Garden gym rooms: the building, the floor, the power and the rules

Most serious home gyms in Britain end up in the garden. What a proper room costs at three levels, what the floor has to carry, how much power you need and where permitted development stops.

Updated September 2026 · UK RRP, delivered · Prices to verify

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The list

Insulated modular room, 4m x 3m

£15,000 to £22,000

SIPs or timber frame, delivered and built in a week.

Bespoke timber-clad room, 5m x 4m

£28,000 to £40,000

Architect-lite; better glazing and finish.

Brick or block outbuilding, 6m x 4m

£45,000 to £60,000

Permanent; usually needs planning.

Base: concrete slab, 150mm reinforced

£2,500 to £4,500

Plates and plunge need it; screw piles will not do.

Power: new circuit from the house

£1,200 to £2,500

32A minimum; 3-phase for a large sauna.

Flooring: 30mm rubber over ply

£40 to £60 per sq m

Plus a platform under the rack.

Heating and ventilation

£1,500 to £3,000

Air-source unit or infrared panels; MVHR if you add a plunge.

Data and AV

£500 to £1,500

Wired ethernet; connected kit hates garden wifi.

Size

Four by three metres fits a rack, bench and one cardio machine with room to move. Five by four fits two cardio machines and a cable tower. Anything with a treadmill, pull-ups or Olympic lifts needs 2.6 metres internal height; most off-the-shelf garden rooms give you 2.4, so ask.

Floor loading

A rack with 200kg on it and a person is a point load of over 300kg. A full cold plunge is 600kg. Standard garden room floors on screw piles are rated for furniture. Specify a reinforced concrete slab or a floor rated to at least 500kg per square metre and tell the supplier why.

Power

A connected bike draws 100W; a treadmill 700W to 1.5kW; an infrared sauna 2 to 3kW; a chiller 500W continuous. A 32A circuit on its own RCD from the consumer unit is the minimum; a large sauna or a traditional heater wants 3-phase or a dedicated 40A. Get the electrician in before the room is built.

Permitted development

In England a garden building under 2.5 metres to the eaves within 2 metres of a boundary, or under 4 metres elsewhere, covering less than half the garden and not used for sleeping, is usually permitted development. Listed buildings, conservation areas and flats are different. Building regulations apply above 15 square metres in most cases and always to the electrics. Check with the council before ordering; it takes a week and prevents a very expensive argument.

Insulation and damp

Rubber floors and hard training produce moisture. Specify insulated walls and roof to at least 100mm PIR equivalent, a vapour barrier, and a ventilation strategy. Cheap rooms grow mould behind the mirror in eighteen months.

FAQs

Common questions

Do I need planning permission for a garden gym?

Usually not in England if it is under 2.5m at the eaves near a boundary, single storey, and takes up less than half the garden. Conservation areas, listed buildings and flats differ. Check with the council first.

How much does a garden gym room cost?

£15,000 to £22,000 for a good insulated modular room around 12 square metres, before base, power and flooring, which add £5,000 to £10,000.

Can a garden room floor take a rack and plates?

Only if specified. Ask for a reinforced slab or a floor rated to 500kg per square metre. Screw-pile floors for garden offices are not enough.

What power supply does a home gym need?

A dedicated 32A circuit from the house on its own RCD is the minimum. Add a sauna or chiller and you may need 40A or 3-phase.

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