Japan Road Setback Calculator(Article 42-2 Road Surrender Math)
Under Japan's Building Standards Act Article 42, Paragraph 2 （建築基準法第42条第2項）, building lots facing roads narrower than 4 meters must surrender land to the municipality when rebuilding. Calculate your exact lot loss below.
Setback Inputs
What the numbers mean
What is a "2-Kō Dōro" (みなし道路)?
Article 42, Paragraph 2 of Japan's Building Standards Act treats narrow existing roads as if they were legal roads for rebuilding purposes, but only if the lot gives up enough land to widen the road to 4 metres. These are called "みなし道路" (deemed roads). Without this setback, the building may be classified as 再建築不可 — impossible to rebuild.
Centerline Setback (中心振り分け) vs. One-Sided Setback (一方後退)
When both sides of the road already contain private plots, the widening burden is split evenly down the center: each side gives half of the missing width. When the opposite side is a river, cliff, railway, or public land that cannot surrender width, your side bears the full burden.
Municipal property tax exemption (減免措置)
The strip you surrender often remains registered on your title while functioning as road. Many municipalities will reduce or exempt fixed asset tax on that portion if you apply with a 減免申請書 and proof of the setback survey. Always confirm the local rule with the city tax office.
Don't want to calculate variables manually?
Paste your raw listing text or URL into the AkiyaCheck Scanner to audit road rules, hazards, and rebuild rights in 30 seconds.