A timber clad extension can make a clear architectural distinction between an existing home and its new space, or quietly connect the two through colour, proportion and repeated details. The result depends on more than choosing cedar or larch from a photograph. Species, grade, profile, board direction, weathering, wall build-up, junctions and delivery quantities all need to work together. This guide explains the decisions that help homeowners, designers and contractors turn timber cladding extension ideas into a useful specification and an accurate project enquiry.
Start with the relationship to the existing house
Decide whether the extension should contrast with the original building or feel like a continuation of it. A dark vertical façade can deliberately separate a contemporary rear addition from brick or stone, while a warm horizontal board may pick up existing roof lines, window proportions or landscape materials. Neither approach is automatically better; the useful question is what the new volume should contribute to the whole property.
Look at the extension from the garden, neighbouring boundaries and principal rooms as well as from the street. Board direction, joint rhythm and colour can change how tall, wide or prominent it appears. A narrow vertical profile often emphasises height, whereas long horizontal courses can make a single-storey addition feel lower and broader.
Collect reference images, but label what you actually like in each one: species colour, knot level, board width, shadow gap, orientation, coating or the relationship between cladding and glazing. This prevents a supplier or designer from trying to reproduce an image without understanding the qualities that matter.
- Choose deliberate contrast or visual continuity
- Review the extension from every important viewpoint
- Define preferred board direction and joint rhythm
- Separate timber colour from profile and finish in reference images
Which timber works for a clad extension?
Canadian Western Red Cedar is often considered for refined residential elevations because selected grades can provide fine grain and a wide range of warm colours. UK-grown cedar usually has a more characterful, knotty face and can suit projects where British provenance is important. The offered grade and origin should always be identified rather than relying on the word cedar alone.
UK larch brings pronounced grain, knots and natural colour variation. It can work well on garden-facing additions, barn conversions and extensions where a confident timber character is welcome. Imported larch products may have different grading and visual qualities, so compare the exact material currently available rather than treating every larch board as equivalent.
Thermowood and treated redwood create further options. Thermowood offers a heat-modified product with a warm brown starting tone, while redwood can be relevant where preservative treatment and an opaque or semi-opaque finish form part of the brief. Request representative boards or a joined sample in the proposed profile before final selection.
Profiles and board direction shape the design
Shadow-gap and open-jointed profiles create clear lines and are frequently used on contemporary extensions. Tongue-and-groove and shiplap form a more closed face, while board-on-board produces deeper relief and a strong vertical rhythm. Feather-edge can introduce a traditional overlapping character that suits rural homes and outbuildings as well as carefully designed modern work.
Profile names are not standard dimensions. Ask for the finished thickness, overall width, installed cover, joint drawing and intended fixing position. Two products called shadow gap may create visibly different joints, and two shiplap boards may cover different areas per linear metre. Those differences affect quantities, cost comparisons and the finished scale of the elevation.
Set out the boards against doors, windows and corners before ordering. The aim is to avoid narrow cut pieces, poorly aligned joints or changes of rhythm around large areas of glazing. A simple elevation drawing showing actual cover width can reveal these issues early and help determine a practical board-length schedule.
Plan the complete external wall, not only the boards
Timber cladding is the visible outer layer of the extension rather than a complete weatherproof wall by itself. The construction may include sheathing, a suitable membrane, battens, counter-battens, a drained and ventilated cavity, insect protection and carefully detailed openings. The appointed designer or contractor should confirm the build-up for the actual structure and site.
Board orientation changes the support arrangement. Vertical timber normally needs a batten configuration that provides secure fixing while maintaining drainage and ventilation. Horizontal boards have their own support and joint requirements. A generic detail should not be copied between profiles without checking the product guidance and the proposed wall.
Fixings need to suit the timber, any treatment or coating, the support and the local exposure. Material, diameter, length, head style, position and edge distance all matter. The correct schedule should come from relevant product and project guidance rather than a universal online rule.
Junctions make or break timber cladding extensions
The most visible problems often occur where the cladding stops: external corners, window reveals, door openings, roof abutments, parapets, cills and the junction with the existing house. Decide whether corners use expressed trims, mitred boards, metal sections or another documented detail before quantities are finalised.
Keep the base of the cladding away from conditions that cause persistent wetting. Paving levels, planting, raised beds, gutters, downpipes and splashback zones should be considered as part of the elevation design. Roof edges and cills need to direct water away rather than allowing it to run repeatedly over vulnerable joints.
Service penetrations also deserve a plan. External lights, sockets, taps, vents and pipes can interrupt board lines and the wall behind them. Coordinate their positions before installation so the membrane, cavity and visible face can be detailed neatly rather than cut retrospectively.
Fresh colour, natural weathering or a coated finish?
Uncoated cedar, larch and Thermowood change colour outdoors. They generally move towards grey as sunlight and weather affect the surface, but sheltered and exposed areas may change at different rates. Deep eaves, neighbouring walls, glazing, orientation and planting can all create uneven transitions across a timber clad extension.
If the design depends on retaining a warmer colour, discuss an appropriate pigmented finish for the exact timber and surface. Clear products cannot be assumed to preserve a fresh-cut appearance indefinitely. If a deliberately weathered look is required, a pre-weathering treatment may be considered as a product-specific system with its own preparation and upkeep guidance.
Factory coating can provide controlled application, but the quotation should identify which faces and edges are treated, how site cuts are handled and which touch-up product is supplied. No exterior finish is maintenance-free, so future inspection and access should be considered at the design stage.
How to calculate timber cladding for an extension
Measure each elevation separately and record the width and height of windows, doors and other large openings. Net wall area is a useful starting point, but timber is normally ordered by piece or linear metre. Convert the elevations using the installed cover of the selected profile, not the board's nominal overall width.
Board direction and available lengths can materially change the order. Vertical boards may be cut around roof slopes and openings, while horizontal courses may span across several junctions. Corners, trims, starter details, selection for appearance and the planned joint layout all require material beyond a simple net-area calculation.
Ask the supplier to state the assumptions behind the quantity: cover width, length mix, trimming, appearance selection and accessories. A drawn setting-out exercise is more reliable than applying one generic waste percentage to every façade.
- Measure every elevation and opening
- Use installed cover rather than nominal board width
- Match board lengths to the intended orientation
- Include corners, trims and starter details
- Record the supplier's quantity assumptions
What affects the cost of a timber clad extension?
The supply cost depends on species, origin, grade, profile, finished dimensions, surface texture, coating, available lengths, quantity and delivery. There is no responsible national square-metre figure that accurately represents every timber cladding extension, and old online prices may describe a different grade or board coverage.
Compare quotations on an equivalent installed scope. One offer may include factory finishing, corners, fixings, sample approval and delivery, while another prices only the boards. Check total area covered and usable face width as well as the price per board or linear metre.
The cheapest board is not necessarily the lowest-cost route for the project. Lengths that suit the elevation can reduce joints and cutting, while a suitable factory finish may change site labour. Conversely, paying for a very clean grade may add little value where a characterful, knotty appearance is central to the design.
Planning, design and project responsibilities
A timber clad extension may involve planning, building regulations, structural design, moisture control, fire performance and boundary considerations. Requirements depend on the property, location, scale and complete construction. A timber species or profile name does not demonstrate that the wall as a whole meets the project's obligations.
The appointed architect, designer, engineer, contractor or other competent professional should confirm which requirements apply and what product evidence is needed. Where a specialist treatment or coating is proposed, its documentation should be reviewed alongside the complete façade design rather than in isolation.
Agree responsibilities before ordering. The supplier can describe the product, profile and available documentation, while the project team confirms suitability, junction design, support, installation and compliance for the extension. Clear roles reduce last-minute substitutions and unsupported assumptions on site.
Preparing a South West extension cladding enquiry
A sheltered Bristol garden, a Somerset village home and an exposed extension in Devon or Cornwall can experience different combinations of shade, wind-driven rain and salt-laden air. Share the postcode, orientation, surrounding buildings and proximity to the coast so the discussion reflects the real site rather than the county name alone.
Send elevation drawings, approximate quantities, the preferred profile and board direction, and photographs of the existing house. Include any finish, grade, sample or documentation requirements, plus delivery access and the intended programme. If decisions remain open, explain the visual outcome you want and ask for suitable alternatives to be compared on the same scope.
The Cladding Centre can compare cedar, larch, Thermowood, treated redwood and relevant profiles for timber clad extensions across the South West. Submit the project through the quote page for a tailored recommendation and supply quotation based on your drawings, location and finish rather than a generic online allowance.
- Project postcode and exposure
- Elevation drawings or measured wall areas
- Existing-house photographs and design references
- Preferred species, profile and orientation
- Finish, grade and sample expectations
- Accessories, delivery access and programme
- Documentation requested by the project team