail battens<\/td>\"\"
NP1<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/div>\n\n\n\n
\n

Use class 3.2:
prolonged wetting conditions (external \u2013 unprotected)<\/h2>\n\n\n\n
Corresponding NTR class<\/th>Description<\/th>Example use (typical products)<\/th>Penetration<\/th><\/tr><\/thead>
\"\"
NTR AB<\/td>		For pine\/permeable softwoods above ground where structures are unprotected against precipitation and moisture, to ensure long service life.<\/td>Fences and screens; trellis\/pergolas; exterior cladding boards; bargeboards\/fascia boards; roof battens; decking above ground<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR AB GL<\/strong><\/td>		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.<\/td>		Trusses, columns, beams, construction elements<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR AB GL2<\/td>		Same as AB GL but treated with dual treatment. First treatment of lamells and second treatment of planed glulam.<\/td>Trusses, columns, beams, construction elements<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR AB mod<\/strong><\/td>		Modified wood class intended for Use Class 3.2-type exposure.<\/td>General UC3.2 applications or according to approval<\/td>\"\"
NP5<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/div>\n<\/div>\n\n\n\n
\n

Use class 4:
ground contact, fresh water, or high moisture load<\/h2>\n\n\n\n
\n

Use class definition (EN 335 service conditions)<\/h3>\n\n\n\n

\u201cWood 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.\u201d<\/p>\n\n\n\n

Note: The wood preservative must have BPR approval for installation in or above water.<\/p>\n<\/blockquote>\n\n\n\n

Corresponding NTR class<\/th>Description<\/th>Example use (typical products)<\/th>Penetration<\/th><\/tr><\/thead>
\"\"
NTR A<\/td>		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.<\/td>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<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR A pole<\/td>		Dedicated class for poles and includes non destructive quality testing<\/td>Transmission, utility poles, round wood<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR A GL<\/td>		For glulam products exposed to high moisture load \/ soil contact, or demanding above-ground structures where integrity is critical.<\/td>High performance trusses, columns, beams, construction elements, fence posts, bridges<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR A GL2<\/td>		Same as A GL but treated with dual treatment. First treatment of lamells and second treatment of planed glulam.<\/td>High performance trusses, columns, beams, construction elements, fence posts, bridges<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR A mod<\/td>		Modified wood class intended for Use Class 4-type exposure.<\/td>General UC4 applications or according to approval<\/td>\"\"
NP5<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Information for jetties and waterside structures<\/h3>\n\n\n\n

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.<\/p>\n<\/div>\n\n\n\n

\n

Use class 5: sea water and extreme conditions <\/h2>\n\n\n\n
\n

Use class definition (EN 335 service conditions)<\/h3>\n\n\n\n

\u201cWood constructions in sea water and constructions subject to extreme conditions or where there are special durability and strength requirements.\u201d<\/p>\n<\/blockquote>\n\n\n\n

Corresponding NTR class<\/th>Description<\/th>Example use (typical products)<\/th>Penetration<\/th><\/tr><\/thead>
\"\"
NTR M<\/td>		Class intended for sea water<\/strong> exposure (marine structures and extreme conditions).<\/td>Marine structures<\/td>\"\"
NP5<\/td><\/tr>
\"\"
NTR M mod<\/td>		Modified wood class intended for Use Class 5-type exposure.<\/td>General UC5 applications or according to approval<\/td>\"\"
NP5<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/div>\n\n\n\n

<\/p>\n\n\n\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Find the right NTR wood protection class NTR classes are related to the EN 335 use classes. Start by choosing the exposure (use class), then select the relevant NTR class for the product type (sawn\/round timber, glulam, modified wood, spruce cladding products). \u201cNTR wood protection classes are defined to ensure that wood and wood products […]<\/p>\n","protected":false},"author":2,"featured_media":12355,"parent":1615,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_et_pb_use_builder":"off","_et_pb_old_content":"

Complete table of all NTR-wood protection class and related use class and product data<\/p>

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