BAU-R-2: Green roofing of federal buildings

The picture shows the metal facade of a modern commercial building almost completely covered with a climbing plant. Click to enlarge
Greened façades and roofs have beneficial effects on urban climates and the building itself.
Source: Photograph: © Martin Debus / stock.adobe.com

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

BAU-R-2: Green roofing of federal buildings

Providing roofs and facades with vigorous vegetation systems can have several beneficial effects – for the climate in residential districts and within buildings, for buffering heavy rainfall, for air quality and for biodiversity. It can help to mitigate localised impacts of climate change. Where appropriate, the incorporation of greening systems in new – or in the refurbishment of extant – federal buildings could step-by-step extend their currently small proportion.

The stack column diagram shows the green roof in millions of square metres for the year 2017 according to three condition classes A no defects, B green roof refresh required and D extensive renovation.
BAU-R-2: Green roofing of federal buildings

The stack column diagram shows the roof greening in million square metres for 2017 according to three condition categories: A no defects, B greening refreshment required and D extensive rehabilitation. The clear majority, with around 0.5 million square metres, is assigned to category A, 0.26 million square metres require refreshment of the greening, and 0.02 million square metres require extensive renovation. The share of the flat roof area is given over one point at 9 percent.

Source: BImA (electronic property management system)
 

Greened buildings – good for adaptation to climate change and for biodiversity

The greening of urban areas is not restricted to parks and park-like areas or to the greening of roadsides and private gardens. Façades and rooftops of buildings also provide a lot of space for greening. For facades there is a range of greening options from climbing plants to densely planted vertical gardens. Building statics permitting, roofs can also be planted extensively with a great variety of largely self-maintaining vegetation ranging from mosses, herbs and grasses to dense planting schemes with crop species, shrubs or trees.

Resilient greening schemes on roofs and facades can have multiple effects which are capable of mitigating adverse impacts of climate change thus benefiting individual buildings and properties. In urban areas these beneficial effects can also be transmitted to the environment of the buildings concerned.

This applies for instance to the cooling effects of greened buildings. By reducing the irradiation of sunlight and plants evaporating water through their leaves, greened roofs and facades effectively cool down buildings as well as the surrounding air. On one hand, this is beneficial to users of buildings on hot summer days or during periods of great heat. On the other, the urban environment also benefits from the absorption of irradiated energy and the transpiration processes taking place in greened buildings resulting in a reduction of the warming process, especially in densely populated and built-up urban areas. NB: The evaporation effect and any associated urban climate effects can only materialise provided the substrate of ‘greened’ roof vegetation contains moisture. This has to be taken into account especially, where greening is done extensively, because as a rule, this type of greening is maintenance-free; however, in hot summer months it may require watering. Another beneficial impact is the air-quality effect of greened roofs and facades. The vegetation surface slows down the air current so that particulate matter and pollutants can easily precipitate.47

Green roofs also serve a useful purpose in downpours. Depending on their design, green roofs can potentially store considerable amounts of rainwater for gradual evaporation once precipitation stops. With a view to potentially frequent and more intensive heavy rainfall, greening systems provide a buffer which absorbs rainwater like a sponge thus slowing down the water cycle. This helps to take the pressure off drainage systems for individual properties or urban districts and protects them from overload situations.

Furthermore, greened roofs and façades contribute to the protection of components of buildings and entire modules. For example, they can reduce damage from heavy rain and hailstones to facades and roofs, and they slow down or prevent the weathering of roof seals. As a ‘bonus’, greened roofs and facades also provide habitats for flora and fauna. Such greening systems provide nesting and foraging spaces for birds, wild bees, butterflies and ground beetles thus increasing biodiversity.

Numerous towns and cities therefore subsidise the greening of roofs and facades either directly or indirectly and have incorporated relevant regulations in their development planning. For its part, the Federal Government has adopted an objective regarding real estate under its own remit, to explore and – where appropriate – implement more greening systems in future development projects.48 In doing so, the Federal Government has also adopted the function of role model for other stakeholders in its capacity as developer and proprietor.49

There are no meaningful data available on the distribution of greened buildings or on municipal funding programmes. Against this background, the indicator represents a makeshift aid intended to illustrate the status and proportion of green roofs, or more precisely, greened flat roofs on federal buildings. To this end, the indicator is based on data provided by the Institute for Federal Real Estate (BImA) which owns more than 18,000 premises and 30,000 buildings, thus administrating the major part of federal real estate used for military and civilian purposes. The data represent the outcome of the simplified assessment of structural condition as used by the BImA continuously in assessing the structural preservation of all buildings in its remit.

The initial status illustrated for 2017 shows that currently only a minor part of federal buildings are fitted with green roofs, i.e. approximately 9 % of the flat roof area or just under 5 % of the overall roof area. The successive extension of this coverage in terms of new buildings and refurbishment projects might provide a starting point for the Federal Government – in individual cases – to get gradually closer to achieving the goals set for the adaptation of federal buildings and properties to climate change and to promote biodiversity.

47 DDV – Deutscher Dachgärtnerverband e. V. 2017: Multitalent Gründach. Online-Informationen des DDV zu Gründächern. BBSR (Hrsg.) 2015: Überflutungs- und Hitzevorsorge durch die Stadtentwicklung – Strategien und Maßnahmen zum Regenwassermanagement gegen urbane Sturzfluten und überhitzte Städte. Ergebnisbericht der fallstudiengestützten Expertise „Klimaanpassungsstrategien zur Überflutungsvorsorge verschiedener Siedlungstypen als kommunale Gemeinschaftsaufgabe“, Bonn: 37, 43. Tröltzsch J., Görlach B., Lückge H., Peter M., Sartorius C. 2012: Kosten und Nutzen von Anpassungsmaßnahmen an den Klimawandel – Analyse von 28 Anpassungsmaßnahmen in Deutschland. Climate Change 10/2012, Dessau-Roßlau, 209 pp.
48 BMUB (Hrsg.) 2017: Weißbuch Stadtgrün – Grün in der Stadt – Für eine lebenswerte Zukunft. Berlin: 42ff.
49 Die Bundesregierung (Hrsg.) 2011: Aktionsplan Anpassung der Deutschen Anpassungsstrategie an den Klimawandel. Beschlossen vom Bundeskabinett am 31. August 2011: 34.

 

 

Interfaces

GE-I-1: Heat exposure and Public awareness

BAU-I-1: Heat stress in urban environments

BAU-I-2: Summer-related heat island effect - case study

BAU-I-4: Heavy rain in residential areas

 

Objectives

Reducing the increasing climate-related heating effects in towns and cities and associated heat stress by means of appropriate architectural design and spatial planning (DAS, ch. 3.2.1)

Distinct increases in greening entire housing estates including the immediate environment of residential buildings (e.g. greening courtyards, small green spaces, greening roofs and façades by 2020 (NBS, ch.B 1.3.3)

Striving for an exemplary building industry by 2020 guided by standards compatible with biodiversity conservation (NBS, ch. B 2.2; StrÖff, ch. D.7)

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 adaptation to climate change  KomPass  monitoring report  space heating  energy consumption  renovation  thermal insulation