- Preservative treatment: Never needed — Siberian larch is naturally Durability Class 3. No fungicide, no preservative, no biocide ever required for above-ground cladding.
- Oiling: Optional — only to maintain the warm honey-gold colour. No effect on durability whatsoever. If you like the silver-grey weathered look, never oil it.
- Going grey: Normal and harmless. UV-driven surface colour change only — not decay. Self-maintaining once established. Structurally identical to newly installed larch.
- Cleaning: Every 1–2 years — soft brush, dilute wood cleaner, top to bottom. Biocidal cleaner for algae. Pressure wash with fan tip for deeper clean.
- Fixing inspection: Every 5–10 years — check A4 stainless fixings are tight.
- Service life: 20–35 years above ground, no treatment. The same whether oiled or left to weather.
Siberian larch is one of the most popular exterior cladding timbers in the UK — and one of the most misunderstood when it comes to maintenance. The two questions we hear most often are: does it need treating? And why is it going grey? The answers are straightforward — no, and because that is what larch does — but understanding why matters both for managing expectations and for making the right decision about whether to oil or leave it. This guide covers the complete maintenance picture for Siberian larch cladding in the UK: what is genuinely needed, what is optional, what is completely unnecessary, and the right approach for keeping it looking its best throughout its 20–35 year service life.
Why Siberian Larch Does Not Need Preservative Treatment
The reason Siberian larch does not require preservative treatment is not a marketing claim — it is a consequence of the species' natural biological durability rating. Siberian larch (Larix sibirica) is classified as Durability Class 3 (Moderately Durable) under BS EN 350, the European standard for timber durability. This classification means it has sufficient natural resistance to biological decay organisms — fungi and bacteria — to perform in above-ground exterior use without chemical preservative treatment throughout its service life.
The durability comes from larch's high natural resin content and the density of its growth rings — both products of the slow growth conditions in Siberian forests. The resin impregnates the wood fibres and makes them hostile to the decay organisms that attack lower-durability softwoods. Standard Nordic spruce and pine are Durability Class 4–5 — they have virtually no natural resistance and will fail within 3–5 years without treatment. The gap between these species in practical service life without treatment is significant: larch lasts 20–35 years, untreated spruce lasts 3–5 years.
This distinction matters practically: if you have Siberian larch cladding and have not treated it, you have not made a maintenance error. The cladding is performing exactly as it should. The absence of preservative treatment is not a risk factor for larch — it is simply the correct specification for a naturally durable species.
Siberian Larch Cladding Maintenance Schedule
Never needed above ground — Durability Class 3. No fungicide, no biocide, no chemical preservative of any kind required throughout the 20–35 year service life.
Larch does not develop the rough fibrous surface breakdown of treated softwood. No sanding back or stripping is needed at any point during its service life.
Only if you want to maintain the warm honey-gold colour. Slows natural greying — does not stop it permanently. Has zero effect on durability if skipped entirely.
Brush and wash to remove algae, surface deposits, and organic matter. Purely cosmetic — does not affect service life if skipped, but keeps the elevation looking its best.
Check A4 stainless fixings are tight. Larch's dimensional movement means fixings should stay firm — but a periodic check is good practice on any timber elevation.
Larch Cladding Going Grey — What Is Happening and Should You Worry?
The most common concern we hear from larch cladding owners is that the timber is turning grey. It is almost always framed as a problem — something going wrong that needs addressing. It is not. The greying of Siberian larch cladding is a normal, expected, structurally harmless process and is one of the defining aesthetic characteristics of the species.
Here is what is actually happening. When larch is first installed, its surface is rich with natural extractives — resins and tannins — that give it the characteristic warm honey-gold colour. When this surface is exposed to UV radiation from sunlight, a photochemical reaction gradually breaks down the lignin in the surface layer of the wood. This process — called photo-oxidative degradation — bleaches the surface and eventually turns it silver-grey. It affects only the outermost layer of the timber, typically less than 1mm deep. The wood beneath this surface layer is completely unaffected.
The grey is not biological decay. It is not rot. It is not damage. A larch elevation that has weathered to silver-grey for 10 years is structurally identical to one installed recently — the same Durability Class 3, the same service life ahead of it, the same performance under BS EN 350 testing. The colour change is purely cosmetic.
Many architects and homeowners now actively choose to leave Siberian larch untreated precisely because the silver-grey weathered appearance is considered one of the most attractive natural finishes available for exterior cladding. The greying is even, attractive, and self-maintaining once established — it does not get worse over time, does not look patchy, and does not require any intervention. If you like the grey, do nothing. If you prefer the warm gold, oil every 2–3 years.
How to Maintain the Warm Gold Colour
If you want to maintain the initial honey-gold colour of your larch cladding, the programme is straightforward — apply a UV-stable penetrating timber oil before or shortly after installation and repeat every 2–3 years. The oil works by providing UV filters that slow the photochemical process driving the greying. It does not create a surface film — it penetrates into the wood fibres and the UV protection works from within.
Recommended product
Koopmans Houtolie is the recommended oil for Siberian larch cladding — a penetrating linseed-based wood oil with UV stabilisers that nourishes the modified wood fibres without forming a surface film that can crack or peel. Apply by brush along the grain, working top to bottom. One coat is standard for maintenance applications; two coats for first application on fresh or thoroughly cleaned boards.
Timing and frequency
- First application: Before installation or within the first 3 months after installation, before significant greying begins. This is the most effective intervention — oil applied to fresh larch penetrates most deeply and provides the best long-term colour retention
- Subsequent applications: Every 2–3 years, after thorough cleaning. Apply in dry conditions — minimum 48 hours of dry weather before and after application. Spring or early autumn are the best times — avoid high summer heat which can cause oil to dry on the surface before penetrating
- Before re-oiling: Clean the cladding thoroughly first — see the cleaning section below. Oil applied over surface contamination does not penetrate correctly and will look patchy
If your larch has already weathered to silver-grey and you apply oil, the result will not be a return to honey-gold. Oil applied to greyed larch will darken it temporarily — it will look wet and slightly darker grey immediately after application — but it will not restore the original warm colour. Once larch has greyed, the surface lignin has already been degraded by UV and the original colour cannot be recovered by oiling alone. For a fully greyed elevation where you want to restore colour, a light abrasive clean followed by a specialist grey protect product is more appropriate than standard oil.
How to Clean Siberian Larch Cladding
Cleaning is the only genuinely recommended regular maintenance task for Siberian larch cladding — and even this is cosmetic rather than structural. Larch will accumulate surface deposits in UK conditions — algae, dust, airborne pollutants, and biological staining — particularly on shaded and north-facing elevations. Annual or biannual cleaning keeps the elevation looking well-maintained and prevents heavy organic accumulation in shadow gaps and board joints.
Cover windows and doors with plastic sheeting. Lay sheeting on planting beds and paving below the elevation to catch cleaning product run-off. Larch's natural tannin content can cause light brown staining on adjacent light-coloured surfaces — particularly in the early years before tannins have largely leached out.
For elevations with visible green algae or biological staining, apply a dilute biocidal exterior wood cleaner and leave to dwell for 10–15 minutes before washing. This breaks down the biological deposits and makes them significantly easier to remove. Do not let the product dry on the surface.
Work from the top of the elevation downward — always. Dirty water runs down over already-cleaned boards if you work bottom to top. Use a soft brush with dilute exterior wood cleaner for routine cleaning, or a pressure washer with a fan-tip nozzle at low-medium pressure for a deeper clean. Never use a concentrated jet nozzle which forces water behind boards and into the cavity.
Rinse the full elevation with clean water, top to bottom, to remove all cleaning product residue. Residue left on larch can cause uneven colouration and will interfere with the adhesion and penetration of any subsequent oil application.
If you plan to oil after cleaning, allow a minimum of 48 hours dry weather before applying oil. Larch's relatively dense grain means it can hold surface moisture for longer than it appears. Oiling damp timber traps moisture, causes uneven penetration, and can lead to surface mould growth under the oil layer.
Larch vs Other Species — Maintenance Compared
| Species | Preservative needed? | Oiling | Cleaning | 30-yr maintenance cost/m² |
|---|---|---|---|---|
| Siberian Larch | Never | Optional 2–3 yrs | 1–2 yrs | £0–£15 |
| ThermoWood | Never | Optional 3–5 yrs | 1–2 yrs | £0 |
| Charred Timber | Never | Optional 5–8 yrs | 2–3 yrs (gentle) | £0 |
| Nordic Spruce | Every 2–3 yrs — essential | Included in treatment | Before each treatment | £45–£75 |
The maintenance comparison illustrates the key practical advantage of Siberian larch over treated softwood: the 30-year cost of maintaining larch is close to zero — a periodic clean and optional oiling — versus £45–£75 per m² for spruce which requires a consistent preservative treatment programme. On a 50m² house elevation, that difference is £2,250–£3,750 in maintenance costs over 30 years. See our timber cladding lifespan by species guide and our Siberian larch cladding cost guide for full species comparison.
Tannin Run-Off — What to Expect in the First Year
One characteristic of Siberian larch that catches some owners by surprise is tannin run-off in the first 12–18 months after installation. Larch contains natural tannins — the same compounds found in red wine and oak — which leach from the surface as rain washes over the fresh boards. The run-off can cause light brown staining on adjacent light-coloured paving, render, or masonry.
This is not a product defect or installation problem — it is a normal characteristic of the species. The tannin content gradually reduces as the surface weathers and the extractives leach out. For a full overview of the species see our ThermoWood vs larch comparison and our low maintenance timber cladding guide. After the first full weathering season, tannin run-off reduces significantly. To manage it during the first year, protect adjacent light-coloured surfaces with temporary flashing or sealant at the base of the cladding, and clean any staining promptly with a dilute acid cleaner while it is fresh.
Does Siberian larch cladding need treating?
No — Siberian larch is naturally Durability Class 3 and does not need preservative treatment for above-ground exterior cladding. It will last 20–35 years without any treatment. Oiling every 2–3 years is optional for colour maintenance only — it has no effect on durability.
Why is my larch cladding going grey?
Larch cladding turns grey due to normal UV-driven photochemical degradation of surface lignin. It is not decay or damage — purely a surface colour change that does not affect the timber's durability or service life. It is self-maintaining once established. Oil every 2–3 years to slow the process if you prefer the warm gold colour.
How do I stop larch cladding going grey?
Apply UV-stable penetrating timber oil such as Koopmans Houtolie before installation and every 2–3 years thereafter. This significantly slows the greying process. Oil does not stop greying permanently — all natural timber will eventually grey — but regular oiling maintains a warm gold tone for the life of the cladding.
How long does Siberian larch cladding last?
20–35 years above ground without any treatment. Correctly installed with a ventilated cavity, 150mm ground clearance, and A4 stainless fixings, 25–30 years is realistic for most UK locations. Service life is the same whether the cladding is oiled or left to weather naturally.
How do I clean Siberian larch cladding?
Soft brush and dilute exterior wood cleaner, top to bottom. Biocidal cleaner for algae — dwell 10–15 mins, scrub, rinse. Pressure wash with fan-tip nozzle at low-medium pressure. Allow 48 hours to dry before oiling. Clean every 1–2 years for most UK elevations.
Siberian Larch Cladding — UK Stock, No Maintenance Required
We supply Siberian larch cladding in shadow gap, shiplap, rainscreen, feather edge, tongue and groove, and loglap from UK stock. FSC and PEFC certified. We also stock Koopmans Houtolie for colour maintenance. Nationwide delivery in 7–14 days.