(Rear or side extension under permitted development – foundations, excavation, concrete, steel, drainage connection) Most homeowners believe the groundwork stage of a rear or side extension takes days or even weeks. The reality? With the right sequence, a mini digger, and a 3-man experienced ground crew, the entire 40 m² footprint can be cleared, excavated, reinforced and concreted in a single day. Your own slides clearly show the process step-by-step — from removing paving slabs to pouring structural concrete.

1. Ground Clearance – 1 hour

(Slide 2 – Removal of Tiles or Concrete Slabs, page 2 of PDF)
The first step is removing whatever is sitting on the back garden:

• Old paving slabs
• Concrete pads
• Patio tiles
• Soft landscaping

A mini digger breaks this up extremely quickly. Labourers lift and stack waste ready for skip removal.
This clears the platform for accurate marking and excavation.

---

2. Excavation of Strip Foundations – 2 hours

(Slides 3 & 4 – Excavations, pages 3–4)

For a 40 m² extension, the trench is generally:

• 600 mm wide
• 1 m deep
• Approx. 18 linear metres

With a competent operator, a mini digger cuts this trench fast. Within hours:

• All topsoil is removed
• The trench is at correct depth
• Spoil is placed neatly on one side for reuse (backfill)

This is why excavation is not expensive. One operator + one machine = rapid production.

---

3. Levelling – 30 minutes

(Slide 5 – Leveling, page 5)

Before reinforcing, the crew checks:

• Trench base is flat
• Depth is consistent
• Foundation level aligns with structural drawings

A rotating laser or water level ensures Building Control accuracy.

---

4. Backfilling & Compaction – 30 minutes

(Slide 6 – Compaction, page 6)

Any soft spots or over-excavated areas are filled with granular material and compacted using a trench rammer.
This ensures:

• No settlement
• Uniform bearing capacity
• Compliance with structural design

Compaction is a small but critical part of quality foundation work.

---

5. Installing Reinforcement – 1 hour

(Slide 7 – Ground Foundation Reinforcement, page 7)

The reinforcement cage is typically:

• Bottom bars (T12 or T16)
• Top bars
• T10 links at 200–300 mm spacing

Fixers assemble cages and position them with spacers to maintain concrete cover.
This reinforcement increases bending & shear capacity and ensures long-term performance, especially near boundary walls.

---

6. Concrete Pour – 1–2 hours

(Slide 8 – Concrete, page 8)

Once reinforcement is signed off:

• Concrete wagon arrives
• Chute or pump delivers concrete into trench
• Labourers level and compact with pokers where required

Concrete quantity calculation

Foundation size:
0.6 m (width) × 0.7 m (depth for working allowance) × 18 m (length)
= 7.56 m³

At £160/m³ + VAT → £1,209 + VAT

This is the true cost of concrete for a typical extension foundation.

---

7. Ground Slab on Grade – Same Day or Following Morning

The extension floor slab (40 m²) is:

• 150 mm C25 concrete
• DPM
• Insulation
• Mesh reinforcement (A142 or similar)

A 40 m² slab at 150 mm thick uses:
0.15 × 40 = 6.0 m³ of concrete
= approx £960 + VAT

---

Real Cost Breakdown of This Entire Operation

Item	Cost
Mini digger (day hire incl. fuel)	£300
3-man labour gang × 1 full day	£600–£700
Concrete for foundations (7.56 m³ × £160)	£1,209 + VAT
Concrete for slab (6 m³ × £160)	£960 + VAT
Reinforcement steel cage	£300–£450
Hardcore + compaction	£200–£350
Waste removal / skip	£250–£350

TOTAL realistic cost:

£3,600 – £4,500 + VAT
For the entire foundation + slab, fully built, signed off, ready for walls and steelwork.

This is why your system makes a 40 m² extension achievable for under £40,000.

---

Why Homeowners Overpay for Foundations

Most quotes hide excavation, concrete, skips, and reinforcement inside inflated totals.
But your method shows the truth:

• It’s simple
• It’s fast
• It’s affordable
• It’s absolutely doable under Permitted Development

And with standardised structural design, everything becomes predictable.