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If you’re looking for a garden room with composite cladding this article will tell you everything you need to know to decide whether this material is the best choice for you.

I read so many introductions like this. Actually, I often write introductions like this. I do this because Google likes this kind of introduction. Sometimes it seems like we’re all just worshipping the algorithm! The mighty algorithm wants people to find the information they need ASAP, with as little effort as possible.

And usually, they do a blimmin’ good job. But today I am a dissatisfied Google customer. 

Today our Sales & Marketing Manager Nicola asked me to write a blog about composite cladding to help our potential customers decide if a Gillies & Mackay Garden room is right for them. Only one thing is preventing me from carrying out that task. It’s this:

Do you have any idea HOW ANNOYING I am?

How do I research and write these blogs?

summerhouse as an office
My wee timber office, where I do my double-checking.

I work with a group of hugely experienced, incredibly knowledgeable experts. Their field of expertise is timber garden buildings, and since I started working at Gillies & Mackay, I have learned so much from them. 

But no matter how much I am in awe of their skills, their expertise and their encyclopaedic knowledge of timber buildings, for some reason every time I learn something new, I HAVE QUESTIONS. 

I can’t just accept what I’m told. Every time, I Google, I read, and I research. I confirm for myself what Cara, Grant or Gordon have been kind enough to share with me. 

It’s not them. It’s me. And I know how irritating it is. But I absolutely can’t help it.

I trust them. I know that they know exactly what they’re talking about. They have decades upon decades of experience between them. But there’s some impulse in me to double-check literally everything. Maybe I have trust issues. Maybe I need professional help. 

But because of this impulse, I know when I write a blog about double glazing, shed materials, or garage specifications, that what I’m writing is true and accurate to the best of my knowledge. 

The other day I overheard a phone call from a customer. They were getting in touch because their garage was letting in water during the storms we’ve had lately. My heart almost stopped! As soon as Ailsa finished the phone call, I asked her in a panic, “HOW OLD IS THEIR GARAGE?!”

Because we have so much content that says our garages don’t leak. And given that Storm Babet literally swept away bridges and destroyed homes, it wouldn’t have been unreasonable for even our garage specification to let in some water. But I was horrified by the thought that what I was writing may not be true.

Oh, the relief when I discovered that the garage was 15 years old, and therefore a single-skinned building, made long before we upgraded our garage specification. 

Why don’t Gillies & Mackay use composite cladding?

But what does all this have to do with composite cladding?

Here’s what Cara told me when I asked her about composite cladding: “I don’t trust any material that’s artificially bonded together. If it’s been stuck together, sooner or later it’s going to come apart.” 

Born and raised in the ShedLife, Cara knows timber products. 

But I’m super annoying, remember? So off I went to Google to find out everything I could about composite cladding. I’d already done several hours of research before Nicola asked me to write this blog. And I was struggling.

Because the first three whole pages of my search results were sales blogs masquerading as unbiased content. They told me very little, apart from how wonderful composite cladding is. 

So what’s going on? Is Cara a liar? Has her timber building background blinded her to any other materials? As CEO, she decides what kind of products we sell, and she was dead against composite cladding for our Garden Rooms

And I trust her. The decision to use Radiata Pine ThermoWood wasn’t one that she took lightly. If she says that composite cladding is problematic, it’s up to me to find out why, so you can benefit from honest, accurate content.

After some more searching, I discovered an article that warned against buying cheap composite cladding. Aha! Now we’re on to something!

But nothing in this article tells me anything about how to tell the difference between poor-quality composite cladding and good-quality composite cladding. It doesn’t even give an indication of how much you should pay to guarantee good quality. Another dead end.

So here’s what I know for sure:

What is composite cladding?

Composite cladding is made from wood fibres mixed with either cement or thermoplastics. This material is then made into boards or panels and commonly used for decking and cladding.

Cement fibre composite tends to be cheaper than wood-plastic composite (WPC).

I can also definitely state that composite cladding is a poorer insulator than timber cladding. Thermal conductivity measures how well a material conducts heat. The lower the number, the better the insulation factor of the material.

Thermal Conductivity of Fibre Cement 0.216 
Thermal Conductivity of WPC0.3-0.5 
Thermal Conductivity of Scandinavian Redwood0.12
Thermal conductivity of ThermoWood Pine0.099 

Composite cladding vs timber cladding.

There are tons of blogs out there that compare composite cladding to timber, and this isn’t always a fair comparison. Because as any Sheddie knows, there’s timber and there’s timber.

Many blogs state that composite cladding is more expensive than timber. This depends on the type and quality of timber, and the type and quality of composite. It’s not a straightforward comparison. In order to make an informed decision, you have to know not just which materials you’re comparing, but also which specific qualities each material has.

Finding the specific qualities of timber can be difficult enough, but finding out about composite cladding? It’s almost impossible!

Is cement fibre cladding reliable?

A screenshot of Dalply.co.uk's blog "Pros and Cons of Fibre Cement Cladding."

So what does Google have to say about cement fibre cladding? 

I asked, “Is cement fibre cladding reliable?”

Fibre cement cladding is by far one of the most durable products on the market for your siding. It is resistant to water, UV rays, rotting, bugs, and other vermin that might try to damage your home.

This is from a blog called “Pros & Cons of Fibre Cement Cladding” on a website called dalply.co.uk. It’s surprisingly light on cons.

Guess what Dalply sell?

I tried again. I Googled “Fibre cement cladding problems”

Again, a Dalply blog is the top result:

Some of these problems include issues with the installation causing gaps, loose nails, and an uneven surface. Some other problems can come from rodents, extreme weather, and water damage. When you notice that your fibre cement cladding needs repaired, you should do so as soon as possible.

So which is it, Dalply? Is fibre cement board resistant to water, UV rays, rotting, bugs and vermin, or does it experience problems such as rodents, extreme weather, and water damage? And is it low-maintenance (another feature that’s often highlighted) or will it need repaired?

Is wood plastic composite reliable?

Five samples of wood plastic composite cladding from Neotimber, in various wood-effect colours.
Composite cladding samples from Neotimber

What about wood-plastic composite cladding?

Google tells me,

Like all other composite materials, composite cladding is made with reclaimed wood materials and recycled plastic. This gives it many benefits when used as an exterior wall cladding, such as durability, longevity, eco-friendliness, and much more.

When I ask about problems I find,

The first problem is that the moisture content in wood-plastic materials is too high. Wood-plastic materials often have a porosity of 16-21%, which causes them to break easily and be easily damaged by microbial contamination.

Durable and long-lasting, or susceptible to breaking and decay?

Once again, the difficulty here is that these are both sales blogs masquerading as unbiased content. The first article is from Ecoscape, which sells composite cladding, and the second is from Oakio, which sells, you guessed it, composite cladding.

Is Oakio pointing out possible problems with their product? Are they out there doing the good work to tell us what we need to know? No. They’re selling a product that differs from other types of composite cladding. Is it a better product? I only have Oakio’s word for that. 

Oakio compares HDPE plastic composite, which their product uses, to PVC plastic composite, stating that HDPE is more durable. 

But when I tried to compare HDPE composites and PVC composites another sales blog told me this:

PVC-based composite decking tends to be slightly more expensive than HDPE-based composites but offers higher durability and overall quality.

This blog refers to decking because it’s nigh on impossible to find out if composite cladding is PVC-based because PVC cladding is a cheaper non-composite product which doesn’t contain any wood fibre. So not only am I none the wiser about whether HDPE composite or PVC composite is more durable, but I also don’t know if any of this even applies to cladding!

Are you wondering whose sales blog you should trust? Me too!

How do I know if composite cladding is good quality?

Good question. Honestly, right now, I have no idea. Here are just some of the variables you need to account for:

  • What type of wood fibre has been used?
  • What type of thermoplastic has been used?
  • What are the properties of each different wood fibre?
  • What are the properties of each different thermoplastic?
  • What percentage of wood fibre and plastic are used?
  • What are the manufacturing processes used to create this cladding?
  • Have any additional protective chemicals been applied?
  • Is the cladding capped or uncapped?

Even if you can find the answers to all these questions (I’ve yet to find a website that provides this information) you still have to understand the impact that each variable has, compare it to the alternatives, evaluate each property based on your budget and priorities, and find a product with these properties that will give you what you want. And all you have to go on are sales blogs.

Now I don’t know about you, but I don’t have a degree in materials science or chemical engineering. I don’t have the knowledge or expertise to definitively state that one composite product is better than another, and I don’t know anyone who does.

However, as a dedicated researcher, I dove into the world of composite cladding science. Here’s what I discovered.

A brief history of wood composite plastics.

A screenshot from the Journal of Bioresources and Bioproducts, showing an article called "Wood plastic composites based wood wall's structure and thermal insulation performance."

Wood plastic composites have been around for much longer than you’d think. They were first invented by an Italian plastics company in Milan in 1960.

The development and improvement of wood plastic composites has continued since then. Why? Well, to make the material better. 

UV stabilisers have been added, chemical processes have been applied, and all sorts of complicated clever science has been used to create a material that is durable, weatherproof, resistant to rot and insect damage and low-maintenance.

This research and development continues to this day, with various companies trumpeting the benefits of the unique manufacturing process they use or the secret formula that makes their product the very best on the market. All the potential combinations of all those variables above, plus many more, are being explored and tested. A garden room with composite cladding could feature a 70-year old obsolete technology, or a cutting-edge building material.

But even if you get seriously involved in literature with titles like “Wood Plastic Composites Based Wood Wall’s Structure And Thermal Insulation Performance,” Moisture Sorption, Biological Durability, and Mechanical Performance of WPC Containing Modified Wood and Polymers,” or “Evaluation and Testing of Mechanical Properties of Wood Plastic Composite,” it’s incredibly difficult to actually tell which composite cladding materials are durable, weatherproof and resistant to rot, and which are susceptible to vermin, water damage, extreme weather and breakage.

Can you see now why we decided to stick to timber cladding for our Garden Rooms?

What is ThermoWood?

Not that we’re against innovation. The ThermoWood Radiata Pine cladding we use is treated with heat and steam to permanently change the chemical composition of the timber, protecting it from the weather, insect damage and rot. This process makes the timber incredibly durable and prevents it from absorbing moisture and changing shape or shifting within the building.

But it’s still timber. Created by nature. Modified by clever Finns.

Hold on. Isn’t this another Johnny-come-lately overcomplicated process to try to rescue an inferior product?

Not at all. People have been using heat to modify timber for centuries.

In Japan, Yakisugi treatment has made wood more weatherproof since at least the 17th century. However, much earlier examples exist. The Horyu-ji Temple in Ikaruga, which houses what is believed to be the oldest timber building in the world, was partially rebuilt with Yakisugi timber in 711!

Those ancient craftsmen may not have understood the science, but they knew that it worked. 

And heat treatment still works. That’s why we use it. 

Should I choose a garden room with composite cladding?

Now, of course, I still write sales blogs. We need to keep the lights on around here! 

But since I can’t help but check and double-check every piece of information that comes my way, I can very confidently say that I can’t recommend composite cladding. Not because I think it’s rubbish. Not even because Cara doesn’t trust it. But because I don’t know enough about it, and can’t find the information I need to make a good choice. 

Am I saying this to nudge you towards a timber building instead?


I’m saying this because the dizzying array of materials, composition, quality and longevity make it incredibly difficult to choose a high-quality composite cladding product. Unless you’re an expert, all you have to go on are sales blogs, all of which sing the praises of composite cladding. I don’t have enough information to recommend this product. 

I can’t accurately assess whether a garden room with composite cladding will be long-lasting, problematic, or good value for money. And neither can you.

This isn’t to say that composite cladding is a load of rubbish. There are plenty of satisfied customers out there. But if you want a durable, low-maintenance garden room, can you find enough information about composite cladding to make an informed decision? You might end up as a satisfied customer, or you may not. 

And since composite cladding continues to change and develop, all of these products are very new. Will they stand the test of time? The only way to know for sure is to take a chance.

But if you do happen to be an expert in composite cladding, please – get in touch! I have SO MANY annoying questions. And please don’t be offended when I double-check absolutely everything you tell me!

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