Farrat Structural Thermal Break Plates (FTB) or Thermal Pads are high performance thermal insulators used between horizontal and vertical connections of internal and external elements to prevent thermal or cold bridging.
Structural Thermal Breaks provide a simple, economical and extremely effective solution to meeting Part L of the Building Regulations by way of reducing heat loss and the risk of internal condensation. Farrat Structural Thermal Breaks are accredited by the Steel Construction Institute (SCI) under the Assessed Product Quality Mark Scheme and manufactured under our ISO 9001:2008 Quality Assurance system.
Farrat Structural Thermal Breaks also meet the NHBC’s technical requirements.
Farrat Structural Thermal Breaks are manufactured from high performance materials. We only use materials specifically developed for use within the building envelope and as such are accredited to ensure that designers and clients have confidence in the product which is used in structural connections.
We offer two grades, Farrat TBK and Farrat TBL.
Both materials have been independently tested and accredited by the Steel Construction Institute (SCI) under the “Assessed Product” Quality Mark Scheme. In the majority of applications Part L is satisfied by using plates between 5 & 25mm in thickness.
|Farrat TBK||Farrat TBL|
|Characteristic Compressive Strength, fck (N/mm² , MPa)||312||89|
|Design Value for Compressive Strength, fcd (N/mm² , MPa)||250||70|
|Elastic Modulus (N/mm² , MPa)||5178||2586|
|Water Absorption (%)||0.14||0.48|
|Thermal Conductivity (W/m-k)||0.187||0.292|
|Colour (may vary)||Amber||Black|
|Thicknesses available (mm) ++||5, 10 ,15 ,20 & 25||5, 10 ,15 ,20 & 25|
|Maximum sheet size (mm)||2400 x 1200||2500 x 1250|
|Temperature Resistance (° Celcius) **||+250 short term (Max)
+210 long term (Max)
|++||Multiple plates can be provided for applications where thicknesses greater than 25mm are required.|
|**||Please refer to page 11 of the Farrat Technical Brochure for information relating to fire performance of connections.|
For further details, please refer to our Structural Thermal Breaks brochure.
There are few standard construction details between projects therefore detailing of the building envelope and penetrations can vary significantly. As a result, the calculation of thermal performance and compliance with requirements can be complex.
There are two aspects to the thermal performance of the building envelope; heat loss and condensation risk. Both issues are covered by Building Regulations and guidance on meeting them is provided in various Approved Documents (England and Wales), Technical Handbooks (Scotland) or Technical Booklets (Northern Ireland). These documents currently require heat loss and condensation risk to be assessed in accordance with the same British Standards, European Standards and BRE Publications.
Unlike proprietary mechanical thermal break systems, the plate type thermal break is very simple to incorporate into most details. This flexibility means that it can be used for a wider variety of applications and is not restricted by the modular nature or the space required for proprietary mechanical systems. This flexibility also provides the Designer with greater freedom to develop a bespoke solution.
Thermal Design Considerations:
How thick does the thermal break need to be?
Ideally the detail should be thermally modelled. This requires not only the members and connections, but the entire fabric of the envelope local to the connection to be included in the model. This applies to both mechanical and plate type thermal breaks.
This issue is often forgotten or considered late in the construction process and due to the cost and time implications, modelling is often not undertaken. However, modelling should be considered where:
- the environmental conditions pose a greater risk (e.g. swimming pools)
- the detailing of the planar elements local to the connection are considered to have an inferior thermal performance to that of the main building envelope
- there is significant repetition of the same detail (e.g. balconies).
If thermal modelling is not undertaken, the following should be considered:
- The thermal break should be located within the insulated zone of the building envelope.
- Selection of the thickest thermal break (up to 25mm) considering cost, thermal performance and structural requirements (limitations).
- Minimisation of the cross sectional area/ mass of the steelwork penetrating the building envelope where possible.
- The performance of the connection detail against the BRE’s Certified Farrat details – information provided below.
Stainless steel bolts are sometimes specified for durability reasons. Isolation using normal methods may need to be considered because of bi-metallic action and corrosion. Isolation using thermal washers and thermal bushes will provide minimal additional thermal performance.
Point thermal bridge
The quantity which describes the heat loss associated with a single penetration is a point thermal bridge(χ-value, W/K). This is pronounced as ‘chi-value’. This is a property of the thermal bridge and is the rate of heat flow per penetration that is not accounted for in the U-values of the plane building elements containing the point thermal bridge.
Linear thermal bridge
The quantity which describes the heat loss associated with a thermal bridge is its linear thermal transmittance (Ψ-value, W/m·K). This is pronounced as ‘psi-value’. This is a property of a thermal bridge and is the rate of heat flow per degree per unit length of the bridge that is not accounted for in the U values of the plane building elements containing the linear thermal bridge.
The Specifier will usually identify indoor and outdoor temperatures and relative humidity conditions under which condensation must not occur. Guidance on suitable conditions is given in BS 5250 Code of Practice for the Control of Condensation in Buildings. From these conditions it is possible to determine the allowable minimum temperature on the construction detail below which there would be a risk of condensation. Finite Element Analysis and similar analysis methods allow the temperature distribution to be predicted.
The temperature factor (f) is used to assess the risk of surface condensation or mould growth and is calculated under steady state conditions. To avoid problems of surface condensation or mould growth, the fRsi should not be less than a critical temperature factor (fCRsi).
A range of appropriate critical temperature factors are identified in BRE Information Paper IP 1/06 and listed below:
|Building type||Critical Temperature Factor (fCRsi)|
|office, retail premises||0.50|
|dwellings, residential buildings, schools||0.75|
|sports halls, kitchens, canteens||0.80|
|swimming pools, laundries, breweries|
Application of performance values
Thermal performance values can be utilised within the following assessment procedures / calculations:
- Standard Assessment Procedure (SAP)
- Simplified Building Energy Model (SBEM)
- Thermal bridge in a link without a Farrat Thermal Break. The temperature of the steel is on the hot side of the outer-wall system (9.8°C) and heat loss (χ value) is 1,31W / K.
- Distribution of temperature with Farrat Structural Thermal Break plate (TBK). The temperature on the hot side of the facade system has been improved to 16.5°C and the heat loss is limited to 0.35 W/K = 73% less heat loss.
Under the SCI Assessed Product Scheme the technical data and structural design methodology for Farrat Structural Thermal Breaks has been independently verified by the SCI. The design
considerations are set out in the Farrat Structural Thermal Breaks Connections Guide.
Unlike proprietary mechanical thermal break systems, the plate type thermal break is very simple to incorporate into most details. This flexibility means that it can be used for a wider variety of applications and is not restricted by the modular nature or the space required for proprietary mechanical systems. This flexibility also provides the designer with greater freedom to develop a bespoke solution.
Structural Design Summary (steel connections)
Connections that include thermal break plates should be designed in accordance with the relevant design standards (e.g. BS EN 1993-1-8) or industry guidance (e.g. SCI publications). The following additional checks should also be undertaken, check that:
- the thermal break plate can resist the applied compression forces.
- any additional rotation due to the compression of the thermal break plate (including allowance for long term creep) is acceptable.
- the shear resistance of the bolts is acceptable given that there may be a reduction in resistance due to:
- PACKS – Clause 126.96.36.199 of BS 5950-1 or clause 3.6.1(12) of BS EN 1993-1-8
- LARGE GRIP LENGTHS – Clause 188.8.131.52 of BS 5950-1 or BS EN 1993-1-8
Structural Design Considerations:
Thermal break plates are contained within the protective envelope of the building and in general Building Regulations do not require them to be fire protected or have a fire performance rating. Where the connection containing the thermal break requires fire protection then the following options can be considered:
|Board Protection||A number of proprietary fire protection board systems are available on the market.|
|Sprayed Fire protection||A number of proprietary sprayed fire protection systems are available on the market. The manufacturer should be consulted regarding the compatibility between the system and the thermal break materials. Alternatively consideration can be given to recessing the thermal break and providing a continuous fire protection strip (Nullifire etc.)|
The majority of thermal break connections are related to secondary elements only.
The Structural Engineer will consider robustness during the design process and will refer to local codes and standards. Where a thermal break is located within a key critical element this may need further analysis leading to either consideration of the complete loss of the thermal break or inclusion, for example, of a physical “fail safe”. The detailing of this can often be undertaken whilst maintaining the thermal performance of the connection.
Handling on site
Thermal breaks are normally procured by the steel fabricator as part of the steel frame package on a project. The delivery from Farrat is normally co-ordinated with the steel work contractor erection schedule. They are delivered to site with each one labelled with a unique reference linked to the steel work contractors drawings.
For identification purposes Farrat TBK and TBL are different in colour. If it is essential to the project that both materials are used on the same project, Farrat normally advise that the connection arrangement (e.g. bolt positions) is unique to ensure that no errors are made during installation. This is in addition to Farrat’s normal labeling protocol.
The general handling requirements for thermal breaks should be in line with other component accessories expected to be handled with the primary steel work. This is covered in the NSSS: Section 8 Workmanship – Erection. The NSSS also sets out the requirements of the Quality Management System expected to be adopted by all competent steelwork contractors working on UK construction projects.
- Structural Thermal Break Plate (TBK) with 4-hole connection, steel-to-steel.
Farrat Thermal Breaks can be used in a wide variety of applications where there is a structural requirement of the thermal insulation:
- Steel to steel
- Steel to concrete / masonry
- Steel to timber
- Concrete to concrete
- Facade system connections to the primary frame
- Brise Solei and Canopies
- Roof plant room columns
- Connections of external to internal primary building elements
- Isolation of sub-structure & basement structure elements
- External staircases or external balconies
- Man-safe systems
- Connections to existing structures
Farrat’s market leading Structural Thermal Break Plates & Pads (FTB) are high performance thermal insulators, used between horizontal and vertical connections of internal and external elements to prevent thermal or cold bridging.
- An effective solution to meeting Part L of the Building Regulations by reducing heat loss and internal condensation
- Not a proprietary modular thermal break, so offers flexibly in detailing your connection
- Supported by independent material testing to European building insulation standards
- Certification and product approvals by recognised organisations (SCI, BRE and NHBC)
- Very high load
- Very low thermal conductivity coefficient
- Variety of thicknesses & length
- Available with custom holes
- Can be used for new and existing structures
Should show a fully detailed connection or one communicating the design intent with a supporting specification (NBS or similar).
Is normally responsible for ensuring that the connection meets the requirements of the Building Regulations Part L (SAP).
Design Output – Thermal performance/ Thickness (Farrat TBK or Farrat TBL).
The Structural Engineer
Is normally responsible for designing the connection or providing a performance specification for the steel work fabricator.
Design Output – Strength (Farrat TBK or Farrat TBL)
Sample Specification for project using Farrat TBK – National Building Specification (NBS)
NBS Clause: G10/ 350 Thermal Break Connection Plate
- Manufacturer: Farrat Isolevel Ltd, Balmoral Road, Altrincham, Cheshire, WA15 8HJ, Tel: +44 (0)161 924 1600, Fax: +44 (0)161 924 1616 www.farrat.com
- Product Reference: Farrat TBK
- Thickness: 25 mm
- Plate Size: As Drawing number – or to be determined by the connection designer
- Hole Size & Positions: As Drawing number – or to be determined by the connection designer
- Accreditation SCI Assured Product/ NHBC
Please be aware there are cheaper alternatives on the market that the supply chain may provide as an alternative, but in our view not of equal performance or accredited for use in building applications (structural)
QMU Graduate Centre
Type: TBK Thermal Breaks
AIRC Cranfield University
Type: TBK Thermal Breaks
Nottingham Trent University
Type: TBL Thermal Breaks
Why Choose Farrat Structural Thermal Breaks?
In 2007, responding to a request from a designer who was concerned with cold bridging on a project, Farrat Isolevel began manufacturing thermal breaks for buildings. Changing legislation in response to climate change and energy saving has meant that Farrat now supply tens of thousands of thermal break plates for the UK and overseas market each year. Constantly driven by engineering excellence, Farrat continue to lead the way in the development of the thermal break plate market.
Farrat Structural Thermal Breaks have been independently tested and accredited by industry recognised institutions, to ensure that design teams and clients can have confidence in a product used in structural connections.
SCI (Steel Construction Institute) has been a trusted, independent source of information and engineering expertise globally for 25 years. Farrat is proud to be a member.
SCI Assessed Product Scheme is an established Quality Mark that has been awarded to testify that the technical data and structural design methodology for Farrat Structural Thermal Breaks has been independently verified by the SCI.
Farrat Structural Thermal Breaks meet the NHBC’s Technical Requirement. NHBC accepts the use of Farrat TBK and TBL thermal break materials for use in structural applications.
Farrat are a member of BRE’s Certified Thermal Details and Products Scheme, which allows users to search a wide range of accurate and independently assessed thermal junction details, products and elements, ensuring accuracy, consistency, credibility and quality throughout the design & specification process.
Farrat Isolevel Limited operates under an ISO 9001:2008 Quality Assurance System. All thermal breaks are manufactured under this system.
Farrat Isolevel Limited operates under an ISO 14001:2004 Environmental Management Standard.
To provide a quotation please submit the following information:
- Material Type – Farrat TBK or Farrat TBL
- Plate Dimensions & Thickness
- Size & Number of Holes*
- Delivery Postcode
We aim to start manufacturing within 3 working days from an order being placed.
*A fully dimensioned drawing is normally required for each type of plate with a unique reference prior to fabrication.
Stephen Blundell BEng(Hons) CEng MICE MIStructE
Technical Director – Structural Thermal Breaks
DD: +44 (0)161 924 1600
Structural Thermal Break Connections
Stephen is a Chartered Engineer with over 35 years experience in civil and structural engineering. As Technical Director for Structural Thermal Break Connections at Farrat, Stephen is the technical lead for thermal break systems and specification.