Following a news article about condensation in conservatories, many asked about how mould occurs and whether your conservatory blinds are at risk.
Mould will only grow when the air in your conservatory is too cold and wet, referred to as Relative Humidity. Mould is a sure sign that your conservatory has inadequate heating and ventilation; sometimes localised to “cold spots” where there is concealed gaps or a small leak that is seeping in.
Mould only occurs in the presence of condensation. Condensation occurs when the RH is too high for the air temperature. This causes the excess water to condense on the nearest surface is at or below the dew point temperature. In a conservatory this is normally the glass.
During a typical winter evening your conservatory could easily have an air temperature of 16°C with a RH of 70%. In these conditions, by the time the air temperature reaches just 11°C the air would have a RH of 100% (saturation). And water droplets (condensation) will appear on walls, windows, floors and even furniture.
Mould requires the RH to exceed 70% for some time before it will start growing. They estimate general human comfort level as being between 30-60% RH, within a temperature range of 18-25°C.
Mould takes the appearance of small black (most common), grey or green spots. This is most commonly seen around window reveals, on external walls and at a high level in external corners.
How to avoid condensation and mould
Improve ventilation so that the air circulates by drawing in fresh air from outside; and expelling moist air from inside your conservatory. This is most achieved by ensuring that your conservatory has adequate cross-ventilation. This involves opening windows are opposite each other and trickle vents. Without adequate ventilation, no other measures will cure the problem.
Avoid Still Air Pockets
Pay particular attention to corners, behind furniture that is close to an external wall or window. Then ensure that you keep blinds and curtains open for a good portion of the day.
Check Cold Spots
Also, check the conservatory for cold spots using a RF temperature probe. Make sure to check the joints between windows and at the eaves. This is because conservatories often have gaps that are only concealed by 1mm thick UPVC trims; they may look solid, but are a common cause of cold.
Check for Leaks
Check your conservatory and house for leaks, particularly guttering and rainwater pipes. As this can cause water to seep into your conservatory, through the walls, or through tiny joints.
The Right Amount of Air Circulation
Whilst it is good practice to leave windows open for an hour a day, just enough to encourage air circulation. Do not leave them open for hours when the temperature is cold; as this will just add to the problem.
Insulation and Temperature Control
Conservatories are very poorly insulated compared to the rest of your home. As a result, they do not meet the requirements of Part L of the Building Regulations regarding heat loss. As a result, they are very much at risk of condensation. It is key to point out for the reasons stated above conservatories are exempt from the building regulation.
Additionally, ensure that the conservatory is kept at a relatively stable temperature. When the temperature is too low, it will take a great deal more heat to raise the temperature once it has reached dew point. Therefore, we strongly recommended conservatory roof blinds.
It is always a good idea to consider background heating in a conservatory; for example, underfloor heating, controlled by a separate room thermostat. This keeps the air temperature above 15°C even at night. Your conservatory will be at its coldest around 3.00-5.00am.
What about conservatory blinds?
As we have seen, mould only grows in the presence of water. But it also requires organic material on which to live. The fabrics on most blinds are completely man-made (except pinoleum.) This means the mould will only thrive on the fabric if it is dirty. The solution, therefore, is to keep your blinds clean at all times and not to allow condensation to occur.
If your blinds show any signs of mould, then you can try washing them in the normal manner. But, mould spores normally attach themselves to the fibres of a fabric at the microscopic level. This makes it almost impossible to remove them without damaging the fabric; so it may be too late by that stage.
This isn’t limited to blinds (which are actually quite resilient) but is equally true of any other fabrics (clothes, furniture etc.) so don’t delay; if your conservatory shows signs of excessive condensation (which is normal when a conservatory is new and it is drying out) then keep your windows and blinds clean, but immediately address the fact that your conservatory has insufficient ventilation and heating.
Nevertheless, we only recommend specialist fabrics that get designed to be suitable for humid environments and which are much more suited to conservatories than most other fabrics you will commonly get offered.