News: Is Oak The Best Timber For A Garden Structure?
28/04/2022
Today, we'll pose the question, is oak the best timber for a garden structure?
Perusing brochures and the internet, you'll find garden structures made from brick, steel, aluminium, plastic, and timber, so what gives?
The material you use will affect durability, aesthetics, and maintenance needs, so it's important.
First and foremost, for natural elegance, you can't beat timber. Even then, you'll have options as to which species of wood is best.
In this article, you’ll learn about the pros and cons of using oak for a garden structure.
As you'll find out later. There’s more to oak than meets the eye.
What Are The Advantages of Oak?
Oak is exceptionally durable, strong and water-resistant. These characteristics, alongside its unique and prestigious aesthetics, make it a prime timber for outside structures. Let’s deep dive into the advantages of using oak outdoors.
Is Oak Durable?
Timber is either hardwood or softwood.
Oak is classified as a hardwood, and unsurprisingly, it’s a very dense and hardy timber.
Though, the hardwood category did not receive its name based on hardness property. Before you shout from the rooftops, hardwood is hardwood because it’s hard. It’s not.
Hardwood comes from deciduous trees. What’s that mean? It just means they lose their leaves annually. Whereas softwood timbers are coniferous trees that remain evergreen.
As it happens, durability depends on the density of the timber governed by the rate of growth. Oak’s density measures at 720kg/m3, Pine, a softwood, measures around 500kg/m3, so oak offers much more durability.
Yet it’s not just denser than softwoods, its on the higher end of the hardwood durability, capable of up to D30 strength grade.
What does this mean? In short, in addition to having impressive load baring properties due to its density and strength, oak resists environmental effects of decay well so you can expect oak to have longevity.
Under normal circumstances as say an untreated outside gazebo, raised away from standing water (on staddle stones or similar), it can easily last up to 30 – 40 years. Which is far more than, if that gazebo was supplied and fitted as ‘posts into ground’ for example, the lifespan would instead be 15 – 25 years. Compared to Ash, another hardwood, that’ll only last up to 5 years. So, for durability, oak is one of the best woods for the outdoors.
Rest assured, you’ll entertain guests for many years under an oak garden structure.
Is Oak Strong?
We often think of steel as the most effective construction material. A book published in 2007 named Green Oak in Construction came up with surprises.
Stress tests showed steel is three times stronger than green oak. No surprise there.
But this tale has a twist. The study also highlighted steel is ten times heavier. Looking at the strength to weight ratio, experts revealed oak as superior to steel.
Worried about oak's strength? You needn't. Oak is strong and will handle the stress of any outdoor structure.
Is Oak Water Resistant?
We are in Britain, so an outside structure must withstand erratic rainfall.
It’s completely normal for oak to absorb and lose moisture throughout the seasons, this is known as moisture movement. However, because it’s a closed-grain hardwood its somewhat water resistant. Which has some interesting science behind it, but don't leave, I'll explain as simply as I can.
Oak has cellular growths called tyloses. These outgrowths plug the oak pores, making oak watertight.
Because of such water resistance, oak was the key material for building 18th-century ships. Let's not forget that its non-porous qualities have also made it a preferred wood for whisky and wine casks.
Safe to say, if oak can sail the seven seas and age the finest single-malt whisky, then it's a prime wood for outdoor use.
That said, while not a necessity, you can make oak more water repellent. A layer of Osmo WR Base Coat does the job. But even without treatment, oak is a weather-resistant wood.
To boot, we source all oak from Europe, not only for its quality but it's already acclimatised to a comparable temperate climate.
Want More Natural Beauty?
Oak is yellowish-brown with a distinct silver grain.
From the outset a striking timber, but over time you'll see changes to oak. Especially with outside oak structures exposed to the environment.
Through exposure to the UV rays of the sun, oak develops a silver hue. As luck has it, many oak lovers want this colour change as it adds to the traditional characteristics.
Silvering not for you? You can treat oak to slow colour change. We suggest UV-Protection Oil.
When using fresh sawn oak, the drying process is slow. During the early stages, natural splits, cracks and surface checks appear. Expect such changes. Again, these add to the classic aesthetics and don't diminish structural integrity.
Quite the contrary, as the oak dries it shrinks and all of the cells are pulled closer together including around joints creating a harder more sturdy structure.
Compared to metal structures, oak offers a more timeless traditional look. And while people have preferences with wood, oak is one of the most loved timbers on looks alone.
How Does Oak Fair Against Infestation?
Hard, durable, and water-resistant, so far it’s the dream recipe for your outdoor structure.
Now throw in the high tannin content, Oaks natural defence against various afflictions and you'll have the ingredients of wood resistant to fungal infestation. Not sure what tannins are? Tannins are acidic chemicals found in the liquid sap, more on that later.
Based on years of research, oak has proven resistant to decay, so you have no worries here, just rot-free performance.
Of course, if you're worried, you can add further protection with our old friend WR Base Coat that'll further safeguard against rot and insect attack.
What Are The Disadvantages of Oak?
Oak is a very unique and desirable timber but as with every timber species it has its own set of difficulties.
Is Oak Hard To Handle?
Oak isn't the easiest timber to work with. As a hardwood, it blunts tools and, to the untrained carpenter, it's easy to splinter.
While a negative to the budding DIY enthusiast, we don't have such problems at Oak Timber Structures. We have high-grade tools to help cut all oak beams with precision. What's more, our experienced artisans with a collective 100 years plus of know-how perform all carpentry work before delivery.
Upon arrival, it's just a matter of assembling the oak garden structure. We do a test build of all our structures to ensure assembly is as straight forward and problem free.
Is Oak An Expensive Wood?
In terms of outright cost compared to other timbers, yes European oak is more expensive. But it's a classic case of you paying for what you get.
Softwoods are, in general, cheaper, so commercially they make up 80% of the wood used worldwide. The price of a softwood outdoor structure will appeal, but comparative to oak they are inferior in every way.
Take Douglas Fir as a softwood example, often favoured for structural use. As an outdoor structure Douglas Fir has a lifespan of 10 to 15 years because of its lack of durability. Compare to an oak structure that’ll stand proud for up to 40 years.
Although oak is more expensive initially, when considering the lifespan versus cost ratio, it works out wiser to go with oak in the long run.
The durability of oak ensures its value for money. Without the need to replace and maintain, you’ll save time, hassle, and in the long term, money.
Does Oak Have A High Tannin Content?
Tannin compounds are found in many species of plants. Oak has a high tannin content alongside woods such as cherry, mahogany, and walnut.
Although tannins offer natural protection and reduce decay, there is a downside, rather, more of an inconvenience.
Throughout the seasons as moisture leaves oak, it discharges the tannins with it that leave behind brown streaks. So during the drying process, you'll find tannin marks down oak beams, and anything the architect sits on, such as brickwork or staddle stones.
Brown streaks down a new gazebo don't sound appealing, but its completely natural and it will stop occurring overtime. In fact, all it takes is water and a household cloth to remove them. For longer standing stains, oxalic crystals will make quick work of streaks on both brickwork or the wood itself.
Another consideration of tannins is that due to their powerful protective properties, they can overtime corrode through iron, so any iron nails or hardware is a no-go. Stainless steel screws and nails are fine, so it's a small sacrifice.
Cleaning tannin stains and ordering stainless steel screws isn't ideal, but the pros of natural tannins outweigh the cons.
Does Oak Have Defects?
Like any wood, oak can have defects. Though, at Oak Timber Structures we only use the best quality oak where defects are purely visual and in most circumstances add to the character of the structure. For a more comprehensive explanation of what’s expected in our oak, take a look at this PDF.
A quick breakdown of some of the terms are described below.
Knots
A knot is a broken or cut-off base of a branch. By receiving nourishment from the stem, dark rings known as knots form.
Sound knots are solid and can even add to the rustic look. Unsound knots, however, are loose and can even fall out. An unsound knot results from a dead branch not fully integrated into the tree at the time of felling.
Ring Shake
A ring shake is a separation between growth rings. Caused by bacteria, and sometimes high winds. These are more harmful than shakes, or cracks, that appear after felling the tree during drying.
Holes
Holes can occur if infested with pests such as an Oak Pinhole Borer (Platypus cylindrus). The larvae bore into the oak, leaving behind holes degrading the aesthetic of the wood.
The previous are examples of oak defects, and although you wouldn't want any of these in your outside oak timber structure, you can avoid them.
How? Pick the respectable grade of oak.
You know at Oak Timber Structures we source our oak from Europe? European sawn oak is subject to EN975-1 grading rules that categorise the quality of timber depending on appearance.
We only use QPA and QP1 grade oak. These are the highest grades available. This ensures our oak has no bark pocket, curly grain, frost crack, ring shake, rot, star shake, unsound knots, unsound sapwood, or white holes.
While less susceptible to defects than other woods, defects happen to oak. It's only natural, but if you're careful where you get your oak from, you'll have no issues.
Is Oak Heavy?
The density of oak means it's heavy. When moving large oak beams, you'll need to call in a few favours from friends to lend a hand.
It can pose a problem for DIYers when assembling their own outside structure, too. Again, it's wise to get person power in place to hold beams in position before joining them.
Have you heard the saying work smarter, not harder? Use a genie lift. A genie lift holds oak beams in place, allowing you or a builder to fix the joints.
If hiring a genie lift, make sure you have a model that'll take the weight of the heaviest part. But this is a smart choice to increase productivity and make light work of heavy oak beams.
Is Oak Wood Suitable For Outdoor Use?
So is oak the best timber for a garden structure?
Possessing durability, water resistance, and natural good looks, oak is an ideal outdoor wood.
Oak structures withstand the hardships of the outdoors better than most timbers. Safe to say, an oak structure has the durability to stand for many years.
As a water-resistant wood, oak needs little to no maintenance. This saves you precious time having to reapply waterproofing. You’ve better things to do at the weekend, right?
Talking of time…
Building an outside structure of oak is much quicker than making one from brick.
When buying our kit form oak garden structures, we’ve done all the cutting and joinery exactly as you want it. You just have to assemble it. Our kit form oak structures make it even faster to have a ready-to-use garden architecture.
When assembled, it'll showcase powerful and traditional looks unachievable with other materials.
What are the pitfalls of using oak for an outside structure?
Truth is, you can overlook a lot of the cons. For example, oak is heavy to work. But such density makes oak so durable.
For such an enduring wood, you'll have to pay more. But consider this, although more expensive than Larch and Douglas Fir, it won't rot and you'll enjoy an outstanding oak timber structure in your garden for many years.
You can avoid other disadvantages by making the right decisions when buying an oak structure. Only get high graded oak and make sure a timber expert performs the carpentry.
Used in construction for generations, it's a traditional building material that won't go out of fashion.
For outside structures with grandeur, longevity and minimal fuss, oak is the best outdoor wood.
Do you want to see an oak garden structure in action? Head over to our oak gazebo, and oak pergola page.