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From Ekki to Greenheart, there are plenty of super strong timber species out there which are ideal for construction, including Oak and Pine. Having said that, there are also factors which can affect the properties of your wood. These can affect durability, dimensional stability and overall strength, leaving you with timber which is not fit for purpose. Our advice? Get to know what can affect the strength of your timber so that you can better choose and maintain your products.

Natural Characteristics That Affect Strength

We grade timber products to understand how variations of the same species are better suited for different projects. Why? In simple terms, structural differences between batches of timber can affect their strength. These natural characteristics can include:

  • Knots: These are areas where branches grew from the tree, and they interrupt the grain which can weaken the timber. Small knots that are few and far between are not much to worry about, but larger knots in clusters can result in more severe strength reductions, especially when located near the edges of beams which are intended to be bent.
  • Sloping Grain: When the timber fibres deviate from the axis of the timber, this is known as a sloping grain and it reduces the strength of the wood. You can also come across spiral grain or cross grain – whether naturally occurring or caused during processing – both of which can weaken timber.
  • Reaction Wood: When a tree leans, it can form irregular growth patterns known as reaction wood. This can actually end up stronger than regular timber in some cases, though it is more likely to experience dimensional instability and we would never recommend it for any structural construction projects.
  • Fissures: Shakes, checks and splits (essentially cracks) in the timber can occur for a variety of reasons, including while the timber dries or at any point when it is under stress. This reduces shear strength and makes it easier for moisture and insects to penetrate the timber, contributing to rot.

Find out more about strength grading in our guide to common strength grading misconceptions.

The Role of Moisture

The moisture content of your timber plays a critical role in its strength. Below the fibre saturation point (FSP) – which is around 25-35% – the strength of timber is inversely proportional to moisture.

The wetter your timber, the weaker it is (both in terms of tensile and bending strength), making it less suitable for structural applications when it’s above the FSP. On the other hand, too little moisture and any bending could cause the wood to splinter and snap.

Duration of Load and Creep

Timber’s strength is reduced under prolonged loads. In fact, a permanent weight on the timber can reduce its strength by up to a whopping 40%! Sustained loads also lead to significant creep deformations, which look like a permanent dip or sag in your timber boards and beams.

Cyclic Loads of Stress

Timber does not hold up well under repetitive stress. Even when it only has small imperfections, it can lose about half of its original strength when it is repeatedly dealing with external forces and heavy loads. If the timber has serious flaws, e.g, knots or sloping grain, the strength loss can be even greater—up to 70%.

Do note, though, that tough timbers will withstand stress and loads for decades without a hitch. It all depends on choosing the right species and grade for the job. If your project requires your timber to be under a lot of stress, we recommend a species like Ekki, Greenheart, and Cumaru. They will handle cyclic loads and constant stress with ease.

Temperature and Fire Resistance

Timber’s strength remains stable under normal temperatures but decreases under prolonged high-temperature exposure. Timber is also combustible; however, its charring behaviour provides some fire resistance. Charred surfaces insulate the unburnt core, maintaining its structural integrity, unlike steel structures. Fire-resistant treatments and protective cladding can further enhance its performance in fire-prone environments.

Find the Right Timber at EcoChoice

Struggling to factor all these characteristics into your final decision? Do not worry, we have got you. At EcoChoice, we will match your project requirements to the perfect timber species for the job, ensuring you make the right (Eco)choice every time. Get in touch with our team today to learn more.

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What impacts timber strength

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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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Good quality, great service, fast delivery!

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Marinella Li

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.

5

Janet Sycamore

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.

5

Tim Saunders

Great quality, service and price. A pleasure to deal with. I would highly recommend Eco Choice.

5

Emma Hurrell

Fantastic company- Mike and the team are the best in the business- worked with them for many years.

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Prem Raja

Always reliable and quality products, easy to deal with company.

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Stone Zone

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Average rating on Google Reviews

  • 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.

Janet Sycamore

  • 6 years ago

Fantastic company- Mike and the team are the best in the business- worked with them for many years.

Prem Raja

  • 6 years ago

Great quality, service and price. A pleasure to deal with. I would highly recommend Eco Choice.

Emma Hurrell

  • 9 years ago

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

Malcolm Coury

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