GLASGrün - Regulation of climate, energy demand and comfort in GLASS buildings through structurally integrated vertical GREEN

Initial Situation, Problem, and Motivation

Modern architecture extensively uses glass in the building sector, particularly in commercial construction. Large-scale glass buildings are widely regarded as architectural highlights but pose significant challenges for urban spaces. Glass has a considerable impact on both the indoor and the outdoor microclimate: The concentration of radiant energy and high indoor temperatures strain energy efficiency and affect user comfort.

Retrofitting glass façades and building glass surfaces with greenery has so far remained a gap in green building solutions due to various challenges: Simple systems fail due to the inability of self-clinging plants to attach to glass surfaces. Climbing aids for container-based systems, as well as hanging structures, are often not viable for structural reasons and, like façade-bound systems, are not apt for retrofit. For maintenance purposes appropriate distances between vegetation and glass façades must be provided. Standard greenery solutions for retrofit shading of glass buildings to reduce solar gains and to provide microclimatic benefits are lacking.

Objectives and Innovative Aspects

GLASGrün aimed to develop, implement, test, and monitor vertical greening options for the external shading of large, glazed façades in commercial buildings and inner-city commercial areas, using deciduous plants. The project sought to address both vegetation-related and structural challenges, and to develop transferable standard solutions. Insights into acceptance and perception of these solutions were also to be gathered.

Methodological Approach

To prepare for implementation, extensive site assessments and spatial-structural analyses were conducted, including legal and structural framework conditions. Conceptual variants were developed. The implementations took place at two demonstration sites, where comprehensive indoor and outdoor monitoring programmes were set up: In addition to stationary measurements for continuous monitoring of microclimatic parameters, manual measurement campaigns were carried out, and plant growth as well as relevant parameters were recorded up to the third year. Indoor monitoring included sensor recordings of thermal comfort and electricity consumption, complemented by simulations of solar gains (IDA ICE 5.1) and thermal comfort assessments according to ÖNORM EN ISO 7730:2023. Based on the b-factor (mean transmission coefficient), a bioshading coefficient (Fbs) was derived for 4 tested climbing plant species over the course of the year.

A perception and acceptance study was conducted, building on a literature review and surveys of employees and passers-by. The study was carried out at both demonstration sites in 2 phases: prior to implementation, to assess the perception of the problem, and after implementation, to evaluate acceptance and impact.

A cost-benefit assessment was conducted based on an evaluation of literature-based assessment models, a quantitative cost analysis and a qualitative description of the benefits.

Results

Two retrofit demonstration projects were implemented: 176 m² of ground-based greenery were installed at ground floor level using two different systems, with four climbing plant species at an MPREIS Baguette store in SÖLL | TIROL. In KREUZGASSE | VIENNA, a planter-based system (77,5 m²) was installed up to the second storey top edge at a commercial office building, requiring the pavement to be opened for integration.

By the third year in SÖLL | TIROL, coverage rates of the target areas exceeded 90 %, reducing the transmission of incoming solar radiation to just 10 %. Bioshading coefficients (Fbs) were determined for four tested climbing plant species over the course of the year. Simulations using IDA ICE indicated a 50–67 % reduction in indoor solar gains. As a result, there was a significant increase in comfortable indoor conditions and a reduction in discomfort levels respectively in number of dissatisfied persons (PPD, according to Ole Fanger).

In KREUZGASSE | VIENNA, where the implementation took place later, in the second project year, a coverage rate of 20 % up to the first floor was achieved by the second growth year. However, sufficient data on transmission and the bioshading coefficient could not be collected within the project period, as plant growth had not yet reached sensor height.

The acceptance of greening measures was confirmed in the survey conducted. Respondents perceived vertical green shading as contributing to greater well-being, due to improved aesthetics, better air quality, and more comfortable perceived temperatures and indoor climate. However, concerns mainly related to maintenance, workload, insects, and dirt.

Conclusions and Outlook

The success of the GLASGrün-systems as vertical greenery-based shading measures exceeded expectations as early as the second year at ground-floor level. New data on greening and shading performance are now available, demonstrating the reduction of solar gains through vertical greenery. These findings can serve as useful indicator values in calculations and models and are relevant for planning. However, limitations arose at both sites regarding cooling cost savings, as valid data could not be collected due to site-specific influencing factors (internal loads, user behaviour, lack of reference spaces/years).

Based on the GLASGrün-findings presented in this scientific report, a GLASGrün-Guide including a Catalogue of Variants (Berichte aus Energie- und Umweltforschung 60b/2025) and a GLASGrün-Maintenance and Care Guide (Berichte aus Energie- und Umweltforschung 60c/2025) were elaborated as stand-alone open access publications. They provide solutions for structural integration, checklists for approval processes and implementation, as well as recommendations for maintenance and upkeep management to optimise the success of green façades.

Project management

University of Natural Life Sciences, Vienna - Institute of Soil-Bioengineering and Landscape Construction

Project or cooperation partners

• GRÜNSTATTGRAU Forschungs- und Innovations GmbH
• lichtblauwagner architekten generalplaner ztgmbh (liwa)
• MPREIS Warenvertriebs GmbH (MPREIS)
• Österreichisches Institut für Bauen und Ökologie GmbH (IBO)
• RATAPLAN-ARCHITEKTUR ZT GMBH

University of Natural Resources and Life Sciences, Vienna
Institute of Soil-Bioengineering and Landscape Construction
Peter-Jordan-Straße 82, Schwackhöfer-Haus, 3. Floor
A-1190 Vienna
Tel.: +43 (1) 47654-87400
E-mail: iblb@boku.ac.at
Web: www.baunat.boku.ac.at/iblb.html