2.3 Timber preservation (natural solid timber)
Appendix 2.3-A
Table 1 - Timber component groups and preservative treatment required (based on BS 8417)
| Component group | Examples | Hazard class | Desired service life | Preservative type required (see note 1) | Preservative treatment not required: | ||
|---|---|---|---|---|---|---|---|
| Copper containing | Organic Solvent or Microemulsion | Boron | |||||
| Internal joinery, intermediate floor joists | Architraves, internal doors, intermediate floor joists | 1 | 60 |  | | | unless a specific request for treatment against insect attack has been made |
| Roof timbers (dry) | Pitched roofs: rafters, purlins, joists, wall plates | 1 | 60 | | | | unless a specific request for treatment against insect attack has been made |
| Roof timbers (dry) in areas with house longhorn beetle | Ditto | 1 | 60 | | | | Where timber used is:
|
| Roof timbers (risk of wetting) | Flat roofs joists, sarking, tiling battens, valley boards, timbers exposed to risk of condensation | 2 | 60 | | | | Where timber used is heartwood only (see note 2) and of durability class 1 - 2 (see note 3) |
| Roof timbers (risk of wetting) in areas with house longhorn beetle | Ditto | 2 | 60 | | | | Where timber used is heartwood only (see note 2) and of durability class 1 - 2 (see note 3) |
| External walls/ground floors | Timber frames, ground floor joists, l-beam studwork | 2 | 60 | | | | Where timber used is heartwood only (see note 2) and of durability class 1 - 2 (see note 3) |
| External joinery, coated (not in ground contact) (see note 4) | Window frames, door frames, doors, cladding (coated), soffits, fascias, barge boards | 3 | 30 |  (see note 5) | | | Where timber used is heartwood only (see note 2) and of durability class 1 - 3 (see note 3) |
| Uncoated external timbers (not in ground contact) | Decking, balcony infill, cladding (uncoated) | 3 | 15 | | | | Where timber used is heartwood only (see note 2) and of durability class 1 - 2 (see note 3) |
| Timber in contact with the ground | Decking timber in ground contact, timber below dpc | 4 | 15 | | | | Where timber used is heartwood only (see note 2) and of durability class 1 - 2 (see note 3) |
Notes to table 1
- Preservative treatment of timber should be in accordance with the recommendations of BS 8417. For preservatives listed in the supplement to the BWPDA Manual treatment recommendations are given in table 9, BS 8417.
- Almost always, packs of timber contain sapwood. It should be assumed that timber is sapwood and preservative treated accordingly unless the timber has been specifically selected as heartwood only.
- Natural durability classes are given in table 2.
- The hardwoods known as Meranti, Seraya or Lauan should be treated in the same way as European redwood / Scots Pine when used for joinery.
- Generally, copper containing preservatives are not used for treating joinery items, but they can be used to treat claddings which are to be coated.
Table 2 - Natural durability of building timbers (heartwood only)
| Durability Class | Timber Type | Timber Species | |
|---|---|---|---|
| 1. Very durable | Softwoods | None | |
| Hardwoods | Opepe | ||
| Padauk-Andaman | |||
| Afromosia | |||
| Greenheart | |||
| Guarea | |||
| Iroko | |||
| Jarrah | |||
| Okan | |||
| Pyinkado | |||
| Teak | - Malaysian | ||
| Kapur | - Sabah | ||
| - Burma | |||
| Padauk | - White | ||
| Peroba | |||
| 2. Durable | Softwoods | Cedar | - Western red (imported) |
| Hardwoods | Basralocus | ||
| Ekki | |||
| Chestnut | - Sweet | ||
| Karri, Kempas | |||
| Louro | - Red | ||
| Oak | - American White | ||
| - European | |||
| Mahogany | - American | ||
| 3. Moderately durable | Softwoods | Pine | - Caribbean pitch |
| Cedar | - Western red (UK) | ||
| Fir | - Douglas (North American) | ||
| - Douglas (UK) | |||
| - Dunkeld (UK) | |||
| Larch | - European | ||
| - Hybrid | |||
| - Japanese | |||
| - Tamarack | |||
| - Western | |||
| - Maritime | |||
| Pine | - American pitch | ||
| Hardwoods | Keruing | - Sabah | |
| - Malaysian | |||
| Oak | - Tasmanian | ||
| - Turkey | |||
| Mahogany | - African | ||
| 4. Slightly durable | Softwoods | Fir | - Noble |
| - Silver | |||
| Pine | - Canadian red | ||
| - Corsican | |||
| - Jack | |||
| - Parana | |||
| - Ponderosa | |||
| - Radiata | |||
| - Scots | |||
| - Southern | |||
| - Western white | |||
| - Yellow | |||
| Redwood | - European | ||
| Fir | - Balsam | ||
| - Grand | |||
| Hem-fir | - USA and Canada | ||
| Pine | - Lodgepole | ||
| Spruce | - Eastern Canadian | ||
| - Engelmann | |||
| - European (Whitewood) | |||
| - Sitka | |||
| - Western white | |||
| Spruce-pine-fir | - Canada | ||
| Hardwoods | Elm | - Dutch | |
| - English | |||
| - White | |||
| Oak | - American red | ||
| Beech | - Silver | ||
| Elm | - Rock | ||
| -Wych | |||
| 5. Not durable | Softwoods | None | |
| Hardwoods | Alder | ||
| Beech | - European | ||
| Birch | - Silver | ||
| - European | |||
| - Paper | |||
| - Yellow | |||
| Chestnut | - European horse | ||
| Lime | |||
| Sycamore |
Appendix 2.3-B
Additional sources of information
BS 8417 Preservation of Timber - Recommendations.
BS EN 599 - Part 1 Durability of wood and wood-based products - Performance of preventive wood preservatives as determined by biological tests - Part 1: Specification according to hazard class.
BWPDA Manual. The British Wood Preserving & Damp-proofing Association,
1 Gleneagles House, Vernongate, Derby DE1 1UP
Tel: 01322 225100; Email: info@bwpda.co.uk
