A hazard map screens for area-wide risk. A geotechnical survey tests the specific soil under your lot. Here is what each one tells you, when banks require a geotech investigation, and how to use both tools in the right order.
You ran a hazard check on the property. Your bank, architect, or broker now mentions a geotechnical survey. These are two different tools for two different questions, and knowing which one you need (and when) saves you time and money.
A hazard map answers one question: based on terrain, geology, and historical data for this area, what natural hazards are likely to affect this location?
The maps come from national agencies. PAGASA models flood return periods (how often a flood of a given depth is expected to reach a location). PHIVOLCS maps active faults and liquefaction susceptibility. The Mines and Geosciences Bureau (MGB) maps landslide, debris flow, and alluvial fan hazard zones. These datasets cover the entire country at a regional scale, usually in grid cells of 10 meters or more.
What hazard maps tell you:
What hazard maps cannot tell you:
Hazard maps screen. They tell you which questions to ask next.
A geotechnical (geotech) investigation is a site-specific engineering study. A licensed geotechnical engineer visits the exact location, drills test borings, and runs laboratory tests on the samples. The output is a site investigation report (sometimes called a soil test report) with engineering conclusions about that specific plot of land.
Typical tests in a Philippine geotech investigation:
A geotech report typically costs between P10,000 and P60,000 in the Philippines, depending on the number of borings and the depth required. Multi-story buildings need more borings. The results go directly into the structural engineer's foundation design.
For a simple purchase of an existing house, a geotech report is not always legally required before transfer. But it becomes expected or mandatory in several situations:
Practical rule: if the structure you plan to build is more than two stories, or if the lot sits in a flagged hazard area, commission the geotech investigation before you finalize the purchase. Findings can change what you are permitted to build, and that affects the value of the lot.
Think of them as stages in your due diligence process, not competing alternatives.
Stage 1 (before you make an offer): Run a hazard check. If results show low to moderate hazard levels, proceed with confidence. If results show high flood risk, active fault proximity, or high landslide susceptibility, negotiate the price, ask the seller for disclosure documents, or walk away. The homebuyer due-diligence checklist walks through this stage in more detail.
Stage 2 (after your offer is accepted, before you finalize construction plans): Commission the geotech investigation. The hazard map told you the area sits on liquefiable soil; the geotech report tells you exactly how deep to drive piles. The hazard map showed medium landslide risk; the geotech report tells you whether the slope behind the lot is stable under load.
Running them in sequence saves money. A hazard check costs P99. A geotech investigation costs tens of thousands of pesos. Do not spend on the investigation before you know the area is worth buying at all.
This is a guide, not a legal standard. Your structural engineer or architect makes the final call for your specific project.
If most of these do not apply and you are buying a finished house in a low-hazard area, you may not need an immediate geotech investigation. But knowing when it is required keeps you from being surprised late in the process.
Hazard maps reflect available national datasets updated on the agency's schedule. Some areas have coarser resolution data than others. A geotech investigation reflects conditions at the time and location of drilling. Neither tool predicts every outcome. Both reduce uncertainty; neither eliminates it.
CheckHazard does not replace a professional geotechnical or engineering survey.