Five by seven by seven.
Everything decided so far, everything still open, and the reasoning for both. Three versions in, the concept is specific enough to quote. It is not yet an engineered drawing, and the page says so wherever that matters.
5 wide. 7 long. 7 tall.
The interior is 5 ft × 7 ft with a 7 ft ceiling: 245 cubic feet of air, smaller than a walk-in closet. Two people stand on 30-inch lanes; a 6-foot platform still fits for the floor series; and the exterior comes in under 8 ft tall, which is the point: it fits under a standard residential ceiling, in a garage or a basement, not only outdoors.
The walls are flat-pack panels with cedar inside, so the room is designed to ship flat, with every panel small enough for a normal door. Expect something close to 6 ft 1 in wide by 8 ft 2 in long by 7 ft 10 in tall at the roofline, confirmed with the fabricator rather than promised here. Under 8 ft is the point: it goes in a garage or a basement as well as on a deck.
The room got here by shrinking. It started at 8 × 12 with two platforms staggered on a diagonal, moved to an 8 × 8 square with platforms facing, and then the floor plan disappeared: one room, two heights.
| Interior | 60 in × 84 in, 84 in ceiling · 245 cu ft |
|---|---|
| Standing floor | Full 60 × 84 in, platform folded away, nothing sticking out of the walls |
| Platform, down | 5 × 6 ft surface, 24 in up · wider at shoulder height than the floor |
| Step-up strip | 60 × 12 in at the door, always clear; the door swings out |
| Mirror wall | Far short end: a full-height studio mirror from inside, with the guided session appearing in it; plain outside TBD · suppliers |
| Door | Entry short end, outswing, as sauna doors are |
| Heat | Warm surfaces where you practice plus a heat pump outside the cabin TBD · supplier |
| Exterior (est.) | ≈ 6 ft 1 in × 8 ft 2 in × 7 ft 10 in, under 8 ft tall TBD · fabricator |
The floor, with nothing sticking out of the walls.
With the platform folded away, the walls are flat from floor to ceiling and the whole 5 × 7 floor is yours. Two people stand side by side on the long axis, each with 30 inches of width, and 84 inches of height above them.
Seven feet is the honest constraint of the standing series and the reason this page has a clearance table. The short version: only two of the thirteen standing postures in the standard 26-posture sequence fully extend the arms overhead, and at 7 ft they clear for practitioners up to about 5 ft 8 in with typical proportions; everyone taller uses the compact variation for those two.
Two feet up, together.
Folded down, the platform is one surface: 5 feet wide, 6 feet long, 24 inches above the floor, and the room is wider there, where your shoulders and elbows are, than at the floor. A standard mat is 72 inches, which is why the platform is that long and why the remaining 12 inches of the room's length at the door stays clear as the step. The cushioned mat surface is built into the platform; a fitted towel, sized to the platform, is the one accessory.
Sixty inches of clearance above the platform is enough for every posture in the floor series at every height we checked, kneeling included: sitting, kneeling, and lying poses all stay well under it. Width is the tighter number: two adults shoulder to shoulder are wider than 60 inches, so on the platform the pair sits staggered, one about half a mat ahead of the other, and both still face the mirror. The platform also lifts the reclined series out of the coldest foot of air, which is the whole point of building it. Why the height matters →
The numeral in our name is the fold.
Look at a 4: a wall, a platform, and the line between them. The platform folds out of the wall for the floor series and back into it for the standing series. It has not been engineered yet, and proving it is the first job of the prototype.
What it does
Folded away (standing series): the wall reads flat, nothing sticks out into the standing zone, and the whole 5 × 7 floor is clear under the full 7 ft.
Folded down (floor series): one level surface, 24 inches up, with the mat reading as one 5 × 6 ft piece, and the room is wider there, at your shoulders, than at the floor.
No legs: the floor under the platform stays clear and moppable, and nothing is left standing in the room when it is folded away.
The mat: not an accessory. A cushioned, grippy, wipeable practice surface is the top face of the platform, and it is warm under you. A fitted towel sized to the platform is the only add-on.
What the prototype proves first
- The fold. A platform that folds down rigid, level and safe every time. This is the single highest-risk point in the design.
- Load. Two adults moving, not sitting, with a safety factor set by the engineer, not by us.
- Wet heat. Every moving part lives at 105°F and high humidity for years, and has to keep working.
- Hands. No pinch points, and a platform any adult can fold without strain.
- The cushion. A practice surface that stays grippy when wet, tolerates heat, and cleans easily.
What we know about the gradient, and how we'll measure ours.
Vertical stratification in a sauna is not in dispute. Finnish sauna engineering references describe temperatures rising by several degrees for every few inches of height at typical sauna setpoints, and the traditional advice that your feet should never sit much colder than your head is why Finnish benches climb toward the ceiling.
Two honest caveats. First, those published values are typical figures at sauna temperatures near 175°F, not measurements of a 105°F room. Second, the gradient in this geometry, with a mirror wall and two people moving, has not been measured. The first prototype gets three logged sensors: 6 inches off the floor, 6 inches above the platform surface, and 6 inches below the ceiling, through warm-up and a full 90-minute class. We publish the curves.
| Sensor A · 78 in | Just under the ceiling. The hottest air, where nobody practices. Tells us the setpoint the heater has to reach. |
|---|---|
| Sensor B · 30 in | Six inches above the platform. The number we design to: the floor series lives here. |
| Sensor C · 6 in | Just off the floor. The coldest air, and the reason the floor series moved up. |
| Also logged | Relative humidity at B, heater duty cycle, time to reach target from cold, recovery after the door opens. |
A heat pump, not a stove.
The room is 245 cubic feet, and the number that matters is the temperature we want, not the volume. Hot yoga is 105 to 110 °F, not sauna heat, and most of what you feel in a hot class is the warmth of the surfaces around you, not the air. So the platform is warm under you and the walls are warm beside you, and a heat pump outside the cabin is designed to do the air, on ordinary 120 V circuits with nothing electronic inside the heat. The target for cold to class temperature is about half an hour, not yet measured; the 5 kW sauna heater on 240 V stays as the option for sauna-hot sessions.
The design holds humidity for you. Two people in a hot class put more moisture into the air than a room this size can hold, so the room is designed to breathe on its own, keep the mirror clear, and run a short dry cycle after every session so nothing is left damp. There is no pouring water on rocks; you would set one felt temperature and step in.
| Heat | Warm platform and wall surfaces plus a heat pump outside the cabin TBD · suppliers |
|---|---|
| Circuits | Designed for ordinary 120 V circuits for the standard build; 240 V only for the sauna-hot option |
| Warm-up | About half an hour from cold to class temperature to be measured on the prototype |
| Humidity | Held automatically; dry cycle after every session |
| Targets | 105 to 110 °F at platform height, 40 to 60 % RH, measured, not assumed |
Who clears the 7 ft ceiling with arms overhead.
Anthropometric tables put adult overhead fingertip reach at about 1.2 times standing height. Elite athletes with long arms can reach closer to 1.3 times. The table uses both against the 84-inch ceiling. Verdict thresholds: more than 4 inches to spare is a clear "full overhead"; 1 to 4 inches is tight; under 1 inch means use the compact variation.
| Standing height | Reach at 1.2× | Clearance | Verdict | Reach at 1.3× (long arms) | Clearance | Verdict |
|---|---|---|---|---|---|---|
| 5 ft 0 in · 60 | 72 in | 12 in | Full overhead | 78 in | 6 in | Full overhead |
| 5 ft 4 in · 64 | 77 in | 7 in | Full overhead | 83 in | 1 in | Tight |
| 5 ft 8 in · 68 | 82 in | 2 in | Tight | 88 in | −4 in | Compact variation |
| 5 ft 10 in · 70 | 84 in | 0 in | Compact variation | 91 in | −7 in | Compact variation |
| 6 ft 0 in · 72 | 86 in | −2 in | Compact variation | 94 in | −10 in | Compact variation |
| 6 ft 2 in · 74 | 89 in | −5 in | Compact variation | 96 in | −12 in | Compact variation |
| 6 ft 4 in · 76 | 91 in | −7 in | Compact variation | 99 in | −15 in | Compact variation |
| 6 ft 6 in · 78 | 94 in | −10 in | Compact variation | 101 in | −17 in | Compact variation |
Which postures this touches. In the standard 26-posture sequence, the standing postures that put both arms fully overhead are half moon (arms over the head, palms together) and balancing stick (arms over the head, then tipping forward). Awkward and triangle hold the arms at shoulder height. Eagle, standing head-to-knee, standing bow, tree, and toe stand do not reach overhead. Standing separate-leg head-to-knee is often taught starting with arms overhead and then folds. So the ceiling changes two, at most three, of thirteen standing postures. At 7 ft that means most adults use the compact variation for those two, which is the price of a room that fits indoors. Teachers: tell us if we have this wrong →
Heights are standing height in bare feet; the 1.2× ratio comes from general-population anthropometric data (Pheasant; NASA anthropometric source book), the 1.3× from athlete measurements. Rounded to the inch. The prototype is the real test: we will have practitioners of several heights run the full standing series inside it and record which postures they modified. If the 7 ft ceiling proves wrong in practice, the design goes to 7 ft 6 in and gives up indoor placement. Sources →
Planned for a US build. Nothing is built yet.
Cedar. The plan is cedar grown and milled in the US rather than imported: most Canadian softwood now enters the US with antidumping and countervailing duties plus a Section 232 lumber tariff that stack to roughly 45% for most mills, and Western red cedar is inside that scope.
Fabrication. A US shop of the kind that already builds custom cedar cabins, not a factory. None is chosen yet.
Mirror wall. A full-height studio mirror from inside, with the teacher life-size in it and the readout in a corner; a plain panel outside. The mirror stays clear at class humidity.
Suppliers for every part are open, so we make no claim yet about where each one comes from.
The next-steps list, unedited.
- Trademark clearance on the name, with counsel. There are live "Hot Room" marks in yoga services.
- Supplier quotes for the shell, the mirror wall, the heat and the platform.
- Every standing posture against real clearance, with practitioners of several heights, in the prototype.
- Two or three hot yoga instructors shown the sequence and the mid-class fold, and asked if it matches how a class flows. That ask →
- Thermometers in the prototype before the heat is specified.
- A US fabricator for the first prototype.
See the prototype measured, not rendered.
The people on the list get the sensor curves and the clearance results before anyone else.