What are the standard decking considerations?

Trying to identify the best outdoor decking board dimension for your brand-new project? Or maybe you’re replacing brand-new boards on an existing deck?

Regardless, to assist you in establishing the ideal decking board dimensions for your job, allow us to start with the essentials, let’s start with joists.

Joists are the core of your deck framework. If you have ever looked at a wooden deck from below, you’ve seen its joist structure.

They are usually placed upright (for strength) and fastened to your home at one end. Joists secure the decking boards, which are fastened onto the joists from above.

Joists are commonly spaced out evenly so as to spread the load, as well as for stability, simplicity of installation, and a clean look.

The section size and the span between joists is a very important matter of safety and should be calculated with the help of a professional.

Deciding dimensions

Now it’s time to think of the boards. Outdoor decking boards can be found in varying dimensions.

The usual sizes are 19×90, 21×145 and 28×145 because they come from standard sawn sizes (25×100, 25×150 and 32×150).

Consider strength

There are two aspects that establish your required board width: Timber strength and joist spacing.

Let’s start with strength, which in this case if measured as the distance a deck board can span between 2 joists. The broader your joist spacing, the stronger decking board you’ll need. Different wood species have different strengths.

Softwood trees, such as treated pine and western red cedar, generally offer weaker timber, but are easier to work with. Hardwoods, such as Cumaru, are exceptionally solid – but require a bit more woodworking skill when installing or if the boards need to be altered.

Durability

Durability is another key element to be considered. This is measured in the number of years that the decking (and joists) will be safe to use and enjoy – also known as life service.

Pine is not very durable; left to its own devices it will rot quicker than other more durable species. So the timber trade usually impregnates Pine (as well as Spruce and Douglas Fir) with chemicals that help lengthen its life service.

Naturally durable timbers, such as Ipe, don’t need any chemical treatment – they will last many years, even without any treatments.

Pitfalls of plastic

There is currently a trend in using composite decking materials. However, these are not wood and today, most people recognize the ecological dangers of using chemicals as well as plastics.

However, among the lesser-known drawbacks is that they can become dry and brittle, which then calls for joists to be put very close together.

If your joists are too far apart, the boards will flex as you walk over them. In time, the boards can develop “deck gullies” as well as frequently fracture or indeed snapping.

The slim joist spacing needed by composite decks increases the expense of your project (more joists = more money) and additionally, the time to install the whole deck area (even more joists = more job).

Width matters

Many people think the width of the board is totally cosmetic or a matter of cost. But, the width of the board is crucial where dimensional security is needed. The narrower the decking board, the less it will move.

We hope this has been helpful in your outdoor deck planning. Feel free to take a look at the decking products we have available on our site.

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What to consider with decking

Ask Joe! Expert industry advice

Unsure which timer is best for your project?

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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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.

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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.

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

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

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Stone Zone

  • 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

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