Technical Data > Technical data Bernardos phyllite > Sustainability and energy efficiency

This section analyses three aspects of great importance in the field of sustainable architecture, to which Bernardos slate brings added value:

These are:

– Sustainability.
– Energy efficiency.
– LEED Certification.


The Brundtland report defines sustainable development as that which “meets the needs of the present without compromising the ability of future generations to meet their own needs”.

This definition implicitly contains at least two conditions:

– Economic growth to ensure that the needs of the present generation can be met.

– Preserving a minimum provision of production factors to guarantee the continuity of growth in the future.

Thus, the abovementioned report highlights the following three aspects, which are to be considered part of the definition of sustainable development:

– Social aspect.
– Economic aspect.
– Environmental aspect.

Picture II-10. Modelo de desarrollo sostenible

This means that a development model can be identified as sustainable if it is financially viable, socially fair and can be maintained in the long-term from an environmental point of view, so that a reasonable equilibrium can be struck between the three aspects of development.

Being acquainted with the previously described sustainability concepts allows an analysis and assessment of the involvement of Naturpiedra Jbernardos in these concepts, and thus have a reasonable overview of the company’s current situation.

– Regarding the economic aspect, the company’s activity generates an increase in direct revenue, in the small municipality of Bernardos as well as in its vicinity, thanks to the prestige acquired by this slate, for its historical and cultural value and for its durability.

– Regarding the social aspect, there has been a steady increase in the creation of new jobs over the years, both directly and indirectly; and the company’s modern and efficient means of production substantially facilitate the extraction and elaboration work. Naturpiedra Jbernardos currently employs more than 100 people directly, a number which shows an upward tendency.

– Regarding the environmental aspect, the entity Naturpiedra Jbernardos complies with all the legal requirements which are imposed upon it, as a company exploiting and working with a natural resource, by the demanding European environmental legislation. Thus, the quarry’s tailings are processed in controlled debris management spots, the slurries from slate-cutting are treated in appropriate spaces, the residual water resulting from the quarry’s drainage is recycled, the oils from the vehicle’s engines and machinery are taken to recycling points, etc. In order to guarantee its compliance with this legislation, Naturpiedra Jbernardos keeps the required restoration plans up-to-date, as well as the corresponding mandatory permits.



The use of energy-efficient materials in the construction of buildings requires a meticulous selection in order to optimise costs and maintain an adequate and comfortable temperature for the inhabitants of large cities, where temperatures tend to be quite high.

It has been recognised and demonstrated that the temperature in urban areas is significantly higher than in neighbouring suburban and rural areas. This phenomenon known as “urban heat island” increases the surface temperature of buildings, leading to an temperature rise of up to 3°C more in comparison with suburban and rural areas.

In this context, the demand for energy to cool down buildings and thus reach a comfortable temperature clearly rises too. For this reason, it is necessary to select efficient materials with surface physical properties − as these determine their capacity to transfer heat − which are suitable for each specific circumstance.

The surface physical properties of the materials used for a cold roof − these must be determined in order to control the temperature of the building’s thermal enclosure − are Solar Reflectivity (R) and Infrared Emittance (ε). The scientific definitions of these two terms are as follows.

– Solar Reflectivity (R) refers to the ability of a material to reflect solar energy from its surface back into the atmosphere.

– Infrared emittance or emissivity (ε) is the proportion of “infrared radiation” shed by a material’s surface due to the temperature which the material reaches in a given environment.

Both values are measured on a scale from 0 to

The closer they are to 1, the colder the surface can remain when exposed to the sun.

Picture II-11. Diagram of the distribution of solar radiation over a cold roof.


Tn being the temperature of a standard black surface.

Tb being the temperature of a standard white surface.

Ts being the temperature of the material analysed.

The higher the SRI, the better the reaction of the surface.

From an environmental and economic standpoint, cold roofs/surfaces present the following advantages:

– Reduction in the building’s temperature rise.
– Significant savings in electricity consumption resulting from the use of air-conditio-ning installations.
– Notable improvement in the conditions of thermal comfort in buildings without air conditioning.
– Lower peak electricity demand.
– Use of cooling installations with lower energy consumption.
– Longer lifespan of the covering system, and thus reduction of maintenance costs.
– Mitigation of the “urban heat island” effect of 1-2°C since less heat is transferred to the external atmosphere.
– Reduction of pollution and CO2 emissions.
– the SRI score gives points for the certification of buildings in the LEED system.

The regulations which require certain materials to be used for buildings with cold roofs are usually defined in ordinances emitted by the competent local authorities. For example, the city of Los Angeles in the US state of California has developed the Ordinance No 183149 − to which all architectural projects must abide − which establishes requirements for, among others, roofing materials, so that the effect of solar radiation can be mitigated in urban areas.

The requirements for roofing slate are as follows:

Solar reflectance or reflectivity (SR).

Value obtained in accordance with the rule ASTM C 1549-04. Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using A Portable Solar Reflectometer.

Measuring range: 0 to 1.

The maximum RS value is ≥ 0.20 for the usual slopes of slate roofs.

Thermal emittance (ε).

Value obtained in accordance with the rule ASTM C 1371. Standard Test Method for Determination of Emittance of Materials near room temperature using portable emissometers.

Measuring range: 0 to 1.

The ε value must be ≥ 0.75.

Solar Reflectance Index (SRI).

Value obtained in accordance with the rule ASTM E 1980-11,Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Slopped Opaque Surfaces.

The maximum value is ≥16.

In order to comply with the above-cited Ordinance, Naturpiedra Jbernardos has requested the competent laboratory to undertake the following tests on its slate product. The results are as follows:

This results confirm that the slate from Naturpiedra Jbernardos complies with the applicable requirements for roofing materials to mitigate the effect of solar radiation in urban areas, in accordance with Ordinance No 183149 of the City of Los Angeles, California (USA).


The LEED® (Leadership in Energy & Environmental Design) Certification is a building certification system created by the US Green Building Council (USGBC) in order to promote the development of sustainable and highly energy-efficient buildings.

With regards to Spain, USGBC recognises Green Building Council España (GBCe) as the sole representative of the LEED system, in charge of presenting all necessary information on this type of building certification.

The system functions with an evaluation of the sustainability of the edification, with an assessment based on a score system, measuring the impact in the following main seven areas:

1-. Sustainable sites.
2.- Water efficiency.
3.- Energy efficiency, renewable energies and emissions into the atmosphere.
4.- Materials and natural resources.
5.- Indoor environmental quality.
6.- Innovation in design.
7.- Regional priority.

Depending on how it is used, Bernardos slate scores points in the following areas: energy efficiency, materials and natural resources, indoor environmental quality and regional priority.

Depending on the number of points scored in each area, the following levels of certification can be obtained:

– LEED Certification (Basic)
– LEED Certification Silver
– LEED Certification Gold
– LEED Certification Platinum

Picture II-12. Sellos certificados LEED