We carry out excavation work as part of most landed rebuilds, basement additions, and major A&A projects in Singapore. It's not just about digging a hole — excavation on a constrained landed site means working within metres of existing foundations, managing groundwater, and ensuring your neighbour's house doesn't shift while we're creating yours. Here's what proper excavation actually involves, based on our builds.

When Does a Landed Project Need Excavation Work?

Not every project requires excavation beyond the shallow footings for a standard slab. We typically carry out significant excavation work when:

• Building a basement: Whether it's a full basement under the entire footprint or a partial basement for a wine cellar, gym, or storage, you're excavating 3–5 metres below the original ground level.
• Lowering the ground floor: Some clients want higher ceilings without breaching height limits. Dropping the ground floor by 0.5–1.5 metres requires excavation and re-levelling.
• Piling and foundation work: On poor soil or sloped sites, we excavate to install piles or construct deeper strip footings. This is structural necessity, not optional.
• Rear or side extensions near boundaries: If the extension requires new footings close to the boundary, we excavate carefully to avoid undermining the neighbour's foundation or retaining wall.

In our experience, about 60% of our landed rebuilds involve some form of excavation beyond standard footing trenches. The scale varies — from 20 cubic metres for a small basement to 300+ cubic metres for a full-footprint basement under a large bungalow.

What Happens Before We Start Digging

Excavation is never the first step. Before a single bucket of soil moves, we complete:

Soil Investigation (SI)

We engage a geotechnical consultant to drill boreholes and test soil bearing capacity. The SI report tells us what we're digging into — marine clay, fill, Old Alluvium — and determines whether we need piling, how deep the excavation can safely go, and what shoring system to use. On landed sites, we typically drill one or two boreholes depending on plot size.

Structural and Shoring Design

Our QP and structural engineer design the shoring system based on the SI findings. Shoring is the temporary support structure that holds back the soil and protects neighbouring properties during excavation. It might be:

• Sheet piling: Interlocking steel sheets driven into the ground around the perimeter. Common for deeper excavations (3+ metres) or sites near boundaries.
• Soldier piles and lagging: Vertical steel H-beams with timber or concrete panels spanning between them. We use this when access is tight or where full sheet piling isn't practical.
• Contiguous bored piles: Overlapping or closely spaced concrete piles forming a wall. Rare on smaller landed plots due to cost, but necessary on some basement projects adjacent to party walls.

The shoring design accounts for lateral earth pressure, surcharge loads from adjacent buildings, and groundwater. If we get this wrong, the neighbour's foundation shifts. We've never had that happen because we don't skip the engineering step.

BCA and URA Submissions

Excavation deeper than 1 metre typically requires structural plans and Building Plan approval from BCA. We handle this as part of our in-house QP submission process. The plans specify excavation depth, shoring method, and how we'll protect adjoining properties. Any basement addition also requires URA approval for the change in GFA and storey count.

How We Actually Carry Out Excavation Work

Once approvals are in place and shoring is installed, the excavation sequence looks like this:

Stage 1: Install Shoring

We install sheet piles or soldier piles around the excavation zone before digging begins. On tight landed sites, we use a small piling rig or a hydraulic press-in method to minimise vibration and noise. Shoring is inspected by our PE (Professional Engineer) before we proceed.

Stage 2: Excavation in Lifts

We excavate in horizontal layers called "lifts" — typically 1–1.5 metres at a time. After each lift, we install walings (horizontal steel beams) and struts (cross-bracing) to support the shoring. This staged approach prevents collapse and keeps lateral loads manageable.

We use a small excavator suited to the site access. On very tight sites with no side access, we've had to use a mini-excavator and remove soil via the front gate in smaller loads. It's slower, but sometimes the only option.

Stage 3: Dewatering (If Needed)

If we hit groundwater — common in low-lying landed areas — we install sump pits and pumps to keep the excavation dry. Continuous pumping is monitored to avoid drawing water from under neighbouring foundations. In marine clay areas, groundwater is almost guaranteed below 2–3 metres depth.

Stage 4: Formation Level and Blinding

Once we reach the target depth (formation level), we trim and compact the soil base. We then pour a thin blinding layer of lean concrete — typically 50–75mm — to create a clean, level surface for the next step: laying reinforcement and casting the basement slab or foundation.

Stage 5: Soil Disposal

Excavated soil is loaded into tipper trucks and disposed of at approved facilities. We use licensed disposal sites and track every load. Depending on soil type, disposal costs run between $30–60 per cubic metre including transport. For a 150m³ excavation, that's $4,500–9,000 in disposal fees alone — it's a real cost that some clients underestimate.

What Can Go Wrong (And How We Avoid It)

Excavation is high-risk work. We've seen other contractors' mistakes when called in to rectify:

• Inadequate shoring: The neighbour's boundary wall cracks or tilts because shoring wasn't designed for the actual soil conditions. This becomes a legal and financial nightmare. We always engage a PE to design and supervise shoring.
• Over-excavation: Digging deeper than approved or removing too much soil from under the boundary, undermining the adjacent property. We work strictly to formation level shown on approved drawings.
• Groundwater drawdown: Excessive dewatering causes settlement in surrounding properties. We monitor water levels and use cut-off methods (like sheet piles driven below formation) to limit drawdown.
• Uncontrolled spoil removal: Leaving excavated soil on-site too long blocks access and creates safety hazards. We schedule tipper trucks to remove soil progressively.

On one of our past projects — a terrace with a full basement — we installed settlement markers on the neighbouring walls before starting excavation. We monitored them weekly throughout the dig. Zero movement recorded. That's the standard we hold ourselves to.

What Excavation Actually Costs

Excavation cost depends on depth, volume, soil type, access, and shoring complexity. As a rough guide from our recent projects:

• Shallow excavation (under 1.5m, minimal shoring): $50–80 per m³
• Basement excavation (3–4m deep, with sheet piling and dewatering): $150–250 per m³
• Complex/tight access (party wall adjacent, restricted access, rock): $250–400+ per m³

These figures include excavation, shoring, dewatering, disposal, and PE supervision. For a typical semi-detached basement (100m³), budget $15,000–25,000 for excavation alone, excluding the basement structure itself.

Clients sometimes ask if they can "save money" by skipping the soil investigation or using a simpler shoring method. The answer is no. Cutting corners on excavation is how houses crack and projects get stopped by BCA. We won't do it.

Excavation vs Renovation Work

If your project is primarily about interior changes, hacking walls, or upgrading finishes — but doesn't involve digging below ground or altering structure — that's renovation work, not excavation. Our sister company, Larry Contractors, handles HDB-licensed renovation and finishing works. We focus on the structural and earthworks side: digging, shoring, foundations, and frames.

Frequently Asked Questions

Do I need a permit for excavation work on my landed property?

Yes. Excavation deeper than 1 metre, or any excavation involving shoring and basements, requires BCA Building Plan approval. We handle the submission as part of our QP service. Digging without approval can result in a stop-work order and fines.

How long does excavation take for a typical basement?

For a semi-detached or terrace with a basement, excavation typically takes 3–5 weeks from shoring installation to blinding pour. This includes staged digging, dewatering, and inspections. Larger bungalow basements may take 6–8 weeks depending on depth and access.

Can excavation damage my neighbour's house?

It can, if done improperly. That's why we always design shoring to protect adjacent properties, monitor settlement, and work within engineered limits. We've never caused damage to a neighbouring property because we don't skip the engineering and supervision steps.

What happens to the soil after excavation?

We load it into tipper trucks and dispose of it at licensed facilities approved by NEA. Soil can't be dumped anywhere — illegal disposal carries heavy penalties. Disposal is included in our excavation quotation, and we provide disposal receipts for record.

Can I add a basement to an existing landed house?

Technically possible, but complex and expensive. You'd need to underpin the existing foundation, excavate beneath it, and manage the structure above while digging below. We've done it, but costs are significantly higher than excavating for a new build. We assess each case individually and advise honestly on whether it makes sense.

Ready to Discuss Your Excavation Needs?

If your landed project involves excavation — whether for a basement, extension, or rebuild — we'll walk you through what's structurally and legally required before you commit. No guesswork, no surprises. Reach us directly on WhatsApp at +65 9107 2601.