ADU Builder: a backyard house from the drawing to the last coat

October 9, 2026 · Eric Richers

I wanted to see a small backyard house before anyone digs. Paper plans do not show the order a crew builds in, and a national cost per square foot does not tell you what a 646 square foot cottage might cost.

The ADU Builder plan chooser, headed From the drawing to the last coat, with cards for the Twin Perch 380 and Perch Cottage 646 showing their floor plans and prices. — Five plans to choose from, each with its floor plan and its price.

How it works

Pick one of five plans. See the floor plan, then watch the house go up one stage at a time: site work, foundation, framing, roof, and finishes.

The floor plan for the Perch Cottage 646, with the living room at 224 square feet and the bedroom at 194 square feet, and a Walk through button. — The floor plan, before any of the stages are built.

The construction stage view, with a 3D model of the framed house on its lot and a panel reading This stage: $3,396 beside a list of stages from site work to painting. — One stage at a time, each adding to a running cost.

Each stage adds to a running cost, and the last step shows loan options. The numbers are an estimate, not a bid.

The cost and loans page, with a materials list in columns and loan options below it, all in the dark theme. — The materials list and the loan options at the last step.

The finished Perch Cottage 646 rendered on its lot, with a panel showing $105,351 and the completed stage list. — The last coat, with the running cost the stages added up to.

Built with

three.js with WebGPU and a WebGL2 fallback, Vite, CC0 textures from Poly Haven and ambientCG, and a denoiser for clean renders.

Common questions

What does ADU Builder actually show me?

Pick one of five plans, see the floor plan, then watch the house go up one stage at a time: site work, foundation, framing, roof and finishes. Paper plans do not show the order a crew builds in.

Are the costs a bid?

No. Each stage adds to a running cost and the last step shows loan options, but the numbers are an estimate, not a bid.

What is it built with?

three.js with WebGPU and a WebGL2 fallback, Vite, CC0 textures from Poly Haven and ambientCG, and a denoiser for clean renders.

Why a 646 square foot cottage specifically?

Because a national cost per square foot does not tell you what a 646 square foot cottage might cost. The plans are for a Eugene lot, and the estimate is built from the stages rather than from a national average.

Oct 8, 2026

ADU Builder: a backyard house from the drawing to the last coat

How it works

Built with

Jev Odds, Setup Score and Ask: market tools that show their work

A social composer that exports in the browser

Clip Calendar: plan, caption and approve short videos