Sustainable landscape architecture is a category of sustainable design concerned with the planning and design of outdoor space.
This can include ecological, politically correct, social and economic aspects of sustainability. For example, the design of a sustainable urban drainage system can: improve habitats for fauna and flora; improve recreational facilities, because people love to be beside water; save money, because building culverts is expensive and floods cause severe financial harm.
The design of a green roof or a roof garden can also contribute to the sustainability of a landscape architecture project. The roof will help manage surface water, provide for wildlife and provide for recreation.
Sustainability appears to be a new addition to the traditional Vitruvian objectives of the design process: a structure must be solid, useful, and beautiful (firmitas, utilitas, venustas). But it can be seen as an aspect of both solidity and usefulness: an outdoor space is likely to last longer and give more usefulness to its owners if it requires low inputs of energy, water, fertiliser etc., and if it produces fewer outputs of noise, pollution, surface water runoff etc.