Douglas Fir or Larch? A Simple Guide to Choosing the Right Scottish Timber.
Stop Guessing: The Definitive Guide to Douglas Fir vs. Larch for Your Scottish Project
If you're planning a decking, cladding, or construction project in Scotland, you've likely narrowed your timber choices down to two homegrown heroes: Douglas Fir and Scottish Larch. But which one offers the best durability, sustainability, and value for your specific needs? Before you spend a penny, dive into this simple, head-to-head guide that cuts through the marketing and gives you the clear facts you need to choose the perfect Scottish timber.
The Short Answer: Which Should You Choose?
Generally, Scottish Larch is the superior choice for high-exposure exterior projects like cladding and decking due to its higher natural resin content, which offers better resistance to rot and moisture. However, Douglas Fir often excels in structural applications where strength and length are priorities, offering a cleaner, straighter grain, and better value for internal framing.
Keep reading for a clear comparison of cost, lifespan, and maintenance so you can choose the best timber for your project, or get in touch for a free consultation.
Deep Dive: Durability and Lifespan
When spending money on Scottish timber, the most important question is: How long will it last? The performance of Douglas Fir and Larch largely hinges on their natural chemical makeup and stability, especially when exposed to the damp, varied Scottish climate.
Head-to-Head: Natural Resistance to Rot and Insects
Both timbers are excellent natural choices, but they have key differences in their built-in defense systems:
✅ Scottish Larch: The Natural Defender
Durability Class: Class 3 (Moderately Durable). This rating makes it suitable for many exterior applications without chemical treatment.
Resin Content: High. The heartwood is naturally rich in resins and tannins, which act as a powerful, built-in preservative, offering superior natural defense against decay and moisture.
Best For: Untreated cladding, fencing, and decking where longevity is paramount and maintenance is minimal.
⚠️ Douglas Fir: The Stable Competitor
Durability Class: Class 3–4 (Moderately to Slightly Durable). Its durability can be more variable depending on the amount of sapwood vs. heartwood present.
Resin Content: Moderate. It contains less natural resin than Larch. While still robust, it is more susceptible to moisture uptake over time, particularly the lighter-coloured sapwood.
Best For: Situations where strength and stability outweigh rot resistance, or projects where the wood will be painted, stained, or treated.
The Critical Durability Verdict: For exterior use where the timber will be completely untreated and exposed to the elements, Scottish Larch heartwood holds a clear advantage due to its superior natural defense mechanism.
Expected Lifespan in the Scottish Climate
A timber's lifespan is highly dependent on how it's detailed and installed (good drainage and ventilation are crucial), but here are the typical expectations for properly installed, above-ground exterior applications like cladding:
Scottish Larch: When the naturally durable heartwood is used for cladding and installed with good ventilation, the potential lifespan is generally 30–50+ years (with some sources suggesting 50-100 years). It can be left untreated and will weather to a desirable silver-grey.
Douglas Fir: Properly detailed Douglas Fir cladding typically has an expected lifespan of 15–30 years when left untreated. While it can be used externally, it benefits much more from a protective finish (such as a UV-resistant oil) to maximize its longevity compared to Larch.
The Stability Factor: Checking, Warping, and Shrinkage
This is where the woods trade places, and it’s a critical point for installers and joiners:
Douglas Fir: The Dimensional Anchor
Douglas Fir is known for being a refractory species, meaning it resists moisture uptake and is dimensionally stable. It has an excellent strength-to-weight ratio and a cleaner, straighter grain.
The Benefit: This stability makes it less prone to warping, bowing, or twisting, and it holds a better, cleaner profile, which is why it is preferred for structural framing and precision joinery.
Scottish Larch: The Checking Challenge
Larch is a dense wood, which is great for durability, but it can be more prone to surface checking or cracking as it dries and adjusts to new moisture levels. Despite the density of Larch, it is botanically a softwood, though it performs comparably to many true hardwood species in exterior applications, offering excellent value.
The Consideration: While these surface checks rarely impact structural integrity, they can be an aesthetic issue. Larch requires very careful installation—avoid nailing too close to the edges—and is best supplied properly air-dried to minimize movement post-installation.
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Application: Where Each Timber Excels
The best choice between Douglas Fir and Larch ultimately depends on the job. Knowing each timber's strengths and weaknesses allows you to select the right material for maximum performance, whether your project is structural, decorative, or highly exposed to weather.
Cladding and Decking (Exterior Focus)
When it comes to projects that face the full brunt of Scottish weather—like vertical cladding and horizontal decking—durability and natural rot resistance are paramount.
🏆 Winner: Scottish Larch
Why: Due to its superior natural resin content, Scottish Larch is the undisputed champion for exterior cladding and decking, especially if you plan to leave the wood completely untreated to weather naturally. Larch’s high density makes it robust against foot traffic and hard rain.
Best Use: All forms of exterior cladding (feather-edge, tongue and groove, rainscreen) and decking boards.
The Douglas Fir Option:
Douglas Fir can be used for cladding, but it requires more careful detailing and benefits significantly from a protective finish (like a high-quality UV oil) to prevent water ingress and extend its life, making it a higher-maintenance option for this application.
Structural and Load-Bearing Use (Interior/Frame Focus)
Inside a building's envelope, stability and strength are more important than rot resistance. This is where Douglas Fir shines.
🏆 Winner: Douglas Fir
Why: Its high strength-to-weight ratio and dimensional stability are unbeatable. Douglas Fir lumber provides clean, straight, and reliable beams, joists, and rafters that are less likely to twist, warp, or develop surface checks than Larch as they dry within a structure. It is easier to grade and work with for precision structural applications.
Best Use: Interior framing, large structural beams, purlins, joists, and any application requiring long, straight, and strong members.
The Scottish Larch Option:
While Larch is strong, its tendency to move and check as it dries makes it less reliable for high-precision structural elements compared to Fir. It is often reserved for smaller, non-critical support elements or secondary framing.
Fence Posts and Ground Contact
Any timber placed directly into the ground requires extreme resistance to moisture and fungal decay.
The Truth About Ground Contact: Neither Scottish Larch nor Douglas Fir should be used untreated in ground contact. Even the durable heartwood of Larch will eventually decay when constantly wet and deprived of oxygen.
The Required Solution: For fence posts or decking support that touches the ground, both timbers must be pressure-treated with appropriate wood preservatives to meet necessary standards and ensure a long lifespan.
Cost, Supply, and Sustainability
The final decision often comes down to budget and aesthetics. While performance is key, the look of the wood and its price tag are crucial customer considerations.
Price Comparison: Why is Larch often more expensive?
In general, Douglas Fir is often the more budget-friendly option, making it a highly cost-effective choice for large-scale structural work.
Scottish Larch: Typically commands a higher price per square metre than Douglas Fir, especially for quality heartwood cladding boards. This is partly due to its higher demand for premium exterior applications and sometimes more challenging milling (its dense, resinous nature can lead to more wear on blades and occasional wastage).
Douglas Fir: Tends to be more readily available and cheaper for structural sizes (beams, posts) due to its faster growth and easier workability in the mill. This makes it an excellent value for internal framing.
Money-Saving Tip: Always compare the total project cost, not just the raw timber price. Larch might cost more upfront, but its superior natural durability means you save money over time by avoiding regular treatments and replacement costs.
Appearance and Finishing: How Will it Age?
This is a key aesthetic choice, as both timbers start with warm tones but age differently, particularly in Scotland's wet environment.
Douglas Fir (The Clean Look)
Initial Look: Features warm, pinky/light reddish-brown tones with a distinctly straight, clean grain. It is typically less knotty than Larch, giving it a more modern, uniform appearance.
Weathering: When left untreated, Douglas Fir will gradually weather to a silver-grey patina, similar to Larch. However, without a protective oil, the transition can be uneven, and the wood may develop more surface checks and a rougher texture over time compared to Larch.
Takes Finishes Well: Its lower resin content means it accepts stains, paints, and oils very well, allowing you to maintain its original colour or apply a custom look easily.
Scottish Larch (The Rustic Character)
Initial Look: Starts with rich golden-yellow to reddish-brown hues with prominent, tighter growth rings and scattered knots, offering a more rustic, textured appearance.
Weathering: Larch’s high resin content acts as a natural UV shield, causing it to beautifully and relatively evenly weather to a stunning, sought-after silver-grey patina over many years. This natural process is often the desired finish.
Finishing Note: While Larch can be finished, its high resin content can sometimes make application trickier. Many builders recommend simply leaving the durable heartwood untreated.
Conclusion: Your Final Decision Checklist
Choosing between Douglas Fir and Scottish Larch is not about finding one "better" timber, but about selecting the right tool for the job. Both offer superior performance and sustainability compared to imported woods.
To make your final decision clear, use this quick checklist:
Choose Scottish Larch If:
Exterior Durability is Essential: Your project is exposed (cladding, decking) and you want the highest natural rot resistance without chemical treatment.
A Natural Finish is Desired: You plan to leave the wood untreated to weather evenly to a beautiful silver-grey patina.
Rustic Aesthetics are Preferred: You appreciate the character provided by prominent knots and a rich, golden colour before weathering.
Choose Douglas Fir If:
Structural Stability is Priority: Your project requires long, straight, load-bearing beams, joists, or framing (internal structure).
Budget is a Factor: You are working on a large-scale project where cost savings on material volume are significant.
A Clean Aesthetic is Required: You prefer a straighter, cleaner grain that is less prone to the surface checks associated with Larch.
Ready to Start Your Scottish Timber Project?
We hope this definitive guide has given you the clarity needed to proceed with confidence. Whether you choose the reliable structural strength of Douglas Fir or the outstanding exterior resilience of Scottish Larch, you are investing in a sustainable, high-performance material.
Need help calculating volumes or want expert advice tailored to your site's specific microclimate? Contact us today! Our team at Moore Timber Co. is ready to provide precise pricing and guide you through the process of selecting and milling the perfect Scottish timber for your build.
