Condensation In Buildings Is Not
Condensation in buildings is not uncommon when considering domestic properties. It can best be described as “a form of dampness caused by water vapour in the air. Among the effects of condensation are misting of windows, beads of water on non-absorbent surfaces, dampness of absorbent materials and mould growth.” (McMullan and Seeley, 2007).
Building design is increasingly trying to improve the efficiency of a house and reduce a building’s carbon impacts on the environment. “Building energy efficiency can provide key solutions to energy shortages, carbon emissions and their serious threat to our living environment.” (Cao, Dai and Liu, 2016). This is most evident in the increase in the level of insulation installed within properties. As buildings develop greater levels of insulation, and so can more easily raise the temperature of the air within the property, the problem of condensation occurring becomes more likely. As the temperature of the air rises, its capacity to hold water vapour is also increased. An increase in the amount of water vapour within the air results in an improved likelihood of condensation throughout the building.
The main problem with detecting the amount of moisture within a building is that it is not easily initially noticed. Unless specific equipment is set up throughout the property to monitor moisture levels within the air, an increase in moisture content can go unnoticed. The first time an occupant may notice an issue related to moisture content within the building, is when the effects of the moisture begin to be seen, i.e. mould developing. This means that instead of the occupant being able to take a proactive approach to dealing with the problem they must be reactive. This reaction is usually to deal with the symptoms caused by the moisture, not to address the underlining problem itself. This means the problem then becomes a recurrence within the property.
Condensation can be classified into two main types; surface condensation and interstitial condensation.
Surface condensation can occur on walls, doors, windows, floors and ceilings. It usually displays itself as either a film of moisture across the body of the surface or as individual beads of liquid. Non-absorbent surfaces will show condensation more clearly, whereas absorbent surfaces will instead show patches of dampness. These damp patches are due to the absorbent materials allowing the ingress of the condensation. Because of this, absorbent surfaces only tend to show signs of the presence of water after repeated or persistent condensation.
Interstitial condensation refers to moisture within the construction of a building. Domestic buildings tend to consist of external materials which are permeable to water to a certain degree. They allow the passage of water vapour through the external materials (i.e. block and brickwork) through air ingress. As the air passes through the building it may reach its dew-point temperature and condense within the layers of the structure. This is displayed in Figure 1.1.
“The moisture capacitance of a building’s materials is important for predicting the indoor humidity.” (Woods and Winkler, 2016). This means that during the design phase of a domestic property each individual material used must be considered as to how it will affect the humidity within the building. This means considering how much moisture a material may retain and for how long, and how permeable a surface will be.
An example of this is most modern constructions use Portland cement based materials between bricks instead of traditional lime mortar. Although Portland cement boasts a higher compressive strength and a quicker setting time than lime based mortars, it is also impermeable to water. Due to this feature of not being able to permeate, water vapour is not as easily able to pass through external walls compared to if lime based materials were used. As moisture travels from high vapour pressure (usually inside a building) to low vapour pressure (usually outside air) it would normally pass through the walls. This cannot occur as effectively using cementitious materials, and so cannot be used as a method of regulating humidity within a property.
Methods of prevention
Causes of condensation within a building can vary. If the building is not airtight enough, water vapour can enter through the outer building envelope. Inadequate ventilation in a building can result in too few air changes per hour; this in turn can also lead to moisture build ups within the rooms of the building. Likewise, if a building is not evenly ventilated, so one room is subject to more air changes than others, “results revealed that overcooling the air-conditioned side increases condensation risk on the non-air-conditioned side of the envelopes”. (Ali et al., 2016). This means if one room is subject to a higher level of air changes over a time period then it will create an instability in the air pressure and the moisture will more likely condense on the barrier between the areas of higher vapour pressure and the lower vapour pressure within the house.
Surface condensation throughout a building can be remedied using several different methods; or most effectively a combination of them.
Appropriate ventilation for a domestic building helps to remove the moist air from the property. If the moist air is removed from the building, then it does not have the opportunity to develop into condensation. Ventilation can either apply to the exact source of the moisture (such as an extraction fan in a bathroom or kitchen) or it can be house-wide. Mechanical ventilation for a building does have some advantages over natural ventilation, such as the opening of windows, which can result in further moisture entering the building. When ventilating, care must be taken to provide air currents that pass through the building; otherwise the moist air could simply be relocated to a different room in the house.
Heating the entirety of a property raises the surface temperature in all rooms. This can aid in maintaining a temperature above the dew-point of the moist air, preventing the build-up of condensation. When air is heated within the house it also has the ability to hold more moisture, meaning larger quantities of moisture can be retained within the air before saturation is reached and the water vapour condenses. When possible the materials and surfaces within the domestic building should not be allowed to cool completely. This can be done by maintaining a constant temperature and reducing any extreme fluctuations.
Heating the property can be done more effectively with the use of appropriate insulation. When selecting an insulation type it is important to consider the thermal resistance of the materials used. A higher thermal resistance means that the insulation is more effective at preventing heat transfer. Efforts should also be made during the design phase of a buildings construction to reduce any thermal bridging which may penetrate the insulation layers. The more effective a building is at retaining heat, the lower the impact both financially and in terms of carbon output will be.
Applying the previously mentioned methods can greatly decrease the likelihood of condensation within a building. This can be done most effectively by combining these methods. Insulation will allow the property to retain heat more easily, this in turn will reduce the amount of heating required to raise temperatures above the water vapours dew point. The moisture burdened air can then be extracted by the ventilation system in place within the building. The more efficient ventilation system used, and the more appropriate the insulation layers selected, the lower the carbon impact will be from the building as a whole in terms of both heating and moisture removal.
It should also be noted here that if ventilation is over used in moisture removal it can also have negative effects on the buildings occupants. Over use of ventilation, specifically mechanical, can result in excessive removal of moisture from the air within the building. If this is the case it can cause discomfort for the residents. This can take the form of symptoms such as the irritation of eyes or other orifices and nasal cavities.
As already stated the presence of condensation within the building can have negative effects throughout the building, for both its structure and its occupants.
A by-product created via the condensing of water vapour throughout a property is mould spores; which have been linked to the deterioration of health. Studies have found “indoor mould exposure was consistently associated with adverse respiratory health outcomes in children living in these diverse countries.” (Antova et al., 2008). The journal mentioned looked into the effects of mould grown on children from a variety of nations and geographical locations. This highlights that mould growth due to condensation within domestic properties is not a just a regionalised issue.
Further evidence that condensation related mould growth is not constrained to areas subject to certain environmental conditions is provided by “Mould growth on building materials is a phenomenon experienced by inhabitants all over the world. It is a performance failure caused by the interaction between the environment and building envelope leading to unhealthy and uncomfortable living conditions.” (Pietrzyk, 2015). This highlights that mould developing does affect residents and create an uncomfortable living environment, but also has implications to the buildings performance.
As well as influencing the occupants of a domestic property, moisture can also affect the structure of a building. Condensation forming on timbers within a building can result in the development of both dry and wet rot. Although dry and wet rot are both caused via the development of fungi, and so can be classified as fungal decay, they are not caused under the exact same conditions.
Wet rot is reliant on moister conditions. Whereas dry rot can cultivate under circumstances where the moisture content of the material reaches 20%, wet rot needs a higher moisture content of 50% to begin growth.
Wet rot is more easily treatable as it can be removed by the extraction of the source of moisture. Once the moisture has been removed from any infected timbers the wet rot will die back and not be able to spread to any further surfaces. It may still leave the original timbers in a structurally unsound state resulting in their removal.
The treatment of a dry rot is not as straightforward as the removal of the moisture source. Once the growth of the dry rot has begun, it can spread to surfaces where the moisture content would not be considered feasibly high enough for decay. Summary
The development of condensation within domestic properties will continue to be a problem due to modern designs and construction techniques, such as an improved use of insulation within a building or the use of cement bases mortar instead of lime based. However, these same modern techniques can also be used to combat the condensation ingress. The use of appropriate ventilation specified in the design phase and the improved quality of workmanship on site are just some of the methods which can be used to reduce condensation and its associated complications.
The use of these techniques to remove moisture from a building to reduce the risk of condensation mean that materials of high insulating value can still be used to maintain a low carbon and low energy house, without having to infringe upon the comfort of the occupant or structural stability of the building.