Insulated garden rooms: what to look for

What "insulated" should mean

Suppliers use "insulated" loosely. Some mean insulated walls only. Some mean a thin layer in the roof. A room that is warm in January has insulation on all six sides: floor, roof and every wall, with well-sealed doors and windows.

Heat escapes most through the roof and floor, and through glass. A beautifully insulated wall can't make up for an uninsulated floor sitting on ground screws with the wind blowing under it.

What to look for

• Floor: rigid insulation board (such as PIR) or an insulated panel floor, raised off the ground and protected from damp.
• Walls: insulation in the frame or an insulated panel system such as SIPs. Solid log walls alone are rarely enough for comfortable winter use.
• Roof: the thickest layer of insulation in the building, with a durable membrane such as EPDM rubber on flat roofs.
• Glazing: double glazing as a minimum, triple if the room has a lot of glass or faces north.
• Vapour control layer on the warm side of the insulation, to stop moisture getting into the structure.
• Airtight details around doors, windows and where the walls meet the floor and roof.

Ask for U-values

A U-value measures how much heat passes through a wall, floor, roof or window. Lower is better. Good suppliers know theirs and will put them in writing.

A garden room under the Class 3 exemption doesn't have to meet the energy standards for houses, but they make a useful benchmark. If a supplier's U-values are close to those of a new home, the room will be comfortable to use and cheap to heat. If they can't tell you, that tells you something too.

Condensation and ventilation

See our full guide to garden room condensation.

Ireland's damp climate makes condensation the most common garden room complaint. A sealed, insulated room with people working or exercising in it produces a lot of moisture. Without ventilation it settles on the coldest surfaces, often windows and corners.

• Fit trickle vents in the windows or a small mechanical vent.
• Keep a low background heat in winter rather than letting the room go cold.
• Avoid drying clothes or using a gas heater inside.

Heating an insulated room

See heating a garden room for options, sizing and running costs.

A well-insulated garden room needs little heat. Common choices are electric panel or oil-filled radiators, electric underfloor heating, and air-to-air heat pumps (air conditioning units that also heat). Smart thermostats help you heat the room only when you use it. Supplier heating packages typically cost €1,000 to €5,000.

What it costs

On catalogue rooms, insulation upgrades start from around €2,000, depending on size and how much is included. Many rooms sold for year-round use include insulation in the base price. Bespoke builders usually include it as standard. When comparing quotes, list what each one includes for floor, walls, roof and glazing. See our quote checklist.