Thermal Conductivity

What Is Thermal Conductivity?

Thermal conductivity measurement is the determination of how much heat the material transmits per unit thickness and unit temperature difference. The sample is placed between two plates, a stable temperature difference is created and the transferred heat flux is measured. The result is given as lambda (W/m·K); Thermal resistance is found by dividing the thickness by lambda.

Purpose of Thermal Conductivity

The aim is to numerically determine the thermal performance of the material and provide input into building energy calculations and insulation thickness selection.

Which Products Is Thermal Conductivity Applied To?

Thermal insulation materials
Wall and flooring materials
Composite structural elements
Plaster and screed materials
Wood and wood-based products

In Which Sectors Is Thermal Conductivity Used?

ConstructionConstructionEnergy

Standards Related to Thermal Conductivity

TS EN 12667 (thermal resistance in products with medium and high thermal resistance)
TS EN 12664 (thermal resistance in dry and moist products)
TS EN 12939 (thermal resistance in thick products)
TS EN ISO 8301 (heat flow meter device)
TS EN ISO 8302 (protected hot plate device)
TS EN ISO 22007 series (transient state methods)

Thermal Conductivity Conditions

average temperature: The measurement is made and reported at the defined average temperature; value depends on temperature
moisture content: The sample is measured dry or at defined equilibrium moisture content; humidity increases lambda
Thickness: The thickness during measurement is recorded
Steady state: The measurement is taken after the heat flux becomes stable.

Equipment for Thermal Conductivity

Shielded hot plate (GHP) device
Heat flow meter (HFM) device
Air conditioning and drying cabinets
Thickness measurement systems
Referans standart numuneler

Sample Requirements for Thermal Conductivity

Conditioning in building materials directly determines the result: concrete with incomplete curing time, damp wood or insulation material that is not balanced will not show its true performance. Sample age and conditioning conditions are always stated in the report.
Flat sample size that covers the device measurement area
Surfaces must be smooth and parallel; gap distorts measurement
Material density and thickness must be declared
Moisture sensitive materials should be measured after drying

Duration of Thermal Conductivity

The measurement itself continues until steady state is reached, and this time depends on the thermal resistance of the material. For highly insulated and thick samples, it takes significantly longer to reach steady state; Prior conditioning is also added to the schedule.

Thermal Conductivity Procedure

1The sample is sized and conditioned.
2Thickness and density are measured.
3The sample is placed between the device plates.
4The defined average temperature and temperature difference are established.
5The heat flux is monitored until steady state is reached.
6Thermal conductivity and thermal resistance are calculated.

Thermal Conductivity Acceptance Criteria

Thermal conductivity is not a pass/fail value, but a declared performance value. The minimum thermal resistance required for the building component is defined by national energy performance regulations. Within the scope of (EU) 305/2011, the test result is not a pass/fail decision, but the performance value to be announced in the Declaration of Performance (DoP). The national regulations and project specifications of the country where the structure where the product will be used determine which performance level is sufficient.

Evaluation of Results

The result cannot be compared without specifying the measurement temperature and humidity condition. Additionally, the laboratory value represents dry and ideal conditions; In practice, moisture, compaction and mounting gaps reduce actual performance. This difference is the reason for the margin in design values.

Thermal Conductivity Report

Material description, density and thickness
Conditioning and humidity
Measurement average temperature and temperature difference
Thermal conductivity (W/m·K) and thermal resistance (m²·K/W)
Measurement uncertainty and the device used

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

Construction Products Regulation (EU) 305/2011
2010/31/EU Energy Performance in Buildings Directive

Construction Materials Testing — What Does This Testing Field Cover?

The section below describes the field that the Thermal Conductivity test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Construction materials testing shows whether a product performs the function it takes on within the structure. A wide field is gathered in this family, from the compressive strength of concrete to the thermal transmittance of glass, from sieve analysis of aggregate to the watertightness of windows.

What sets this family apart from the others is that the result turns directly into a REGULATORY DECLARATION. For products covered by construction products legislation a declaration of performance (DoP) is mandatory, and every essential characteristic in the declaration rests on a test result. Reaction-to-fire class, thermal conductivity, compressive strength, water permeability and release of dangerous substances are declared in this way. The declaration is a legal text carrying the manufacturer's signature; the test record behind it is the first document requested in an inspection.

The second distinguishing feature is that the product is assessed over its SERVICE LIFE. An electronic device runs for five years; a building component stays in place for fifty and is exposed throughout that time to freeze-thaw cycles, UV, moisture, chemical attack and load. Durability tests (freeze-thaw, carbonation, alkali-silica reaction, ageing) therefore carry as much weight in this field as classical strength tests.

Tests are separated by material type and each group has its own set of standards: cement and concrete, aggregate, masonry units, wood-based panels, thermal insulation, glass and glazing units, ceramic tiles, floor coverings, screeds, joint fillers and coating systems. Where the product will be installed determines which set applies — the same panel is assessed against different standards on a wall and on a floor.

Factory production control (FPC) is a continuous component of the field. CE marking on a construction product is not obtained with a single test and then left; the manufacturer must set up a system showing that it monitors production consistency, takes samples regularly and intervenes when there is a deviation. Depending on the product group, this system may have to be audited by a notified body.

Site testing is a separate body of work. In the laboratory the product is approved; on site it is checked that the product really is of the declared class and that it has been applied correctly. Fresh concrete slump, cylinder sampling, aggregate sieve analysis and in-situ watertightness tests fall within this scope.

Method groups in this field

Concrete and cement
Slump, air content and unit weight in fresh concrete; compressive and flexural strength, water permeability and freeze-thaw resistance in hardened concrete. For cement, compressive strength, setting time and composition analysis.
Aggregate
Sieve analysis, particle shape, Los Angeles abrasion resistance, freeze-thaw, alkali reactivity and density/water absorption.
Thermal and energy performance
Thermal conductivity and thermal resistance, calculation of thermal transmittance (U value) in glazing units, solar energy transmittance.
Facade and joinery
Air permeability, watertightness and wind load resistance in windows and doors; fire performance in facade systems.
Fire performance
Reaction-to-fire classification and fire resistance tests; these are two separate concepts and are addressed by separate standards.
Masonry, tile and flooring
Compressive strength, water absorption, abrasion resistance, slip resistance, stain and chemical resistance.
Emissions and dangerous substances
Formaldehyde release from wood-based panels, VOC emissions from construction products, leaching behaviour of aggregates and waste.

Commonly confused in this field

REACTION to fire and RESISTANCE to fire are different concepts: one describes the material's contribution to a fire, the other how long a component holds the fire back.
A declaration of performance is not a certificate; it is the manufacturer's declaration. Notified body involvement varies with the product group and the assessment system.
A test result is valid for the mounting arrangement in which the product was tested. A different substrate, a different thickness or a different joint detail may require reassessment.
A site sample and a laboratory sample are not the same thing. A concrete cylinder taken on site also reflects application and curing conditions; it does not replace product approval.
ASTM and EN construction standards measure similar quantities with different specimens and scales; the results cannot be converted one-to-one.

Which decisions these results support

Declaration of performance (DoP) and CE marking
Establishing and maintaining the factory production control system
On-site conformity control of concrete, aggregate and workmanship
Meeting fire and energy performance requirements
Verifying the technical items in the project and tender specification

Related Tests

Frequently Asked Questions About Thermal Conductivity

We got different lambda value from different laboratories, why?

The most common reason is that the measurement average temperature and sample humidity are different. Lambda is sensitive to both; Results cannot be compared without equalizing conditions.

Can a single lambda be given for a composite wall?

A layered structure does not have a single lambda value; The thermal resistance of each layer is calculated and summed. The total thermal transmittance (U value) is calculated this way or measured by the hot box method.