20x20 Tiny House Plan | 400 Sq Ft 1 Bedroom ADU Blueprint

A Complete 400 Sq Ft Tiny House Plan Built for Real Life

Whether you're adding a backyard ADU for rental income, building a guest house for family, or starting small with your first owner-built home, this 20x20 one-bedroom plan packs everything you need into a smart, buildable footprint.

The Layout

Step through the covered entry with double glass doors into an open living room (9'5" x 12'8") that flows straight into a full kitchen (9'5" x 6'6"). The bedroom (9'5" x 9'6") fits a queen bed and sits next to a dedicated closet (5'9" x 3'0") and a full bathroom (9'5" x 5'10") with tub, toilet, and vanity. A stacked washer/dryer closet means no trips to the laundromat. Large windows on every side fill the space with natural light, and a loft plan is included in the drawing set for extra sleeping or storage space.

Key Specs

• Conditioned living area: 400 sq ft
• Footprint: 20 ft x 20 ft
• Bedrooms: 1 | Bathrooms: 1 full
• Building height: 19'3" with 12 ft plate and 9 ft openings
• Gable roof with black corrugated metal roofing
• T&G cedar rain-screen siding over insulated 2x4 walls

What's Included

Your purchase includes the complete working drawing sheet set as a print-ready PDF at A3 size, plus a CAD file so your local designer or engineer can make edits. Depending on your plan package, you also receive the itemized material list and a reverse (mirrored) plan. The set covers the ground floor plan, loft plan, slab layout showing the load-bearing wall, sections, ceiling and roof outlines, all four elevations, kitchen and bath detail sheets, rafter details with five insulation options, wall and window installation details, foundation details with insulation and drainage specs, cedar siding rain-screen details, door and window schedule, framing details, a full electrical plan with fixture legend, a complete plumbing plan, and an itemized material takeoff your lumber yard can price directly.

Construction You Can Trust

The plan is drawn to 2022 California residential codes (IRC 2021 with amendments) with wind loads per ASCE 7-16. Details go beyond the basics: rigid foundation insulation, under-slab vapor barrier, perimeter drainage, termite shield, GFCI-protected electrical with interconnected smoke detectors, a 220V receptacle, and low-flow plumbing fixtures on copper supply with PVC Schedule 40 DWV.

Estimated Build Cost

Roughly $130–$220 per square foot depending on region, finishes, and labor, or approximately $52,000 to $88,000 total.

Instant Digital Download

Files are delivered immediately after checkout. Print at 100% scale at any local print shop. This is a digital product only; no physical item ships. Plans should be reviewed by a local engineer or building official before permitting, as codes vary by jurisdiction. For personal use only. © Home Plan DIY.