**5. Certifications for Sustainable Construction**

In order to evaluate the impact of green roof system implementation on major sustainable construction certifications, a preliminary qualitative impact analysis must be developed to assess the decision process. A suggested impact of the green roof system that varies from not related to high is presented in Tables 4 and 5, which summarize the impact of green roofs on the overall certification systems based on the degree of relevance of green roof benefits concerning the main criteria for each system. Thus, criteria regarding energy and water involve a strong (high impact) relationship (efficiency, cost reduction), while indoor and outdoor environment improvements involve indirect benefits (medium impact). Finally, innovation is considered as a less relevant criterion since its measurement in buildings is still subjective in terms of green roofs, and it can be interpreted as an indirect benefit or consequence.


**Table 4.** Suggested impact of green roof systems in sustainable construction certifications.


**Table 5.** Impact of green roof systems on different sustainable construction certifications.

High impact: ;; medium impact: ;; low impact: ; not related: .

From the analysis of the impact of green roofs on construction certifications, it is clear that the British Accreditation, BREEAM (Building Research Establishment Environmental Assessment Method), considers the use of this technology more relevant. BREEAM assumes a high impact of green roofs in energy, water, pollution, land use, and ecology. Contrary to BREEAM, the Japanese Accreditation, CASBEE (Comprehensive Assessment System for Built Environment Efficiency), does not consider the use of green roofs crucial for sustainable construction. However, this accreditation system gives a reasonable importance to green roofs regarding energy resources and materials and in outdoor environments. On the other hand, LEED (Leadership in Energy and Environment Design), BEAM Plus (Building Environmental Assessment Method), and ESGB (Evaluation Standard for Green Building) give a medium impact of using green roofs in their accreditation systems.

In general, for the accreditation systems, green roofs are considered as a low-level innovation, unless they are integrated with other technologies such as renewable energies, cogeneration, and so on. That is due to the fact that green roof systems were implemented in many projects worldwide in the past. However, the real fact is that the impact of the implementation was never properly quantified

for the hydraulic and thermal performances. Thus, other environmental benefits such as reduction of the heat island effect and sewage system load, improvement of runoff water and air quality, and reconstruction of natural landscapes remain to be estimated for each green roof case.

As a reference for the reader, a description of major construction certifications is included in Table 6.

**Table 6.** Description of major sustainable construction certifications based on Park et al. (2017) [49] and Lee (2013) [50].


#### **6. Conclusions and Research Challenges**

Although green roofs were used in major ancient buildings, their implementation in modern infrastructure was restricted until Le Corbusier included them among the main building conceptual design points. However, green roofs became more a landscaping action rather than a technical solution with significant environmental, technical, economic, and social benefits. This is mainly due to the fact that there was no proper design, construction, and maintenance of these biological coatings. Intensive, semi-intensive, and extensive green roofs require a proper conceptualization that allows identification of each component and their functions for the overall performance.

Currently, the economic benefits from reducing building energy consumption and sewage system load attracted the attention of urban developers for implementing green roofs on buildings. This review showed that, only regarding the hydraulic performance, retention capacities vary from 45% to 78% for different green roof systems reported in the literature. Thus, more research has to be conducted to estimate the real impact of substratum depth, initial water content, vegetation age and type, and precipitation regime on the hydraulic performance. Similarly, although thermal gradients up to

10◦ were reported using green roofs in tropical climates, more research on the application of green roofs in cold climates has to be done. In this case, when the substratum is saturated, the isolating effect is significantly reduced. Therefore, combined models that integrate hydraulic and thermal performances should be developed. Thermal and hydraulic performances mostly control the complete green roof system.

Even though most accreditation systems for sustainable constructions do not give significant importance to green roof implementation, an accurate quantification of the environmental, technical, economic, and social benefits of green roofs might help to improve this situation, as well as address the lack of legislation for this technology in most countries.

Finally, from this review of the state of the art, research challenges that can be undertaken in the short or medium term toward an effective implementation of green roofs are presented in Table 7.


**Table 7.** Research challenges facing green roofs reported in the literature.

**Author Contributions:** Conceptualization, methodology, and editing, A.M.-R. and H.M.; components, classification, and technical performance, A.N. and A.C.; certification for sustainable construction and research challenges, J.M.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors thank Dos Mundos (Cali, Colombia) and Pontificia Universidad Javeriana Cali (Colombia) for the technical support given during the experiments reported in this article.

**Conflicts of Interest:** The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
