Designing healthy buildings

posted 24 Jul 2010, 10:41 by robert evans   [ updated 14 Mar 2012, 18:39 by Susan Gilbert ]

The existence or otherwise of ‘sick-building-syndrome’ is a matter of debate and while informed opinion is divided, it has been popularised as the result of the trend towards artificially-ventilated, hermetically-sealed building.  In this type of building, the detailing typically minimises ventilation losses through the fabric.  Reducing uncontrolled ventilation lessens the building’s ability to ‘breath’ and ‘perspire’.

Ventilation through the building fabric is likely to be lessened further by the continued revisions to the Building Regulations to require ever higher levels of energy efficiency in buildings.  The Building Regulations 2000 in part L1 stipulate a robust approach to minimising uncontrolled ventilation losses from houses and impose a more stringent approach for other buildings in part L2.   Whether or not this will cause ill-health to the occupants it certainly may harm the building fabric if done without enough thought.  This is illustrated by the developing problems of interstitial condensation which grew in pace with the introduction of energy control measures during the last century.

The traditional open fire in poorly insulated buildings, whilst inefficient, had advantages.  As the fire was built up it drew air through the room and expelled expiated air along with the smoke through the chimney.  Waste heat passed through the uninsulated walls driving out moisture.  The more vigorously the fire burnt, the better the ventilation, the higher the heat flow through the fabric and the more potentially harmful moisture was dispelled. 

The replacement of the open hearth with the distribution of heat via hot water pipes to well-sealed and insulated rooms was accompanied by an increase in condensation damage.   The better the rooms were sealed and insulated the more the condensation risk.  The heating was no longer accompanied by ventilation to remove vapour and the well insulated building envelope remained cold on its outside whilst heated internally.  The result was raised internal vapour pressures, colder parts of the building fabric and the accumulation of condensate in concealed voids within the building envelope.  Condensate has eaten through lead and corroded steel as well as encouraged organic decay and potentially harmful environments. 

As the injurious side effects the 20th century’s strides into energy efficient building were recognised, steps were introduced to prevent collateral damage.  These followed rather than preceded improvements in thermal efficiency.  The process was one of failure followed by remedy.  Further improvements in energy use, which the government promises will move on apace; risk a continuation of this process.

Certain matters are indisputably related to the health of building occupants such as the need to keep them sufficiently warm in cold climates to prevent hypothermia.   Conditions of humidity conducive to mould and fungal growths may also be seen as a health issue in that released spores may be harmful, particularly to asthmatics and those with weak immune systems. 

The creation of healthy internal environments is a critical issue in building design.   There are several aspects to this including the control of relative humidity.  The ambient humidity in a room affects many of the biological, bacterial and physical causes of ill health.  It has been argued that controlling this through air-conditioning can increase the problem.  Passive control of humidity relies heavily on the porous and hygroscopic nature of certain materials. Surfaces such as timber, plaster and clay will regulate ambient humidity as long as they are not given impervious coatings such as some conventional paints and varnishes.  With this in mind, it may be that to ensure the risks of ill health to occupants are minimised, surface coatings should be specified so as not to obstruct the natural hygroscopicity of these materials.

Associated with improved control of ventilation and the use of sealed heating systems is increasing concern over health problems caused by mould.  This has caused something of a scare in the USA.  Whilst toxic mould phobia has yet to be exported this is a potential concern to building insurers who may exclude cover for the consequences of mould in buildings leaving the designer and builder, particular of building services, in the firing line.

Mould spores cover the planet.  It is one of earths natural clean up systems, eating dead or decaying organic matter. Hundreds of thousands of mould types exist of which some 16 types have been identified to be toxic to man.  All of these have been identified in water damaged buildings.

Exposure to any mould can cause allergenic effects such as skin rash, flu-like symptoms and, on some views, depression.  It is not the moulds but the toxins they create which cause the severest risk to health.  Typical toxic types such as Aspergillus, Stachybotrys, Trichoderma create extremely toxic mycotoxins.[1]  (Known as T2 toxins these have lethal military applications). 

Toxins from mould can cause severe health problems.  Symptoms may include: sore eyes or throat, runny nose, rash, asthma, coughing up blood and nose bleeds and may, on some views, possibly lead to cancer of the lung, liver brain or kidney.

Typical mould spores are between 1 and 20 microns.  Although any particle which is less than 7.5 microns is respiritable, those under 2.5 microns can be the most dangerous as they can lodge in deep lung tissue where they can be infused directly into the blood stream.  Mould can be a health threat even when dead or inactive.



[1] The chemical contents of the mould spore are known as metabolites, some of which are mycotoxins which are in effect Microbial Volatile Organic Compounds (mVOCs).  It is these chemicals which cause health problems.

Comments