Decision Guide
How should you insulate a garden room or shed?
Eco Spray Foam Insulation insulates garden rooms, garden offices, sheds and outbuildings across Orpington and Kent. These are non-residential uses, so spray foam is an option.
Updated 8 November 2026. Prices are our rates and published UK estimates, not a quote.
The short answer
Insulate the roof, walls and floor, and stop condensation. Spray foam suits garden rooms, sheds and outbuildings because it seals gaps in one layer; rigid boards are the main alternative. Published UK guides put spray foam at about £20 to £50 per m². We price each job after a free survey.
Where does a garden room lose heat?
Mostly through the roof, then the walls and the floor. A timber building with no insulation heats up fast in summer and goes cold quickly in winter. The other common problem is condensation: warm, damp air inside meets a cold roof or wall and turns to water, which can drip, stain and rot timber.
Good insulation deals with both. It slows heat loss, and it keeps the inside face of the roof and walls warmer, so less condensation forms.
What should you insulate first?
- The roof. It loses the most heat and is where condensation shows first.
- The walls, especially in a room you will use as an office or gym.
- The floor. A suspended timber floor needs insulation between the joists, or the room will always feel cold underfoot.
Spray foam or boards?
| Spray foam | Rigid boards (PIR) | |
|---|---|---|
| Gaps and awkward shapes | Fills them in one layer | Need cutting and taping |
| Condensation on cold surfaces | Closed-cell foam resists moisture | Needs a separate vapour barrier |
| Disruption | Sprayed in place, usually quick | More cutting and fixing |
| Best for | Timber frames, metal sheds, uneven roofs | Flat, regular walls |
| DIY friendly | No, needs a trained installer | Yes, with care |
Spray foam suits buildings with lots of gaps, uneven framing or metal roofs. Boards suit neat, regular walls where you can cut and fit them accurately. Some jobs use both: spray foam in the roof and boards in the walls.
Open-cell or closed-cell foam?
Open-cell foam is softer and lighter. It seals gaps and dampens sound, but it lets some moisture through, so it needs the right lining.
Closed-cell foam is denser and harder. It resists moisture and adds some stiffness to thin panels, which makes it the usual choice for metal roofs, containers and vans. It costs more.
What affects the price?
The size of the roof, walls and floor is the main factor. The type of foam, how easy the building is to reach, and whether it is already lined all change the price too.
Published UK guides put spray foam at about £20 to £50 per m² (Duratite, 2026). We price garden rooms, sheds and outbuildings after a survey, because sizes and builds vary so much.
Sheds, workshops and outbuildings
The same approach works for sheds, workshops, stables and outbuildings. Metal and corrugated roofs often drip with condensation in cold weather; a layer of closed-cell foam on the underside stops it. We also insulate shipping containers, camper vans, caravans and boats.
Planning and building rules
Insulating an existing garden room does not usually need permission. A new garden room may need planning permission or building regulations approval depending on its size, position and use, especially if anyone will sleep in it. Check with your council before you build. We install spray foam for non-residential uses only, so we do not spray foam a garden room that is used as living accommodation.
For an all-year garden room, insulate the roof, walls and floor, and deal with condensation.
Common questions
Do you spray foam garden rooms?
Does a garden room need a vapour barrier?
How much does it cost?
Want to use your garden room all year? Book a free survey.
Call 01689 390157 (Monday to Sunday, 9am to 7pm) or use the form below.