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By Kieran Bain on 06 Jul 2021

What is the best timber thickness for a timber building in Scotland?

Stop me if I’m wrong, but you’ve been looking around for a timber building and noticed that almost every different supplier uses a different thickness of the timber. It’s almost as if us suppliers are picking numbers between 7mm and 19mm out of a hat and going: “yep, that’ll do!”

To make it even worse, some suppliers use different timber thicknesses for different parts of their buildings. 

It’s a frustrating feeling!

Especially if you’re new to the timber industry. Because there is no real explanation as to what the different qualities of each thickness are. Most importantly though, there is no way to decipher which thickness is best for YOU and your needs. 

At G&M we want oor Sheddies to be fully informed about what they are buying, whether it’s from us or another supplier. 

Let’s dive straight into it then shall we? By the end of this blog, you will feel like a leading timber thickness expert, armed with the knowledge you need, to dive headfirst into the world of timber buildings.  

What to think about when deciding on thickness of wood? 

There are lots of important questions to ask yourself when deciding on the thickness of timber to use.

If you’re lucky enough to call Scotland home, then your building needs to be extra durable

Firstly, let’s remember that for those of us who are lucky enough to embrace the Scottish weather, our buildings must be extra durable…it is Scotland after all! 

At Gillies and Mackay, the decision about our timber thickness comes down to eight main important factors. Those being;

  1. Longevity
  2. Sturdiness
  3. Weatherproof
  4. Insulation 
  5. Security 
  6. Appearance
  7. Machinability 
  8. Cost

Let’s take a dive into each of the different factors that helped Gillies and Mackay settle on 19mm Scandinavian Redwood. 

inside shed timber thickness

1. Longevity

Despite being one of the most important factors, there are no articles online explaining why thicker timber lasts longer. Can you believe it?

Thicker wood typically lasts longer because it is more sturdy meaning it won’t bow and sag. In addition, the thicker the wood, the less prone it is to water damage, meaning it’s less likely to rot.

Ticker timber lasts longer because of the joints where each bit of cladding is joined together. Most Tongue and Groove sheds start from 12mm in external cladding thickness, and anything less than that is not fit for T&G purposes.

Tongue and groove joints split the wood into three sections. And when this happens on 12mm wood, you can anticipate each section to be just 4mm thick.

Splitting a 19mm panel, however, leaves you with two 6mm and one 7mm sections. That’s 50+% thicker. 

Thinner wood usually comes with a downgrade to shiplap cladding, which causes more problems such as water ingress and sagging. For that reason, we recommend that you don’t go below 12mm cladding thickness for your timber building.

Take a read of the reviews section on any ‘cheaper’ sheds/summerhouses and you’ll see what we’re on about. 

One of these ‘cheaper’ timber buildings will typically last around 5years IF they have been assembled correctly.

Compare this to something at the thicker end of the scale, such as a 19mm Scandinavian Redwood. If you look after this, it has a life expectancy of 30 years. And you can expand the lifespan even further by applying a high-quality Sadolin Superdec. Don’t go buying all the tins of Sadolin from your supplier now, we need some too😉.

2. Sturdiness

The sturdiness of your building also has a direct correlation to the thickness of wood that you are using.

To ensure that your timber building is strong enough to withstand even the most extreme Scottish island weather you need high quality, thick timber. If not, each thin joint will easily break apart, and you will end up with a pile of firewood rather than a shed.

If the timber for your shed isn’t thick enough, you can expect the roof to bow and sag, as well as the walls. No one wants a roof that looks like it’s about to collapse or a trampoline-like floor. We’ve seen some bad sheds in our days.

3. Weatherproof

Timber is a porous object, meaning that there are small holes in it. This is because timber comes from the wood on a tree, and the tree that it comes from needs air.

Unfortunately, these small holes also mean that your timber can absorb moisture. Luckily, a thicker cladding means that it is harder for moisture to penetrate your timber and make its way inside. If moisture makes its way into your timber, you’ll end up with rotting problems, which is not good.

4. Insulation

We knew you ‘wood’ want to hear about this one. If you’re going to use your timber building all year round, you don’t want to be freezing in the winter. 

Insulation is an easy one to get your head around, the thicker the timber, the more difficult it is for heat to escape. 

If you want to take a bit of a deeper dive into this one, you can talk about the different types of timber. Redwood timber is grown in slower climates, making the wood denser.

On the other hand, whitewood timber (such as Scottish Pine), is grown more quickly. This means that the wood does not have time to bind together and isn’t as dense. However, that’s for another article and it’s one we’ve already written.

5. Security

This is one that often gets overlooked, although at G&M we think that a good timber should have you covered in all aspects of #ShedLife. 

Trust us when we say that thin timber, like 7mm timber, is easy to pull apart. Storing anything valuable in a 7mm timber shed or summerhouse is a definite ‘no no’ from us. To look at it another way, 7mm isn’t even 1cm thick!

The thicker your wood is, and the better the design of your building, the more secure your goodies inside will be.

timber security

6. Appearance

Yes, this is a genuine consideration when picking the timber thickness to use in your timber building. However, it might not be for the reason might not be exactly what you think. 

Thick timber is typically cut from the heart of the tree, meaning that it has beautifully smooth, clean, dressed grains. Timber cut from the heart of the tree also has far fewer knots and imperfections than thin wood.  

We promise there’s a method behind our picky shed-madness!

7. Machinability

Who would’ve thought that this was a word?

The guys in the workshop assure us that machinability is hugely important to them when creating timber buildings. The thickness of the timber can affect how well it can be worked by their tools. Our workshop team tell us that 19mm is pretty good for machinability meaning they can do magical things with it…like build your G&M. 

Machining thinner timber means that the margins for error are much smaller, and more worryingly these errors often go unnoticed. One poorly machined bit of timber in a thin cladding wall can send the whole building crumbling.

Compare this to a thicker timber where the structure/support from the rest of the building can support any small mistakes. These rarely occur, however this can help you understand how important the timber thickness is.

Imagine a game of Jenga. At the start of the game, you can make small mistakes and not ‘topple the tower’ because there is a strong structure (thick timber). After a few rounds, however, you get to the ‘thin timber’ stage and one small mistake can cost you the game. That’s a good analogy…we think. 

timber thickness cutting wood


Last but not least, ‘let’s talk about cost, baby!’. Often the deciding factor when trying to figure out which product is the best value for money. 

It’s easy to buy a cheap timber building with something like 7mm wood, but it’s not going to last you.

At the opposite end of the scale is good quality, thick timber, but this usually puts a dent in your wallet.

We’re definitely not cheap, but over the 35+ years, we’ve experimented with many different thicknesses of timber. We’ve come to the decision that 19mm is the ideal compromise between unnecessary cost and good quality timber. 

Why don’t we use thicker timber?

You must be thinking: “If thicker timber is better, why don’t I just buy a timber building advertised as 44mm?”

It’s a no-brainer. And they are advertised around the same price too.

If only it was that simple!

Tiger Sheds 44mm Summerhouse Example

Let’s look at Tiger Sheds ‘Siberian Summerhouse’. They are advertised as 44mm, however, the breakdown is:

  • 44mm External Cladding (Walls)
  • 19mm Flooring and Roofing 
  • Timber sourced from Europe. 
  • Made using a combination of whitewood and redwood. 

Hiding thick walls and thinner than advertised flooring and roofing in the small print…sneaky!

Heat rises, so flooring and roof are just as important as external cladding (walls of the building) in order to keep your summerhouse toasty.

The next thing to talk about is the type of timber. It’s not strictly thickness related, but it’s a good bit of information to have. 

Tiger Sheds source their timber from Europe, and while there are lots of great timber sources in Europe, there are also lots of poor timber sources. So, we don’t want to comment on the quality of their timber (but you could find out yourself by giving them a phone).

It’s also worth noting that Tiger uses a mixture of whitewood and redwood, which we’ve already discussed. Whitewood grows in faster-growing climates, and as such, isn’t as dense. Therefore water ingress and rotting is more likely than if a slow-growing, dense, redwood is used.

In addition, thicker wood tends to be ‘interlocking log’, which is true in the instance of Tiger Sheds. Interlocking log was designed for use in Northern Canada, where the weather is only cold (not hot and cold like we get in Scotland). When used in Scotland, the timber shifts, splits and bows…which is no good.

  • You can read more about this in our interlocking log blog here. 

It’s not quite as simple as it may first appear then, but we like to summarise the relationship between timber thickness and timber quality like this…

“A high quality 19mm redwood is better than a low quality 44mm whitewood.”

The wrap up…

Okay, that was a #ShedLoad of information! So let’s recap as to why the timber thickness of your building is so very important. 

In a short, but sweet explanation, the thicker the timber of your building, the longer it is going to last you, and the fewer problems you are going to have along the way. 

If you’re looking to invest in a beautiful timber building that will last you a lifetime, it’s best to spend that little bit more to get a thicker, higher quality timber. A building that might cost you 1.5x more, will last you at least 5x longer! That’s not a bad return. 

If only things were as easy as picking the thickest shed and going for that one…unfortunately though, it’s not. There are also considerations to be made on the quality of wood. For example, the difference between a 19mm spruce shed, and a 19mm redwood shed, well, that’s a story for another day. 

Now that you’re an expert in timber thickness, you might want to read about the other things to look out for when buying a timber building. There are so many differences on the market, don’t just take the suppliers’ word for it, do your research. 

All the best in your shed hunt! 

Natty x

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