Building on Forest Land —
Mountain Use Permits and Slope Standards

Cheap Land Has a Reason

Forest land is far cheaper than building lots in the same region. So the consultation keeps coming: "If I buy forest land and build a country house, isn't that a good deal?" The conclusion up front: the gap between developable and non-developable forest land is extreme, and even developable land often ends up no cheaper than a building lot once permit and civil works costs are added.

Forest land is not land you can simply reclassify. A separate law, the Mountain District Management Act, guards it, requiring passage through a three-gate sequence: mountain-use conversion permit → development activity permit → building permit.

The First and Largest Gate — Slope

The statutory standard for a mountain-use conversion permit is an average slope of 25 degrees or less. In practice, however, the local development activity permit ordinance is strengthened well below this, making that ordinance the de facto cutoff. On the same hillside, developability can split with a single city-boundary difference. Elevation standards and timber-volume (tree density) standards operate alongside.

Slope cannot be eyeballed. It requires average-slope analysis through surveying, and the figure can change depending on how the development area is drawn within the parcel. This is why slope analysis is the number-one check in forest land purchase review.

The Hidden Costs

Even where a permit is possible, the cost structure differs from a building lot. Replacement forest resource fees (conversion area × unit amount, published annually), restoration deposits, mountain-use conversion design services, and above all civil works — access road construction, retaining walls, cut-and-fill — are substantial. Even at half the land price, the total project cost often reverses, so a rough civil-works estimate must be included in any comparison.

We are currently reviewing a development that includes forest land in Suji-gu, a textbook case where mountain regulations, slope, and access roads are layered together. For such land, you must untangle not each regulation individually but the combination of regulations, making comprehensive pre-purchase review especially important.

Frequently Asked Questions

Q. What's needed to build on forest land?

A three-stage sequence: mountain-use conversion permit → development activity permit → building permit. Unauthorized damage is subject to criminal punishment.

Q. What's the slope standard?

The statutory standard is 25 degrees or less, but most local ordinances strengthen it, so checking the relevant jurisdiction's ordinance is essential.

Q. Is forest land really cheaper than a building lot?

The land is cheap, but development and civil costs often reverse that. A total-project-cost review before purchase is advised. LEA Architects conducts forest land reviews in Yongin. Contact us →