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Timber’s mechanical properties refer to how it responds to external forces. In the engineering world, that refers to load, stress and bending, for example. To say it is pretty important that the material you choose for a construction project has the mechanical properties to match the application is an understatement! So what are the mechanical properties of timber? Let’s take a look.

Strength Parallel to Grain

If you are looking for the strongest, stiffest properties for your timber products, it is best to look in the direction which runs parallel to the grain, so the fibres support the weight.

In this orientation, your boards will display their highest tensile strength (the maximum amount of stretching or pulling stress they can withstand before breaking) and compressive strength (the maximum amount of squeezing or crushing stress they can withstand before deforming or failing.) A higher tensile and compressive strength will create a timber which is more durable, resistant to bending or breaking under pressure, and better suited for structural applications.

You can also measure the modulus of elasticity, which is a measure of stiffness, indicating how much it can or will deform under a given load while returning to its original shape once the load is removed. For example, if you add a weight to a timber board and the timber bends, will it become flat again when the weight is removed?

  • Tensile Strength: Softwoods, at 12% moisture content, generally have tensile strengths ranging from 70 to 140 MPa. Hardwoods, because of their denser cellular structure, tend to have a higher tensile strength.
  • Compressive Strength: While lower than tensile strength, compressive strength typically falls between 30 to 60 MPa for softwoods, with hardwoods again performing better.
  • Modulus of Elasticity: typically between 7 and 14 GPa for both hardwoods and softwoods.

It is also important to note that knots or irregularities in the grain can reduce each of these values and, in some cases, tensile and compressive strength can drop by up to 90%.  That is why timber with a lot of knots is not recommended for structural applications.

It is therefore vital you work with a timber supplier who knows how to select and grade the right timber boards for your application, such as our team of experts at EcoChoice.

Strength Perpendicular to the Grain

When you look at timber strength perpendicular to the grain (across the fibers), you will notice that it is a lot weaker than when looking parallel to the grain (along the fibers). Here is a quick overview of the values so that you can compare:

  • Tensile Strength: Wood is much weaker when stretched across the grain. Radial and tangential tensile strengths are only 5–8% and 3–5% of the strength along the grain. This means designs should avoid tension in these directions by minimizing joints or notches which would create weak points.
  • Compressive Strength: Wood can withstand only 10–20% of its strength along the grain when compressed. In this direction, compression leads to the densification of cell walls, which increases resistance but also causes significant deformation. In other words, your timber will start to crush and compact rather than break, leading to noticeable shrinking and deformation before it ultimately fails.
  • Modulus of Elasticity: The stiffness of wood perpendicular to the grain is much lower, at just 4–9% of the parallel-to-grain values.

You can learn more about the mechanical properties of different timbers in our timber species guide. Download technical specification sheets to learn more about your timber choices.

Ekki, for example, has a compressive strength of 96 MPa and a modulus of elasticity of 21,420 MPa. Oak has a compressive strength of 58 MPa and a modulus of elasticity of 13,300 MPa.

Flexure and Shear

Larger boards of timber are more likely to have defects than shorter boards, making them typically the weaker option of the two.

Timber also has shear strength, which refers to sliding or tearing, such as when parts of the board move parallel to each other in opposite directions.

  • Shear Parallel to Grain: This type of shear happens along the grain and can cause a brittle break. Its strength ranges from 5 to 12 MPa.
  • Shear Perpendicular to Grain: This is rarely a concern because timber is usually designed to avoid heavy loads in this direction.
  • Rolling Shear: This occurs in certain loading conditions but is not common for most applications.

Find Strong, Durable Timber at EcoChoice

Not all timber species are equal in terms of mechanical properties. If you are looking for timber products which can bend, for example, Glulam is an excellent choice as it is made up of many smaller parts of timber glued together. For a strong, weight-bearing timber, consider Oak or Western Red Cedar.

The simplest option to find the right timber for your project? Get in touch with the EcoChoice team. We will be happy to work out the mechanical properties you need from your timber and match you with the ideal species, taking the leg work out of finding your next construction materials.

Mechanical properties of wood

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Our timber experts have years of experience and will be able to match the perfect species to your project, as well as provide a quote for sustainable timber at highly competitive prices.

Frequently asked questions

Do you supply timber for domestic uses?

Yes, we supply timber for domestic applications as well as commercial and public constructions. From garden decking to shed cladding, we will be happy to supply smaller deliveries for home use.

Is your timber FSC-certified?

Yes, all timber we supply is FSC or PEFC certified and sourced from independently verified responsibly managed forests. If we can’t find your request in FSC/PEFC certified timber we’ll suggest an alternative that is certified or clearly note that the offer is minimum EUTR.

Where does EcoChoice deliver to?

EcoChoice delivers to construction sites, warehouses and homes across the UK, as long as there’s access and unloading for our trucks.

What are the best timber species for exterior use?

There are many different timber species suitable for exterior use and which is the best for your project depends on your requirements. In general, though, we recommend EkkiGreenheartOpepe and Oak for heavier civil/marine uses. For intermediary external use such as decking, where the timber needs to be both strong and durable but not on the same level as civil engineering (bridgespiling, etc) we usually supply CumaruIpe, Jatoba, and Balau. And for the lighter exterior use where the timber is non-structural such as cladding, we deliver CedarLarchThermowood and others.

Which timber is the most durable?

Durability Class 1 timbers are the most durable. This of course depends on the use (hazard) class they’ll be in service for. For direct ground and water contact such as sleepers, fenders, marine piling, etc, Ekki and Greenheart are known to be the most durable timbers available. For decking and cladding where there’s no direct ground contact (use class 3) there’s a much wider range of timbers such Larch, Cedar, Thermo modified Pine or Ash and others.

What’s the best timber for internal cladding?

Internal cladding, where your timber is not in ground and not exposed to the elements can be classed as either use-class 1 or 2 – in which case most timbers will meet this durability criteria. That is not to say they’ll be the best, since internal environments have lower humidity (moisture) levels than outside. So in these cases, it’s best to go for a kiln-dried timber cladding board as these are more stable and delivered already in lower MC (moisture content) than the usual fresh sawn timbers sent to external applications. A word of caution – as timber reacts to variations in moisture, it’s best to avoid cladding any areas inside your bathroom.

How can I make decking less slippery?

The first thing is to ensure your deck boards are kept clean from leaves and other debris which will, over time, cover the surface and make it more slippery. Grooved boards can be used to improve grip if installed and used perpendicular to traffic, so especially useful in narrow passages and footbridges. Lastly, you can add our Grip-Choice strips: these are a mix of epoxy with aggregates that add gripping ridges to your deck area. Gripchoice is an easy way to make decking less slippery and safer, especially over large areas or where there’s high traffic. We can pre-install Grip-Choice strips for your decking before delivery or ship the strips separately to add to your existing deck’s grooves as a retro-fit solution.

What wood machining services do you offer?

We can offer planing, sawing, drilling and profiling of rough-sawn wood to any profile you require: from handrails to large port fenders.

Can you supply pre-drilled timber?

Yes, we will be happy to provide pre-drilled timber which is tailored to your needs for quick installation, thus saving you valuable time on site.

What cladding profiles do you supply?

We provide a wide range of cladding profiles, including tongue and groove, featheredge and shiplap. You can check the standard profiles here – but we can also match or custom make profiles to suit your specific needs.

Does timber change colour?

Yes, timber is well-known for changing colour over time. Some species can darken quickly right after installation, and like most untreated wood will eventually weather to a beautiful silver-grey. Interior timber is less likely to change colour (depending on conditions), and timber can be stained, painted or treated with UV-resistant oils to reduce colour change.

Do I need to treat exterior timber?

Some timbers such as Oak and Ekki, can withstand the strains of exterior use without any treatment. However, to extend the lifespan and maintain the aesthetic of your wood, we do recommend treating your timber with stains and oils. Pre-treated timber, such as ThermoWood and OrganoWood, are low-maintenance options which are more durable, but can have their life service extended by applying a clean and stain maintenance schedule.

Do I need to treat interior timber?

Depends on what area the timber is being used. For floor joists and timber rafters, it is common to see timber treated, or least very well kiln-dried. Other uses such as flooring may benefit from varnishing while internal timber cladding for decorative purposes shouldn’t require any treatment other than if you want to change its colour with different types of stains or oils.

Where are you based?

We’re based in Cambridge, UK, and coordinate multiple sawmills all over the world to manufacture your order. We then organise delivery with a range of hauliers so that your orders gets to your site on time.

What are the usual decking sizes?

Timber decking is usually 21x140mm or similar. For heavier applications where there’s more load and traffic, we deliver 35 or 45mm thick boards (such as Hastings Pier). Narrower boards are also possible: 95-90mm is a standard width – but we can manufacture whatever size you require.

What are the usual cladding sizes?

Typical cladding section sizes are 18×95 and 18x145mm although we can always custom make a section to suit your project’s design requirements. That includes waney edge boards in Oak or Chestnut as well as extra wide 195mm boards.

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Always helpful! One of our valued TDCA DeckMark and CladMark accredited supplier members which means their quality procedures are routinely audited and stand up to scrutiny giving you extra peace of mind.

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Having needed the supply of cladding, decking boards and other specified timbers through out the year Eco choice have been very helpful in sourcing the specified timbers and quantities required at a very competitive price.

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  • 3 years ago

Always helpful! One of our valued TDCA DeckMark and CladMark accredited supplier members which means their quality procedures are routinely audited and stand up to scrutiny giving you extra peace of mind.

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Experts in Timber, Nationwide delivery

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Great service, quality products and very easy to deal with. Thank you.

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