Choosing the right preservative treated timber

Hazard Classification Classes in SA

Choosing the right preservative treated timber

As with most commercially grown timber, South African plantation grown pine and eucalyptus are not durable and are therefore subject to attack from fungus and termite. This is why it is necessary to 'treat' timber with wood preserving chemicals if you require confidence in its performance. Taking this a step further, SAWPA together with the SABS and representatives from the timber industry established the Hazard Classifications.

The purpose for which the timber is being purchased defines the treatment required. A piece of timber to be used in the roof need not be treated with the same amount of chemical as a piece of timber being used for a jetty. The treatment changes with different applications. The chemicals need not penetrate to the same depth, nor need the solution be the same. These two factors are called penetration and retention levels respectively.

The main chemicals used in this country are CCA (Copper Chrome Arsenate) and Creosote. CCA gives the timber a greenish look whilst Creosote leaves the timber pole dark brown to black. Other chemicals available are Boron and TBTNP (Tributyltin naphthenate – permethrin). TBTOL (Tributyltinoxide Lindane) and PCP has been removed from the market place because of its proven damaging environmental properties.

Chemicals should not be brushed on. The timber is put into a treatment vessel and through various processes, the chemicals are deeply impregnated into the timber, thus obtaining the correct penetration depth and chemical retention for the predetermined hazard class. Boron may, under specific conditions, also be applied by means of a dip-diffusion process.

In South Africa we have 6 hazard class levels of treatment.

H0-i INTERIOR

This is for interior uses only. Protection is only offered for prevention of certain commonly occurring insects and is a mild treatment process. All other hazard classes given below offer protection against insect and fungi attack. The products in this category are specifically for mouldings, ceilings, flooring boards and joinery.

H1

International trends set a H1 level. Because South Africa followed the international example when setting up its own Hazard classification, it was felt that H1 in the South African context would not be required, as this caters only for countries in which there are no termites.

H2 INTERNAL (Low Hazard)

This is also for interior use only and timber treated under this classification should be roof trusses, laminated beams, internally used structural timber, ceiling boards, flooring, paneling, doors, cupboards, skirting, window frames and plywood. Chemicals used here would be mainly CCA, TBTNP and Boron.

H3 EXTERIOR ABOVE GROUND (Moderate Hazard)

CCA and Creosote are mostly used for this and higher H class treatments. H3 covers balustrades, fencing bearers and slats, outdoor decking and beams, garden furniture, laminated beams, weather board, steps, cladding, stairs, log homes, gates, fascia boards and plywood. Spacers and cross arms used with electrical, distribution, telephone and light poles are treated to H3.

H4 GROUND CONTACT (High Hazard)

This level of treatment helps prevent agricultural posts and landscaping structures from rotting and termite attack. Also recommended for treatment in this hazard class are playground structures, fencing, pergolas, carports, flower boxes, decking, bridges and stakes, as well as electrical, distribution, telephone and lighting poles.

H5 FRESHWATER (High Hazard)

Timber which falls into this category, is timber exposed to continual wetting or where the timber is planted in wet soil. Timber which will fall into this category could be jetties, drains, walkways, retaining walls and slipways.

H6 MARINE (High Hazard)

Only the use of the CCA chemical with Creosote is recommended for this application. Only timber treated with both these chemicals will offer complete protection against marine borers. Jetties, slipways, retaining walls and walkways will fall under this section.


In South Africa all treatment plants producing treated timber are monitored through a compulsory third party product certification scheme. All treated timber is required to show not only the product certification mark of one of the approved certification bodies, but also to which H class the timber has been treated.

Your treated timber will be marked with one of the symbols listed below:

HAZARD CLASS SYMBOL HO-i H2 H3 H4 H5 H6
END USE APPLICATION (typical examples) Internal Internal External Above Ground In Ground Contact In Fresh Water / Wet Soils In Sea Water
Mouldings
Ceilings
Joinery
Flooring
Boards
Laminated
Beams

Roof Trusses Structural
Timber

Ceiling Boards Flooring
Paneling
Doors
Cupboards
Skirting

Window frames

Plywood
Balustrades

Fencing bearers and slats

Outdoor decking and beams

Garden furniture

Laminated beams

Weather board

Steps
Cladding
Stairs
Log Homes
Gates
Fascia boards
Plywood
Agricultural posts

Landscaping structures

Playground structures

Fencing
Pergolas
Carports
Flower boxes
Decking
Bridges
Stakes
Garden Edging
Transmission Poles
Piling
Retaining Walls
Slipways
Culverts
Groynes
Flood Gates
Jetties
Drains
Walkways
Piling
Retaining Walls
Slipways
Groynes
Jetties
Walkways