Undulating terrain is hilly, uneven ground with marked differences in height, where the surface is not flat but rolls, rises and falls. In construction the term signals that a building plot cannot simply be treated as a level parcel of land.
Characteristics
You can recognise undulating terrain by:
- Height differences — sometimes a few decimetres, sometimes several metres across a plot
- Slopes and embankments — sloping faces of ground
- Irregular surface — humps, hollows and gentle rolls
- Variable groundwater level — depending on the elevation
Consequences for the design
Building on undulating terrain calls for extra attention:
- Earthworks — usually a combination of cutting (excavation) and filling (raising) to create a buildable level surface. Moving soil can be a significant cost.
- Foundation — with large height differences, builders often choose to found on different levels, add a retaining wall on the uphill side, or use a pile foundation to avoid uneven settlement.
- Drainage — water flows to the lowest point. Good surface drainage and land drains are essential to keep water away from the building.
- Access — driveways, paths and landings must bridge the differences in height.
Application
For DIY projects such as a garden room, shed or carport on a slope, undulating terrain means you first have to create a flat and stable working surface. This is often done with a retaining wall, a raised platform, or a pad-and-beam foundation that absorbs the height differences. Always measure the levels carefully with a spirit level or laser before you start digging or pouring.
Related terms
- Foundation
- Earthworks
- Sloping site
- Retaining wall
- Drainage
Learn more about construction terms in our knowledge base on fredsdiyplans.com.