Why 20mm Timber Cladding Outperforms 18mm: The Smart Specification for Performance and Longevity

QTD Ltd
Jul 9
3 min read

In the world of external timber cladding, small decisions can have a big impact. One of the most overlooked, yet crucial, choices is cladding thickness. While 18mm boards are becoming more common, 20mm timber cladding offers significant advantages across thermal efficiency, durability, and overall long-term value.

At QTD Ltd, we’ve worked with countless residential and commercial projects, and we always recommend 20mm as the minimum standard.

Here’s why:

1. Better Thermal Performance: Every Millimetre Matters

When it comes to thermal performance in timber cladding, thickness plays a key role.

20mm boards provide improved U-values, meaning better insulation and greater energy efficiency.
That additional 2mm enhances your building’s ability to retain heat in winter and stay cool in summer.
Thicker timber supports eco-conscious designs aiming to meet Passivhaus, BREEAM, or other sustainable building standards.

With energy efficiency more important than ever, 20mm timber cladding isn’t just smart—it’s future-proof.

2. Enhanced Dimensional Stability: Less Movement, Less Maintenance

Timber naturally expands and contracts with changes in moisture. Choosing 20mm cladding increases stability over time.

Thicker boards are less prone to warping, cupping, and splitting, especially in exposed environments.
Fixings hold better in 20mm timber, reducing the risk of screws or clips loosening over time.
It creates a stronger barrier against long-term wear caused by UV, wind, and rain.

For high-performance façades that look better for longer, 20mm is the reliable choice.

3. Long-Term Durability: Built to Last

Investing in 20mm timber cladding means fewer repairs, fewer replacements, and less hassle.

Over a 25–40+ year lifespan, 20mm timber outperforms 18mm in structural integrity, visual appearance, and overall lifespan.
Greater resistance to dents, knocks, and surface wear from pressure washing or maintenance.
Reduced lifecycle costs make it the smart choice for homeowners and commercial developers alike.

In short: you pay a little more upfront, but you gain significantly more in long-term value.

4. Superior Finishing and Fixing: Looks Matter, Too

That extra thickness isn’t just functional—it’s also aesthetic.

Crisper profiles and cleaner detailing are possible with 20mm timber, enhancing the visual quality of profiles like tongue & groove, shiplap, or rainscreen.
Fixings penetrate deeper, ensuring a secure hold even in vertical or concealed systems.
Oils, stains, and paints adhere more evenly and last longer on thicker timber.

The result? A cladding solution that not only performs well—but also looks premium.

5. Insurance, Warranty & Compliance: Reduce Your Risk

Insurance providers and warranty schemes are increasingly favouring 20mm+ external cladding for a good reason.

Thicker timber is seen as a lower-risk material for weather exposure and fire resistance.
It aligns more closely with UK Building Regulations and best practices in modern construction.
Some warranties may exclude coverage for cladding under 20mm—don’t let 2mm put your project at risk.

For peace of mind, 20mm timber cladding supports better compliance and coverage.

6. Why 18mm Is a Compromise

Some suppliers recommend 18mm cladding due to ease of handling, reduced weight, and slightly cheaper sawn sizes (e.g. 23mm instead of 25mm raw boards). But these are short-term wins with long-term costs:

Less stability = more maintenance.
Less material = lower thermal resistance.
Thinner boards = higher risk of failure under environmental stress.

At QTD, we don’t believe in cutting corners. We stand for value, performance, and longevity. And when it comes to timber cladding thickness, 2mm can make a material difference.

Choose 20mm Timber Cladding with Confidence

From insulation and weather resistance to visual appeal and long-term savings, 20mm timber cladding delivers across the board. Whether you’re specifying materials for a new home or a large commercial scheme, this one simple choice can dramatically affect your building’s performance.

Size does matter - especially when it comes to protecting your investment. Choose smarter. Choose stronger. Choose 20mm.

📞 Ready to Specify 20mm Timber Cladding?

Speak to the experts at QTD Ltd. We offer a wide range of premium timber cladding profiles, all expertly machined to 20mm for durability, beauty, and performance.

👉 Order your sample today or get in touch for tailored advice on your project.