Retaining walls are the most common structure on sloping Philippine lots and the least often engineered. Here is what to look at before you trust one.
On any sloping lot there is usually a wall holding soil back. It might be behind the house, along the driveway, or at the boundary. It is doing a real job: resisting the pressure of a mass of earth that wants to move.
Most buyers look at it and see a wall. It is not a wall, it is a structure carrying a load, and whether it was designed for that load is one of the most consequential unknowns in a hillside purchase.
Drainage. This is the big one. Soil behind a wall gets heavy when it is wet, and saturated soil pushes far harder than dry soil. A properly built retaining wall has a drainage layer behind it and weep holes through it, so water leaves rather than accumulating.
A wall with no weep holes, or with weep holes that have been sealed or plastered over, is being asked to hold back water pressure as well as soil. Many are not designed for that.
Foundation and reinforcement. A retaining wall needs a footing sized for the load and steel where the bending happens. From the outside you cannot see either. What you can see is whether it looks like a considered structure or a stack of hollow blocks.
That last question matters. A wall retaining engineered fill placed in compacted layers is one thing. A wall retaining loose fill that was pushed over the edge to make the lot bigger is another.
The mapped layers tell you what the wall is up against. On the same lot, look at:
A modest wall on gentle ground with low susceptibility is a small question. A tall wall on steep ground rated for landslide susceptibility is a large one, and it needs a licensed civil or structural engineer before you buy, not after.
If the wall holding up the ground above you belongs to somebody else, its condition still determines what lands on your property. Inspect it with the same care and find out who is responsible for maintaining it, in writing if possible.
A hazard screening reports slope, landslide susceptibility, and fault distance at your coordinates from public national datasets. It cannot see a wall, assess its reinforcement, or know what is behind it. That is exactly the kind of question a licensed engineer answers, and on a hillside lot it is the visit worth paying for.
CheckHazard does not replace a professional geotechnical or engineering survey.