Few people move into a tiny house dreaming about the bathroom, but everybody ends up thinking about it. Thirty square feet has to hold a real shower, a toilet you can actually use, and somehow a washing machine, all without turning mornings into a scheduling crisis. The bathroom is where tiny house optimism goes to get tested.
The ten layouts in this guide each survive that test. You will get wet baths, pocket-door tricks, under-stair baths, Japanese-style separated baths, and laundry integrations that keep drain runs short and breakers untripped, along with the plumbing dimensions, venting math, and waterproofing specs that separate working micro-baths from expensive mistakes.
Thirty Square Feet Is Plenty, If You Engineer It
The tiny house bathroom is where floor plans go to die. Toilets need 21 inches of clear space in front of the bowl. Showers need 30×30 inches minimum by code, and anyone who has used one knows 32×32 is the honest minimum. A standard washer-dryer pair eats 54 inches of wall. Add it up and you need roughly 55 square feet, but you only have 30. The solution is not magic; it is overlap. Every layout below works by making one footprint serve two functions: the shower floor is the bathroom floor, the hallway is the laundry room, the vanity is the hamper. Here are ten layouts that fit a full shower and laundry into 30 square feet without making the bathroom feel like a punishment.
1. The Classic Wet Bath (5×6)
The wet bath is the highest-density bathroom known to residential construction: the entire 5×6 room is the shower. A wall-hung toilet, a small wall-mounted sink, and a single floor drain with the whole floor sloped at 1/4 inch per foot toward it. You shower standing where you brush your teeth. Laundry goes in a 24-inch-wide stackable unit recessed into the hallway wall directly outside the bathroom door, sharing the bathroom’s water supply and drain through the common wall.
Waterproofing spec: cement board plus liquid-applied membrane on every wall surface to 72 inches, floor membrane lapped up the walls 6 inches minimum. A wet bath that is not fully tanked is a future rot repair.
2. The Split Wet-Dry (6×5)
Divide the 30 square feet with a glass panel or shower curtain on a ceiling track: a 30×48-inch shower zone on one side, a dry zone with toilet and a compact 16-inch-deep vanity on the other. The stackable washer-dryer lives in a 27-inch-deep closet carved from the adjacent bedroom wall, back-to-back with the shower plumbing wall so hot, cold, and drain runs stay under 6 feet.
Plumbing rule: keep the washing machine within 8 feet of the main drain stack. Longer runs invite slow drainage and the dreaded washer-drain gurgle through the shower trap.
3. The Combination Washer-Dryer Bath (5×6)
A ventless combination washer-dryer unit is 24×24 inches, roughly half the footprint of a stacked pair. Put it inside the bathroom itself, in the corner opposite the shower, and the laundry never leaves the wet zone. Drying takes longer with a combo unit (typically 2 to 3 hours for a full load), but in a 30-square-foot bathroom the trade is almost always worth it.
Electrical note: most 120V combo units draw 11 to 13 amps. Give the bathroom a dedicated 20-amp circuit; sharing with a hair dryer or space heater will trip the breaker mid-cycle.
4. The Hallway Laundry Nook (Bath 5×5 + Hall Closet)
Keep the bathroom at a tight 25 square feet (5×5 with a 32-inch corner shower, wall-hung toilet, and pedestal sink) and steal the laundry from the hallway. A 30-inch-deep hallway closet with bifold doors holds a stacked pair, and the bifold doors mean zero swing clearance is needed in the hall. This is the best layout for narrow 8-foot-wide THOWs where the bathroom cannot grow past 5 feet in any direction.
Venting: if you use a vented dryer, the dryer vent run must stay under 25 equivalent feet (subtract 5 feet per 90-degree elbow). In a tiny house this is rarely a problem, but route it before you frame, not after.
5. The Corner Shower + Pocket Door (6×5)
A 32×32-inch neo-angle corner shower frees the opposite corner for a 24-inch stackable unit, with the toilet tucked between them. The secret weapon here is the pocket door: a swinging bathroom door needs 21+ square feet of swing clearance, which in a 30-square-foot room is catastrophic. A pocket door reclaims all of it. Frame the pocket with a proper steel-stud pocket kit, not site-built 2x4s, or the door will drag within a year.
Sound note: pocket doors transmit more sound than solid swing doors. If privacy matters, specify a solid-core pocket door slab and add acoustic seal brushes top and bottom.
6. The Japanese-Style Separated Bath (5×6)
Borrow the Japanese unit-bath concept: a small dry vestibule (toilet + sink, 3×5) separated by a door from a dedicated shower room (3×5) with its own drain. The shower room doubles as the laundry drying space on a retractable wall-mounted line, and the separation means one person can shower while another uses the toilet, a genuine quality-of-life upgrade in a family tiny house.
Ventilation math: two wet zones need real exhaust. Size the fan at 1 CFM per square foot of bathroom (50 CFM minimum here) and duct it straight through the roof or gable wall, never into the attic or wall cavity.
7. The Under-Stair Bath (Lofted THOWs)
In lofted tiny houses, the volume under the stair or ladder run is dead space roughly 3 feet wide, 7 feet long, and 4 to 6 feet tall at the high end. Fit the toilet and a small sink under the low end, and put a 30×30 shower at the tall end where headroom reaches 6.5 feet. The stackable laundry goes in the bedroom closet directly above the bathroom, stacked vertically over the plumbing to keep drain runs short.
Headroom code: most codes require 6 feet 8 inches of headroom at the shower, but tiny houses on wheels typically fall under ANSI or NOAH standards rather than the IRC. Know which standard your build is certified to before you frame.
8. The Outdoor Shower Hybrid (Warm Climates)
In warm climates, move the shower outside. An enclosed outdoor shower (4×4 with privacy screening and a simple roof) removes the largest fixture from the interior entirely, leaving the indoor 30 square feet for a full half-bath plus a stacked washer-dryer with room to spare. Plumb the outdoor shower on the same wall as the indoor bathroom to share supply lines, and add a freeze-proof sillcock-style shutoff if temperatures ever dip.
Privacy engineering: a 6-foot privacy screen with a 12-inch gap at the bottom reads as intentional design, not an afterthought, and the gap keeps the floor dry by allowing airflow.
9. The Laundry-Bath Combo Wall (8-Foot-Wide THOW)
Run all wet functions along a single 8-foot exterior wall: 32-inch shower at one end, toilet in the middle, 24-inch stackable at the other end, with a narrow trough sink mounted above the washer (yes, this exists, and yes, it works). One plumbing wall means one drain line, one vent stack, and all supply lines in a single insulated chase, which is also the easiest wall to keep from freezing in winter.
Freeze protection: in cold climates, keep this plumbing wall interior (not on the exterior sheathing side) or box it with R-15 insulation on the cold side plus heat tape on the supply lines.
10. The Fold-Away Shower Seat Bath (Accessible 6×5)
Design the 30-square-foot bath for aging in place from day one: a 36×36 curbless shower with a fold-down teak bench, grab-bar blocking at 33 to 36 inches on two walls, a comfort-height toilet, and a floating vanity with knee clearance. The stackable unit goes in an adjacent closet with a 32-inch door. This bathroom costs about 15 percent more to build and works for every body for the life of the house.
Blocking map: photograph every piece of grab-bar blocking with dimensions before drywall. Future-you will thank present-you.
The Non-Negotiable Dimensions
- Shower minimum: 30×30 inches code minimum; 32×32 honest minimum; 36×36 comfortable.
- Toilet clearance: 21 inches clear in front of the bowl; 15 inches from centerline to side wall.
- Stacked laundry: 27 inches wide x 30 inches deep x 76 inches tall for a full-size pair.
- Combo unit: 24×24 inches footprint; 33 to 39 inches tall.
- Door: 28 inches absolute minimum for a bathroom; pocket doors save ~20 sq ft of swing.
- Vent fan: 1 CFM per sq ft, 50 CFM minimum; duct to exterior, timer or humidistat control.
Drainage: The Invisible Dealbreaker
Small bathrooms fail at the drain, not the fixtures. A washing machine discharges 15 to 20 gallons in a few minutes; if the 2-inch drain line has insufficient slope (less than 1/4 inch per foot) or the vent is undersized, the shower trap gurgles and gray water backs up. In a THOW, where the whole drain system may run just 12 inches below the floor, slope is precious. Keep the washer within 6 to 8 feet of the main stack, maintain full 1/4-inch-per-foot slope with no sags, and vent every fixture individually. This is the least glamorous paragraph in tiny house design and the most expensive to ignore.
Final Considerations
Thirty square feet is not a compromise; it is a design brief. Pick the layout that matches your climate, your household, and your tolerance for togetherness, then plumb it like you mean it. A well-drained, well-vented 30-square-foot bath with laundry beats a cramped 50-square-foot afterthought every single time.