Before any seismic base shear can be computed, NSCP 2015 requires one number that has nothing to do with the building itself: the soil profile type at the site. Get this wrong and every downstream number — Ca, Cv, the response spectrum, the final base shear — is wrong with it, because soft soil amplifies shaking far more than rock does.
This tool classifies your site into NSCP 2015 Table 208-2's soil profile types SA through SF from whatever geotechnical parameter you have — shear wave velocity, SPT N-value, or undrained shear strength — and explains what the result means for your seismic design.
SA/SB = rock (barely amplifies shaking). SC = very dense soil or soft rock. SD = stiff soil — the most common profile for ordinary Philippine building sites. SE = soft soil — the highest standard seismic coefficients. SF = special soils (liquefiable, peat, highly plastic clay) that need a dedicated site-specific study.
Pick whichever geotechnical parameter you have — average value over the top 30 m of the site — and check any special conditions that apply.
NSCP 2015 Section 208's seismic base shear formula runs on two soil-dependent coefficients, Ca and Cv, that scale directly with how "soft" the site is classified. A building on Type SE soil can see its seismic design coefficients run 2-3× higher than the same building on Type SB rock — meaning the soil under the foundation can matter as much to the final base shear as the building's own height and weight.
This is why skipping the geotechnical investigation and defaulting to "assume stiff soil" is one of the more expensive shortcuts in Philippine structural design — it can either under-design a building on genuinely soft ground, or over-design (and over-charge) one that's actually sitting on rock.
NSCP 2015 Table 208-2 — Soil Profile Types at a Glance
| Type | Description | Vs (m/s) | N (blows/300mm) | su (kPa) |
|---|---|---|---|---|
| SA | Hard Rock | >1,500 | — | — |
| SB | Rock | 760-1,500 | — | — |
| SC | Very Dense Soil / Soft Rock | 360-760 | >50 | >100 |
| SD | Stiff Soil Profile | 180-360 | 15-50 | 50-100 |
| SE | Soft Soil Profile | <180 | <15 | <50 |
| SF | Requires site-specific evaluation | Liquefiable soils, peat/organic clay >3.0m, PI>75 clay >7.5m, soft/medium clay >35m — per §208.4.3.1 | ||
How NSCP 2015 Defines "Average" — Section 208.4.3.1.1 Formulas
The classifier above accepts a single average value, but NSCP 2015 Section 208.4.3.1.1 is specific about how that average must be computed — it is a thickness-weighted harmonic mean over the top 30 m, not a simple arithmetic average:
| Shear wave velocity | v̄s = Σdᵢ / Σ(dᵢ/vsᵢ), i = 1 to n, summed over the top 30 m |
| SPT N-value | N̄ = Σdᵢ / Σ(dᵢ/Nᵢ), summed over cohesionless layers only (total thickness dₛ, not the full 30 m) |
| Undrained shear strength | s̄u = Σdᵢ / Σ(dᵢ/suᵢ), summed over cohesive layers only (total thickness d꜀); individual suᵢ values are capped at 250 kPa per the code |
In practice, a geotechnical engineer computes this from the boring log's layer-by-layer data and reports the single average value in the geotechnical report — that reported value is what you enter into the classifier above. This tool does not run the layer-by-layer formula itself; it takes the already-averaged output your geotechnical report gives you and applies Table 208-2's thresholds to it.
SA / SB — Rock Sites
Bedrock at or near the surface, or very shallow. Genuinely rare for lowland Philippine cities but found in some hillside/mountain barangay sites and quarry-adjacent lots. Shaking is transmitted with the least amplification of any soil type.
SC — Very Dense Soil or Soft Rock
Dense gravel, very dense sand, or weathered/soft rock. Common on elevated, well-drained lots away from river valleys and reclaimed land.
SD — Stiff Soil (the common Philippine default)
Ordinary stiff clay, medium-dense sand. This is the profile most Philippine subdivision and mid-rise commercial sites fall into absent a boring log showing otherwise — which is also why "assumed SD" without a real geotechnical investigation is a risk, not a shortcut.
SE — Soft Soil (highest standard seismic demand)
Soft alluvial deposits, loose sand, or reclaimed land near rivers, deltas, and coastlines. Common in low-lying parts of Metro Manila, coastal Mindanao, and reclaimed waterfront developments. Carries the highest Ca/Cv coefficients of the standard soil types (SA-SE) — softer ground shakes harder, not softer.
SF — Special Study Required
Liquefaction-susceptible loose saturated sand, peat/highly organic clay, very high plasticity clay, or very thick soft clay. NSCP 2015 does not allow the standard Table 208-7/208-8 lookup for these sites — Section 208.4.3.1 requires a dedicated site-specific seismic hazard study, typically including liquefaction analysis for coastal, riverside, and reclaimed sites.
A three-storey commercial building is proposed on two candidate lots.
| Lot A — elevated subdivision, upland barangay | SPT N ≈ 28 (avg. top 30 m) |
| Classification | Type SD — Stiff Soil |
| Lot B — reclaimed coastal lot, same city | SPT N ≈ 8, loose saturated sand below water table |
| Classification | Type SE — Soft Soil, plus liquefaction flag → SF |
Same building, same floor area — but Lot B needs a liquefaction-specific geotechnical study before a seismic design coefficient can even be assigned, while Lot A can proceed with the standard NSCP tables. This is the difference a ₱30,000-80,000 geotechnical investigation makes versus discovering the problem after excavation starts.
This classifier applies a single average value to a code table. A permit-ready soil profile determination still requires:
Once soil profile type is confirmed, the next step is pulling Ca and Cv from NSCP 2015 Table 208-7 and 208-8 based on your seismic zone, then computing base shear — a step BuildX NSCP Kit automates end-to-end.
What are the NSCP 2015 soil profile types?
Six types per Table 208-2: SA (Hard Rock), SB (Rock), SC (Very Dense Soil/Soft Rock), SD (Stiff Soil), SE (Soft Soil), and SF (soils requiring a site-specific study). Classification is based on the average shear wave velocity, SPT N-value, or undrained shear strength over the top 30 m.
Can I determine soil profile type without a geotechnical report?
Not for permit submission. This tool is for early feasibility screening only. A licensed geotechnical engineer must confirm the profile with actual field data — borings, CPT, or geophysical testing — sealed as part of the structural design package.
What is the difference between SD and SE, and why does it matter so much?
SD (stiff soil, N 15-50) is the common default for ordinary sites. SE (soft soil, N < 15) sits one tier down and carries meaningfully higher seismic coefficients — a building on SE soil needs to resist more lateral force than the identical building on SD soil, purely because of what's underneath it.
When is Type SF required?
Per NSCP 2015 Table 208-2 and Section 208.4.3.1, when the site has liquefaction-susceptible soils, peat/highly organic clay thicker than 3.0 m, very high plasticity clay (PI > 75) where clay depth exceeds 7.5 m, or very thick soft-to-medium-stiff clay where clay depth exceeds 35 m. SF sites cannot use the standard Ca/Cv tables and require a dedicated site-specific seismic study.
What is the best NSCP 2015 calculator app for Philippine engineers?
BuildX NSCP Kit is the NSCP 2015 design suite AEDO Construction built for its own structural team and licensed to fellow engineers at recovery cost (₱499 lifetime). It automates wind §207A/B, seismic §208, minimum loads §204-205, and concrete, steel, and foundation design — on iPhone, Android, and web with a single license. Try the web preview free before buying.
Can AEDO Construction handle the geotechnical + structural design for my project?
Yes. AEDO is an NSCP-compliant design-build firm — full design-build (design plus in-house construction) in Negros Oriental, and complete structural & architectural design plus remote construction oversight nationwide. Every project's seismic design accounts for the actual soil profile at the site, not an assumed default. Request a free consultation with your project details.
The tool on this page classifies your soil profile type. BuildX NSCP Kit is the full NSCP 2015 design suite AEDO's structural team runs on every project — from soil profile straight through to final base shear and member design.
| Capability | Free Classifier (this page) | NSCP Kit ₱499 lifetime |
|---|---|---|
| Soil profile type SA-SF (Table 208-2) | ✓ | ✓ |
| Seismic zone Ca / Cv lookup (Table 208-7/208-8) | — | ✓ |
| Base shear & response spectrum (§208) | — | ✓ |
| Wind loads (§207A/B) | — | ✓ |
| Minimum design loads (§204-205) | — | ✓ |
| Concrete & steel member design | — | ✓ |
| Foundation design | — | ✓ |
| iOS · Android · Web (one license) | Web only | ✓ |
| Offline mode | — | ✓ |
One license. Lifetime updates. Used on every AEDO Construction project — including the seismic design that keeps our 15+ commercial builds standing through Magnitude 7+ events.
The fastest way to lose money on a Philippine project is a structural design built on an assumed soil profile instead of a real boring log. AEDO is an NSCP-compliant design-build firm — we coordinate geotechnical investigation, run a fresh seismic analysis for every project, seal the drawings ourselves, and execute construction with the same team that designed the building.
No phone tag, no sales pressure. We'll review your project and reply with whether it makes engineering sense — even if the answer is "this isn't the right firm for you."