Piled Wall Insulation: The Smarter, Future Proof Choice with Closed Cell Spray Foam
With the rise of basement construction and urban infill projects across the UK, the pressure is on to deliver faster, more reliable, and fully compliant below ground solutions. One of the most overlooked, yet critical, areas is how we insulate piled walls. These are often found in contiguous or secant wall systems, where surfaces are rough, irregular, and highly prone to water ingress.
Traditionally, many have defaulted to concrete infill to level these walls. However, this method is slow, costly, and inflexible.
Closed cell spray foam is changing that. It offers a modern alternative that is quicker to install, provides superior thermal and moisture performance, and eliminates the need for extensive prep work.
If you’re constructing a commercial basement, an underground car park, or a high spec residential project, switching to spray applied insulation could save you time on site, cut unnecessary material costs, and simplify compliance with current UK building regulations.
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Why Choose spray foam for piled wall insulation?
Contiguous and secant piled walls are rarely consistent. Their irregular, uneven profiles make it difficult to prepare a smooth surface for waterproof membranes or structural follow on works. Historically, this challenge has been met with trimming, shuttering, and backfilling using concrete a process that is messy, time consuming, and expensive.
Closed cell spray foam offers a smarter, more efficient solution. It is applied directly to the surface, adapting seamlessly to complex geometries while delivering multiple performance benefits in a single layer:
• Direct Bonding: Sprayed directly onto the piled wall, it adheres to rough, uneven contours without the need for trimming or additional prep work.
• Surface Uniformity: Instantly creates a continuous, flat surface suitable for membrane application or finishing layers.
• Multi-Functionality: Provides thermal insulation, vapour resistance, and moisture control in one system, reducing the need for multiple material layers or specialist trades.
For quantity surveyors and main contractors, this translates into shorter programme times, simplified sequencing, fewer site interfaces, and cleaner project handovers.
Rethinking the Traditional Approach to Piled Walls
THE TRADITIONAL METHOD: CONCRETE INFILL
• Requires trimming or shuttering of the pile face to prepare a flat surface
• Involves large volumes of concrete, increasing cost and site logistics
• Extended cure times delay the critical path of the build
• Offers poor adhesion for membranes, risking long-term performance issues
• Adds unnecessary labour and holds up follow-on trades
THE SMARTER ALTERNATIVE: CLOSED CELL SPRAY FOAM
• Applied directly to the raw piled surface with no trimming required
• Expands to fill voids, contours, and surface irregularities seamlessly
• Cures rapidly in thin layers, allowing faster progress on site
• Creates a consistent substrate for membranes or tanking systems
• Delivers thermal insulation and vapour resistance in one integrated system
Seamless Performance: One Application, Multiple Benefits
Nexseal closed cell spray foam delivers outstanding thermal and moisture performance in a single installation. With a thermal conductivity as low as 0.025 W/m·K, it meets the most demanding Part L U-value targets for piled walls and foundation systems.
BUILT IN ADVANTAGES:
• Thermal Insulation: Significantly reduces heat loss through earth-retaining structures, supporting compliance and energy efficiency targets.
• Moisture Control: Resistant to water ingress and sustained humidity, ideal for basements and below ground environments.
• Vapour Barrier: Acts as an integrated vapour control layer, removing the need for additional membranes.
• Adhesion: Forms a secure substrate for direct membrane application, reducing failure risk and simplifying sequencing.
Specification Highlight: Closed cell spray foam achieves a vapour resistance of up to 88.93 μ, exceeding BS 5250 standards for managing condensation risk in below-ground structures.
Built to Withstand the Elements
Our closed cell spray foam insulation does more than retain heat, it protects the structure in even the harshest environments. Its exceptionally low water absorption rate, less than 0.41 kg/m², ensures long term stability in below ground conditions where hydrostatic pressure and moisture are ongoing risks.
Key Performance Attributes
✓ Resists hydrostatic pressure without compromising adhesion or structure
✓ Achieves a Class 1 fire rating to BS 476 Part 7, suitable for internal applications
✓ Withstands freeze thaw cycles, maintaining performance over time
✓ Performs consistently across a wide range of temperature fluctuations
Practical Tip: Where enhanced flame resistance is specified, we can apply DC315 intumescent coating over the cured spray foam. This achieves a Class B fire rating in line with European standards, offering additional protection without compromising on efficiency or build sequence.
How It’s Installed: Layered for Precision and Performance
Closed cell spray foam is only as effective as its application method. Unlike rigid boards or poured concrete, spray foam is installed in controlled layers that follow the wall geometry and cure rapidly, allowing for faster, more accurate builds.
Installation Highlights
Layered Application: Installed in passes of up to 100 mm for optimal cure and adhesion
Fast Curing: Each layer cures in 20 minutes, enabling rapid progress on site
Total Depths: Builds of up to 450 mm completed in a single day over multiple lifts
BBA Certified: Nexseal LE closed cell foam, tested and approved for below ground use
High Precision: Mirrors the irregular pile surface with no gaps or cold spots
Expert Required: Large depth applications require experienced operatives to ensure accuracy and compliance
Why This Matters On Site
This method allows QA teams to visually confirm thickness and flatness after each pass. The end result is a monolithic, continuous insulation layer that eliminates thermal bridges and creates a bond-ready surface for membranes and liner wall installation.
Technical Insight:
Nexseal LE offers a compressive strength of 78 kPa (EN 826). While it is not a structural material on its own, it contributes to the overall performance of the wall assembly when combined with the reinforced concrete liner and steel structure. Complete build-ups can meet loading requirements exceeding 200 kPa.
A Simpler Site for Your Project Team
Closed cell spray foam does more than meet performance requirements, it makes the construction process easier from the start. By conforming directly to the contours of the piled wall, it removes the need for shuttering, trimming, or manual insulation board handling.
This helps reduce labour demands, shortens preparation time, and speeds up the transition to membrane installation and liner wall construction.
Since the foam is applied in consistent layers, quality checks are simple. Site teams can confirm coverage and thickness using gauge pins and profiles before progressing to the next phase. This approach prevents thermal bridging, avoids cold spots, and ensures membrane compatibility across every curve and fixing point.
From a delivery perspective, this leads to fewer trades on site, less rework, and a more dependable programme, especially in complex or restricted access basements.
Step by Step Application Sequence
Every successful spray foam installation begins with preparation and ends with a structure ready for long-term performance. Here’s how the full process typically unfolds on site:
1. Substrate Preparation
All exposed piled walls are cleared of dust, debris, or standing water. Any fixings or penetrations are marked out or installed ahead of spraying to avoid disruption later in the process.
2. Layered Spray Application
Closed cell foam is applied in passes of no more than 100 mm per layer. Each layer is allowed to cure before the next is applied, ensuring full bonding and structural consistency. In deep builds, total thickness can reach up to 450 mm, applied in four to five lifts.
3. On Site Quality Checks
After each pass, technicians use vertical alignment pins and gauge profiles to verify flatness and insulation depth. This ensures complete coverage, eliminates thermal bridging, and prepares the surface for follow on works.
4. Membrane Bonding
Once QA is complete, a fully bonded waterproof membrane is installed directly over the cured foam. The spray foam’s closed cell surface provides excellent adhesion without the need for primers or mechanical fixings.
5. Liner Wall Construction
Reinforcement mesh and formwork are placed in front of the membrane, followed by the pour of the concrete liner wall. This completes the below ground wall build-up with no need for backfilling or formwork removal.
Fully Compliant with UK Building Regulations
Closed cell spray foam insulation meets key British Standards and supports full compliance across below ground construction projects.
✅ BS 5250:2021 – Moisture Control: The foam’s high vapour resistance helps prevent interstitial condensation, which is essential for maintaining dry conditions in humid basement environments.
✅ BS 8102:2009 – Protection Against Water Ingress: Spray foam forms a secure, bondable surface for waterproof membranes. It maintains system integrity even under sustained water pressure.
✅ Part L (England) – Energy Efficiency: With a thermal conductivity as low as 0.025 W/m·K, closed cell foam contributes to thermal continuity and supports compliance with SAP and Part L energy performance targets.
Important note:
Waterproofing membranes applied over spray foam must be compatible with polyurethane substrates. These membranes should also comply with BS 5250, BS 8102, and Approved Document Part L to maintain full system compliance.
