Commerzbank, Frankfurt

A client's decision to build high, rather than just high-density, is liable to be a high-energy one because of an adverse environment, and the difficulties of using natural ventilation and drawing light deep into the plan. If we decide to build high around the world, then Foster's response is an informative model. It is the fashion of height that needs questioning environmentally.

Both bank and Unit 1 on the Eco Park are appropriate to their location. The bank for its density and central location that potentially reinforce the city as a hub and increase the viability of public transport (though it is sometimes said that Germans love their cars more than their children). The Eco park is a focus for local work, deliberately kept small, a maximum for four units.

Embodied energy is typically less significant than transport energy, but not to be ignored. For these two buildings there is no comparison. One crude but reasonably effective indicator of embodied energy is the building cost, the cost of resources going into it. The bank's cost/m2 is three times that of Unit 1. The Unit 1 designers have worked at reducing embodied energy, as well as collecting a full set of 31 BREEAM points. A study of embodied energy in Unit 1, carried out for the client by Davis Langdon & Everest, concluded: 'Nearly all of the individual elements (of the building) have close to exemplary low initial and lifecycle embodied energy and CO2.' This is attributed primarily to the use of locally manufactured low mass construction and the avoidance of energy-intensive fit-out.

In operation, Unit 1 promises to be robust because of its near-domestic simplicity, while the bank is highly dependent on sophisticated building management equipment and people. However the occupants of both buildings should find them operationally legible. The way the bank works in energy terms for occupants and how they can intervene looks more intuitively obvious than many a domestic central heating system and its controls.

What these buildings may symbolize environmentally is somewhat paradoxical. The Bank does make a stand for low energy with natural ventilation and daylighting, but the abiding image is of the gardens in the sky. Why do we need the rural tokenism of trees 150m in the air, and talk of (aerial) villages , as though architecture is not enough to feed the human spirit? It suggests that real green is somewhere else, that the green road is back to nature.

While Unit 1 does draw on local materials and minimise their processing, it does not always say that the most natural materials, the most raw, is the greenest. It embraces a range of prefabricated components and assemblies. And with its materials, for example, it deliberately caps the timber roof lights with aluminium to improve durability and cut maintenance. In its rural context it is the most avant-garde building around. It suggests that the green road is forward to nature, a new interpretation.