Cladding a Garden Room: What to Know Before You Start

Cladding is the part of a garden room everyone sees, so it is natural to start with how it will look. But the boards themselves are only half the job. What sits behind them, how they are fixed and how the corners and openings are detailed decide whether the cladding still looks sharp in ten years or starts cupping, staining and letting water in after a couple of winters. Here is what is worth thinking through before the first board goes on.

Start with the structure behind the boards

Cladding is a rainscreen, not a waterproof skin. Some water will always get behind it, so the wall build-up has to deal with that. On a typical timber-framed garden room, the layers from the inside out usually look like this:

• The timber frame, with insulation between the studs
• Sheathing board, such as OSB or a breathable sheathing, to stiffen the frame
• A breathable membrane that sheds water but lets vapour escape
• Vertical treated battens, usually 25mm or more, to create a ventilated cavity
• Insect mesh at the top and bottom of the cavity to keep wasps and rodents out
• The cladding boards themselves

That ventilated gap is the bit most often skipped on cheaper builds. Without it, boards fixed straight onto the membrane stay damp on the back face, move unevenly and rot far sooner. If you are having the whole building put together, our exterior carpentry work covers the frame, battens and cladding as one job, so the layers are planned together rather than patched up later.

Choosing a cladding material

There is no single best option; it comes down to budget, looks and upkeep.

Western red cedar is light, stable and naturally durable, and weathers to a silver grey if left untreated. It is soft, so it marks easily, and it needs stainless steel fixings because it reacts with ordinary steel. Larch and Douglas fir are tougher, more affordable home-grown or European options. They move a little more and can weep resin in the first summer, but they weather well and suit a rustic or contemporary look.

Thermally modified timber, often sold under brand names, is heat-treated to make it more stable and rot resistant. It costs more but holds its shape well. Pressure-treated softwood is the budget choice; it works, but expect more movement and more maintenance. Composite and fibre cement boards are also available if you want something close to maintenance free, though they lack the warmth of real timber and need their own fixing systems followed to the letter.

Profiles, direction and fixings

Shiplap and tongue-and-groove boards give a neat, tight finish. Feather edge and board-on-board give a more traditional, textured look that suits rural plots and older Hampshire gardens. Open-jointed or slatted cladding looks modern but relies entirely on the membrane behind it, so a UV-stable membrane is a must.

Fixings matter more than most people expect. Use stainless steel ring-shank nails or screws, especially with cedar and oak, otherwise black streaks appear around every fixing within months. Leave the expansion gaps the supplier recommends, as timber swells in a damp Hampshire winter and shrinks back in a dry summer.

Details that make cladding last

Most cladding failures start at the edges, not in the middle of a wall:

Keep the bottom board at least 150mm above ground level or decking so it is not sitting in splash-back. Cut a slight angle on the bottom edge so water drips off rather than wicking up. Seal end grain on every cut board, because that is where moisture gets in first. Around windows and doors, use proper flashings and drip details rather than relying on sealant, which will fail eventually.

It is also worth checking the rules before you build. Many garden rooms fall under permitted development, but height limits apply near boundaries, and larger buildings or ones close to a boundary can bring building regulations into play, including the choice of cladding material. If your home is listed or in a conservation area, as plenty are around Winchester and the New Forest edges, speak to your local council first.

Finishing and looking after your cladding

You can leave naturally durable timbers such as cedar and larch to weather, or keep their colour with a UV-protective oil or stain. If you go for a finish, it is far easier to treat boards on all faces before fixing than to try to reach the backs later. Expect to re-coat every couple of years on south and west facing walls, which take the most sun and rain.

A quick look each spring is enough for most buildings: check for split boards, popped fixings, blocked vents at the base and any green growth where water is sitting. Small fixes caught early stop bigger problems later. If you are also planning a deck or a pergola beside the room, matching the timber and finish ties the whole space together.

Get your garden room clad properly

Every building and budget is different, so costs depend on the size of the walls, the timber you choose and how much detailing is involved. If you are planning a new garden room or want to re-clad a tired one, take a look at our exterior carpentry services and get in touch for a free, no-obligation quote. We work across Hampshire and are happy to talk through the options on site.