How to choose the right timber for the job

[Adam_W]

Choosing the right timber for your project is the key to success. It must be strong and durable enough for your needs and give you the kind of finish you want.

There are a lot of names, codes and abbreviations used in labelling timber. Here’s our simple guide to the ones you’re most likely to see.

Timber types

The most common terms are softwood and hardwood, which are sometimes abbreviated to SW (or SWD) and HW (or HWD).Merbau is a hardwood that is stronger and more durable than softwoods such as Pine.

Softwoods come from conifers or Pine trees, with the most common being plantation radiata Pine. Softwoods are lower-density and generally lighter to handle and easier to drill and cut.

Hardwoods come from flowering trees, including many native eucalypts. They are dense timbers that are stronger and more naturally durable. They can be extremely heavy and are more challenging to work with.

One example: treated Pine decking is a softwood, while Merbau decking is a hardwood.

Timber finishes

This treated Pine rougher header has been milled with fine grooves to cut down on splinters.The timber you buy will have been sawn and milled in one way or another. There are various terms for the level and type of finish that results, including:

• Rough sawn – As it looks straight from the saw. Treated Pine sleepers are one example.
• Rougher header – Timber that has been machined to have a fine-grooved surface to cut down on splinters.
• Dressed – Timber that has been finished to a fine, smooth standard on at least one face.
• DAR (dressed all round) – Timber that has been finished on all faces.
• Clear timber – Refers to the visual quality of the timber. Clear Pine, for example, will be free of knots and other conspicuous imperfections. Clear timber is more expensive and generally only needed when the timber will be seen through varnish or oil.
• Select grade – Similar to clear but used most often for describing floorboards or cabinet-making timber.
• T&G – Tongue and groove. Generally only found in floorboards. One side of the board has a milled groove and the other a tongue so they can lock together.
• End matched – like tongue and groove, but on the ends of the board. Most often seen on weatherboards.

Timber processing 

This MicroPro sleeper is suitable for use in vegetable beds and children's play areasThere is a range of processes applied to different timbers for different purposes. They include:

• Unseasoned, green or wet – This timber has not been subjected to any drying process and will have a high moisture content. It is inclined to shrink as it dries, potentially bowing or twisting. It needs to be secured as soon as possible to prevent movement or deformation. Never use unseasoned timber where shrinkage or movement will cause problems.
• Seasoned – Timber that has been dried to a specific moisture content so that it is considered stable in use. This may be done by kiln or air drying, or a combination of both. Timber that is air-dried alone is not always considered seasoned for specific needs.
• KD – Kiln-dried timber. Kiln drying enables the most accurate measuring of moisture levels and results in the most stable timber.

Timber treatments

Timber is also treated differently according to its intended use. Treatments include:

• CCA – Designates timber treated with chromated copper arsenate to protect against fungal decay and insects such as termites. Its use is now restricted, and it should only be used in situations where there is no risk of human or animal contact.
• ACQ – Alkaline copper quarternary is a newer wood-preservative treatment. The methods of treatment and the degree of protection from fungal attack and insects are similar to CCA but there is no arsenic involved so it is considered safe for use in all situations.
• Micropro – This is a brand name for timber that has been treated with microscopic particles, most often micronised copper azole (MCA), which are forced under pressure into the timber. This is considered a very safe treatment.
• LOSP – Light organic solvent preservative is another form of safer timber preservative treatment. 

Hazard rating

Labels or stamps on timber show treatment details. Here it's H3.The “H” or hazard rating of timber relates to the level of timber perseverative treatment. The higher the number the greater the level of treatment applied to the timber. The ratings are:

• H1 – Must be used indoors in well ventilated areas only, protected from all moisture and insects such as termites.
• H2 – Must be used indoors only and protected from any moisture.
• H3 – Outdoors, above ground only.
• H4 – Outdoors, in-ground and in situations where timber may be exposed to continually damp surfaces.
• H5 – Outdoors, inground and in constantly wet situations, including standing in fresh water.
• H6 – Outdoors in extreme situations including constant contact with salt water.

Strength ratings

The strength of Pine timber is measured on the MGP scale.These ratings tell you how much load timber can take. This then relates to the allowable length of spans of bearers and joists for decks and house flooring and situations such as cantilevered balconies.

There are two rating scales. The F scale is primarily used for hardwoods, while the MGP (machine-graded Pine) classification is used for Pine.

If you are working with plans that specify an F or MGP rating do not substitute one for the other without seeking professional advice.

• MGP10 is a regular strength for general use and is the minimum required for building work and framing of walls.
• MGP12 is suitable for framing of walls and some floor joists.
• MGP15 is used for heavy loading, such as supporting walls and frames and joists.

F ratings start at F1 for the weakest timbers. Examples include:

• Blue Gum F14 to F24.
• Merbau from F22 to F27.
• Ironbark F22 to F42.

Manufactured timbers

Laminated veneer lumber (LVL) is a manufactured timber that can be produced in very long spans.Not all the timber we use comes straight from a tree. Manufactured timbers, also known as engineered timbers, are increasingly used for a broad range of applications.

Their manufacturing processes can maintain consistency in smoothness, strength and other properties, whereas natural timber may be more variable.

Here are some of the manufactured timbers you’re most likely to encounter:

• Laminated – Most often refers to boards such as plywood that are created by gluing together thin layers of different timbers. If using laminated products outdoors make sure they are intended for such conditions.
• LVL – Laminated veneer lumber. These are generally larger beams (also called engineered beams) that can be produced in very long spans that are not achievable with most natural timbers.
• FJ – Finger jointed. Timber pieces glued together using finger joints to create longer lengths or larger boards. This is very useful for timbers that don’t typically come in longer lengths but may be needed for uses such as posts.
• MDF – Medium-density fibreboard. Often called craftwood, these boards have a fine texture and a multitude of uses in shelves, cabinets, door panels and so on. You’ll also find architraves, skirting and other mouldings made from MDF.
• Particle board – A low-density fibreboard also known as chipboard for its larger, distinctly visible woodchips. Most commonly used for kitchen cabinets and flat-pack furniture. Most homes today have floors of large particle board flooring panels. Available in water-resistant boards for use in wet areas.

More help and inspiration for your timber projects

Check out our step-by-step guides, which include How to build a deck, How to build a retaining wall, How to build a planter box with bench seats and How to build timber screening. And please let us know if we can help with your project – we'd love to help you get a fantastic result for your home.

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