Timber is available in a wide range of species, each with their own specific properties and capacity in terms of strength and durability. It is important to specify the most appropriate product for the application and carry out the necessary maintenance and attention to detail to ensure its long term performance. The service performance of any timber component in weather exposed situations or high moisture enviroments depends on protecting it from the absorption of moisture. High moisture content in timber can encourage timber degradation while timber kept dry will not decay. The preferred detailing suggested below is aimed at reducing the ingress of water into the timber component by providing non-permeable surfaces and details which do not trap water.

The following information and diagrams offer guidance in acceptable uses of timber components in weather exposed areas. The natural durability and hazard level treatments are detailed in tables 1-3

Hazard Class	Exposure	Service Conditions	Biological Hazard
H1	Inside above ground	Fully protected well ventilated	Borers only
H2	Inside above ground	Protected from wetting and leaching	Borers and termites
H3	Outside above ground	Moderate wetting and leaching	Decay, borers & termites
H4	Outside in ground	Severe wetting & leaching	Severe decay, borers & termites
H5	Ground contact	Extreme wetting, leaching &/or critical use	Very severe decay, borers & termites
H6	Marine waters Nth & Sth	Prolonged immersion in sea water	Marine wood borers & decay
H6SW	Marine waters Sth only	Prolonged immersion in sea water	Marine wood borers & decay

Type	H1	H2	H3	H4	H5	H6
Water/Boron
CCA
ACQ
Solvent/LOSP
Double/CCA + Creosote

Note: Untreated class 3 & 4 timber shall not be used for weather exposed structural, i.e Post, joists & bearers of decks or unprotected beams protruding from the house

1. External timbers are regarded as protected if they are covered by a roof projection (or similar) at 30 degres to the vertical & they are well detailed and maintained (painted or stained & kept well ventilated)

2. Framing in extremely damp or unventilated locations should have the durability required for the external above-ground situations.

3. All horizontal exposed timbers i.e bearers & joists, should be coated with a film forming coating i.e paint, oil based water repellant, ect, to enhance long term performance

Detailing for Durabliity

Attention to detail is most important i.e quality of timber, workmanship. fixings, finishes and maintenance. Failure to maintain high standards of quality in any of these factors expressed below may lead to a shortened service life

Timber

The timber used should be free of core wood (material within 50mm of the trees center) and free of splits, checks, loose knots and cavities. Timber should preferably be free of sapwood (lighter coloured wood found on the outer layer of the tree)

Joints & Connections

Use corrosion resistant fasteners i.e hot dipped galvanised, stainless steel or composite bolts, nails or nailed metal connectors. All timber-to-timber interfaces for all the joints should have a seal coating of preservation formulation. Preservation formulation should also be applied inside bolt holes and to the end grain of the timber. Housed, checked or birdsmouth joints and all other details that may trap water should be avoided. Some treatment chemicals used may react with the fasteners, ensure manufacturers instructions are followed in this regard.

Application	Conditions of use	Heartwood Durability	Preservative Treatment of Sapwood
Verandah posts, stumps or poles supported on brackets Verandah decking & supporting bearers and joists Roof beams, rafters or other members protruding from a building to form a pergola or other exposed structure	Clear of the ground & exposed to the weather	Class 1 or 2 Some Class 3 & some untreated Class 4 timbers are suitable for non-critical applications providing design, installation, finishing & maintenance practices are used	H3
Posts, stumps or set into the ground	In-ground contact or persistently damp situations	Class 1 Class 2 timbers can be used where the members can be easily replaced or are protected from full weather exposure	H4 & H5

Finishing

Refer to manufacturers' specification regarding method of application, number of costs and maintenance. Suggested finishes are:

• Pigmented oil based stains, or

• Pigmented paint over an oil based primer.

A wax free preservation pre-treatment is recommended for both finish systems.

Unpigmented finishes including clear film finishes have limited life when exposed to UV-light (sunlight) and should be avoided.

Maintenance

Finishes should be re-applied before the finish begins to break down. This may be done as required, usually at intervals of one to three years. When the maintenance schedule is followed, along with good detailing, timber will continue to look good and maintain its capacity for many years.

Note: This information is intended to give guidance to designers, builders and owners who are aware that species of durability Class 3 & 4 are generally not recommended for full weather exposed environments. However, providing special attention is paid to design, construction and regular maintenance, satisfactory performance can be obtained when used in weather exposed applications outlined herein.

Good Building Practice

Patio roof & Support Post

Free Standing Unroofed/Roofed Pergola

Pergola Connected to Ledger or Fascia Roofed/Unroofed