Insulating the bottom of the crawl space is pointless. Read why. 

Insulating the bottom of the crawl space is pointless. In addition, a dry house uses ±30% less energy compared to a wet house. Therefore, a contractor should first legally investigate whether the house is dry. If the house and crawl space is not dry, the contractor cannot install soil insulation in the crawl space without causing more damage.

The contractor intended 3 to 4°C increase in temperature of the ground floor by installing soil insulation in the crawl space. However, as the temperature increases, at the same relative humidity, the vapour pressure in the crawl space increases. As a result, there is more damage on the ground floor. Bottom insulation does not insulate the ground floor but the just the (sand) bottom of the crawl space.

Since higher vapour pressure goes to places with lower vapour pressure, insulating the bottom of the crawl space will result in a higher vapour pressure than on the ground floor. As a result, moisture absorption and hence energy loss will be higher. The insulation material in the crawl space therefore measures through wetness.

 

The International Agency for Research on Cancer, part of the World Health Organisation, has classified EPS as group 2B - potentially carcinogenic. So that's not a material you want in your crawl space.

Saturation vapour pressure is the pressure exerted by vapour in thermodynamic equilibrium with the liquid or solid phase at the prevailing temperature. This vapour under saturation vapour pressure is called saturated vapour. A vapour at a pressure lower than the saturation vapour pressure is called unsaturated vapour. The degree of saturation is the ratio of the pressure exerted by vapour to the saturation vapour pressure of that vapour at the prevailing temperature. 

Relative humidity is the ratio of the amount of vapour to the maximum amount of vapour at the saturation vapour pressure. 

 

By definition, every contractor is obliged to warn the client in time for inaccuracies in the order, which he knows or should know about, and for defects or unsuitability of items originating from the client, including the substrate for the work, also insofar as he knows or should know about them.

Read more in blog article: Contractor's liability.

 

The higher the temperature, the greater the saturation vapour pressure. A consequence of this, for example, is that the vapour pressure in a wet crawl space in summer will be much higher than in cold winter months.

 

The smaller the droplet and the curvier the surface, the greater the saturation stress. Above a flat surface, condensation occurs at a relative humidity of 100% in a relatively pure state. Contaminated water droplets already grow in a basement, crawl space or underlying cistern at a relative humidity of 95 or even 90% rH. 

 

In any gas mixture, the total gas pressure is the sum of the partial pressures of the compound gases. This is Dalton's law represented as follows: Ptotal= P1 + P2 + P3 ..., even in a crawl space, basement or car park.

The amount of each gas in a mixture can be represented as a pressure. The main constituents of air are nitrogen, oxygen and water vapour. The total atmospheric pressure consists of the partial pressures of these three gases. While nitrogen and oxygen exist in stable concentrations, water vapour concentration is highly variable and must be measured to be determined.

The maximum partial pressure of water vapour is strictly a temperature function. An example: at 20°C, the maximum partial pressure of water vapour is 23.5 mbar. The value (of 23.5 mbar) is said to be the ‘saturation vapour pressure’ at 20°C. In a ‘saturated’ environment of 20°C, adding more water vapour leads to condensation formation. This condensation phenomenon can be exploited to measure the water vapour content. 

The temperature at which condensation is formed is called the ‘dew point temperature’. Since there is a unique correlation between temperature and saturation vapour pressure, measuring the dew point temperature of a gas is a direct measurement of the partial pressure of water vapour. Once the dew point temperature is known, the corresponding saturation vapour pressure can be calculated or looked up.

 

The following table shows some values for the temperature and the corresponding saturation vapour pressure:

 

Temperature °C	Saturation vapour pressure Pa
20	2340
18	2065
16	1818
14	1599
12	1403
10	1229

 

The term ‘pressure dew point’ is found when measuring the dew point temperature of gases at a pressure higher than atmospheric pressure. It refers to the dew point temperature of a gas under pressure. This is important because changing the pressure of a gas also changes the dew point temperature of the gas.

Increasing the pressure of a gas increases the dew point temperature of the gas. 

 

Example: the air in a crawl space, at an atmospheric pressure of 970 mbar with a dew point temperature of 12°C. From the table above, it can be seen that the partial pressure of water vapour (‘e’) is 1403 Pa. If this air pressure increases to 1040 mbar, according to Dalton's law, the partial pressure of water vapour is also increased to the value of 1504 Pa. The dew point temperature corresponding to 1504 Pa is about 13°C, showing that increasing the air pressure also increased the dew point temperature of the air. 

In contrast, if a compressed gas is expanded to a lower atmospheric pressure, the partial pressure of all component gases including water vapour decreases, so the dew point temperature of the gas also decreases. The relationship between the total pressure and the partial pressure of water vapour, can be expressed as follows: P1/P2 = e1/e2

By converting the dew point temperature to the corresponding saturation vapour pressure, it is easy to calculate the effect of the changing total pressure on the saturation vapour pressure. The new value of the saturation vapour pressure can then be converted again to the corresponding dew point temperature. 

 

Sewer gas is a gas mixture produced by the fermentation of organic waste in sewage. It consists mainly of methane, hydrogen sulphide and carbon dioxide. About 30 litres of gas are produced from one person's waste every day.

Each gas has a different specific gravity and volatility. Volatile organic compounds are those that have a vapour pressure greater than 0.01 kPa at 20°C. Ammonium residue is weakly acidic. In an alkaline environment, it will behave like an acid and split off an H+ ion. The reduction results in immediate decomposition, forming ammonia and hydrogen.

CO2 44.0095 g/mol Carbon dioxide, 1.97 kg/m³; CO carbon monoxide 1.25 kg/m³; H2S 34.08088 g/mol, 1.58 kg/m³; Hydrogen sulphide is a strong-smelling toxic gas. H2S is already harmful to persons in low concentrations. The limit value in the Netherlands for H2S is 1.6ppm. H2SO4 98.07848 g/mol sulphur, 2.86 kg/m³; Methane 16.04 g/mol, 0.72 kg/m³; Helium 0.18 kg/m³; O3 Ozone 47.9982 g/mol; Ammonia gas 0.765 kg/m³; Hydrogen gas 0.09 kg/m³; Air has a theoretical molar mass of 28.97 g/mol.

 

Depending on the different types of gases present and the concentration, this can be as high as 3%. As a result, in a crawl space where domestic wastewater flows into, via leaking (adjacent) pipes, the dew point is reached 5 - 10% faster. The consequence shows itself in the floors and floors above.