Development of Clay Tile Coatings for Steep-Sloped Cool Roofs

Anna Pisello,Lucia Brinchi,Andrea Nicolini,Franco Cotana

doi:10.3390/en6083637

Abstract

Most of the pitched roofs of existing buildings in Europe are covered by non-white roofing products, e.g., clay tiles. Typical, cost effective, cool roof solutions are not applicable to these buildings due to important constraints deriving from: (i) the owners of homes with roofs visible from the ground level; (ii) the regulation about the preservation of the historic architecture and the minimization of the visual environment impact, in particular in historic centers. In this perspective, the present paper deals with the development of high reflective coatings with the purpose to elaborate “cool” tiles with the same visual appearance of traditional tiles for application to historic buildings. Integrated experimental analyses of reflectance, emittance, and superficial temperature were carried out. Deep analysis of the reflectance spectra is undertaken to evaluate the effect of different mineral pigments, binders, and an engobe basecoat. Two tile typologies are investigated: substrate-basecoat-topcoat three-layer tile and substrate-topcoat two-layer tile. The main results show that the developed coatings are able to increase the overall solar reflectance by more than 20% with acceptable visual appearance, suitable for application in historic buildings. Additionally, the effect of a substrate engobe layer allows some further contribution to the increase of the overall reflectance characteristics.

Highlights

The widespread use of materials with high reflectivity to the solar radiation and high spectral emissivity, i.e., cool materials for building envelope applications, is considered as one of the most effective techniques to reduce energy requirements for cooling [1] and to mitigate urban heat islands, which are related to higher temperatures registered in urban areas with respect to the rural surroundings [2]
The darkest samples, i.e., N1G and W1G, present the overall mix of these pigments, which purpose is to obtain a visual appearance of the tile as close as possible to the ancient traditional clay tiles found in Italy (Figure 4)
The application of such coatings shows that: (i) the appearance of the tiles is very close to that of natural clay tiles of ancient buildings starting from the C series of samples to the G series, which color is equivalent to the natural clay color; (ii) the final appearance of the tiles does not show any perceivable difference between the natural tile (N series) and the tile with the white engobe (W series) as substrate

Summary

Introduction

The widespread use of materials with high reflectivity to the solar radiation and high spectral emissivity, i.e., cool materials for building envelope applications, is considered as one of the most effective techniques to reduce energy requirements for cooling [1] and to mitigate urban heat islands, which are related to higher temperatures registered in urban areas with respect to the rural surroundings [2]. Cool roofs represent acknowledged solutions for energy saving, their application is still limited to high reflective coatings for non-sloped roofs, mainly concerning industrial, commercial, or office buildings [11]. These building typologies are characterized by higher internal gains, which tend to increase the energy requirement for cooling and the consequent cool roof efficacy [12]

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