Regulation Guide · 2026. 07

The Complete Extension Guide —
From Reporting Thresholds to Hidden Pitfalls

Q: Is an extension a permit or a report?

An extension with total floor area within 85㎡ falls under building report; beyond that, a building permit is required. Even under the reporting threshold, all code requirements — lot coverage ratio, floor area ratio, daylight setback, etc. — must still be met, and if the existing building has violations, filing the extension itself may be difficult.

Q: My lot coverage ratio is maxed out — is there really no way to extend?

Sometimes there is. If the site is within a Growth Management Plan zone, a relaxed lot coverage ratio may apply on condition of complying with that plan, enabling extension. In our Sangha-dong, Yongin house, this approach let us combine demolition of an illegal extension with a lawful new one.

Q: Can I add an elevator to an existing building as an extension?

Yes. This is done by attaching an elevator and shaft to the building's exterior as an extension, requiring both a structural review of the existing building and a check against evacuation and accessibility-facility standards. Demand is rising for barrier-free retrofits in both public and private buildings.

LEA Architects · Junsu Kim, Architect

The First Question of Extension — 85㎡

An extension increases an existing building's floor area, number of stories, or height. The threshold is clear: total floor area within 85㎡ means a report; beyond that, a permit. Adding a room or storage space to a single-family house typically falls within the reportable range. (See our full permit vs. report guide for the broader distinction.)

But "report" doesn't mean a lighter review. The added area counts against lot coverage and floor area ratio, added height can hit the daylight setback line, and structural review comes with any change in load. An extension is a "small new build" — all the code of a new build follows along in miniature.

Extension procedure and key review gates

Case 1 — Extending a House at Full Lot Coverage

The most common frustration is "the coverage ratio is already maxed, I can't add anything." Our detached house project in Sangha-dong, Yongin faced exactly this. With no remaining allowance after demolishing an illegal extension, we confirmed the site fell within a Growth Management Plan zone, applied for the relaxed lot coverage ratio, and converted the plan into a lawful extension. Extensions that look blocked can sometimes open up through local zoning incentives. View this project →

Case 2 — Attaching an Elevator to a Building

Extension isn't only about adding floor area. Attaching an elevator shaft to the exterior of an existing building is also a form of extension — elevator extension. Our project installing an elevator at Hankyong National University fell into this category, requiring a review of the connection to the existing structure, evacuation routes, and accessibility-facility standards together. Demand for this kind of barrier-free retrofit is rising across public and private buildings alike. View this project →

Frequently Asked Questions

Q. Is an extension a permit or a report?

Within 85㎡ is a report; beyond that, a permit. Even reports must fully satisfy lot coverage, floor area ratio, etc., and existing violations can block filing.

Q. My lot coverage ratio is maxed out — is there really no way to extend?

Sometimes. A Growth Management Plan zone can grant a relaxed lot coverage ratio. We used this approach in an actual Sangha-dong, Yongin house project.

Q. Can I add an elevator to an existing building as an extension?

Yes. Attaching an elevator shaft to the exterior as an extension requires structural review plus evacuation/accessibility checks.

Extension Permit · Extension Report · 85㎡ Extension · Extension Procedure · House Extension · Elevator Extension · LEA Architects

Back to Journal