Mould growth in your building: Not with UdiINSULATION SYSTEMS!
06.December 2010

Mould growth in your building: Not with UdiINSULATION SYSTEMS!

Black spots in the corners of the bedroom, dark patches under the window in the bathroom:   Mould growth on walls is a common problem.

Air-tight construction methods and thick insulation layers save energy in buildings.


However, developers are increasingly finding that this method of building leads to problems of mould growth. Unfortunately, most buildings are still insulated with traditional insulation materials. These save energy but cause problems due to excess moisture as they are not vapour permeable. This leads to mould growth! More and more developers are contacting us and informing us about this ‘black phenomenon’ despite the fact that the external walls are insulated.


Our answer to this problem:

In correctly insulated buildings using Udi INSULATION SYSTEMS, there is no mould growth development. We even provide you with a ‘mould-free’ guarantee. Simply contact us for more information – we are happy to be of service. Mould is a fungus and needs moisture in order to grow. Scientific tests have shown that mould grows best at humidity levels at and above approximately 70%. Mould can occur due to building damage, for example due to a leaking roof or a faulty pipe in the wall.


The most common cause of mould development however is due to room air moisture. If the interior side of a wall is cold or oversaturated after a long period of cold weather, the circulating air that comes into contact with these surfaces is no longer able to retain its water vapour. This condenses and supplies the fungus with the necessary moisture it needs to grow. The worse an external wall is insulated, the colder the interior side will be and consequently the quicker mould can develop due to condensation. In very many cases mould develops in the areas of so-called ‘thermal bridges’ through which the exterior cold finds an easy path into the interior of the building i.e. in window reveals or where a balcony adjoins the property. The problem is however increasingly evident in traditionally insulated buildings.


As a consequence, there are always two main factors to consider when combating mould growth: the room humidity must be reduced and the correct type of exterior wall insulation must be selected. The first can be achieved by regular ventilation, which unfortunately may lead to higher energy losses. Cold air can not retain as much vapour as warm air. Therefore periodic ventilation in which the warm room air is replaced by cold air from outside i.e. opening windows or doors for short periods, can lead to a reduction in the humidity level as this cold air warms up and absorbs the new moisture. Continually having to remember to ventilate the rooms is not however a sensible, permanent solution. A better approach is to use our highly vapour permeable wood-fibre insulation materials. These do not hinder the accumulated moisture from drying out and thereby actively counter the development of mould growth.


Many older buildings partially achieve this exchange of air independently: Warm air continuously flows out of the building through poorly sealed windows and is replaced by the cold exterior air. An air exchange through the walls is not however generally the rule – the wall must have holes in it! The amount of moisture that is transported via the walls is minimal in comparison to that which is transported in the air: ‘walls that breathe’ which supposedly transport large volumes of air moisture to the outside of the building simply do not exist. A wall can, at best, only absorb air moisture for a short period of time and therefore only serves as a ‘climate buffer’.


It is a fallacy that an air-tight insulated building leads to mould growth development. One factor that has led to this widely-held mistaken belief is that in many older buildings the windows are replaced before the external insulation is installed (which is usually a far more expensive and involved process). These modern, air-tight windows prevent the previously available ‘forced ventilation’ and the humidity in these rooms can rise rapidly – if this is not counteracted by the occupants through regular manual ventilation – and moisture and mould can develop on the still poorly insulated exterior walls.


The solution for most mould growth problems is therefore good exterior wall insulation. This eliminates thermal bridges and the cooling of the external walls which prevents the development of mould. This is proven by the extremely well insulated and hermetically sealed passive houses in which mould growth is almost unknown.


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