Cladding a Garden Room
Full exterior cladding for a garden room, office pod or summerhouse — the whole stack: membrane, battens, cavity, cladding, trims and ventilation. The flagship version of an exterior cladding project.
What you'll need
Materials
- Cladding boards (feather-edge, shiplap, rainscreen or vertical), 38×25 or 25×50mm treated battens, breathable membrane (Tyvek, Solitex, Pro Clima), counter-battens for a true cavity, stainless A4 nails or screws, insect mesh, corner trims, head/sill flashings.
Tools
- Mitre and circular saw, table saw helpful, impact driver, level (long), chalk line, staple gun for membrane, snips for tape, sturdy ladder or low scaffold tower, hammer drill if anchoring trims.
Material complexity: High
Allow 15% on cladding boards — windows, door surrounds and ends create more cuts than a flat run. Buy battens to total length plus 12%.
Main risk: A missing membrane or a blocked cavity — the boards look fine for a year, then fail from the back.
Cut list
3×4m garden room, after window and door deductions. Allow 15% extra on boards.
- Cladding: 80–100 linear metres of 18×144mm feather-edge, shiplap or rainscreen. Buy the longest lengths you can handle
- Battens: 70–80 linear metres of 38×25mm or 25×50mm treated. Vertical at 600mm centres; add a counter-batten layer if the cladding is horizontal and you want a continuous cavity
- Breathable membrane: enough for about 36m² of wall plus laps — a 50m² roll is the usual buy
- Insect mesh at the base and head, all the way round
- Corner trims, window and door trims, head and sill flashings
- Stainless A4 nails or screws for cedar, typical 50–65mm, one per board per batten, 25mm from ends
Treated redwood on the same room is a lower band — typically £1,200–£1,800 for the same stack. The flagship figure above is cedar.
Step-by-step
Plan the faces, openings and the stack
Sketch each wall: where boards meet at corners, how they finish at windows, and how they meet the roof and the ground. From the wall out the stack is breathable membrane, batten (the cavity), then cladding. Order full lengths for the show faces.
Tip: The trims take longer than the field. Buy flashings and corner trims before you start, not on week four.
Wrap the building in membrane
Staple breathable membrane all round, upper sheet over lower, taped at joints. Dress it into window openings. Leave extra at the base to lap over the insect mesh later.
Watch out: Never skip the membrane. Boards on bare OSB or ply trap moisture and the job fails from the back.
Fix battens — counter-batten if the boards are horizontal
Vertical 38×25mm battens at 600mm centres give a 25mm cavity; 38mm is better. If the cladding is horizontal, fix horizontal battens first, then vertical ones, so water can run down and out. Fit insect mesh at the open base before the first board.
Hang the first courses and the openings
Start each wall from a dead-level first board, 150mm off the ground. Work around windows and the door with trims or housed finishes as you go — do not leave a ragged hole to tidy later. One A4 stainless fixing per board per batten, 25mm from ends.
Fill the field, then the corners
Run the remaining boards, staggering joints onto battens. Mitre external corners or use a proper corner trim — never a raw butt. Keep 3–5mm expansion at ends and openings.
Flashings, head and base vents
Fit head and sill flashings, check the base and eaves can still breathe, and walk the building after the first storm. Recheck fixings in the first year as the boards settle. Store a few spare boards dry for later replacements.
Tip: Trims and flashings are most of the long-term maintenance. Failed boards are easy; failed sills are not.
Tips & traps
- Skipping the membrane.
- No cavity, or a cavity blocked at the base by soil and leaves.
- Two fixings across each board — they split as the wall weathers.
- Joints in the middle of a show face because you bought short boards.
- Windows and flashings left until last with no plan — they take longer than the cladding.
Planning & timber detail
Why build this?
Cladding a garden room turns a shed-grade outbuilding into something that looks permanent. Done with a full cavity and decent timber it lasts decades, and the sequence is the same one you would use on a house wall later.
Where it works best
Any garden building that needs a step up from felt or basic cladding — and any new self-build that should look considered rather than temporary.
Planning notes
Permitted development covers most garden rooms under 2.5m and within size limits — check yours. The stack from the wall out is breathable membrane, vertical batten (cavity), then cladding. Never skip the membrane. For horizontal cladding, counter-batten so the cavity is continuous.
Typical sizes
Flagship worked example: 3×4m room, 28–32m² of cladding after openings.
80–100 linear metres of 18×144mm board. 70–80 linear metres of battens. Order full lengths to keep joints off the main faces.
The cost band is timber, battens, membrane, stainless fixings and trims. It excludes windows, doors, the building itself and labour.
Default dimensions
Building: 3×4m.
Cladding area after openings: 28–32m².
Battens at 600mm centres. Cavity 25mm minimum, 38mm preferred.
Keep cladding 150mm off the ground, with a vented, meshed base.
Design variants
Cedar flagship (this page) — light, stable, can be left to silver.
Larch — stronger colour, more movement, needs oil to look its best.
Treated redwood — the budget clad; plan to re-coat.
Horizontal vs vertical — horizontal is familiar; vertical needs counter-battens so the cavity can drain.
Suitable timber options
Cedar — light, stable, no maintenance if left to silver. The gold standard for whole-building clads. Larch — strong, richer colour, more movement to manage, needs oiling to look its best. Thermowood — modern, stable, slightly brittle at fixings. Accoya — premium, exceptional stability, paint-friendly if you want a coloured finish.
Fixing and finishing
Stainless A4 for cedar and any coastal or oak work. A2 minimum elsewhere. Fix above the overlap on shiplap and feather-edge so heads are hidden. One fixing per board per batten. Pre-drill thermowood and any hardwood. The trims and flashings take longer than the field of boards.
Plan the layout BEFORE first cut: where do boards meet at corners (mitre or trim), how do they finish around windows (proprietary trim or housed), and how do they meet the roof and ground (flashing and ventilation detail). The trims and details take longer than the cladding itself.
Maintenance
Annual walk-around: check the bottom edge for clear ventilation, look for any failed boards. Re-coat oil finish before it goes chalky. Check trims and flashings — they fail before the boards do.
First 12 months: re-check all fixings as boards settle. Trims and flashings are 80% of long-term maintenance. Have spare boards stored dry for individual replacement when needed in future.
Timber behaviour
Durability
UC3 battens minimum — UC3 means timber kept off the soil (above ground). UC4 if any batten could touch the ground — UC4 means timber that sits in soil or stays wet. The cladding species can be naturally durable (cedar, larch) and need no use-class stamp. Keep cladding 150mm off the ground, with a continuous vented gap at the base protected by insect mesh.
Movement
Whole-building cladding has serious movement to manage. Single fixing per board per batten, 3–5mm expansion gaps at ends and openings, 8mm minimum gap at vertical butt joints. Plan for ~5mm of seasonal swing across each board width.
Go deeper
Get the Timber Buying Companion
An 8-page practical guide to choosing better boards, avoiding waste and spotting common timber problems before you buy.