Improving the indoor environment

There is general agreement that plants improve the indoor environment, by helping to hide unsightly features, personalise large spaces and provide a useful weapon in the fight against the modern phenomenon known as sick building syndrome (SBS).  No specific cause of SBS has been identified, but poor air quality, excessive background noise and inadequate temperature and light control are thought to be important factors.  Because plants have a large surface area and exchange water and gases with their surroundings, they have a unique ability to tackle many such environmental problems. In particular, plants can:

Reduce levels of carbon dioxide

Carbon dioxide can accumulate in buildings from the breathing of its occupants and the by-products of heating systems and electrical equipment. This can lead to feelings of lethargy and tiredness, especially if the room is also warm and low in humidity.  Click here to see how carbon dioxide levels vary in buildings.

Plants naturally extract carbon dioxide during photosynthesis and may therefore help to keep concentrations down.   Most species extract carbon dioxide from the air in the presence of light (i.e. during the day), but some succulents have evolved to only open their leaf pores in darkness (during the relative cool of the desert night) as  a way of reducing water loss.  Their use to remove carbon dioxide in occupied buildings would, therefore, be limited. 

You should also remember that most office environments are too dimly-lit for photosynthesis to take place at rates anything more than is sufficient to keep most plants 'ticking over'.  To be most effective, you should select plants that are adapted to low light conditions, as they will be physiologically quite active and thus photosynthesising.

Increase relative humidity

This should be between 40% and 60% RH for maximum human comfort.  The air inside buildings can often be a lot lower than this, especially when buildings are heated; the relative humidity drops as the air is warmed unless supplementary moisture is added.  Under these conditions the building’s occupants may become fatigued and more susceptible to SBS and other ailments.  Mechanical humidifiers are often used to increase relative humidity levels in buildings.  However, these devices can be both noisy and unsightly and can become contaminated with micro-organisms.  Plants on the other hand release water vapour naturally through transpiration and evaporation from the soil surface.  Further details can be found in module 4.

Reduce levels of certain pollutant gases

These include formaldehyde, benzene and nitrogen dioxide, which are released in small quantities by a whole range of materials and human activities. Most of the work was carried out in the USA on a small laboratory scale and there is still a shortage of scientific data taken inside "real" buildings.

Click here for further information, and see also module 4.


Reduce airborne dust levels

Research in the USA (carried out by Virginia Lohr) suggests that the accumulation of particulate matter on horizontal surfaces in interiors can be reduced by as much as 20% by adding foliage plants. Lohr’s experiments did little to explain the mechanisms at work, but suggested that particulate matter is reduced by impacting and adhering to plant surfaces.

Reduce air temperatures

As water evaporates it extracts heat from the air. Plants therefore have a cooling effect on the air around them.   The greater the temperature and the level of transpiration/evaporation the greater the level of cooling.  Research to date, principally at Reading University in the UK, suggests that the cooling effect can be significant in rooms subjected to hot summer sun.

Reduce background noise

Trees and shrubs have been used for many years to reduce traffic noise from busy roads.  Research now shows that plants can also help to reduce background noise levels in buildings.  Some plant species are more effective than others and the benefits are most pronounced in buildings with hard, reflective surfaces. Click here for more information about the acoustic benefits of indoor plants.

Soften/hide less attractive features

However well designed, most buildings have features that are best kept covered, such as service areas, storage facilities and harsh structural elements. Plants, with their wide range of size, shape, habit and leaf form provide an elegant solution that is both attractive and functional.  Containers, such as this example, were developed with this purpose very much in mind. The interlocking pots can be used to create plant 'walls' and create a continuous area of greenery around pillars and other immovable obstructions.

Draw attention to features of interest

The organic and irregular shape of plants against the rectilinear shapes of a building can attract the attention of people.  This can help you direct attention to a feature of particular interest, such as a fine detail in the building's structure or to something more mundane (but perhaps more important) like an item of merchandise that a retailer is keen to sell.

Break up large open areas

The vast expanses of open space found in airports, stations, shopping malls and open plan offices look soul-less and intimidating unless broken up by familiar objects. Plants are the most common solution, providing natural divides and reference points that make the space look more friendly and inviting.

Other benefits

As well as these tangible physical and aesthetic benefits, there is a considerable body of research that suggests that the symptoms of SBS alleviated by plants is also due to the psychosocial effects caused by a change in the environment.  A major study in Norway (conducted by Professor Tøve Fjeld) showed that self-reported symptoms associated with SBS were significantly reduced by the addition of plants to an office environment, and that such a reduction in complaints may be the result of a psychological feeling of well-being as well as a physical improvement in the indoor environment.  Click here for more information.