James Ashworth
A garden room is one of the best additions you can make to a British home — a studio, a spare bed for guests, or simply somewhere to sit with a coffee and watch the rain. The catch is that most garden rooms are built as summer spaces and then asked to behave like real rooms in January. The good news is that the fixes are mostly straightforward, and they are far cheaper than extending the house.
Start with the shell, not the sofa
Insulation is what turns a shed-shaped box into a year-round room, and the order matters: walls, roof and floor, all three. A typical timber-framed garden room has 70–100mm of space between the studs. Fill it with rigid PIR boards cut snugly, foil-taped at the joints, and leave a 25mm ventilated cavity behind the external cladding so moisture can escape. In the roof, aim for 100–150mm, and consider a continuous layer across the rafters to reduce cold bridging.
For the floor, 50–75mm of rigid board beneath 18mm plywood or OSB makes an enormous difference to how a room feels underfoot, and it sits happily on a damp-proof membrane. Glazing is the other weak point: specify double-glazed units with a low-emissivity coating if you are buying new, and check that sliding or bi-fold doors have adjustable hinges and brush seals. Fit draught excluders to the threshold.
Ventilation is not the enemy
The most common mistake is to insulate and seal a garden room beautifully, then wonder why the ceiling goes black at the corners. Warm, damp air from people, kettles and wet coats has to go somewhere. Keep relative humidity between about 40 and 60 per cent — a cheap hygrometer will tell you where you stand.
- Fit trickle vents to any new windows and use them, even in winter.
- Open a window and the door together for ten minutes on a dry day to purge the air rather than leaving one ajar all day.
- Run a small electric dehumidifier with a humidistat for a few hours daily through the damp months.
- Avoid drying laundry inside, and never store damp gardening kit under the bench.
- Leave a 50mm gap between furniture and external walls so air can move.
In summer, do the opposite: ventilate early in the morning and close blinds on south-facing glass before the heat builds.
Heat it gently, and in layers
Once the room is insulated, you need far less heat than you would expect. A noisy fan heater is the wrong tool; a thermostatically controlled oil-filled radiator or a wall-mounted infrared panel will hold a steady temperature quietly and cheaply. If you are laying a new floor anyway, an electric underfloor mat is a lovely thing in a small room, but it is not a substitute for insulation.
Set the thermostat to around 10–12°C as a background setting through the coldest weeks, then boost to 18–20°C when you are actually using the space. A timer or smart plug means you can warm it before you walk down the garden. Ceiling fans are not just for summer — run one in reverse in winter to push warm air back down.
On power, do it properly: a dedicated armoured supply from the house, its own small consumer unit with RCD protection, and a qualified electrician to sign it off. Add a mesh Wi-Fi point while the walls are open, because signal rarely travels well through foil-backed insulation.
Plan for two jobs, not one
The most useful garden rooms do two things well rather than one thing perfectly. Decide on a primary use and a secondary one — desk and guest bed, studio and reading retreat — then zone the floor accordingly. A slim desk under the window, a daybed or small sofa against the back wall, and storage built into the eaves or beneath a bench.
- Choose furniture that folds, stacks or hides: a wall-mounted drop-leaf desk, a storage ottoman, a sofa bed with a proper mattress.
- Keep a clear spine of floor from door to window; it makes a small room feel generous.
- Scale down. A two-seater sofa usually reads better in a garden room than a three-seater.
- Think about the view from the house — this is a room you will look at every day.
Furnish for warmth and texture
Hard surfaces — glass, timber cladding, painted plasterboard — make a garden room feel colder than it is. Soften everything. Thermal-lined curtains hung wider and longer than the window will genuinely reduce heat loss overnight, especially with a woven blind behind them. A wool rug over a rubber underlay, a sheepskin thrown over a chair, cushions in corduroy and boucle, and a couple of throws will do more for comfort than another degree on the thermostat.
Lighting matters just as much. Aim for several pools of warm light — table lamps, a wall light on a dimmer, a picture light — rather than a single bright ceiling fitting. Choose bulbs at around 2700K and avoid cool white. Earthy colours suit the British garden: oatmeal, clay, moss green, soft charcoal. Timber and stone bring their own warmth.
Seasonal housekeeping
Ten minutes, four times a year, keeps a garden room working. In autumn, clear gutters and check the roof covering and door seals before the rain sets in, and re-oil or re-stain timber cladding if it is looking tired. Through winter, watch the hygrometer and ventilate on dry days. In spring, clean the glazing inside and out, check for any soft patches in the floor near the door, and make sure the base is not sitting in standing water. In summer, fit insect mesh to opening windows and shade the sunniest glass.
Do those things and the room stops being a fair-weather treat. It becomes the quietest, most useful square metres in the house — and in February, that is worth a great deal.
