For many years, environmental questions have been central societal concerns. Consequently, increasing attention is paid to energy consumption in general. The real estate sector has not escaped this trend. Indeed, residential and commercial buildings account for 40% of the European Union's total energy consumption. Moreover, as the real estate sector is expanding, particular attention has been paid these past few years to means of reducing energy consumption in the sector and promoting the use of energy produced from renewable sources.

In order to achieve these goals and allow the European Union to conform to the Kyoto Protocol, the European Parliament and the Council of the European Union adopted on 19 May 2010 a new directive on the energy performance of buildings. This directive reiterates the obligation for the Member States to put in place a certification system for the energy performance of buildings and to provide such a certificate upon the sale or lease of the building. It also requires all new buildings occupied and owned by public authorities to be nearly-zero energy buildings by 31 December 2018. This deadline is extended to 31 December 2020 for other buildings.

Alongside these legislative initiatives at the Community level, various private initiatives have been taken in the construction sector over the past few years in order to encourage property developers and building owners to take into consideration the environmental impact of future buildings. In this context, various environmental certification programmes for buildings have been introduced in Belgium (mainly Valideo, BREEAM and HQE) for the purpose of measuring and objectively publicising the "sustainability" of buildings.

However, energy performance certificates and environmental certification programmes for buildings are primarily concerned with a fixed point in time (even though, for certification purposes, the future use of the building is taken into account, to a certain extent).  The effectiveness of these instruments can thus be diminished when the occupant of the building does not use it in an environmentally responsible manner and fails to respect its specificity. An owner which has obtained environmental certification for a new building must thus impose on the occupant(s) certain standards of use in order to ensure that  the sustainability objectives are met in the long term. Likewise, it makes no sense to acquire a building whose energy certificate indicates high-quality performance if the occupant makes completely unreasonable use of the energy produced by the building.

When a building is used by a third party, the lease agreement is the main legal instrument governing the owner-occupant relationship. When the building in question is "certified" or has extremely good energy performance, it is in the lessor's interest to work out a form of cooperation with the lessee by including in the lease agreement specific clauses intended to maintain and achieve the building's environmental objectives.

Pursuant to the principle of freedom of contract, provided the mandatory provisions of specific legislation governing principal residence leases and commercial leases are respected, the parties are free to determine, for example, objectives with respect to energy and water use in the building, the treatment of waste, etc. These objectives can either be worded in a general manner or more specifically detailed, mentioning target figures to be achieved. The parties can also specify in the lease agreement how they plan to achieve these objectives (e.g. undertakings with respect to energy, water and electricity consumption, waste production and recycling, the manner of performing development and maintenance works, etc.) and oversee their achievement (sharing of information and data, regular environmental audits). The additional costs associated with this type of lease can either be borne in full by the lessee, who will benefit from the savings associated with reduced energy consumption, or determined on a lump-sum basis, in which case any possible reduction in costs will benefit the lessor. One compromise solution would be to determine a fixed amount to cover these costs for predefined use of the leased premises, with any savings or additional expenses being shared equally by the lessor and the lessee.  

A building owner that wishes to guarantee the long-term energy performance of its property should thus pay special attention to the relationship with its tenant. To this end, it can use in the lease agreement the instruments developed in the field to ensure productive lessor-lessee cooperation.