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JADU Efficiency Bathroom.

Full-bath function in 30 square feet of well-planned space.

JADUs require a full bathroom — toilet, sink, and either tub or shower — but the entire JADU is capped at 500 sqft, so the bath usually has to fit in 30–45 sqft. We design these to feel like real bathrooms (full-height shower glass, decent vanity, code-compliant ventilation) rather than dorm-room half-baths.

Typical range

$8K – $24K complete

Per unit

$220 – $500 / sqft of bath

Timeline

2–3 weeks once plumbing rough is complete.

The short version.

The minimum JADU bathroom is roughly 30 sqft: a 30 in x 30 in shower (or 36 in x 36 in for comfort), a wall-hung toilet to save floor space, and a 24 in vanity. Fitting a tub-shower combo requires about 45 sqft minimum (60 in tub + 24 in vanity + toilet). Most JADU baths we build land at 36–40 sqft with a shower-only design — owners and renters consistently prefer the shower for usability.

The plumbing tie-in is usually straightforward — tap the existing main-house drain and supply lines wherever they're closest to the bath wall. The added load on the existing system is minimal (one toilet, one shower, one sink), but we verify the existing vent and drain capacity in the feasibility phase. Tankless or point-of-use water heaters are common to avoid running long hot-water lines.

Ventilation is non-negotiable. Bathrooms need 50 CFM continuous or 50 CFM on a humidity-sensing switch (CMC §403.7). For a JADU bath that gets daily use, we recommend humidity-sensing — turns on with shower steam, runs until the air dries, automatic. Skipping bath ventilation in California's humid coastal zones (SF, the Peninsula, Westside LA) leads to mildew within months.

What you can actually pick.

  • Shower-only with wall-hung toilet (30–36 sqft)

    Pros — Most efficient use of space, modern aesthetic, easy to clean.

    Cons — No tub for renters who want one.

    $8K–$18K complete25+ years

  • Tub-shower combo with floor toilet (45 sqft+)

    Pros — Maximum function in larger JADU, broader renter appeal.

    Cons — Requires more space, longer plumbing rough.

    $10K–$22K complete25+ years

  • Curbless shower + wall-hung toilet (aging-in-place)

    Pros — Accessible, modern, no threshold to step over.

    Cons — Requires recessed subfloor and linear drain, higher cost.

    $11K–$24K complete30+ years

What we deliver.

  • Floor plan — minimum 30 sqft, layout optimized for the JADU's main entry
  • Plumbing rough — tap existing main-house supply and drain
  • Electrical rough — GFCI receptacle, lighting circuit, ventilation fan circuit
  • Ventilation fan — 50 CFM continuous or humidity-sensing
  • Shower waterproofing — Schluter Kerdi or hot-mopped pan
  • Tile install — wall, floor, niche if included
  • Toilet install — wall-hung or floor-mount per layout
  • Vanity install — 24 in or 30 in with integral counter
  • Glass enclosure or curtain (curtain saves $1.5K–$3K)
  • Final fixture install and test

The code parts most owners miss.

  • Bathroom requires either a window or 50 CFM ventilation (CMC §403.7).
  • GFCI required at all receptacles in bathroom (NEC 210.8).
  • Shower minimum interior dimension 30 in x 30 in (UPC §411.7).
  • Toilet clearance: minimum 21 in front clearance, 15 in side clearance from any fixture or wall.
  • Tankless water heater serving JADU bath: gas units need combustion air per CMC §701; electric units need a dedicated 40A circuit.

Why getting this right pays off.

The bathroom is the make-or-break room in a JADU. A well-designed 35 sqft shower-only bath with full-height glass, good tile, and silent ventilation feels modern and usable. A poorly designed bath of the same size feels cramped and pushes renters or family members away from the unit.

Ventilation specifically determines whether the JADU stays mildew-free over years of use. The $250–$500 cost difference between a basic 50 CFM fan and a quality humidity-sensing fan (Panasonic WhisperGreen, Broan-NuTone) returns 10× in avoided mildew remediation.

What goes wrong — and how to avoid it.

  • Skipping bath ventilation — mildew within months in coastal climate
  • Putting the toilet across from the door — opens to bad sightline from JADU entry
  • Cheap fan with rated 1.5 sone — too loud to want to use, defeats the purpose
  • No GFCI at the vanity receptacle — fails final inspection
  • Floor-mount toilet in 30 sqft bath — wall-hung saves 8 in of floor

After we hand you the keys.

  • Clean fan grille every 6 months to maintain CFM rating
  • Re-caulk silicone at shower change-of-plane joints every 3–5 years
  • Inspect under-sink for any leaks monthly
  • Treat any grout discoloration as a moisture issue until proven otherwise

In short.

How small can a JADU bathroom be?
Practical minimum is 30 sqft with a 30 in x 30 in shower. Tub-shower combo requires 45 sqft minimum. Most JADU baths we build land at 36–40 sqft with a shower-only design.
How much does a JADU bathroom cost?
$8K–$24K complete depending on layout. Shower-only with wall-hung toilet: $8K–$18K. Tub-shower combo: $10K–$22K. Curbless shower with linear drain: $11K–$24K.
Do I need a tub in a JADU?
No — state law requires a full bathroom (toilet + sink + tub OR shower). Most JADU owners go shower-only for space efficiency.
Can the JADU share the main house's bathroom plumbing?
Yes — the JADU bath taps the existing main-house drain and supply lines. We verify the existing system has capacity for the added fixtures during feasibility.
What's the best ventilation fan for a JADU bath?
Panasonic WhisperGreen with humidity sensor (50–80 CFM, < 0.3 sones) is the best-in-class — quiet enough to leave on, automatic moisture control. Cost is $250–$400 installed.
Do I need a separate water heater for the JADU bath?
No — most JADUs share the main-house water heater. A point-of-use tankless heater is an alternative if the main heater is far from the bath or undersized.
How long does a JADU bath take to install?
2–3 weeks once plumbing and electrical rough is complete. Tile setting and waterproofing is typically the longest phase.
Can I install a curbless (zero-threshold) shower?
Yes — requires a recessed subfloor (or floor build-up around the shower) and a linear drain. Adds $1,500–$4,000 vs a curbed shower. Worth it for aging-in-place or for the modern aesthetic.

Keep reading.

Planning jadu efficiency bathroom?

Send us the address and the scope. We'll come back with a line-item budget, a permit path, and a realistic schedule — before you spend on drawings.

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