Cork and nanofiber insulation

TID-EFE.08
Cork an nanofiber solution to improve the acoustic comfort of buildings

Implementation
period

2013 → 2015

Background Information / Main Objective

Every day, there is more interest in developing construction techniques that replace traditional methods for more innovative ones capable of improving on-site performance, quality of construction and optimization of the resources used, all without adversely affecting the final cost of the process and encouraging the creation of specialized jobs. These general trends lead to the concept of Industrialized Construction, a system based on the integration of all subsystems and components into a global assembly and execution process.

Based on this concept, and used as a starting point for this project, Casa Patio 2.12 is an industrialized construction project carried out as part of the well-known SOLAR DECATHLON EUROPE competition in 2012 (hereinafter, SDE12). This project, awarded first prize in Energy Efficiency and second prize in the finals of the SD12, was based on creating a self-sustaining modular home, recreating the traditional Andalusian patio and putting native and natural building materials to good use.

The original design of the housing prototype focused mainly on improving energy efficiency by implementing a series of innovative construction solutions based on the mimicry of the “botijo (container of water)” evaporative effect. This design offered some room for improvement in terms of acoustic comfort, so OPENCORCHO opted to exploit this margin of improvement and optimize the acoustic performance of the Casa patio 2.12 project.

The objective of the project was, therefore, to achieve a new design of the original prototype enclosure to improve the acoustic comfort of the Casa Patio 2.12 home, making several modifications to the structural configuration and the materials, as well as trying various combinations of the binomial design-material. The final construction solution was based on the implementation of cork sheets with optimized properties (size and thickness of the pieces, porosities, etc.) in the enclosure structure, being a highly efficient, versatile, elegant solution, compatible with the other construction materials used, while also not being detrimental to the energy efficiency of the Casa Patio 2.12 prototype.

Likewise, the modelling work carried out with different solutions and the “in situ” assessment of its acoustic behaviour led to virtual acoustic prediction models that allowed variations of the enclosure design to be assessed very precisely, as well as to validate the new proposed design as the best solution in terms of performance and compatibility with other materials. The validation of the computational models allowed the project to reduce the number of products tested on the Casa Patio 2.12 prototype, thus saving both costs and time.

Description

Cork is an eco-efficient material and provides the highest degree of acoustic insulation among all natural solutions. Its use as an acoustic insulation is an integral part of both the Casa Patio 2.12 facades and its flooring was based on computational models that let use evaluate the performance of cork solutions of different thicknesses, densities and other physical characteristics. This let us choose an optimal solution, compatible with the other construction materials used, which would combine significant improvements with respect to the original facade of the prototype home, while not incurring an excessive increase in the dimensions of the walls.

Although the use of cork as an acoustic insulation is not a novelty per se, its incorporation in an enclosure like the one designed for this project is both highly energy efficient and provides high levels of sound insulation, well above the legally required levels.

It was necessary to carry out a series of studies that would determine the options for improvement of the solutions used for the different facades and the floor of the house. Reverberation time (3 hypotheses), studies of acoustic insulation to aerial noise (through walls) and impact (through the floor), are some of the parameters that characterise the acoustic quality of a home.

Different programs were used to model the different enclosures (rooms) of the Casa Patio 2.12 prototype, taking into account the physical characteristics of the materials that make up the walls, floors, etc. to estimate the reverberation time that sounds of different frequencies would produce within these enclosures, the noise reduction rates of aerial and impact noise, etc. Subsequently, these factors were measured “in situ” to assess the computational models.

After evaluating new designs and/or materials to improve the acoustic behaviour of the enclosure, it was observed that there was a relationship between the degree of acoustic insulation and designs whose original function was to provide proper thermal insulation in homes with geographic locations in colder and more humid environments than the Casa Patio 2.12 prototype (Andalusia). Therefore, a design with double-layer walls, significantly thicker with more layers of materials (insulation, absorbent, etc.) added better acoustic insulation, indirectly to the thermal slope.

Considering the above, and that the improvement of acoustic behaviour should not lead to any detriment to the heat transfer properties of the enclosure (which was optimised with the inclusion of a polymer membrane), the structural designs had to allow a configuration capable of accommodating an intermediate layer of a material that is compatible with the other components while improving the overall acoustic behaviour of the prototype home. It was concluded that it would be advisable to test modifications of the enclosure in the designs (homogeneous single- or multi-layer walls, standing waves and resonance frequencies in double walls, seals, porosities, indirect transmissions, vertical/horizontal separation elements, flanks of indirect transmission, etc.) and incorporate acoustic or thermo-acoustic (never exclusively thermal) materials.

After evaluating different materials (e.g. phase change materials), it was decided to integrate layers of cork in the inner line, with greater thicknesses and controlled porosity to allow improved interior acoustic comfort, trying solutions with different combinations of weight and thickness, leading to a certain degree of porosity and even layers including fibres within the cord framework.

A wide variety of cork products of different densities and porosities were therefore evaluated, with a list of possibilities being applied to cork sheets between 5 and 20 mm thick, with densities of 180 kg/m3, evaluating “in situ” (facade, floor, etc.) the acoustic behaviour of the cork sheets of different dimensions, densities and compositions, etc.

The results obtained at this point established the compromise that had to be made between the size of the sheets and the conditions of acoustic improvement that were obtained, besides evaluating the different acoustic/floor insulation configurations, always bearing in mind the objective of not significantly modifying the original dimensions of the Casa patio 2.12 enclosures.

It was concluded that the best conditions for the impact noise insulation for floating floors would be obtained using cork agglomerate sheets with thicknesses between 5 and 20 mm, which would provide an improvement to the acoustic insulation to impact noise of at least 20 dB. Thus, for example, the application of this project’s floating floor solution (5 mm cork agglomerate) and absorbent coating (on the interior facades of the bedroom) allowed the reverberation time to be reduced to 0.6 seconds, and the impact noise reduction, which was to be below 65 decibels, was set at 9 dB. These results showed the efficiency of the work carried out in this project.