Check the lot before you commit
- Look the lot up on the geohazard maps of the Mines and Geosciences Bureau (MGB), which show landslide and flood susceptibility.
- Ask the City Planning office about the zoning and any restrictions in the area. Areas hit by landslides can be declared no-build zones.
- Have a geodetic engineer do a topographic survey. Accurate contours are where a hillside design starts.
- Have a soil investigation done. The structural engineer needs it to design the foundations and retaining walls.
Design with the slope, not against it
- Split-level or stepped floor plans follow the contours and cut down on excavation and retaining walls.
- Stepped foundations let the house sit into the hillside instead of on a large flattened platform.
- Place the house on the most stable part of the lot, and keep deep cuts away from the bottom of the slope.
- Balance cut and fill, so soil isn't hauled away or dumped on the slope.
- Plan the driveway, parking and entrance at road level early. Access often decides the layout.
Retaining walls and foundations
Retaining walls and foundations on a slope must be designed by a licensed civil or structural engineer, following the structural code and the soil investigation. Walls need drainage behind them, such as weep holes and free-draining backfill, so water can't build up pressure. Tall walls should not rely on unreinforced stone or riprap.
Drainage is the most important detail
Most slope failures during the rainy season are triggered by water. On a hillside, drainage deserves as much attention as the house itself:
- Collect all roof water in gutters and downspouts, and pipe it away from the slope.
- Lead surface water through lined canals to the street drainage.
- Install subsurface drains behind retaining walls and around foundations.
- Don't let water pond near the house or soak into the slope above it.
- Keep or plant deep-rooted vegetation on slopes you don't build on.
Budget for the slope
Excavation, retaining walls, deeper foundations and drainage can add a lot to the structural cost on a steep lot. A design that follows the slope keeps that extra cost down. Our guide to house construction costs in Baguio explains how to build up a realistic budget.
Permits
A house on a sloping lot needs the same building permit as any other, with structural plans that cover the foundations and retaining walls. If the lot has trees, especially Benguet pines, cutting or relocating them needs government approval. Our building permit guide lists the documents.
Common Questions
Is it safe to build on a steep lot in Baguio?
Often, yes, when the lot isn't in a high landslide-susceptibility area and the house, foundations, retaining walls and drainage are engineered for the site. Check the MGB geohazard maps and get a soil investigation before you design.
Is building on a slope more expensive?
Usually. Excavation, retaining walls, foundations and drainage add cost. A design that follows the slope, with split levels and stepped foundations, keeps the extra cost down.
Do I need a soil test for a sloping lot?
It's strongly recommended. The structural engineer needs the soil data to design safe foundations and retaining walls for a hillside.
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