Mould is a type of fungus that grows on damp or decaying matter and is often found in buildings. According to the NHS, “moulds produce allergens (substances that can cause an allergic reaction), irritants and, sometimes, toxic substances. Inhaling or touching mould spores may cause an allergic reaction, such as sneezing, a runny nose, red eyes and skin rash, and can also cause asthma attacks.” Mould is a fairly obvious and common symptom of an unhealthy home. We use the term symptom because mould is exactly that; a visible warning sign of a wider problem with how the building was built or how it is being used. Mould is typically caused some form of damp, whether that be; penetrating damp (i.e. a leak in the building fabric through which water is penetrating), rising damp (i.e. moisture rising up from ground as a result of a missing or ineffective damp proof course or membrane), or condensation (water drops that appear when moist air comes into contact with a colder surface like a wall or window). According to MOULD GROWTH CONSULTANTS (MGC) 80-85% of mould problems are attributed to condensation. Older properties constructed with solid wall construction are most prone to condensation and mould problems, but homes with conventional cavity wall construction are also susceptible especially where insulation and ventilation are inadequate. In such properties, it is still common to find damp and mould forming on window panes, or around windows, or in corners because of cold bridges – i.e. areas in the building envelope where a gap in the insulation that allows heat to escape and cold to pass through. Homes built with modern methods of construction (MMC) often use more insulation and achieve greater u-values but careful detailing is still required to limit cold bridging.