- For UK exterior cladding: ThermoWood wins on technical performance — lower moisture absorption, better dimensional stability in wet UK conditions, 30-year BRE endorsed service life, zero maintenance.
- For cost: Broadly comparable upfront — ThermoWood £55–£95 per m², Cedar £55–£140 per m² depending on grade. ThermoWood cheaper over 25+ years due to lower maintenance.
- For appearance: Cedar has a warmer initial colour and finer, more consistent grain. ThermoWood has a richer, darker brown tone that suits contemporary design. Both weather to silver-grey.
- For sauna: ThermoWood has a technical edge — lower thermal conductivity, no aromatic compounds, better stability under heat cycling. Cedar retains its traditional aroma advantage.
- For availability: ThermoWood is consistently available from UK stock. Cedar supply has tightened since 2022 — clear grades in particular are less available and more expensive.
- Our recommendation: ThermoWood for UK exterior cladding. Cedar remains a strong option if the aesthetic or aroma is specifically wanted.
Western Red Cedar was the dominant premium timber cladding species in the UK for decades — well-loved by architects for its light weight, natural beauty, and good above-ground durability. ThermoWood has increasingly challenged that position since the mid-2010s, and supply constraints on Canadian cedar since 2022 have accelerated the shift. This guide compares the two species honestly across every dimension that matters for UK cladding projects — durability, cost, maintenance, UK weather performance, availability, and whole-life value — so you can make the right choice for your project without bias.
What Are ThermoWood and Western Red Cedar?
ThermoWood is thermally modified Scots pine (Pinus sylvestris) or Norway spruce (Picea abies), heat-treated at 190–212°C in a controlled steam process without chemicals. The treatment permanently alters the wood's cell structure — reducing equilibrium moisture content from approximately 12% to 4–6%, upgrading biological durability from Class 4–5 to Class 2, and improving dimensional stability by approximately 60%. We supply Lunawood ThermoWood — produced by Lunawood Oy in Finland — in a full range of profiles including shadow gap, triple shadow gap, shiplap, and rainscreen. Full technical data is available in our ThermoWood technical guide.
Western Red Cedar (Thuja plicata) is a naturally durable softwood native to the Pacific Northwest of North America — primarily Canada and the US Pacific coast. It is Durability Class 2–3, naturally resistant to biological decay due to its natural oil content (thujaplicins), lightweight, straight-grained, and dimensionally stable relative to most softwoods. It has been imported into the UK as a premium cladding species for over 50 years and is available in knotty, select, and clear grades at significantly varying price points.
Head-to-Head Comparison
| Property | ThermoWood Thermo-D | Western Red Cedar | Winner |
|---|---|---|---|
| Durability class (BS EN 350) | Class 2 — Durable | Class 2–3 — Durable/Mod. durable | Draw |
| Equilibrium moisture content | 4–6% | 12–14% | ThermoWood |
| Dimensional stability | Excellent — ~60% less movement | Good — better than most softwoods | ThermoWood |
| Service life (above ground) | 30 yrs (BRE endorsed) | 20–25 yrs in UK conditions | ThermoWood |
| Treatment required | None — ever | Oil/stain every 2–3 yrs to maintain colour | ThermoWood |
| Material cost per m² | £55–£95 | £55–£140 (grade dependent) | Draw / ThermoWood for value |
| 30-yr whole-life cost/m² | £55–£95 | £100–£200 (inc. maintenance) | ThermoWood |
| Initial colour | Rich honey-brown | Warm reddish-brown — distinctive | Cedar (preference) |
| Weathered colour | Silver-grey | Silver-grey | Draw |
| Weight | 362–404 kg/m³ | ~320–370 kg/m³ — lighter | Cedar |
| UK availability | Consistent — from UK stock | Tightening — clear grades scarce | ThermoWood |
| Aroma | Minimal — removed by heat treatment | Distinctive — traditional cedar scent | Cedar (if aroma is wanted) |
| FSC / PEFC certified | Yes — both | FSC available — less consistent | ThermoWood |
UK Weather Performance — Where ThermoWood Has the Clear Edge
The most important performance differentiator between ThermoWood and Western Red Cedar for UK exterior cladding is moisture behaviour. The UK's climate — high annual rainfall, persistent wet-dry cycling, and relatively low UV compared to North America — places exterior timber under sustained moisture pressure rather than UV pressure. This fundamentally favours ThermoWood's dramatically reduced equilibrium moisture content.
Western Red Cedar performs exceptionally well in its native Pacific Northwest climate, which shares the UK's rainfall levels but has lower winter temperature variation and different seasonal patterns. In UK conditions, particularly on exposed west-facing and north-facing elevations, cedar's higher moisture absorption — approximately 12–14% equilibrium moisture content versus ThermoWood's 4–6% — results in more swelling and shrinkage across the seasons, more surface checking over time, and greater biological vulnerability on the back face of boards where moisture can sit behind battens. On sheltered south-facing elevations the difference is less pronounced.
ThermoWood's 60% reduction in dimensional movement means boards installed with correct gap spacing maintain that spacing consistently across the seasons — an important detail for shadow gap and rainscreen profiles where the gap is part of the aesthetic. Cedar boards in the same profiles on exposed UK elevations will show more seasonal gap variation.
For exposed elevations in the UK — particularly west and north-facing, coastal, or upland sites — ThermoWood's superior moisture resistance gives it a measurable performance advantage over Western Red Cedar. For sheltered south-facing elevations in moderate UK locations, the difference is smaller and both perform well. ThermoWood is the stronger technical specification for UK exterior cladding in most conditions.
Cost Comparison — Upfront and Whole-Life
| Cost element | ThermoWood | Western Red Cedar |
|---|---|---|
| Materials — knotty/standard grade | £55–£75 per m² | £55–£75 per m² |
| Materials — select/clear grade | £75–£95 per m² | £90–£140 per m² |
| Treatment cost over 30 years | £0 | £45–£75 per m² (10 applications) |
| 30-year whole-life cost — standard grade | £55–£75 per m² | £100–£150 per m² |
| 30-year whole-life cost — clear grade | £75–£95 per m² | £135–£215 per m² |
At standard knotty grade, ThermoWood and Western Red Cedar are comparable on upfront material cost. The 30-year whole-life cost swings heavily in ThermoWood's favour once the maintenance cost of cedar is factored in. For clear grade cedar — which is increasingly expensive and scarce in the UK — ThermoWood represents genuinely better value even upfront, let alone over the service life. For full per-m² cost breakdowns see our ThermoWood cost guide and our timber cladding cost per m² guide.
Which Should You Choose?
- UK exterior cladding is the primary application
- Zero maintenance is a priority
- The building is exposed — west or north-facing
- You want consistent UK stock availability
- Contemporary shadow gap or rainscreen profile
- 30-year service life with no treatment
- Sauna interior — lower thermal conductivity
- FSC/PEFC certification is required
- Cedar's distinctive aroma is specifically wanted
- Traditional sauna bench aesthetic is the brief
- Lighter weight is a structural consideration
- The visual warmth of cedar's reddish tone is preferred
- Sheltered, south-facing elevation in moderate location
- Maintenance schedule will genuinely be maintained
Western Red Cedar supply from Canada has tightened considerably since 2022 due to export restrictions, forest management constraints, and increased domestic demand. Clear and select grades are significantly more expensive and less consistently available than three years ago. If your project requires a specific grade of clear cedar, confirm current lead times and pricing before committing — and consider ThermoWood as the alternative if availability becomes an issue mid-project.
ThermoWood vs Cedar for Sauna Use
Both species are used extensively for sauna interiors, and both perform well in the heat and humidity cycling of a sauna environment. ThermoWood's thermal modification gives it a measurable advantage in two specific areas — lower thermal conductivity means surfaces remain cooler to the touch at high sauna temperatures, and the removal of aromatic compounds during heat treatment makes it suitable for users who are sensitive to cedar's natural oils. Cedar retains one important advantage: its distinctive, traditional aroma that many sauna users strongly associate with the sauna experience.
For sauna exterior cladding, ThermoWood has a clearer advantage — its superior moisture resistance and dimensional stability in the repeated wet-dry cycling of a UK outdoor sauna is directly relevant to performance and longevity. For sauna bench slats, both work well — cedar's lighter weight and lower density makes it marginally more comfortable in direct skin contact. For the full comparison see our best wood for sauna UK guide.
Is ThermoWood better than cedar for cladding in the UK?
For UK exterior cladding, ThermoWood Thermo-D has a measurable advantage over Western Red Cedar in most conditions — lower moisture absorption (4–6% vs 12–14%), better dimensional stability, 30-year BRE endorsed service life versus cedar's 20–25 years in UK conditions, and zero maintenance versus cedar's 2–3 year treatment cycle. Cedar retains advantages in natural aroma and lighter weight.
How much does ThermoWood cost compared to cedar cladding?
ThermoWood costs approximately £55–£95 per m² for materials. Western Red Cedar costs £55–£140 per m² depending on grade — knotty grades comparable to ThermoWood, clear grades significantly more expensive. Over 30 years ThermoWood's whole-life cost is £55–£95 per m² versus £100–£215 for cedar once maintenance treatment is included.
Does cedar cladding need more maintenance than ThermoWood?
Yes — Western Red Cedar requires UV-stable oil or stain every 2–3 years to maintain colour and slow the greying process. ThermoWood requires no treatment at all to maintain performance — it can be left completely untreated or oiled every 3–5 years to retain colour. Over 30 years the maintenance cost difference is approximately £45–£75 per m² in ThermoWood's favour.
Is Western Red Cedar still available in the UK?
Yes, but supply has tightened and prices have increased significantly since 2022 due to Canadian export restrictions and forest management constraints. Clear grades in particular are less available and more expensive. ThermoWood from Finnish and Scandinavian sources is fully available from UK stock with consistent 7–14 day lead times.
Can ThermoWood replace cedar for sauna use?
Yes — ThermoWood Pine is an excellent alternative to cedar for sauna interiors. Lower thermal conductivity keeps surfaces cooler to the touch at high temperatures, and no aromatic compounds makes it suitable for those sensitive to cedar's natural oils. Cedar retains its traditional aroma as its main sauna advantage. Both can be combined — ThermoWood for structure and exterior, cedar for bench slats.
ThermoWood Cladding — UK Stock, Nationwide Delivery
We supply Lunawood ThermoWood Pine Thermo-D in shadow gap, triple shadow gap, shiplap, feather edge, rainscreen, and tongue and groove from UK stock. FSC and PEFC certified. Full technical data sheet available for building control submissions. Nationwide delivery in 7–14 days.