2.3 Timber preservation (natural solid timber)

2.3 - Appendix 2.3A
	Table 1	Timber component groups and preservative treatment required (based on BS 8417)
	Table 2	Natural durability of building timbers (heartwood only)
2.3 - Appendix 2.3B
	Additional sources of information

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 organic	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: softwood - heartwood only (see note 2) and of durability class 1 - 3 (see note 3) or hardwood
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)
Sole plates (see note 4)		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 5)	Window frames, door frames, doors, cladding (coated), soffits, fascias, barge boards	3	30	(see note 6)			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

1. Preservative treatment of timber should be in accordance with the recommendations of BS 8417 (with the exception of sole plates - see note 4). For preservatives listed in the supplement to the WPA Manual treatment recommendations are given in table 9, BS 8417.
2. 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.
3. Natural durability classes are given in table 2.
4. Sole plates should be positioned above dpc. Preservatives used should be resistant to leaching or, for boron, treatment should be to full cross section retention standard. Treatment should be carried out in accordance with the WPA manual.
5. The hardwoods known as Meranti, Seraya or Lauan should be treated in the same way as European redwood / Scots Pine when used for joinery.
6. Generally, copper organic 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.

Industrial Wood Preservation - Specification and Practice ('the WPA Manual') (2008). The Wood Protection Association,
1 Gleneagles House, Vernongate, Derby DE1 1UP
Tel: 01322 225104; Email: info@wood-protection.org