This paper evaluates the private and social costs and benefits of adopting an extensive green roof as opposed to a
cool roof in an existing industrial building in Trieste (North-Eastern Italy). The evaluations from social and
private viewpoints both consider costs and benefits of refurbishments, energy consumption, and maintenance.
From the social side, the externalities derived from green or cool roofing, such as aesthetic aspects, biodiversity
preservation and natural habitat provision, carbon reduction, air quality improvement, and hydrological aspects,
are monetized using cost-benefit transfer approaches. The first analysis result is the poor convenience of
adopting a green roof compared to a cool one from the private investor's viewpoint. The second finding is the
positive net present value of the social cost-benefit analysis for the green roof compared with the cool roof, due
to the positive externalities of the former. Monetization of externalities allows calculating the economic incentives
needed to promote the spread of green roofing in the Mediterranean area. Consequently, two different
types of incentives are proposed: direct contribution for refurbishment intervention and annual reduction of
local property tax. A final sensitivity analysis using the Monte Carlo method is performed on intrinsic and
random variables, defined by triangular or uniform distributions. The probability evaluation of economic affordability
is provided from the private investor's viewpoint, first considering private costs and benefits and,
second, introducing the financial incentives for balancing the public benefits provided by an extensive green
roof.
