Topical Subjects

In this section we provide guidance for specifiers and users of wood and wood products on topical subjects.

Strength graded timber

Specifiers should be aware that all timber to be used for structural purposes in the UK must be strength graded and marked in accordance with the relevant British/European Standards. A descriptive leaflet on the subject produced by BM TRADA Certification can be can be downloaded from here. Strength Graded Timber.pdf

Timber Trade Federation Conduct Assurance Scheme

This Code of Conduct Scheme, which is supported by all STTA Member Companies, aims to ensure that products supplied by STTA Member Companies comply with customer requirements and are fit for purpose, thereby demonstrating a professional and responsible approach to business. A descriptive leaflet and the Code of Conduct document in full can be downloaded from here. Code of Conduct.pdf View descriptive leaflet

Specifying Timber

Some background information for specifiers....

Timber is a versatile and unique material and has unparalleled environmental credentials, after all, it is the only truly renewable construction material. The timber industry in the United Kingdom has made significant progress in sourcing its materials from legal and sustainable sources. Chain of custody certification is now well established in the industry, which provides specifiers and users with the assurance that wood and wood products have been obtained from legal and sustainable sources where forest management is carried out in accordance with internationally recognised standards.

Members of STTA undertake responsible purchasing and are supporters of the objectives of  Forests Forever, the timber industry’s campaign to safeguard the forests of the World and our future timber supplies, by promoting 'sustainable forest management’.

The main species of timber and their end uses....

Some things to think about....

Timber has an excellent and highly predictable performance in fire, as the charring rate depends on density and enables fire performance to be closely calculated. Unlike some other common construction materials it will not flake or spall in fire nor will it soften or melt. Timber is also highly resistant to corrosion - more effectively so than many metals - hence it is used in marine applications and in areas exposed to corrosive chemicals. Timber also offers excellent cradle to grave energy consumption as the manufacture and processing of timber components requires very low energy inputs.

For example, to produce 1 tonne of building material it takes:

435Kw hours for timber

3,780Kw hours for steel

20,169Kw hours for aluminium.

Elements to include when specifying timber....

Description/end use

Species

Dimensions - nominal or actual

Finish - e.g.: sawn; dressed; moulded; sanded; or primed.

Quantity

EN ISO/BS references

Delivery date

Delivery address

Packaging (where required)

Labelling (where required)

Seeking to ensure environmental status....

We suggest the following statement as an addition to your Bill of Quantities preamble:

"The contractor shall obtain all of the timber products for the works from a timber or wood supplier which has adopted the Environmental Policy agreed by Forests Forever or shall supply evidence in compliance with an alternative and comparable policy."

You should also require that the contractor provides evidence that:

The supplier is committed to an environmental policy

The policy is being implemented

All timber being supplied is derived from legal and sustainable sources managed in accordance with the laws governing forest management in the producer country or countries.

Some appropriate Standards to use when specifying timber and wood based sheet materials....

Structural timber

• BS 5268: The structural use of timber.
• Part 2: Code of practice for permissible stress design, materials and workmanship.
• Part 3: Code of practice for trussed rafter roofs.
• Part 4: Fire resistance of timber structures.
• Part 5: Code of practice for the preservative treatment of structural timber.
• Part 6: Code of practice for timber frame walls.
• Part 7: Recommendations for the calculation basis of span tables.
• BS EN 1995 Eurocode 5. Design of timber structures.
• BS EN 14080 Timber structures. Glued laminated timber. Requirements.
• BS EN 14081-1 Timber structures. Strength graded timber with rectangular cross section. General requirements.
• BS 4978 Visual strength grading of softwood.
• BS EN 519 Structural timber - Grading - Requirements for machine strength graded timber and grading machines.
• BS 5756 Specification for visual strength grading of hardwood.
• BS EN 385 Finger jointed structural timber.

Timber sizes

• BS EN 336 Structural timber. Sizes, permissible deviations.
• BS EN 844 Round and sawn timber. Terminology, terms relating to moisture content.

Trussed rafters

• BS 5268:Part 3: Code of practice for trussed rafter roofs.

Tiling/slating battens

• BS 5534 Code of practice for slating and tiling.

Joinery and wood trim

• BS EN 942 Timber in joinery. General requirements. Replaces BS 1186 Part 1.
• BS 1186: Timber for and workmanship in joinery.
• Part 2: Specification for workmanship.
• Part 3: Specification for wood trim and its fixing.

Wood based sheet materials

Plywood

• BS EN 313 Plywood. Classification and terminology.
• BS EN 635 Plywood. Replaces BS 6566
• BS EN 635 - 1 Classification by surface appearance: General.
• BS EN 635 - 2 Classification by surface appearance: Hardwood.
• BS EN 635 - 3 Classification by surface appearance: Softwood.
   
• BS EN 636. Plywood. Specifications.
• BS EN 636-1: Requirements for plywood for use in dry conditions.
• BS EN 636-2: Requirements for plywood for use in humid conditions.
• BS EN 636-3: Requirements for plywood for use in exterior conditions.

Structural plywood (Click here for Structural Plywood Grading Tables)

• BS 5268:Part 2: Code of practice for permissible stress design, materials and workmanship.

Marine plywood

• BS1088-1 Specifications for plywood for marine craft. Replaces BS1088 and BS4079.

Particleboard (chipboard, OSB, cement bonded particleboard).

• BS EN 309: Wood particleboards. Definition and classification. Replaces BS 5669.
• BS EN 312: Particleboards. Specifications.
• Part 2: Specification for wood chipboard.
• Part 3: Specification for oriented strand board (OSB).
• Part 4: Specification for cement bonded particleboard.

Fibreboard, including hardboard, medlumboard, softboard and MDF.

• BS 1142: Specification for fibre building boards.

Oriented strand board (OSB)

• BS EN 300: OSB. Definitions, classification and specification.

Glue laminated timber (glulam).

• BS EN 386. Glue laminated timber. Performance requirements and minimum production requirements.

Preservative treatment

• BS 5268:Part 5: Code of practice for the preservative treatment of structural timber.
• BS 5589: Code of practice for the preservation of timber.

Exterior finishes for timber

• BS EN 927-1. Paints and varnishes. Coating materials and coating systems for exterior wood. Classification and selection.

Floors and flooring

• BS 1297: Specification for tongued and grooved softwood flooring.
• BS 8201: Code of practice for flooring of timber, timber products and wood based panel products.

Kitchen furniture

• BS EN 1153: Kitchen furniture. Safety requirements and test methods for built-in and free standing kitchen cabinets and worktops.

Fencing

• BS 1722: Fences.
• Part 4: Specification for cleft chestnut pale fences.
• Part 5: Specification for close boarded and wooden palisade fences.
• Part 6: Specification for prefabricated wood panel fences.
• Part 7: Specification for wooden post and rail fences.
• Part 11: Specification for woven wooden and lap boarded panel fences.

Scaffold boards

• BS 2482: Specification for timber scaffolding boards.

Nomenclature

• BS EN 13556: Round and sawn timber. Nomenclature of timbers used in Europe. Replaces BS 7359.

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While not exhaustive, this list covers most of the common topics referred to in timber specification and the relevant British Standards are listed under these topics.

WHILE EVERY EFFORT IS MADE TO ENSURE THE ACCURACY OF THE ADVICE GIVEN, THE ASSOCIATION CANNOT ACCEPT LIABILITY FOR LOSS OR DAMAGE ARISING FROM THE USE OF THE INFORMATION SUPPLIED.