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Technical

Slope

The angle of the land surface with the horizontal; expressed as percentage (%) or degrees (°). Affects construction conditions and whether basements qualify as FAR-exempt.

Slope (Turkish: eğim) is the angle of land with the horizontal plane. Expressed in percent (%) (rise in 100 m run) or degrees (angle to horizontal). 100% slope = 45°; 10% slope ≈ 5.7°.

For zoning and construction, slope is a critical parameter:

- 0-3%: flat land, most suitable for building - 3-10%: gentle slope, buildable with standard projects - 10-20%: moderate slope, requires retaining walls, terracing - 20-35%: steep, landslide risk assessment, extra engineering cost - 35%+: very steep, mandatory geological survey, building ban in some areas

The Planned Areas Zoning Regulation imposes special rules on grading and eave kot calculations for sloped plots. Slopes above 15% require cut-fill balance and landslide risk assessment. The Regulation on Buildings in Disaster Zones may ban construction on slopes over 35% (subject to local risk).

Slope calculation: Kot difference divided by horizontal distance between two points. Example: point A at +50 m, point B at +55 m, 100 m apart → slope (55-50)/100 × 100 = 5%. Close-packed contour lines indicate steep slope; widely spaced ones indicate flat terrain. A Digital Elevation Model (DEM) is ideal for automated slope computation.

Examples

  • 1.In Karşıyaka (İzmir), a plot with 25% slope — the contractor plans a 3 m retaining wall + drainage system at the back; construction cost rose 15%.
  • 2.A 40% slope sea-view plot in Bodrum — the local regulation denies permits above 35%; the building permit requires a geology report + special authorisation.
  • 3.A drone-derived DEM feeds ArcGIS's 'Slope' tool, automatically computing the parcel's mean slope percentage and producing a colour-coded map.

Frequently Asked Questions

Is a sloped plot buildable?expand_more
Depends on local zoning regulations and geological conditions. 10-20% slope is still suitable for standard construction but adds retaining wall + drainage costs. 20-35% needs serious engineering — ground survey, landslide analysis, special foundation design. Above 35% is banned or heavily restricted in most municipalities. Consult the municipal planning office before buying.
How is slope measured?expand_more
**Manually**: Clinometer or smartphone gyroscope app + direct ground measurement. **GPS + kot**: distance and kot difference between two points → slope formula. **Map/DEM**: ArcGIS Slope tool, QGIS 'Slope' raster calculation. **Drone**: photogrammetry DEM production, then slope raster. Most cadastral maps include a slope layer.
Is slope shown in zoning plans?expand_more
Not as a direct value, but the **base topographic map** shows slope via contour lines. Plan notes may include general provisions like 'special measures required on sloped plots'. Some special-plan areas (e.g. protection zones, landslide areas) specify slope limits explicitly.
How much does a sloped plot increase construction cost?expand_more
Varies by local conditions, but rough indicators: 10-20% slope → cost up 5-15%; 20-35% slope → up 15-40%; above 35% → 40%+ increase plus permit issues. Main extras: retaining walls (TRY 1,500-3,500/m², 2026 prices), deep foundations, drainage, more fill, terracing. Balanced cut-fill can reduce costs.

Related Terms

Elevation (Kot)Zoning Status (İmar Durumu)Setback Distance

Sources

  • • Planned Areas Zoning Regulation (provisions for sloped terrain)
  • • Regulation on Buildings in Disaster Zones
  • • Türkiye Earthquake Hazard Map and Ground Survey Regulations

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Last updated: 2026-04-24