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Spec new build foundation slab.
Raft, slab-on-grade or pile-and-beam — designed to engineer's loads and SAP energy spec.
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Costs, timelines, pitfalls and the right questions to ask before any groundworks starts on new Build Foundation Slab.
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Hiring a groundworks, without the regret.
Four moves that separate a smooth job from a nightmare.
Inadequate insulation
Part L requires 100-150mm under-slab insulation. Cheap quotes skimp.
Soil investigation skipped
Unknown soil = wrong foundation type. £1,000-£3,500 well spent.
Drainage falls wrong
Underbond drainage falls not correct. Affects long-term.
Service routing
Underground services need proper routing during construction. Coordination critical.
Costs & timeline
Know what it costs. Know when it ends.
Indicative UK ranges and what affects price.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Soil investigationGeotechnical
£1k–£3.5k
Strip foundation excavationStandard home
£2.5k–£6.5k
Strip foundation concreteC25/C30 grade
£3.5k–£8.5k
DPC and brickworkAbove ground
£2k–£5.5k
Floor slab + insulationPart L compliant
£3.5k–£9k
Drainage installationPart H
£2k–£6.5k
!
Quote spread is typically ± 18% — always get 3 quotes.
At a glance
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New build foundations require full slab + foundations. Significant project. Expect to pay £15,000–£35,000 for UK new build foundation slab on a typical home.
What Does the Work Involve?
Structural engineer designs full foundations. Soil investigation. Trench excavation. Reinforced concrete strip foundations. Damp-proof course (DPC). Brickwork up to floor level. Floor slab with insulation (Part L). New build often includes wall and slab in one phase.
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Soil investigation | 1,000 | 3,500 | Geotechnical |
| Strip foundation excavation | 2,500 | 6,500 | Standard home |
| Strip foundation concrete | 3,500 | 8,500 | C25/C30 grade |
| DPC and brickwork | 2,000 | 5,500 | Above ground |
| Floor slab + insulation | 3,500 | 9,000 | Part L compliant |
| Drainage installation | 2,000 | 6,500 | Part H |
| Standard new build slab | 15,000 | 25,000 | 3-bed semi typical |
| Premium/large house slab | 25,000 | 50,000+ | Detached/large home |
How Long Does It Take?
Foundation phase: 4-8 weeks. Including curing time, drainage, services.
DIY or Professional?
Specialist groundworker only. Structural engineer mandatory. Building Regs notification.
Choosing the Right Tradesperson
NFB or FMB member specialist. Structural engineer. Building inspector approval.
UK Regulations
Full Building Regs notification. Part A (structure), Part L (thermal — slab insulation), Part C (moisture), Part H (drainage). Building inspector multiple visits.
Common Problems
- Inadequate insulation: Part L requires 100-150mm under-slab insulation. Cheap quotes skimp.
- Soil investigation skipped: Unknown soil = wrong foundation type. £1,000-£3,500 well spent.
- Drainage falls wrong: Underbond drainage falls not correct. Affects long-term.
- Service routing: Underground services need proper routing during construction. Coordination critical.
Frequently Asked Questions
Cost as % of new build total?
Foundations: 8-12% of new build total. £200,000 home: £15,000-£25,000 foundation phase.
Strip or raft for new build?
Strip: standard, suits most soils. Raft: for poor soils. Soil survey determines.
Underfloor heating in slab?
Yes — wet UFH integrates with new build slab. £1,500-£5,000 additional for typical home.
How long is foundation construction?
4-8 weeks total. Excavation + concrete cure + brickwork + slab + drainage.
Insurance during construction?
Specialist construction insurance during build. Standard buildings insurance from completion.
Building inspector visits?
Multiple — at excavation, before concrete, after DPC, before slab cover. Sign-offs at each stage.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
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