Insulated Raft Foundation SystemBuilt for Low-Energy Construction
KIWA-certified and Passivhaus-approved. Eliminates cold bridging and installs in hours. Trusted by architects, self-builders, and developers across the UK.
See How It WorksRequest a Callback →
The Foundation Detail That Matters
What Is an Insulated Raft Foundation?
An insulated raft foundation - also known as a Passiv-slab - is a single concrete slab that sits on a continuous layer of high-performance EPS (expanded polystyrene) insulation, wrapped right around the full perimeter edge as well as underneath. Because the insulation runs under the whole footprint, the slab spreads your building's load evenly across the ground - so there's no need for separate footings, unlike a traditional strip foundation.
Because that insulation wraps continuously from under the floor up around the base of the wall, there's no thermal bridge at the wall-floor junction - the "cold spot" that standard foundations can never fully design out. This junction is also where a foundation's Psi (Ψ) value is decided: every bit as important as the more familiar U value, and one of the figures worth asking about when you're comparing systems.
ISOQUICK® takes this a step further with a KIWA-certified, factory-engineered system: every component arrives on site pre-cut and numbered, ready to assemble and pour - normally within hours, not days.
Why ISOQUICK?
The fast route to a better foundation.
Half the construction time
Fewer trades, fewer stages, and a foundation system that can be assembled in hours on a prepared site.
Excellent thermal performance
Great U-values, strong PSI performance, and a continuous insulated edge where foundations usually lose heat.
Pre-engineered certainty
Edge components are prefabricated, numbered, and made for your project before they arrive on site.
How the ISOQUICK® System Works
Scroll through the construction sequence to see how the ISOQUICK® insulated raft is installed on site.
Step 01
Whether Big or Small
Each project starts the same way.
Step 02
Strip to Formation Level
The site is marked out and soil stripped to the formation level. The actual depth will depend on the local site conditions.
Step 03
Install the Sub-Base
The free draining sub-base is installed in strict accordance with the engineer's specification.
Step 04
Prepare the Grit Layer
A base layer of grit, for example 4/8, is applied over the capillary-barrier layer of frost-proof material. The formation level provides a clean, flat and level base for the modules of ISOQUICK The Insulated Raft.
Step 05
Install Edge Modules
The edge modules are assembled according to the supplied ISOQUICK installation plan. The dovetail locking system ensures a secure connection during installation and concreting work.
Step 06
Complete the Perimeter
The last edge module fits perfectly into place.
Step 07
Check Position and Diagonals
The thermally insulating boarding provided by the ISOQUICK edge modules is soon installed. It is then aligned again with the batter boards and checked by measuring the diagonals.
Step 08
Install Ground and Deck Modules
The base modules and the top modules are now put in place. Continuous joints are avoided by covering the edge modules with top modules and by using an offset installation pattern.
Step 09
Work Row by Row
Installation can now proceed row-by-row. The offcuts from one row are used to start the next row, thus reducing waste to a minimum.
Step 10
Lock the Modules Together
The intelligent profile pattern system ensures that the individual modules are tightly positioned and that no sliding takes place during installation and concreting work.
Step 11
Cut Where Needed
Cutting guides are moulded on the smooth sides of the modules to make cutting easier inside the grid. The modules can be easily cut using a hot wire cutter.
Step 12
Form Service Openings
Where pipes run through the thermal insulation, holes are sawn out or drilled out, as shown here. The hole can be closed again using construction foam.
Step 13
Ready for Reinforcement
ISOQUICK The Insulated Raft is completed and ready for reinforcement and concrete.
Step 14
Minimise Waste
A minimal amount of waste offcuts arises for an ISOQUICK The Insulated Raft of around 150 m², if the offset installation pattern is strictly adhered to.
Step 15
Handle Irregular Shapes
Not a problem. As usual, the edge modules are precut at the appropriate angle.
Step 16
Install Angled Rows
A row of base and top modules is laid at right angles to the edge modules. The remaining modules are installed in an offset pattern along the row.
Step 17
Install DPM or Radon Barrier
A standard DPM, or radon barrier if required, is installed and the required reinforcements installed in ISOQUICK The Insulated Raft.
Step 18
Lay Reinforcement
The reinforcement, typically fabric sheets, is laid on concrete spacers, tied and checked prior to the pour.
Step 19
Ready to Pour
Robust, but simple: the slab is ready to fill with concrete.
Step 20
Place Concrete
Concrete can be poured into ISOQUICK The Insulated Raft using a crane or concrete pump, as shown here, without the need for further shuttering.
Step 21
Finish the Concrete
The concrete is then finished in the usual manner.
Applications & Build Types
ISOQUICK® works across a wide range of construction types - from single self-builds to large commercial developments.
Self-Builders
Passivhaus-certified insulated raft foundation for one-off homes. Backed by 15+ years of UK experience. Expert design support included.
Timber Frame Companies
Precise tolerances and simplified connection details for timber frame systems. No cold bridging at the critical wall-floor junction.
Architects
Compatible with any type of wall construction. Exceeds Part L and Passivhaus thermal targets.
Builders & Developers
Predictable costs, faster construction, and reduced programme complexity on housing developments, schools, and commercial projects.
Thermal Performance & Cold Bridge Elimination
What is cold bridging - and why does it matter?
A cold bridge occurs where heat bypasses the insulation at a junction or local weak point. At the wall-floor junction, traditional foundations create an unbroken conductive path from the cold ground to the warm interior.
ISOQUICK® wraps insulation continuously around the entire perimeter. There is no gap. Heat stays in. Condensation risk drops. Heating demand falls. Passivhaus certification becomes achievable.
Independently verified to Passivhaus Institut standards and backed by Kiwa BDA Agrément certificate BAF-20-179-S-A-UK.
Certifications & Compliance
Industry-leading standards you can trust
Installation Process
From first conversation to completed foundation, the ISOQUICK® process saves time and eliminates on-site complexity.
First Conversation
Tell us about your project. We'll discuss your needs, timeline, and build specification.
Bespoke System Layout
We develop the ISOQUICK® layout and thermal specification around your project, working with the qualified structural engineer responsible for the foundation design, loadings and reinforcement.
Factory Manufacture
Edge components are precision-cut to your dimensions off-site. Delivered numbered, ready to assemble.
On-Site Assembly
No specialist labour required.
Assembly as low as 2 hours. Concrete can be poured the same day, subject to the project structural engineer's slab reinforcement design.
* Assembly time refers to the placement and interlocking of ISOQUICK® components on a prepared sub-base. Actual total installation time will vary depending on project size, site conditions, slab reinforcement design, and readiness of concrete supply.
Case Studies & Projects
Award-winning ISOQUICK® insulated raft foundation installations across residential, commercial, and self-build developments throughout the UK.
UEA Enterprise Centre
Passivhaus certified • RIBA Award Winner
Passivhaus Self-Build
Certified Passivhaus • Hertfordshire
Staffordshire University
750+ Student Accommodation Units
Timber Frame Passivhaus
Modern Low-Energy Home
Hackbridge Primary School
UK Passivhaus Awards Winner
Bespoke Self-Build
Pre-cut, interlocking insulated foundation system
Why Choose ISOQUICK®?
Certified & Trusted
KIWA BDA Agrément · Certified Passive House Component
Full third-party certification accepted by building control, warranty providers, and Passivhaus certifiers.
Installs in Hours, Not Days
Pre-engineered and prefabricated. Assembles on site in 2-6 hours on a prepared site, reducing programme risk.
Eliminates Cold Bridging
Continuous insulation from floor to wall. No thermal bridges at the wall-floor junction. Condensation risk eliminated.
Expert Technical Support
Construction details are reviewed and coordinated with your appointed structural engineer. Project-specific U-value reports are included; structural design and calculations must be provided or approved by a qualified structural engineer.
Proven Across the UK
Over 16 years of UK installations. Used on award-winning buildings from Passivhaus homes to schools.
Works with Any Build System
Compatible with timber frame, ICF, brick and block, SIPs, and modern methods of construction.
"ISOQUICK® gave us the thermal performance we needed for Passivhaus certification. The installation was incredibly fast and the team provided excellent technical support throughout the project."
"The precision of the ISOQUICK® system meant our timber frame went up exactly as designed. No thermal bridges, no cold spots. It's the foundation system we specify on all our Passivhaus projects now."
Frequently Asked Questions
Is ISOQUICK® accepted by building control?
Yes. ISOQUICK® holds KIWA BDA Agrément certificate BAF-20-179-S-A, providing independent third-party confirmation of structural and thermal performance. This is accepted by local authority building control and approved inspectors across the UK.
Can ISOQUICK® achieve Passivhaus certification?
Yes. ISOQUICK® is a certified Passivhaus component verified by the Passivhaus Institut. It has been used on numerous certified Passivhaus projects in the UK including award-winning buildings. Our team provides the thermal data and PHPP inputs your certifier needs.
What U-values does the insulated raft foundation achieve?
Depending on specification, ISOQUICK® achieves slab U-values from 0.08 W/m²K upwards. Edge PSI-values can even be negative thanks to the unique ISOQUICK® edge profiles. We provide a full thermal report specific to your project dimensions and insulation depth.
How long does installation take?
Assembly as low as 2 hours on a prepared site. Actual time depends on the project size, site conditions and structural design. All edge components arrive pre-cut and numbered, and concrete can be poured once the project structural engineer's reinforcement requirements have been met.
Is it suitable for timber frame construction?
Yes - ISOQUICK® is one of the most widely used insulated raft systems for timber frame builds in the UK. The precision-cut edge beams provide the exact tolerances and level sill required for timber frame erection, while the continuous insulation eliminates the wall-floor cold bridge that is a common weak point on timber frame projects.
Get a Quote
Tell us about your project and we'll provide a detailed quote, thermal calculations, and design proposal - usually within 2-3 business days.
Not ready to quote? Explore our technical guides, U-value documents, and installation resources.
Visit the Knowledge Centre →