Training and recovery are two sides of the same coin. A gym with no way to wind down after a session is only half the solution — especially if what you really want is a proper wellness space in your own garden.
More and more clients ask us about a Gym Box that combines a workout space with a sauna. Here’s how to plan it — and why it’s worth thinking it through before you start building.
What the client wanted
The brief was a complete train-and-recover setup in the garden: a gym, a Finnish sauna and a shower — in one building, ready to use all year round.
The requirements were specific:
➜ Large glazed front — maximum view of the garden while you train
➜ Sauna built into the module — not a separate structure
➜ Shower in its own partitioned room
➜ Underfloor heating across the whole floor
➜ Remote-controlled air conditioning
➜ Year-round use — and a UK climate makes that genuinely realistic, with no extreme winters to design around
The design challenge: a sauna inside the module
A sauna built into a Gym Box is technically possible — but it’s demanding. Timber at elevated temperatures (80–100°C), high humidity, condensation, and thermal insulation separated from the rest of the module all call for the right materials and construction details.
In practice that means:
| Element | Standard Gym Box | Gym Box with internal sauna |
|---|---|---|
| Walls | PIR/EPS sandwich panel 100 mm | PIR 100 mm + vapour barrier at the sauna |
| Sauna door | — | Sliding, rated to 100°C |
| Sauna floor | Training rubber | Lime (basswood) timber |
| Ventilation | Air conditioning | Vents top and bottom |
| Build cost | lower | higher by 20–35% |
The technical fundamentals — load ratings, wall build-up, sandwich panels, the 2,700 mm height — are the same module we deliver across the UK. The sauna is the part that needs extra engineering.
Two approaches to a Train & Recover project
Approach 1: everything in one module
An 8×4 m module with three rooms: gym (~20 m²), sauna (~4 m²), shower (~4 m²).
Pros:
- One clean building, consistent look
- A short walk from sauna to shower
- Everything ready from day one
Cons:
- Higher cost to get in
- More complex build
- Harder to modify later
Estimated cost: from £32,000 net (from £35,000 net for the full premium spec). Our packaged Train & Recover Gym Box starts at from £24,200 net (from £29,700 incl. VAT) for a more compact gym-plus-sauna layout.
Approach 2: phased — Gym Box now, sauna later
A 6×4 m module as a fully functional gym, pre-prepared for a future sauna (shower zone near the entrance, services run in advance). The sauna comes later as a separate outdoor unit, added when the time and budget suit.
Pros:
- Lower cost to get started
- Gym Box usable straight away
- An outdoor sauna is often cheaper and better ventilated than an internal one
- Flexibility — the sauna can have any finish, independent of the Gym Box
Cons:
- Two separate structures instead of one
- You need to plan the plot layout ahead of time
Estimated cost, Phase 1: from £23,000 net
Outdoor sauna (Phase 2): quoted individually
What does the most advanced Train & Recover project look like?
One client came back to us with their own specification after a few weeks of conversations and put together what you could fairly call a complete wellness module. The scope included:
- 100 mm PIR panel (a higher standard than basic EPS)
- A reinforced floor frame under heavy equipment
- Wet underfloor heating (whole module except the sauna)
- Glazing across the full 6-metre wall with an inward-tilting balcony window
- Full plumbing: three water feeds, drainage, recirculation
- Recessed floor sockets with sliding covers (for machines)
- Electric external blinds on every window
- A roof frame ready for a solar PV install
- A basswood sauna with vapour barrier and water-resistant insulation
This is a project for someone who knows exactly what they want. It takes a longer lead time and a precise quote — but the end result is a genuine home spa with a training zone attached.
Running costs — the honest part
A sauna is the one element that adds noticeably to your bills. An 8 kW heater takes a 4 m² sauna to 80°C in 30–40 minutes and then holds the temperature on the thermostat. Reckon on roughly 5–6 kWh per full hour-long session — at UK rates of around 28p/kWh, about £1.50–£2 per session. Two or three sessions a week is a modest add-on; daily use is worth budgeting for.
The gym itself (heating, AC, lighting, chargers) runs to 800–2,000 kWh a year, or roughly from £225 a year at current prices. If you’re already thinking about a PV-ready roof, it pairs neatly with a sauna build — see our note on solar panels on a container gym.
Where to start?
If a gym with a sauna is what you’re after, start with a few honest questions:
- How much room is there on the plot? One large module or two separate buildings?
- How soon do you want to be using it? A phased approach gets you in faster at a lower cost.
- What’s the budget? From £23,000 versus from £32,000 are two different projects — both achievable.
- How heavily will you use the sauna? An outdoor sauna often works better technically for frequent use.
A quick note on the legal side: in most of the UK a garden gym of this size sits within permitted development, but a sauna’s heater, plumbing and electrics can change that — and a Building Control sign-off on the electrical work is sensible either way. Check the specifics with your local planning authority before you commit. We cover the general picture in our garden gym planning permission guide, and there’s more detail on the sauna build itself in container gym with a sauna.
Dreaming of a garden gym with a sauna? We’ll draw up a plan for your plot.
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