Choosing a foundation system is an important part of planning a new building. Before you can establish a suitable solution and obtain a project-specific quotation, there are several pieces of information worth bringing together.
For an insulated raft foundation, the design needs to account for more than the footprint. Ground conditions, structural loads, wall construction, floor levels and thermal performance all influence how the foundation is developed.
You do not need every technical detail finalised before making an initial enquiry. ISOQUICK works with self-builders, architects, structural engineers and contractors to review proposed construction details and establish an appropriate insulated foundation arrangement.
This guide explains what is useful at the quotation stage, what can follow later and how to prepare for a productive technical discussion.
Start with your architectural drawings
Architectural drawings are the starting point for understanding the foundation footprint and its relationship with the building above. Ideally, provide the latest available:
- Ground-floor plans showing the footprint, overall dimensions and external and internal walls.
- Building sections showing floor construction, wall build-ups and relevant levels.
- Elevations providing context for the geometry and external finishes.
- Site plan showing the building's position and relevant constraints.
These drawings can expose areas needing further coordination, such as projections, level changes or unusual wall positions. Complex shapes are not automatically unsuitable; they need to be developed around the actual project rather than treated as a standard rectangle.
What if your drawings are not finalised?
Early-stage plans may be sufficient to begin reviewing the proposed system. Identify the current drawing revision and explain which elements remain subject to change. More developed information will be needed before the final layout and technical details can be established.
Explain your intended wall construction
The external wall system is one of the most important details. Common methods include timber frame, structural insulated panels (SIPs), insulated concrete formwork (ICF), brick and block, and other engineered systems.
Each presents different requirements for support and for coordinating the wall-to-floor junction. Timber frame, for example, requires consideration of sole plate positions, bearing, fixings, insulation continuity and moisture protection. The design must account for the actual wall build-up, not simply its broad category.
Provide the construction type, indicative build-up and thickness, the system supplier where relevant, any existing wall-to-foundation detail, and whether the system is confirmed. If you are working with a frame or SIPs manufacturer, involve them early and review what the wall and foundation teams should agree before construction.
Share what you know about the ground conditions
An insulated raft is a structural foundation system, and suitability depends on the ground and building loads. Relevant matters can include bearing capacity, soil variability, made ground, groundwater, site levels, trees and nearby structures.
The appointed structural engineer must assess the ground conditions and design the foundation accordingly. A ground investigation or geotechnical report may be required for that assessment.
Do you need a ground investigation before requesting a quote?
Not necessarily. Share a report if one is available; otherwise explain what is currently known. An initial discussion can identify what will be needed before structural design is completed. An indicative quotation is not confirmation that a particular arrangement is suitable for the site.
Identify your thermal performance targets
An insulated raft positions load-bearing insulation beneath the concrete slab and around its perimeter, helping to control heat loss through the floor and wall junction. Explain whether the project targets Building Regulations compliance, a higher-performance low-energy specification, Passivhaus certification or another defined target.
Include a target floor U-value if one has been established. Passivhaus teams may also need to assess the thermal bridge at the wall-to-floor junction. ISOQUICK provides project-specific U-value guidance and standard thermal junction information; bespoke thermal bridge calculations can be discussed separately. Make clear which requirements are confirmed and which remain under review.
Highlight any unusual foundation details
Call attention to large or flush-access thresholds, changes in finished floor or foundation level, unusual geometry, drainage and service penetrations, internal load-bearing walls, concentrated loads and interfaces with adjoining structures.
These can affect edge arrangements and coordination. A large sliding door may need specific structural support, levels, weather protection and insulation continuity; services must be coordinated before concrete is poured. The ISOQUICK Technical Details Library provides starting points for standard sections, wall junctions, thresholds, drains and ducts, but each selected detail must suit the project.
Establish the structural information available
The foundation transfers building loads to the supporting ground. Its structural design is separate from the supply and configuration of the insulated foundation components. The client's appointed structural engineer remains responsible for designing and approving the concrete slab, reinforcement and other structural elements.
Useful information can include structural drawings, load-bearing wall positions, point loads, frame supplier loading information and ground investigation data. Identifying what has been designed and what remains outstanding helps establish next steps. ISOQUICK can coordinate its system layout and thermal details with the qualified structural engineer.
Explain your intended construction programme
Where possible, give the expected groundworks and installation dates, planning status, structural design status, and whether a main contractor or groundworks contractor has been appointed.
ISOQUICK uses prefabricated EPS components assembled on a prepared sub-base before the required membranes, reinforcement and concrete are installed. The overall programme depends on site readiness, ground preparation, engineering, contractor availability and other project-specific factors, so it should be planned as part of the wider build.
Understand what the quotation covers
Distinguish between the insulated foundation system and the wider works needed to complete the foundation. ISOQUICK supplies the EPS insulated foundation system with project-specific technical advice and installation support. The appointed structural engineer remains responsible for structural design and calculations.
Groundworks, reinforcement, concrete and associated site operations are typically arranged by the client or appointed contractors, subject to the agreed scope. Clarify what is supplied, what is provided by others and how the elements will be coordinated. For pricing factors and fair comparisons, use the existing Costs & Budgeting guide.
Your insulated raft foundation quotation checklist
Before contacting ISOQUICK, gather as much of the following information as you reasonably can.
| Information | Useful at initial enquiry |
|---|---|
| Project location | Yes |
| Proposed building use | Yes |
| Ground-floor plans | Ideally |
| Building footprint and approximate dimensions | Ideally |
| Proposed wall construction | Yes, if decided |
| Building sections and floor levels | If available |
| Ground investigation report | If available |
| Structural engineering information | If available |
| Thermal performance target | If known |
| Unusual thresholds or level changes | If relevant |
| Proposed construction dates | If known |
Do not delay a first enquiry simply because some information is outstanding. Explain what is known, what is being developed and which information is still needed.
What happens after you contact ISOQUICK?
The first step is a project discussion. The team can review the available architectural information, proposed wall construction and thermal requirements, and consider how the insulated raft system could be incorporated.
As the project develops, the system layout and construction details are coordinated with the design team and appointed structural engineer. The quotation and associated information can then be developed around the agreed requirements. The precise process depends on the information available and the foundation's complexity.
For self-builders, ISOQUICK also provides design advice and practical installation guidance to explain how the system fits into the wider construction programme.
Ready to discuss your foundation?
Whether you have early-stage plans or a developed construction package, you do not need every detail resolved before getting in touch. Share your plans, wall construction and intended performance requirements so the team can identify the next information needed.
Technical note: Foundation suitability, ground-bearing requirements, structural slab design and reinforcement must be assessed and approved by appropriately qualified professionals. Published technical details should be reviewed for suitability before use on a specific project.