Timber cladding brings natural variation, texture and warmth to elevations that brick or render cannot match. It is also among the most labour-responsive materials: a well-chosen species with minimal maintenance can last 40–60 years; a poorly treated softwood in a damp exposure zone can fail in a decade. Species, profile, fixing method and initial treatment together determine how the cladding performs over its life.
Species Overview
Treated Softwood (Scots pine, Spruce, Redwood)
European softwood — typically Scots pine (Pinus sylvestris) or Spruce — is the most cost-effective option. Untreated, it has a natural durability class of 5 (not durable) to the classification in BS EN 350-2, meaning it deteriorates rapidly in exposed conditions. To achieve serviceable life as external cladding, softwood must be pressure-treated with a suitable preservative to achieve Use Class 3.2 (above ground, repeatedly wetted) per BS 8417:2011 (preservation of wood — code of practice).
Tanalised or Vacsol-treated softwood in UC3.2 is widely available and competitively priced. It performs well when details are correct (ventilated cavity, back-primed before fixing, all end-grain cuts re-treated on site), but it must be decorated — typically painted or opaque-stained — and redecoration is needed every 3–5 years in moderate UK exposure.
Cost: £8–£14/m² supply; £18–£30/m² installed (including battens, breather membrane, fixings).
Western Red Cedar (Thuja plicata)
Western red cedar is naturally durable, Class 2 (durable) per BS EN 350-2, with natural oils that resist decay without preservative treatment. It is dimensionally stable and lightweight — approximately 370 kg/m³ — which makes it easier to handle and fix than hardwood alternatives.
Cedar weathers to an even silver-grey within 1–3 years if left untreated; this silvering is a surface oxidation process that does not compromise the wood’s structural integrity. Many architects specify untreated cedar precisely for this weathered appearance, which eliminates ongoing decoration costs. If the natural colour is preferred, a UV-stable oil or clear finish requires reapplication every 4–6 years.
Cedar is well suited to the UK climate, performs in moderate-to-severe exposure zones, and — unlike softwood — does not need pressure treatment. Its main disadvantages are cost and supply chain: most UK cedar is imported from Canada or North America.
Cost: £18–£28/m² supply; £35–£55/m² installed.
Siberian Larch (Larix sibirica)
Siberian larch has become the mainstream ‘quality’ cladding timber in UK new-build and self-build, largely replacing western red cedar on cost grounds. It is naturally durable, Class 3–4 (moderately durable to slightly durable), with a tight grain and resin content that gives better weathering resistance than European spruce. Density is approximately 520–590 kg/m³ — noticeably heavier than cedar but this adds impact resistance.
Larch weathers similarly to cedar, progressing from honey-gold through orange-brown to silver-grey over 2–4 years. It can be left untreated or finished with an oil for colour retention. Movement on drying is moderate; good kiln-dried stock (target EMC 16–18% for external cladding in the UK) minimises gapping and cupping.
Siberian larch from FSC-certified sources is widely available in the UK; European larch (Larix decidua) is a domestic alternative with similar properties and marginally lower cost.
Cost: £14–£22/m² supply; £30–£50/m² installed.
Thermally Modified Timber
Thermal modification (trade names include Thermowood, Plato Wood) heats timber to 180–230°C in a steam atmosphere, breaking down the hemicellulose sugars that decay fungi feed on and reducing equilibrium moisture content. The process transforms naturally non-durable species (ash, pine, birch) to durability Class 1–2 without chemical preservatives. Thermo-ash and thermo-pine are the most common UK-market products.
Thermally modified timber is darker in colour (mid-brown to chocolate, depending on temperature), more dimensionally stable than untreated timber, and has lower density (approximately 10–15% weight reduction). It is particularly valued in Passivhaus and low-VOC projects where chemical treatments are undesirable.
The main risk is brittleness: thermal modification reduces bending strength (MOR) and tensile strength by approximately 20–30% compared to virgin timber. Thermally modified cladding should not be used in structural applications and requires pre-drilling at fixing points to avoid splitting.
Cost: £20–£35/m² supply; £40–£65/m² installed.
Profiles
Cladding profile affects drainage behaviour, shadow lines, and the total quantity of timber required per m² of elevation.
| Profile | Description | Typical board width | Coverage ratio |
|---|---|---|---|
| Featheredge (bevelled) | Tapered section, thin at top, thick at bottom; overlapping | 100–150 mm | 1.2–1.4× face area |
| Shiplap | Rebated overlap, gives horizontal shadow line | 95–125 mm | 1.15–1.25× |
| Tongue and groove (TGV) | Interlocking; can be vertical or horizontal | 95–120 mm | 1.05–1.10× |
| Open-joint vertical (rainscreen) | Boards fixed vertically with open gap; wind-wash ventilation | 95–150 mm | 1.1–1.3× (incl. gap) |
| Waney-edge (live edge) | Rustic profile retaining natural edge | Variable | 1.3–1.5× |
Featheredge and shiplap are the traditional UK choices for horizontal cladding; open-joint vertical boards are common in contemporary architecture and allow faster drying of any penetrating moisture.
Weathering and Silvering
All timber cladding weathers if left untreated, and the rate of silvering depends on UV exposure, rain washing, and species. On south-facing elevations, silvering can occur within 6–12 months; on north-facing walls, the same process may take 3–5 years. Uneven silvering on mixed-orientation elevations is a common complaint.
To accelerate uniform silvering at installation, a dilute iron-tannate solution (‘accelerated weathering’ wash) can be applied. Alternatively, an iron-oxide pigmented wood oil in a silver-grey tone gives an immediately consistent appearance.
If maintaining natural colour, penetrating oil-based finishes (Osmo, Sikkens Cetol, Rubio Monocoat etc.) are preferred over film-forming paints. Oils breathe with the wood; paint traps moisture beneath a film and eventually peels.
Fixings
Fixings in contact with naturally acidic timbers (cedar, larch, oak) must be stainless steel grade A4 (316) or hot-dip galvanised to prevent black staining from tannin-iron reaction. Bright zinc-plated (BZP) fixings corrode visibly within 12–18 months in wet UK conditions. This is specified in BS 1202 (nails) and BS 4190 (bolts).
Hidden fixing systems (clips that engage the board profile from the rear) give a clean face without exposed fastener heads, but must allow for thermal and moisture movement — boards should not be pinned rigidly at both ends.
Back-priming all boards before installation seals the rear face and reduces moisture cycling, which is the primary driver of cupping and splitting.
Ventilated Cavity
All timber cladding requires a ventilated cavity between the cladding and the breather membrane or substrate. Minimum cavity depth is 25 mm per NHBC Standards Chapter 6.9 and BS 8000-0 (workmanship on building sites); 38–50 mm is preferable in moderate-to-severe exposure. The cavity allows moisture that penetrates gaps or joints to drain and evaporate; without it, cladding remains wet for extended periods and decay is accelerated even in naturally durable species.
Cost Comparison Summary
| Species / product | Supply cost (m²) | Installed cost (m²) | Maintenance interval | Natural durability class |
|---|---|---|---|---|
| Treated softwood | £8–£14 | £18–£30 | 3–5 years (decorate) | 5 → UC3.2 treated |
| Siberian larch | £14–£22 | £30–£50 | 6–10 years (oil) or none | 3–4 |
| Western red cedar | £18–£28 | £35–£55 | None (silver) or 4–6 years (oil) | 2 |
| Thermo-ash / thermo-pine | £20–£35 | £40–£65 | 5–10 years (oil) | 1–2 |
Costs are 2025–2026 UK supply prices (softwood and larch widely available; cedar and thermowood from specialist merchants). Installed costs include counter battens, breather membrane, stainless fixings and labour, but not scaffold.
Relevant UK Standards and Guidance
- BS EN 350-2 — durability of wood and wood-based products: natural durability classification
- BS 8417:2011 — preservation of wood: code of practice (use class specification)
- BS EN 335 — durability of wood: use classes (UC 1–5)
- NHBC Standards Chapter 6.9 — cladding of external walls
- BS 1202 — nails for use with wood (material specifications)
- Building Regulations Approved Document B — fire spread (check cladding combustibility for buildings > 18 m)
- BRE Good Building Guide 47 — choosing external timber cladding
For most UK self-builds and renovation projects in moderate exposure zones, Siberian larch represents the best balance of cost, durability and low maintenance. Cedar remains the premium natural choice where budget allows; thermally modified timber suits contemporary projects where chemical preservatives are undesirable and weathering to a dark tone is acceptable.
