Insulated Foundation Systems

At Castleforms we pride ourselves in manufacturing and supplying high quality insulated foundation systems.



Raft Therm

Raft Therm is an insulated foundation system used in the construction of residential & commercial buildings. Reduced cold bridging and exceptional U values as low as 0.1wW/m²K are achieved by wrapping the sides and underneath of the concrete foundation and ground floor in a continuous layer of high density expanded Polystyrene.

Raft Therm components are pre-formed in our factory requiring minimal preparation on site.  Each Insulated Raft is specially designed according to the client's specification and requirements.These insulated foundation systems are suitable for use in conjunction with various wall types including masonry, timber frame, light gauge steel and ICF.


• Raft Therm is a fully insulated foundation system that can achieve U values to meet passive house standards.
• Raft Therm an efficient solution that delivers build programmers on time, concrete foundations and floors are poured simultaneous while rising walls are eliminated.
• Raft Therm suitable for use in conjunction with various wall types including masonry, timber frame, light gauge steel and ICF.
• Raft Therm components are pre-formed in our factory requiring minimal preparation on site.
• Raft Therm is comparable in price to traditional foundations offering exceptional value with superior thermal performance.
• Raft Therm utilizes the thermal mass of concrete by absorbing and retaining heat when the building is warm then releasing this heat back into the building as it cools thereby maintaining a more  constant temperature.
• High scoring Psi value reduces risk of condensation occurring at floor/wall junction.
• Suitable for use with underfloor heating systems.
• A permanent and sustainable insulation solution that requires no maintenance, unlike walls and roofs it is virtually impossible to retrofit insulation underneath or around foundations and floors.
• Effective at conserving energy by drastically reducing heat loss through the floor and cold bridging through the rising walls
• Suitable for residential and commercial applications.
• CE marked- manufactured to harmonized technical specification EN 13163:2012+A1:2015.
• Makes commercial sense because it delivers lower U and Y values in the ground floor structure thereby reducing the requirement to score costly SAP points elsewhere in the structure.
• Lightweight and easy to handle with no specialized equipment required for assembly

Design and Assembly:

When a projects design specifications have been finalized the Raft Therm foundation and floor components are moulded and cut to exact dimensions in our factory. L section components
and floor sheets are typically supplied in 2 meter lengths. Onsite the footprint of the building is marked out and a flat surface prepared with drainage, DPC***and services installed as per the project engineer’s instructions.

Because of the lightweight nature of the components the system is quickly assembled without the need for any lifting equipment. L shaped components create a shuttering profile for the concrete edge beam located at the external loadbearing walls. Flat EPS 100 sheets are placed underneath the floor area while higher density EPS 300 flat sheets are carefully fitted underneath internal loadbearing walls where the concrete slab is usually thickened. Once assembled the components are secured with steel combs and plastic pins, steel reinforcing and heating pipework are fixed and concrete placed to floor level.
The combination of High density EPS and reinforced concrete delivers a super-insulated sustainable structure onto which walls are constructed.
*** Instruction should be taken from project engineer and / or manufacturers specification as to the preferred location of the DPC/gas membrane.

Thermal Performance: 

A building with a well-balanced U value, good air tightness and carefully designed junction details will deliver a high thermal performance and require less energy to heat.
Buildings typically lose heat through the ground floor in two ways:
1. Through the fabric of the floor
Measuring the rate at which heat passes through one square meter of all the
components combined to make up the floor is referred to as the U value
In Ireland, compliance with Part L of the building regulations demand a minimum ground floor U value of 0.21W/m2K and where underfloor heating is used 0.15W/m2K. In the UK, the requirement is to achieve energy usage performance better than the Target CO2 Emission Rate (TER) whilst also achieving the Target Fabric Energy Efficiency rate (TFEE). While not
specific on actual component performance levels, the notional specification requires floors to achieve 0.13W/m²K.
Raft Therm's ability to typically achieve U values of 0.1W/m2K and lower, subject to design, make a great contribution to achieving the regulatory performance and make it suitable for low energy housing and enhanced Passive standard detailing.

2. Through the rising walls also known as cold or thermal bridging
Measuring the thermal transfer or conductivity of heat for every linear meter at a thermal bridge is referred to as the Psi value (W/mK). The psi value measures the extra heat flow through the linear meter over and above that of the adjoining elements (floor and wall). The psi values for any given junction are multiplied by the lengths of those junctions to give the total HTB (Heat Thermal Bridge) which is then divided by the total m² of the envelope (walls, floor, roof) to calculate the buildings Y value.
The Standard Assessment Procedure (SAP) applies a default value of Y 0.15 to all junctions if modelled Y and Psi values are not available. CastleForms Raft-Therm details have been modelled by a qualified Thermal Modeller and certified Psi values are available for these foundation details. These Psi values can be used in y-value calculation method 2 in appendix K of SAP 2012 to determine the y-value on any building using these details.

Furthermore, because the Psi values achieved by Raft Therm are better than the “Approved” Psi values in table R2, it can be assumed that, provided all other details in the building are also equal or better than the “Approved” details, the overall y-value will meet or surpass the reference building y-value of 0.05w/m2k referenced in table R1 of SAP Manual 2012. A lower y-value reduces the requirement to make up SAP points in more costly areas of the structure by adding additional insulation or renewable technologies.

NSAI Certified

Our  raft therm system  is NSAI Certified.

Click here to view our NSAI cerificate for our Raft Therm System