How to Check If a Lot Is Buildable Before You Buy It

The listing says 300 m², corner lot, clean title, great price. What the listing doesn't say is how much of that 300 m² you're actually allowed to build on — and that number is the one that decides whether the property is a bargain or a trap.

Every lot comes wrapped in invisible rules: setbacks that push your walls in from the boundary, occupancy limits that cap your footprint, floor-area ratios that cap your total build, height limits that cap your ambition. Two lots of identical size on different streets can legally carry very different buildings. Buyers who skip this check discover it at the worst possible time — after purchase, when the architect delivers a first sketch that's 40% smaller than the dream that justified the price.

The check itself isn't difficult. It takes four numbers, a boundary, and about fifteen minutes. Here's how to do it — first the method, then a free browser tool that automates the arithmetic and gives you a PDF report to bring to your architect (or your family group chat).

The four constraints that shape every lot

Terminology varies by country, but nearly every zoning code controls the same four things. In the Philippines, the National Building Code (PD 1096) and local zoning ordinances use these terms:

Setbacks. The minimum distance your building must keep from each property line — front, sides, and rear. Setbacks alone can be brutal on small lots: a 10 m × 15 m lot with a 4.5 m front setback and 2 m on the remaining sides doesn't leave 150 m² to build on; it leaves roughly 66 m².

PSO — Percentage of Site Occupancy. The maximum share of the lot your building footprint may cover. A PSO of 70% on a 300 m² lot caps your ground-floor footprint at 210 m², regardless of what the setbacks would otherwise allow. Whichever is smaller — the setback envelope or the PSO cap — governs.

FLAR — Floor to Lot Area Ratio. The multiplier that caps your total floor area across all storeys. FLAR of 3.0 on a 300 m² lot means 900 m² of gross floor area, maximum. This is the number that determines yield: how many storeys, how many units, how much rentable area.

BHL — Building Height Limit. The ceiling, in metres or storeys, set by the zoning district — and sometimes further clipped by airport clearance zones or special overlays. A generous FLAR is worthless if the BHL won't let you stack the floors to use it.

Pro tip: These four constraints interact, and the binding one changes with lot shape. On a wide shallow lot, setbacks usually govern. On a large lot in a low-density zone, PSO bites first. In high-density commercial zones, FLAR is almost always the ceiling. Run all four before concluding anything — the constraint you ignore is the one that governs.

The method: from title to buildable envelope

Whether you do this on paper or in software, the sequence is the same.

1. Establish the true boundary. Work from the technical description on the title or the approved survey plan — not the fence line, and not the shape you can eyeball on satellite imagery. Fences drift; titles don't. If the lot is irregular, plot every corner.

2. Identify the zoning classification. Your local government's zoning map (or the city planning office) tells you whether the lot is R-1, R-2, C-1, and so on. That classification is the key that unlocks the correct setbacks, PSO, FLAR, and BHL from the ordinance.

3. Draw the setback envelope. Offset each boundary inward by the required distance for that zone and street type. What remains is the maximum footprint by setback.

4. Apply PSO. Multiply lot area by the PSO percentage. Compare against the setback envelope; the smaller value is your allowable footprint.

5. Apply FLAR and BHL together. Lot area × FLAR gives maximum gross floor area. Divide by your footprint to see how many storeys that implies, then check the result against the BHL. The lower outcome wins.

6. Sanity-check the yield. Now translate rules into reality: at, say, 75–85% efficiency (net usable area after circulation, walls, and services), does the allowable floor area actually fit the units, office space, or house you have in mind — plus parking, which in many ordinances consumes ground area faster than buyers expect?

Do this honestly and you'll know, before any money moves, whether the lot supports the project — or whether that "bargain" is priced for a building it can't legally hold.

The 15-minute version: running it in your browser

Manual offsetting and arithmetic is fine once. If you're comparing three candidate lots on a Saturday, use the DSYNTEC Site Feasibility Calculator — it runs entirely in your browser, so the lot details and your plans stay on your device, and it's free with no sign-up.

1. Define the plot boundary

Draw the boundary directly on the map, or input your corner points to match the technical description. Irregular lots are fine — the tool works from whatever polygon you give it.

Type in the setbacks per side, PSO, FLAR, and BHL for your zoning classification. Keep the zoning ordinance (or the planning office's reply) beside you — the tool computes whatever rules you feed it, and real ordinances vary by city and district.

The calculator draws the setback envelope over your lot and reports the numbers instantly: allowable footprint (setbacks vs PSO, whichever governs), maximum gross floor area from FLAR, and implied storeys checked against the BHL. Adjust any parameter and watch the envelope and figures update in real time — useful for testing "what if this were rezoned?" or comparing the same lot under residential versus commercial rules.

One click generates a feasibility report — boundary, parameters, envelope, and compliance summary — as a PDF. Bring it to your architect as the starting brief, attach it to a loan or investment discussion, or file it against the lots you rejected so you remember why you rejected them.

What a feasibility check won't tell you

A desktop check screens lots; it doesn't clear them. Before purchase, you (or your professionals) still need to verify things no calculator can see: the title's authenticity and encumbrances, easements such as waterways requiring their own legal setbacks, road-widening reservations, flood and hazard overlays, soil conditions, and utility availability. Treat the feasibility check as the filter that decides which lots are worth that deeper — and costlier — due diligence.

If the lot passes and you're moving toward design, the natural next step is translating "900 m² allowable" into an actual room-by-room brief — our space programming guide in the Knowledge Base covers how to do that before a single line gets sketched.

Try it now

Have a lot in mind — or three? Run the numbers before the seller runs them for you:

Open the Site Feasibility Calculator → — free, no account, and your lot data never leaves your browser.

Feasibility results are indicative estimates based on the parameters you enter. Zoning rules vary by locality and change over time. Before any purchase, permit application, or financial commitment, verify the applicable regulations with your local planning office and have the findings confirmed by a licensed architect, engineer, or geodetic engineer.