Mould and ventilation management

Mould will always mean there has been (or is) significant dampness present – but there are many possible reasons for dampness. Many companies market products to eliminate condensation, but mould can develop from other causes:

• condensation;
• a plumbing leak;
• penetrating damp;
• rising damp;
• following a natural flood;
• fabrics/clothes etc. become damp from damp air; and
• other sources, e.g. trapped moisture, construction moisture, fire fighting water, cleaning, spillage.

Mould from condensation:

Often condensation is caused by unsatisfactory heating, ventilation, insulation, or possibly 'lifestyle'. The remedy here would normally involve improving heating and ventilation of the property, sometimes applying internal or external insulation, perhaps in tandem with some acceptable lifestyle changes. Where property is rented, there is a fine line between lifestyle that is deemed acceptable and unacceptable.

Mould stemming from a plumbing leak:

This can be quite extensive if the leak has continued unknown for some time. Pipe leaks are usually easy to repair once pipework is isolated.

Mould from penetrating damp:

Areas of mould usually spread outwards from the point of water entry. It may be combined with condensation damp. It is often possible to find the cause of penetration from internal and external visual inspection.

Mould from rising damp:

Condensation and rising damp can co-exist. There may well be salts present at and near the surface of plasters subject to rising damp, but the dampness could dampen timber skirtings to create a damp micro-climate behind, conducive to mould.

Mould following a natural flood:

Mould only takes 24 hours to develop, so it is important to bring air conditions under control quickly after a flood – e.g. reduce air humidity and heat up the building interior – to prevent 'secondary mould'.

Mouldy clothes/fabric from damp air:

You will often find cases where there is not much or any actual condensation occurring on cold walls or floors, but piled up fabrics and clothes in wardrobes suffer mould because the materials are absorbent and take in water vapour from humid air. Mould takes hold with a vengeance.

Mould from other sources:

These include entrapped moisture, construction moisture, fire fighting water, cleaning, spillage etc. For example, wet timber could be built into the building structure and moisture sealed in by plastic membranes – ideal conditions for mould. Even well stored timber could be superficially damaged by 'blue stain in service' – a mouldy discoloration of blue-black streaks. See BRE guidance: Recognising wood rot and insect damage in buildings.

When is there a real mould problem?

'Significant mould' is enough mould to damage, degrade or adversely affect the appearance or undermine the performance of building material, fabric, component or finish to adversely affect use and enjoyment of the building or health and well-being of users and occupants. It can be symptomatic of an underlying/evident damp problem that needs to be remediated to reduce further or ongoing risk to the building, building occupants, users or other interested party.

There are 3 levels of mould severity that are used: 'trivial mould', 'larger areas' and 'extensive outbreaks'.

As with any other defect we survey, we may visit a property on date X, and over time the subject defect could be:

• diminishing, as the cause has already been resolved;
• more or less stable/static; or
• worsening.

It is probably true that the very minor cases of 'trivial mould' will be quite easy to identify and assess, and the serious extensive mould colonisations obvious to any surveyor, but in between the extremes are cases of mould development that are more difficult to categorise.

There will also be cases where mould has been cleaned or hidden by occupiers or building users. You can directly ask if this has taken place, or look for evidence of cleaning/remediation/cleaning materials on site, etc. Some experts advise that 70% of mould is hidden – so immediately you could have a problem if only a small amount of mould is visible without any stripping out.

Area is one way of assessing the extent of mould. Intensity must surely be another. And many factors other than area of contamination need to be taken into account, such as:

• the history of the building;
• the type of building;
• the type of material;
• whether the material is wet or dry (wet materials hold onto spores);
• health of building inhabitants (e.g. infants and women tend to react before men);
• the activity levels in building - spore movement;
• the use of building; and
• the location within building, e.g. cellar or bedroom.