Before the first wall, soil, survey, and the underground trap
The numbers that move a landed budget the most are not in the renderings. They are in the ground, and the surveys happen early, in a fixed sequence, pre-construction survey, soil investigation, cable detection, asbestos survey (if applicable), and topographical survey, each tied to a project milestone.
A soil investigation comes first: boreholes, a geotechnical report, and the classic five-strata borehole log that shows what sits at each depth. BCA needs it to design the foundation. It decides whether simple strip or pad footings will do or whether you are piling, and switching to a bored-pile foundation can add roughly S$60–150k (indicative). Nothing else swings the structural bill as hard, and you cannot know it without the test, so order it before you commit a foundation budget.
A topographical survey by an LSB-registered land surveyor maps levels, slopes, existing structures, boundaries and trees, and feeds the setbacks and platform levels. It is compulsory for a rebuild, runs an indicative S$4–5k, and is anchored to a Temporary Bench Mark (TBM), a survey datum peg physically installed on site (you will see it tagged with a code such as "TBM 'B' ZF-01-170") that fixes every subsequent level measurement to one fixed point. While you are doing this site due diligence, check whether the plot sits in a flood-prone or low-lying area, PUB publishes a current list of flood-prone areas, because that feeds your platform levels and your drainage design. On trees: in a Tree Conservation Area, removing a tree with a girth above 1m (measured a metre above the ground) needs NParks' written approval, supported by a certified arborist's assessment, and NParks can require you to plant a replacement tree as a condition. Moving a mature tree is hard regardless, because a tree's root ball extends well beyond its canopy. The survey is usually paired with a precomputation / encroachment ("precomp") report that flags whether anything crosses the boundary.
A cable-detection survey locates buried services before anyone trenches, performed by a Licensed Cable Detection Worker; the results are typically treated as good for only about three months, since utilities shift underground. Excavation itself is slow and wet, on the order of ten working days of continuous digging on a typical lot.
For a teardown of an older house, an asbestos survey joins the battery (covered below).
Ownership underground has a clean line, and it decides which repairs land on your bill. On the water side, up to the water meter the supply pipe is yours to maintain; past it, the main is PUB's. On the sewer side, your sanitary drain-line is yours until it joins the public sewer.
The basement question. As a general rule, flat land is the cheaper, more predictable site to build on, a sloping plot adds retaining walls and more involved drainage. Going underground is expensive, but it is not automatically double the cost. Indicative figures put basement construction at around S$2,000–4,000+/m² against ~S$1,800–3,000/m² above ground, roughly 1.3–1.5x in most cases, reaching about 2x only on bad soil. The premium is excavation, earth-retention (ERSS), waterproofing and M&E; a single-storey basement commonly starts around S$500k. The practical rule: if you only want more floor area, adding a storey is usually cheaper than digging one. A sloping plot changes the math, building into a hillside means excavating less to reach the same level, so a basement on a slope can pay off where a basement on flat ground will not. (These are indicative market figures, not a government benchmark.)
The ground is not uniform. Woodlands and much of the north sit over Bukit Timah Granite, an igneous rock; sound granite is excellent bearing rock. The catch is the weathered residual-soil mantle above it, studded with hard corestones that make piling unpredictable. The East Coast's "bad soil" reputation is half right: marine clay (the Kallang Formation, soft, compressible, tens of metres thick) is the classic problem ground, but it underlies the reclaimed foreshore, not the natural east. Natural eastern Singapore is mostly Old Alluvium, a dense, well-cemented sand-and-gravel that builds well and covers more than half the island. Treat "Woodlands strong, reclaimed coast soft" as a useful sketch, not a verdict on your lot, your borehole log is the only authority that matters for your site.
