Toxicology of Construction

This specialist discipline takes into account observation of design, adequacy of structural elements, moisture ingress, building alteration and adaptation. The internal enviroment of a building can be adversely affected by such factors. Poor or defective design, materials, construction methods and supervision can give rise to moisture ingress and poor ventilation. Poor ventilation can create conditions giving rise to condensation.

The effects of condensation are to create a medium in which fungal spores (typically measured as CFU/M3 – Colony Forming Units per cubic metre in a wide range of year round typical occurrence from 100 – 10,000 CFU M3) present in all air will germinate, reproduce and increase in number until a person with a weakened immune system may potentially become seriously ill.

Interstitial condensation is also a potential source of toxic mould. Even fully monitored and cleansed air quality within a building can then be compromised by such continuing hidden and inaccessible threats.

Moisture required to support fungal germination and growth is described as water activity scale 0 – 1. Water Activity of 0 will not support any fungal growth. (BSI 16000-19 covers sampling procedures).

Internal ventilation has to be understood in terms of air movements within a building. In the late 20th and early 21st Century, this has to be particularly evaluated within the context of many new materials included within the structure of a building its fixtures, fittings, décor, furnishings and textiles.

Condensation is potentially serious once mould growth becomes visible. Vinyl wallpapers and paint encourage growth as absorption and spread on porous surfaces is prevented. Thus modern décor can exacerbate a problem.

In older buildings construction materials such as lime plaster connected with lime joints and ‘sucked’ moisture out of a building. Chimneys would constantly ventilate and cause air movement. Gaps around doors and windows would contribute to ventilation.

Thus failing to identify condensation and undertaking damp proofing works in older properties using sand and cement internal renders would prevent this natural evaporation through masonry. Cement repointing then sealed in the external wall surface. This would then potentially cause moisture to rise within the wall. Add to this moisture rising via capillary action from the ground below where there is no damp proof course, or drying out following remedial work to install one, and a wall normally dry would potentially become damp.

Use of lime in construction largely died out after the First World War as cement took over from lime due to its quicker setting time. Thus installation of a damp proof course would stop rising damp but may encourage internal condensation and the misidentified cause of the ‘dampness’ would not be cured by a damp proof course.