The location of the building site itself has an impact on the quality of indoor air. In cities, fine particulate air pollution is usually far higher than in the countryside. Near urban parks, however, it can be reduced by the filtering effect of trees and shrubbery. Ozone concentrations following summer smog can also be lower in the vicinity of green spaces. In contrast, high ozone levels often occur in less green areas and, with a time delay, in areas outside the city.
On the other hand, suburbs where there are few trees can be more suitable to live for people who are allergic to pollen. Wetlands adjacent to streams, waterways and bodies of water as well as forests with their shady and moisture-rich atmosphere are commonly ridden with mould spores.
A special issue is the increased level of radon pollution in areas of volcanic origin. Radon is a radioactive gas that escapes from the ground. As the gas is heavier than air, it gathers in basements and in the lower layers of indoor air. When it breaks down, the gas releases alpha radiation which, when inhaled, is carcinogenic. If an examination of the ground shows that 100 Bq/m3 is exceeded as an annual average, special attention must be paid to making basements impermeable to both air and to humidity.
During the preliminary design phase, the planner should take into account the spatial interrelationships between rooms and the consequences thereof for indoor hygiene. For people who are allergic to mildew, it is advisable that household waste be removed via the shortest route. The kitchen should therefore be as close as possible to an entrance to the home. Moreover, during cooking, emissions occur that can often be unhealthy. A kitchen as a separate room with a suitable extractor fan is therefore preferable for health reasons.
A central air purification system is an important element of healthy indoor rooms; not only for allergy sufferers. It removes house dust, mite excrement and the like from the air and deposits them in a central collecting vessel. The used air is efficiently filtered and blown outside the building.
The ventilation system is another fixed component of healthy buildings. Systems with short pipelines are preferable, especially for fresh air coming into the individual rooms, as they are easier to maintain. The longer the pipe system and the less accessible it is, the more difficult it is to maintain and clean the pipes.
Where possible, building materials tested by well-known testing agencies and institutes (eco-Institut, natureplus e.V., Eurofins) should be used. However, blind trust in labels and quality marks is not advisable as only individual tested building materials are available but no product systems for complete layered structures. Use of such materials can lead to chemical incompatibility of the different building products or even to technical construction problems. Tested systems from one manufacturer are therefore to be preferred over individual building materials from different manufacturers.
The planner must also carefully consider where the respective material is built into the building. The nearer a material is to a surface on the inside, the greater is the probability that it will release its components into the indoor air. The Sentinel Haus Institut has developed an evaluation matrix that categorises the building materials in relation to their position in the building and the amount used (Ill. 7).
The realisation that ‘eco is not automatically healthy’ is important. Coatings made of renewable raw materials can emit large amounts of solvents. In spite of this, a lot of building products made of renewable, or mineral raw materials and tested by independent agencies have some outstanding qualities in terms of healthy living. For a safe choice of building materials, it is essential to make sure that they have been subjected to reliable and independent emission tests.
Construction sites of buildings in which a particularly high indoor air quality is to be achieved are especially in need of supervision by the site manager. On the basis of the delivery notes, the exact product codes on the packaging and the tender-invitation/order documents, it is necessary to check that the correct products with the requested characteristics have been delivered.
From the moment when the envelope of the building is made airtight (this is usually the time when the windows and house door are installed) at the latest, the building site is to be monitored with special care. In addition to agreed indoor air measurements in the course of construction, as well as after completion, the air temperature and humidity can be monitored easily and effectively with a commercially available thermometer/hygrometer. The installation of a window-mounted ‘climate handle’ (Ill. 10), which acquires and stores ventilation data, can also be of help. The handle provides the residents with direct information on whether ventilation has been carried out sufficiently, for how long and when. Knowledge of the decay curves of important groups of harmful substances is also advantageous (Ill. 11).
The current trend towards stipulated health or sustainability goals for buildings throws up numerous legal questions. How are such goals to be agreed on in contracts? Who is liable for their achievement? Who bears what risks?
Neither ‘sustainability’ nor indoor hygiene are clearly defined terms. On the contrary, they are indeterminate and thus require clear definition for each building project. Planners and architects, in particular, must ensure clarity in the contract – if only in the interest of limiting their own liability. Frequently, general references to existing rules and systems, such as DGNB or LEED, are insufficient as these systems change continuously. The reference scale and time must therefore be specified in the contract wherever reference is made to these criteria. Otherwise, newer, stricter values than those envisaged during planning and tender invitation may be applicable at the time of the building handover. As this can be a liability trap for planners and contractors, the precise contractual definition of success in respect of health or sustainability is crucial. Neither ‘indoor hygiene’ nor ‘sustainability’ can be achieved through adherence to individual standards. They are a qualitative performance ‘plus’ that is due and whose failure can only be rectified retrospectively with great difficulty.
Accordingly, the sustainability and health goals must be specified precisely and uniformly in all the contracts with those who are actually involved in construction. This especially applies if subcontractors are employed. If so, it must be ensured that there are no gaps in the chain of liability.
‘Healthy’ or ‘sustainable’ building projects often differ from conventional ones in terms of complexity. With external consultants, auditors and certification bodies (e.g. DGNB), additional players become involved in the building process and therefore appear in the matrix of contracts entered into. A professional editing of contracts and corresponding contract management should therefore be indispensable components of all such building projects.
