Condensation Control
Condensation, Musty Odours, Black mould.
Typically observed problems:
Significant surface moisture meter readings (damp) are obtained within a property, and the levels may be generally insufficient to sustain fungal decay yet being higher than would normally be expected in an area of accommodation.
Areas of black mould growth, mildew, musty odours are noted, often behind furnishings or within cupboards, wardrobes, draws where ventilation is by nature restricted and at corners of rooms, particularly at external walls.
The air within a room acts in many ways in a similar manner to water in a tank; Imagine a large square tank of water which you place your hand into and swirl your hand around in a circular motion, the water in the middle of the tanks will be agitated far more than the water in the corners, eg. the water in the corners moves far less than the other areas. In rough terms this analogy holds true from the air in a room. Air movement in corners is far less than movement within the main space of the room, even if the room is empty of furnishings. Indeed furnishings will reduce air movement still further.
Explanation:
In the event that the musty odours, damp and black mould are present, the most probable direct cause for the damp and mould is condensation of water vapour produced by the occupants' day to day living being greater than the quantity of water vapour that the property's current levels of heating and ventilation can cope with.
The presence of condensation does not preclude the possibility of other sources of damp though it is generally advisable to deal with this issue in the first instance unless another damp source is clearly evident (such as a plumbing leak).
When a property produces more water vapour than it can dispose of on a daily basis for extended periods of time, the moisture which is not removed will build up within the fabric of the property. This build up of moisture can be thought of as a moisture debt which will require to be repaid in addition to removing the ongoing daily water vapour production within a property. Effectively the property can be in a negative downward spiral systematically adding to the moisture debt. The levels of heating and ventilation (and possibly dehumidification) require to be increased so that more water vapour than the normal daily production is removed from the building and thereby reducing and eventually eliminating the moisture debt within the building. This process is far from instant and will likely take a minimum of 8 to 12 weeks to achieve depending on the level of the problem and the magnitude of the steps taken to address it.
MOISTURE AND RELATIVE HUMIDITY
To help explain condensation it is necessary to understand the basics about water vapour in the air. A volume of air can hold a specific quantity of water vapour at a given temperature,increase the temperature and the same volume of air can hold more water vapour whilst lowering the temperature would mean that the volume of air could hold less water vapour.
Eg: Air at 10ºC is saturated when it contains 7.6g water per kg dry air and, air at 20ºC is saturated when it contains 15.3g water per kg dry air - just over double.
This relationship is know as Relative Humidity (RH).Relative humidity is the amount of water vapour in the atmosphere at a given temperature expressed as a percentage of the maximum possible at that temperature.
Or more accurately; Relative humidity is defined as the ratio of the partial pressure of water vapour in a gaseous mixture of air and water to the saturated vapour pressure of water at a given temperature. Relative humidity is expressed as a percentage.
Condensation will occur at Dew Point which the term for Relative Humidity reaching 100%, either by a change in temperature or an increase in the quantity of water vapour.
Surface condensation typically occurs when moisture laden air comes into contact with a cold surface. As moisture-laden air gets close to the cold surface it starts to cool thereby the relative humidity increases; if the air is cooled sufficiently the dew point temperature is passed and liquid water drops out the air as condensation.
It is worth noting that if other damp issues are present within a property such as damp walls or damp solid floors due to either rising or penetrating damp that these will not significantly add to the water burden in the air as such areas result in very low comparative water vapour production when compared to breathing or other water producing activities. This is highlighted by the BRE who by using a validated model showed that a "saturated" floor slab of 8sq.m in a room at 60% RH and 20oC lost around 36mls of water per day. This is very small when compared to the fact that a typical household will produce around 15 litres per day, around 416 times as much. Though such areas are likely to be cooler and more prone to condensation of moisture from other areas forming.
We have included below a small table of approximate vapour production values.
| Water vapour source in an typical house per day | Approximate water generated in litres |
|---|---|
| 4/5 people asleep | 1.5 |
| 2 people active | 1.6 |
| Cooking | 2.6 |
| Washing up | 1 |
| Washing clothes | 4 |
| Drying clothes | 4.5 |
| Bathing/washing | 0.5 |
| Approximate total | 15.7 litres |
Please note that under BS5250 properties are categorized as one of the following:
Dry Occupancy, Moist Occupancy or a Wet Occupancy, the above table would typically be referred to as a Wet Occupancy. This is an over simplification as internal vapour pressures must be taken into account though as a rough guide it should suffice.
Suggested Recommendations for condensation control
The client will typically require to increase the level of heating and ventilation within the property to combat the levels of condensation.
It is worth noting that a modest but consistent temperature is typically more effective that sporadic aggressive bouts of heat.
The practice of drying laundry indoors whither on clothes horses, over radiators or any other means other than tumble drier which is vented directly outside or has a efficient self condensing function should not be carried out.
Installation of extractor vents to kitchens and bathrooms where they have not been previously installed or the overhaul of defective units would be beneficial.
The client should give consideration to the use of a dehumidifier unit within the property, though, in our opinion, to be most effective the unit should be located in a generally central location and run on a 24 hour a day, 7 day a week cycle.
Miller Preservation can offer the installation of additional ventilation utilising positive input units such a Nuaire or Envirovent System, further information is available on request.
Miller Preservation can also offer mould control kits for the cleaning down and control of mould growth while the client implements controls for the levels of moisture within the property.
We would recommend that a significant condensation issue be addressed prior to any damp proofing works (not timber repairs), as control of the condensation levels will highlight areas, which are affected solely as a result of atmospheric moisture, and not rising or penetrating damp. This course of action would help prevent over specification of damp proofing works and potentially result in a saving for the client.
Condensation Monitoring Service
Should there be any dubiety as to the extent of a mould or condensation issue or alternatively if you are unsure whither "condensation" is an issue within your own property, a property that you let or lease Miller Preservation is pleased to offer a monitoring and analysis service.
Monitoring a property involves the temporary installation of Data loggers to record temperature and humidity, typically at a number of locations within the property for a period usually of two weeks. After which, temperature and relative humidity profiles can be produced and water vapour pressures calculated to categorize the property for daily water production and ventilation rating.
This allows the accurate empirical records to be produced in regards to relative humidity, temperature and vapour pressures to be produced and will allow for a more tailored approach for any potential recommendations.
Get in Touch
Should you need assistance regarding condensation or our Condensation Monitoring Service please don't hesitate to contact the friendly, knowledgeable team here at Miller (Preservation)Ltd on 01475 726 925 or 01475 728 118. Alternatively, email us via the form on our contact page or direct on info@millerpreservation.co.uk. We look forward to hearing from you!