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Sustainable Cladding

Timber, modified wood, brick slips, terracotta, metal, and render: how to choose and what to check

3 min readUpdated November 2026

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Check the fire limits first

Cladding choices are limited by fire guidance before aesthetics or carbon come into it. In England, a dwelling of 11m or less has no external surface provision where a wall is 1m or more from the relevant boundary, while walls closer than 1m need at least class B-s3, d2. Above 11m, Approved Document B Volume 1 asks residential buildings for A2-s1, d0 or better, which rules out timber in most cases.

Other building types have different rules, and all walls need the rest of the fire strategy to work. See our guide to fire performance for more detail, and confirm your project with building control.

The main options

Each cladding balances carbon, maintenance, appearance, and fire class differently.

  • UK-grown larch or Douglas fir

    Strengths
    Biobased, short supply chain possible
    Trade-offs
    Movement and weathering
    Check
    Heartwood content, grading, and sourcing claim

  • Western red cedar

    Strengths
    Naturally durable and stable
    Trade-offs
    May be imported
    Check
    Origin and stainless fixings

  • Oak or sweet chestnut

    Strengths
    Durable heartwood
    Trade-offs
    Tannin staining, movement
    Check
    Fixings and run-off onto surfaces below

  • Thermally modified timber

    Strengths
    Better durability and stability
    Trade-offs
    Energy for treatment
    Check
    Durability class, EPD, and fixing guidance

  • Acetylated timber

    Strengths
    High durability and stability
    Trade-offs
    Higher cost, chemical process
    Check
    Independent data on durability and carbon

  • Charred timber

    Strengths
    Distinctive and can reduce finishing
    Trade-offs
    Char can vary and be damaged
    Check
    Do not assume charring improves fire class

  • Reclaimed timber

    Strengths
    Reuses existing material
    Trade-offs
    Limited supply, unknown treatments
    Check
    Remaining life and contaminants

  • Brick slips

    Strengths
    Brick appearance with less material
    Trade-offs
    Carrier system and adhesives
    Check
    Full system test evidence

  • Terracotta

    Strengths
    Durable and non-combustible
    Trade-offs
    Kiln energy and support rails
    Check
    EPD including the rail system

  • Metal

    Strengths
    Long life, recyclable
    Trade-offs
    High primary production impact
    Check
    Recycled content and coating

  • Lime or mineral render

    Strengths
    Can suit vapour-permeable walls
    Trade-offs
    Maintenance and detailing
    Check
    Compatibility with the substrate

Making timber cladding last

Well-detailed timber can last decades, but the details matter more than the species name. Durability ratings generally apply to heartwood, and sapwood has little natural resistance to decay, so ask what proportion is allowed.

  • Provide a ventilated, drained cavity behind the boards, and insect mesh at openings.
  • Keep boards clear of the ground and away from standing water.
  • Use stainless steel fixings, especially with cedar, oak, and other tannin-rich timber.
  • Allow for movement in the board width, profile, and fixing pattern.
  • Protect end grain and top edges, and avoid details that trap water.
  • Expect uncoated timber to change colour, often unevenly under eaves and overhangs.

Tip. Decide how you want it to age at the start. Letting timber silver naturally can mean less maintenance than a film coating that needs regular renewal.

Fire-retardant treated timber

Factory treatment can raise timber's reaction to fire class, but check how it was classified and how long it lasts outdoors. Ask for the full class, including smoke and droplet ratings, and for evidence that the treatment suits exterior use. BS EN 16755 is the durability classification to look for.

Treatment and coatings may also affect recycling and reuse at end of life, so factor that into your choice.

Watch out. A classification applies to the product as tested. Charred, coated, or differently fixed boards may not match the result, so check that the evidence covers the proposed build-up.

Count the whole system

Cladding is more than the visible layer. Rails, brackets, membranes, cavity barriers, and fixings can add a lot of carbon, particularly with aluminium support systems. They can also create thermal bridges, so compare complete wall build-ups where possible.

  • Compare EPDs on the same area, service life, and scope.
  • Include replacement and maintenance over the same study period.
  • Ask whether the system can be taken apart, with boards or panels reused.
  • Favour responsibly sourced timber, with FSC, PEFC, or Grown in Britain claims you can check.

Using Matera

Ask suppliers for the species or product, fire class, durability data, fixing guidance, and any certification claim. Request a weathered sample or project photos, as a new board may look very different after a few years.

Sources

Where the facts in this guide come from. Standards and guidance change, and some sources are suppliers or trade sites, so check the original before relying on a detail.

Browse the libraryNext guideFire Performance of Biobased Materials