The average bunker tank system will cost several thousand pounds. The primary goal is to prevent groundwater, but how often do we think about naturally occurring indoor atmospheric humidity? We ignore this at our peril. Basement cistern and other forms of basement waterproofing can react with moisture and cause condensation problems… My last article on basement cistern and condensation looked at what condensation is. Condensation occurs anywhere humidity and temperature combine to create the “dew point.” So we need to look at those specific factors in a tank or waterproofed cellar that cause temperature and humidity to converge in this way.
Temperature
Waterproof coatings or films are usually not thermally effective so it can get cold. It is usually applied to the inner surface of the exterior walls during cellar conversion or basement waterproofing project to keep it cooler. If we put an insulation in front of the waterproof membrane, this insulation makes the cold static (the insulation keeps the heat in the room and thus away from the membrane).
heating patterns
If the basement or cellar is heated on an infrequent basis, it can lead to periods when the temperature is too low for condensation to be avoided.
moisture
The moisture vapor in the air will move in all directions, so the moisture vapor not only comes to the basement or cellar from the ground outside, but also goes from the inner air space of the cellar or basement to the outside. An effective waterproof barrier (reservoir system), designed to be effective against groundwater ingress, will also prevent internal moisture vapor infiltration. Ventilation of underground rooms is usually more difficult due to the lack of windows and doors. General life generates damp vapour, and even breathing and sweating, also cooking, drying clothes, boiling kettles with shower or bath without sufficient suction all contribute to indoor moisture vapor. This in itself is not necessarily a problem. It only becomes a problem is which part of the cellar or basement as the temperature is equal to or below the dew point temperature and the most likely location for the (cold) dew point temperature is the waterproof barrier itself. In my own professional experience, I’ve seen many cases of good basement conversion and basement waterproofing projects ruined by condensation.
In my next article, I will examine the damage it can do, not only to the fabric of a building, but also to the health of its occupants.
In the meantime, to learn more about bunker tank problems and how to avoid them, click here bunker cisterns.