Project Content and Objectives

The HEDWIG project aimed to record the effects of building greenery on the indoor and outdoor environment and to calculate well-founded and reliable performance parameters. The findings are intended to promote further mainstreaming of building greening and to be the basis for argumentation and review processes. In view of advancing climate change and the increasing overheating of urban areas (Urban Heat Island Effect), green infrastructures (GI) are becoming especially important as a strategy for climate change adaptation. Although the positive effects of building greenery – such as evaporative cooling, shading and biodiversity – are qualitatively recognised, there is often a lack of reliable, standardised measurement data for quantitative impact assessment in planning practice.

The HEDWIG project addressed this gap by carrying out systematic continuous monitoring over a period of two years as well as supplementary measurement campaigns on 16 representative roof and façade greening objects in Vienna and Lower Austria. The aim was to determine the effects of standard-compliant greening of buildings, representative vegetation and performance parameters, which serve as a basis for thermal building simulations and for the optimisation of planning processes.

The HEDWIG report series comprises 4 stand-alone reports in the same publication series „Berichte aus Energie- und Umweltforschung": The here presented Report of Results includes the full documentation of the applied methodologies and instructions, the HEDWIG-Parameter Tables, the synthesis and recommendations for a practical monitoring concept (Stangl et al. 2026). The HEDWIG-Data Catalogue (Jalits et al. 2026) presents all object and outdoor and indoor measurement data of all HEDWIG-sites collected during the permanent monitoring and during measurement campaigns. Additionally, the Study on the International State-of-Knowledge (Jalits et Stangl 2026) and the Documentation on the Stakeholder-Engagement (Leitner et al. 2026) are available as stand-alone-publications.

Methodology and Research Design

The study was based on a multi-dimensional approach linking microclimatic, building-physical and plant physiological parameters. In addition, stakeholders and experts from the GRÜNSTATTGRAU network were involved to ensure the transdisciplinary usability and traceability of the data.

Measurement setup and sensors

HEDWIG developed and verified a measurement setup that is suitable for the collection of valid measurement data, their comparability and for the evaluation of demonstration projects in the building greenery sector. The documentation of the methodology is considered a working manual.

Outdoor conditions: A measurement-setup was developed and verified based on permanent monitoring and on measurement campaigns. It included the use of weather stations and permanent sensors to record global radiation, air temperature and humidity in front of and behind vegetation as well as substrate heat flow. Vegetation-related plant physiological parameters (coverage ratios, (wall) leaf area index, electrical conductivity, etc.) were collected in measurement campaigns. A sensor-based registration of the short-wave radiation balance was supported by thermography.

Building physics and interior conditions: A hybrid measurement network was used to record the indoor air conditions and thermal interaction with the building envelope. For the evaluation of thermal comfort, 2 complementary approaches were used (adaptive comfort model according to ÖNORM EN 16798-1 and comfort model according to Freymark and Leusden). The exemplary energy assessment and quantification of the cooling capacity by the building greening was carried out using numerical simulation (IDA ICE). The aim was to translate the real physical effects of vegetation – in particular the reduction of the solar input and the thermal buffering effect – into an energetic calculation model.

Key Results

Microclimate, Reduction of Radiation and Bioshading Coefficient

A major effect of greening is natural shading. Measurements showed that dense plant bodies (e.g. in the case of the object MA48 Gürtel with a WLAI of up to 6.5) can massively reduce solar input. In heat wave phases, a reduction of up to 97% in solar radiation behind the green body was measured. The Bioshading Coefficient BSC serves as a key characteristic value and solid basis for comparison for technical sun protection.

Surface temperatures and evaporation

Infrared images illustrate the thermal relief of façades. While conventional components (e.g. sheet metal attics or plastered walls) reached surface temperatures of up to 60 °C, greened areas remained up to 20 °C cooler. This cooling capacity results primarily from the transpiration of the plants, measurable by the stomatal conductivity. Vital climbing plants evaporate up to 1.3 l/h/m² here. It became apparent that these effects are massively limited in the case of extensive sedum green roofs or in the case of lack in coverage.

Radiation balance: transmission, reflection and absorption

On basis of the measurement campaigns, approximate short-wave radiation balances could be determined at all HEDWIG objects. This revealed that the leaf bodies absorb up to 59 % of the incoming radiation and convert it into non-perceptible (latent) heat if there is sufficient water supply. The balance component and albedo values of all objects are available in the HEDWIG Parameter Tables.

Building Physics Effects and Indoor Thermal Comfort

According to the adaptive comfort model, the operating room temperatures during the summer months were almost exclusively in comfort categories I (high comfort level) and II (normal standard). Critical overheating hours (category III or worse) hardly occurred. The effect of the façade greening on the opaque façade components was significantly influenced by uninsulated wall thicknesses and the associated thermal storage mass.

Heat Flux and Soil Moisture in the Substrate

The examination of the roof and façade structures showed that greenery or the substrate layers significantly buffer the heat flow towards the building envelope during summer. On hot days, negative heat fluxes were measured in wall-based, irrigated systems. This indicates outward heat emission from the building envelope and an active cooling effect due to the moist substrate and the vegetation layer.

In the case of living walls with automatic irrigation, the heat flow from the building envelop outwards is amplified. A high substrate saturation of the green roofs (e.g. after rain events) particularly increases the thermal inertia of the structure and prevents temperature peaks in the component.

Conclusions and outlook

The HEDWIG results confirm the high effectiveness of building greenery as natural cooling systems and radiation shields as reported in many international studies (Jalits et Stangl 2026). The data collected were used to validate thermal building simulations. A high correlation between the measurement data and the models was found (e.g. R² > 0.99 for temperature data). Parameter studies showed that the combination of thermal inertia of the building mass and the cooling effect of the façade greening is the most effective strategy against summer overheating.

The HEDWIG project provides a novel and broad, empirically validated database for different types of building greening under real site conditions. The derived parameters enable a more precise integration of building greenery into simulation tools. All HEDWIG output is available open access to promote the mainstreaming of building greening in architecture and urban planning and to create the basis for future certification and approval processes.