Timber Cladding Calculator

Q: How many timber cladding boards do I need per square metre?

Divide 1 m2 by the covering width of a single board. For shiplap with a 120 mm covering width, you need 1 / 0.12 = 8.33 boards per linear metre of height, so 8.33 linear metres of board per m2 of wall. For a 30 m2 wall area, that is 250 linear metres before waste. Add 10-15% for cutting waste around openings and corners. Most suppliers quote coverage in linear metres rather than m2, so always convert using the covering width of the specific profile.

Q: What are the main types of timber cladding profile?

The most common timber cladding profiles for external use in the UK are: featheredge (tapered board, overlapping, traditional appearance), shiplap (rebated edges that interlock, clean modern look), tongue and groove (interlocking boards with no visible gap, often used vertically), and channel rustic (similar to shiplap with a more pronounced reveal). Square-edge boards and board-on-board (alternating boards with gaps) are also used for contemporary projects. Each profile has a different covering width relative to its nominal width, which must be used when calculating quantities.

Q: What timber species are best for external cladding?

Western red cedar is the most popular choice for external timber cladding - it is naturally durable (Durability Class 2), stable, lightweight, and weathers attractively to a silver-grey if left untreated. Larch (European and Siberian) is a dense, durable hardwood that performs well outdoors. Siberian larch in particular has become popular as a cost-effective alternative to cedar. Accoya (modified radiata pine) offers exceptional durability (Class 1) and stability, and is suitable for factory painting. Douglas fir and modified timber (Thermowood) are also used. Avoid untreated softwoods such as Scots pine for external use without pressure treatment.

Q: Do I need planning permission to clad the outside of my house?

In most cases, re-cladding an existing house with timber or fibre cement cladding in a similar material and appearance is permitted development and does not require planning permission. However, you will need planning permission if: the property is a listed building or in a Conservation Area; the cladding changes the external appearance significantly; or the property is a flat or maisonette (where permitted development rights are more restricted). Always check with your Local Planning Authority before starting work. Building Regulations approval is required if the cladding affects thermal performance (Part L) or structural integrity (Part A).

Q: What fire rating do I need for external timber cladding?

UK Building Regulations Approved Document B (Fire Safety) places restrictions on the combustibility of external wall cladding, particularly on buildings over 11 m in height. On buildings over 18 m, all materials in the external wall must achieve European reaction-to-fire classification A2-s1, d0 or better - timber does not meet this requirement without a fire-retardant treatment or protection. On buildings under 11 m, untreated timber cladding is generally permitted. For buildings between 11 m and 18 m, the requirements depend on the proximity to boundaries and the building use. Fire-retardant treated timber cladding products with appropriate classification are available.

Q: What waste allowance should I use for timber cladding?

Allow 10% waste for a simple rectangular elevation with few openings. Use 15% for elevations with many windows, doors, or changes of direction. Corners require mitred or scribled joints that waste material. For profiles that need to be laid vertically or at an angle, increase to 15-20%. Buy boards from the same batch to ensure consistent grain, colour, and treatment. For stained or painted boards, keep a small supply for future patching.

Board on board, shadow gap, open joint, and lap profiles - with full batten system quantities

Cladding Profile

Two layers of boards - front boards cover the gaps between back boards. The standard contemporary UK timber cladding detail.

Timber Species

Durable Class 3 - Natural oil finish recommended - Allow to weather to silver-grey or treat annually to retain colour.

Board Width (mm) Face width of each board

Board Length (m) Standard: 3.0, 3.6, 4.2, 4.8, 6.0 m

Front Board Overlap (mm) How much the front board covers the back board on each side - typically 30-50 mm

Gap Width (mm) Visible gap between boards - typically 15-30 mm for shadow gap, 20-50 mm for open joint

Lap Overlap (mm) Overlap between courses - typically 25-40 mm

Effective Coverage

- enter board dimensions

Batten System Counter battens fix to the wall studs; cladding battens run perpendicular and carry the boards.

Counter Batten Spacing (mm) Fix to studs - typically 400 or 600 mm centres

Cladding Batten Spacing (mm) Perpendicular to boards - typically 300-600 mm

Batten Length (m)

Waste Factor (%)

10%

10% standard; 15% for complex shapes or many penetrations

Wall Sections

Job Costing (optional)

Cost per cladding board

Counter / cladding batten per m

Fixings per board (screws)

Finish / treatment per litre ~8-12 m² per litre depending on porosity

Labour cost

Rate x total area

Delivery (flat fee)

UK Market PricesFills in the material cost fields with current UK market prices. You can review and edit each price before applying.

Results

Cladding Boards

Net Cladding Area
-
m² (less openings)

Boards to Order

inc. waste

Linear Metres

boards total

Back Boards

first layer

Batten System

Counter Battens

lengths

Cladding Battens

lengths

Total Batten LM

linear metres

Wall Breakdown

Wall	Gross Area	Openings	Net Area	Boards	Counter Battens (lm)	Cladding Battens (lm)

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Frequently Asked Questions

How many timber cladding boards do I need per square metre?

Divide 1 m² by the covering width of one board. Shiplap at 120 mm covering = 8.33 linear metres per m² of wall. Add 10-15% waste. Suppliers quote in linear metres - always convert using the covering width of your specific profile, not the nominal board width.

What are the main types of timber cladding profile?

Featheredge: tapered overlapping board, traditional look. Shiplap: rebated interlocking edges, clean modern look. Tongue and groove: fully interlocking, often vertical. Channel rustic: pronounced reveal. Board-on-board: alternating boards with gaps, contemporary. Each profile has a different covering width vs nominal width.

What timber species are best for external cladding?

Western red cedar: most popular - naturally durable (Class 2), stable, weathers to silver-grey. Siberian/European larch: dense and durable, cost-effective cedar alternative. Accoya: modified pine, Class 1 durability, excellent for factory painting. Thermowood: thermally modified softwood. Avoid untreated Scots pine for external use.

Do I need planning permission to clad the outside of my house?

Re-cladding in a similar material is usually permitted development - no planning permission needed. Exceptions: listed buildings, Conservation Areas, significant change of appearance, or flats. Always check with your Local Planning Authority. Building Regulations approval required if cladding affects thermal performance (Part L) or structure (Part A).

What fire rating do I need for external timber cladding?

Approved Document B: buildings over 18 m require all external wall materials to be A2-s1, d0 or better - untreated timber does not comply. Under 11 m: untreated timber generally permitted. 11-18 m: requirements depend on proximity to boundaries and use. Fire-retardant treated timber cladding with appropriate classification is available for taller buildings.

What waste allowance should I use for timber cladding?

Simple elevation, few openings: 10%. Many windows, doors or direction changes: 15%. Diagonal or angled layouts: 15-20%. Buy boards from the same batch for consistent grain, colour, and treatment. Keep a small supply for future patching.

UK Building Regulations Part B • Part C • BS EN 14915

Profile Guide

Board on board - Vertical boards fixed to cladding battens, with a second layer of front boards covering the gaps. Very popular contemporary detail. Two boards per "slot".
Shadow gap - Vertical boards fixed with a precise gap between them. The gap creates a shadow line for a clean, modern look. A breather membrane behind is essential.
Open joint rainscreen - Similar to shadow gap but with wider gaps (20-50 mm), used on ventilated rainscreen systems. The wall behind must be weatherproof independently.
T&G vertical - Tongue and groove boards fixed vertically. Secret-fixed through the tongue for a clean face. Very tight, weathertight profile.
Larch / Cedar lap - Horizontal lapped boarding, similar to featheredge but in premium timber species. More traditional look than vertical profiles.

Species & Durability

Larch - Durable Class 3-4. Good value, weathers to silver-grey. The most commonly specified UK cladding timber.
Western Red Cedar - Class 3-4. Lightweight, stable, aromatic. Naturally resistant to decay; treat to retain colour.
Oak - Class 2. Extremely durable but heavy. Tannin staining from fixings - use stainless steel only.
Douglas Fir - Class 3. Strong and stable. Good alternative to larch at lower cost.
Accoya - Modified pine, Class 1 durability. 50-year guarantee above ground. Very stable, minimal movement.
Thermowood - Heat-treated pine or ash. Class 2-3. Dark colour, reduced movement, eco credentials.
Treated Pine - Pressure-treated softwood. Class 3-4 with treatment. Most economical option.

Batten System

Counter battens - Fixed horizontally to the wall structure through a breather membrane, creating a ventilation cavity behind the boards.
Cladding battens - Run perpendicular (vertically for horizontal boards; horizontally for vertical boards) to carry the cladding.
Minimum 25 mm ventilated cavity behind all external timber cladding
Use stainless steel or hot-dip galvanised fixings throughout - never standard zinc
Allow 10-15 mm gap at ground level for drainage and airflow

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Timber Cladding Calculator

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