Swimming Pools Published: 10/6/2025

Your private underground wellness sanctuary — expertly engineered for London homes. From concept and planning to excavation, waterproofing, MEP and finishing, our team delivers end-to-end design & build with safety and compliance at the core.

Why choose a basement pool + spa + steam room?

A subterranean pool complex offers year-round use, complete privacy, and precise climate control — while making efficient use of under-utilised space and adding genuine prestige to your property.

  • All-season comfort: Stable water and air temperatures, independent of the weather.
  • Total privacy & security: Hidden from view with controlled access and alarms.
  • Value & uniqueness: A signature feature in London’s premium market when executed well.
  • Integrated wellness: Combine pool, hydro-spa, steam, sauna, changing and lounge zones.

These are among the most technically demanding domestic projects. Success relies on expert structural design, excavation and underpinning, robust waterproofing, specialist HVAC/dehumidification, pool hydraulics, electrical safety, and careful coordination with planning, building regulations and the Party Wall etc. Act 1996.

Key design & engineering considerations

Domain What it covers Best-practice notes
Excavation & structure Underpinning, load paths, soil & groundwater, lateral pressures Water exerts ~9.8 kN/m³; design walls/slab for hydrostatic and uplift; sequence works safely.
Waterproofing Protection against ingress & hydrostatic pressure Use Type C cavity drainage or hybrid systems; build in redundancy and maintainability.
Pool shell Reinforced concrete, joints, movement control Control shrinkage; detail expansion joints; specify durable, chemical-resistant finishes.
HVAC & dehumidification Latent load from evaporation, ventilation, pressure regimes Dedicated dehumidifier/AHU; keep slight positive pressure to adjacent areas; design for ~50–60% RH.
Plant room Pumps, filters, boilers/heat pumps, dosing, access Allow service clearances; acoustic isolation; thermal and moisture control equal to pool hall.
Envelope & glazing Condensation risk, thermal bridges, airtightness Use high-performance insulated glazing with thermal breaks; continuous vapour control layer.
Spa & steam Steam generator, enclosure sealing, drainage Vapour-tight assemblies; slope ceilings (steam) to control condensate; corrosion-resistant hardware.
Acoustics Plant noise, vibration, duct breakout Decouple equipment; specify anti-vibration mounts; attenuate ducts; isolate walls/floors as needed.
Safety Access control, supervision, surfaces, lighting Non-slip tiling, compliant lighting/electrical zones, safety covers and alarms, clear egress routes.

Note: Final solutions are bespoke to each site’s ground conditions, structure, access and planning context.

Indicative costs & timelines (London & South East)

Work element Typical range (GBP) Notes
Excavation & underpinning £200 – £600+ per m³ Soil type, depth, proximity to boundaries and sequencing drive cost.
Shell & waterproofing £1,500 – £4,000+ per m² (pool shell) Waterproofing redundancy is essential for basements.
HVAC & dehumidification £50,000 – £150,000+ Scale, air volumes, and heat recovery strategy affect budget.
Plant & water treatment £30,000 – £100,000+ Pumps, filters, dosing, controls, optional UV/ozone.
Finishes & glazing £500 – £2,000+ per m² Premium mosaics, feature lighting and specialist glazing increase cost.
Steam/sauna fit-out £20,000 – £70,000+ Depends on enclosure size, controls and finishes.
Professional services 8% – 15% of project cost Architectural, structural, MEP, building control & coordination.
Contingency 10% – 20% Recommended allowance for underground unknowns.

Programme guide: 9–18 months from feasibility to handover, subject to permissions, scale and site constraints.

Planning, building regulations & UK compliance

London basement pools must be designed and delivered in line with UK law. Typical requirements include:

  • Planning permission: Often required for new excavations, footprint changes or external alterations. Works wholly within an existing basement may be permitted without planning, but always confirm with your Local Planning Authority (LPA), especially for listed buildings and Conservation Areas.
  • Building Regulations approval: Structure, fire safety/egress, ventilation (Part F), energy/thermal performance (Part L), electrics near water (Part P), and drainage/waterproofing details.
  • Party Wall etc. Act 1996: Notices and awards where works affect shared/adjacent structures or involve deep excavations near boundaries.
  • Health & safety: Non-slip finishes, safe access control, compliant electrical zones, safety covers/alarms, chemical storage and COSHH where applicable.
  • Insurance & warranties: Notify your insurer; consider waterproofing and structural warranties.

Our end-to-end process

1) Feasibility

Surveys, ground/structure checks, utilities mapping, outline scheme, budget bands and programme.

2) Concept & permissions

Architectural layout; planning strategy; party wall notices; building control pathway agreed.

3) Detailed design

Structural sequencing, waterproofing design, HVAC/dehumidification, pool hydraulics, steam/sauna integration, acoustics.

4) Construction

Excavation & underpinning, shell, membranes/drainage, plant install, first/second fix, finishes, glazing and lighting.

5) Commissioning

Water treatment, HVAC balancing, controls setup, safety checks, documentation and client training.

6) Aftercare

Planned maintenance and performance reviews to protect finish quality and running efficiency.

questions/answers

FAQs: Indoor basement pools, spas & steam rooms

Not always. If a pool is installed wholly within an existing enclosed basement without external alterations, formal planning permission may not be required. New excavations, footprint changes, listed buildings and Conservation Areas typically do require permission. We confirm the correct route with your Local Planning Authority and handle submissions where needed.

Expect approvals covering structural safety, fire/egress, ventilation and moisture control (Part F), energy/thermal performance (Part L), and electrical safety in and around water (Part P). Drainage, waterproofing design and safe chemical storage are also reviewed. We coordinate with building control from the outset.

Indoor pools generate high latent loads. We specify dedicated dehumidification/AHU systems, maintain pool hall RH at ~50–60%, design airtight, insulated envelopes with vapour control layers, and keep a slight positive pressure relative to adjacent spaces to prevent moisture migration.

There’s no universal statutory height, but around 2.4 m finished headroom is a common comfort target. Achieving this may require excavation and underpinning, which we sequence safely and design to protect the existing structure and neighbours.

They’re straightforward with the right detailing: sealed enclosures, sloped ceilings for condensate control (steam), vapour-tight doors, thermal insulation, adequate drainage and corrosion-resistant fittings. We coordinate MEP so steam/sauna systems complement the pool HVAC.

Energy for heating water/air, electricity for pumps and dehumidifiers, water treatment chemicals, and routine servicing. We reduce costs via insulation, heat recovery, efficient plant selection and smart controls; we’ll model options during design.

We integrate non-slip surfaces, coded/locked access, pool alarms, compliant lighting and safe egress. Optional automatic covers add both safety and energy savings.

Yes. Movable floors let you vary depth or create a flush, load-bearing surface. They require precise structural and mechanical integration, which we design from first principles.

When designed and sequenced correctly, risks are managed through underpinning, temporary works, monitoring and party wall procedures. We provide full structural design, method statements and neighbour liaison to protect all parties.

Book a feasibility review. We’ll assess your property, outline planning/building-control routes, propose layouts and give initial budget bands and programme. Speak to our pool specialists.

Luxury Basement Pools & Spas

Design and build specialists for basement swimming pools, saunas and steam rooms across London and the South East. From excavation and waterproofing to pool plant and finishing — handled by one expert team with 30+ years of experience.

  • ✔ Full design & build delivery
  • ✔ Basement pools, spas & wellness suites
  • ✔ Planning, party wall & building control included
Contact us to get your pool started
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Indoor Basement Swimming Pools, Spas & Steam Rooms