Why Garden Rooms Feel Colder Than They Should

Most garden rooms, sheds and converted outbuildings were never built to be lived in through January. They are usually a timber frame with a bit of insulation in the walls, a single-glazed door and a thin roof, which means heat escapes in every direction at once. The result is a space that feels lovely in May and frankly hostile in December.

The good news is that you rarely need to rebuild anything. Cold garden rooms are usually losing heat through a handful of predictable places: gaps around the door, uninsulated floors, bare windows and a roof that acts like a radiator in reverse. Deal with those, and a modest heater can keep the room at a comfortable 18°C or so without your smart meter spinning into a blur.

Work through the list below in order. The cheap fixes come first, because stopping draughts is far more effective than paying to heat air that immediately leaves.

Stop the Draughts Before You Spend a Penny on Heating

An unsealed gap under a door can move a surprising volume of cold air. A brush or rubber draught excluder screwed to the bottom of the door is a ten-minute job and one of the best value improvements you can make.

• Door bottoms: fit a brush strip or a rubber seal, and check it still clears the threshold through the full swing.
• Door frames and windows: run self-adhesive foam or rubber strip around the frame where the door or window closes against it.
• Fixed gaps: seal permanent gaps around frames, pipe entries and cable holes with silicone or expanding foam.
• Keyholes and letterboxes: a cover or a small flap costs pennies and blocks a genuine little chimney of cold air.
• Between the walls and the floor: run a bead of sealant along the skirting, especially on the windy side of the building.

Go round with the back of your hand on a cold, breezy day. Anywhere you feel a distinct coolness, you have found a leak worth sealing.

Insulate the Floor and Add a Proper Rug

Floors are the forgotten surface. If your garden room sits on timber joists over a void, cold air circulates underneath all winter and the floorboards will feel permanently chilly, even with the heater on.

If you can access underneath, push insulation between the joists and cover it with a breathable membrane. If you cannot, work from above. A thick rug with a felt or rubber underlay transforms how a room feels underfoot, and the underlay matters as much as the rug. A wool rug of 10mm or more gives noticeably better insulation than a thin cotton flatweave, and it will take the edge off the whole room.

Rugs also help acoustically, which makes a small garden room feel more like an indoor space and less like a shed with a sofa in it. For very cold floors, interlocking foam tiles under the rug add another layer cheaply.

Dress the Windows and Doors with Thick Curtains

Glass is a poor insulator, and a garden room often has more of it than the average house. Heavy, thermal-lined, floor-length curtains make an enormous difference, particularly if you close them before the room cools rather than after.

• Hang curtains from a track fixed as close to the ceiling and wall as possible, so warm air does not slip behind them.
• Let them reach the floor or slightly overlap the sill, and overlap the two panels in the middle.
• Draw them at dusk and open them in the morning to let in whatever sun is going.
• For glazed doors, consider a separate pair of curtains rather than relying on the door seal alone.
• Secondary glazing film, fitted with a hairdryer to shrink it tight, is a cheap addition on single-glazed panes.

Blinds alone are much weaker than curtains, but a thick Roman blind mounted inside the recess at least traps a layer of still air against the glass.

Choose a Low-Energy Heater and Run It Sensibly

A small, well-sealed garden room does not need a big heat source. A 700W to 1500W oil-filled radiator or a low-wattage infrared panel will usually do the job, and both are quiet, which suits a space used for reading, working or guests.

Run it on a plug-in thermostat rather than leaving it on full. Setting the heater to hold 15°C in the background and then nudging it to 18°C when you use the room costs far less than blasting it from cold, because the fabric of the building never gets properly chilled. If you use the room at predictable times, a simple timer will do the same job.

As a rough guide, a 1kW heater running for an hour uses one kilowatt hour of electricity, so check your own tariff to work out the cost. Fan heaters warm a room quickly but are noisy and thirsty, so treat them as a top-up rather than a plan.

Small Habits That Keep the Warmth In

• Ventilate briefly but properly. Open a window wide for five minutes once a day rather than leaving a trickle vent open all afternoon, which just drains heat.
• Watch for condensation on windows and cold walls. A small dehumidifier prevents damp, and dry air feels warmer than humid air at the same temperature.
• Move furniture slightly away from external walls so air can circulate rather than pooling cold behind the sofa.
• Keep the door to the house closed when the garden room is in use, so you are not heating the garden.
• Check the roof. If it is uninsulated, a layer of rigid insulation board between the rafters is often the single biggest improvement available.

Do the draught-proofing, add the rug and the curtains, and choose a modest heater you control properly. A garden room treated this way becomes a genuinely usable space all winter, not just a place you look at longingly from the kitchen window.