(This page was automatically translated from German. Luftfeuchte3)

Atmospheric humidity in the apartment - cause of the mold-formation

1. Interaction humidity and construction-mantle
1.1. Building material and humidity
1.2. The dew-water-formation and the humidity in the brickwork
2. Atmospheric humidity in the accomodation
2.1. Humidity in apartments
2.3. Heat-demand for energy - gas-mixture and heating (ventilation-replacement)
2.4. Case in point ventilation-heat-requirement at a single-family home
3. The dampness-production and the ventilation-replacement
   Online-calculation - atmospheric humidity, dew point and mold-formation

3. The dampness-production and the ventilation-replacement

In this model-bill, a 8-hour night-quiet is assumed where the window menus are locked. The space includes a volume of 50 , the dampness-production of the respiration of an adult human being amounts to 0,1 liters of water / hour.
Interior: Relative humidity of 50 per cent corresponds 7 g waters / , temperature 17ºC as constantly views and
Outsides: 6 g waters correspond to 5ºC with a relative humidity of 90 per cent / m3 air

DurationRelative atmospheric humidity in dependence on ventilation-part payment and people
[H.]Water / air
[g / m3]
0,3 air-changes / hour.
and 1 people
Water / air
0,3 air-changes / hour.
and 2 people
Water / air
[g/ m3]
0,5 air-changes / hour.
and 1 people
Water / air
0,5 air-changes / hour.
and 2 people
Water / air
[g / m3]
0,8 air-changes / hour.
and 2 people
0 7 7 7 7 7
1 8,5 10,1 8,3 9,5 8,6
2 9,5 12,3 8,6 10,8 8,9
3 10,2 13,8 8,8 11,2 9,0 (about). 61 %)
4 10,6 14,3 (100 %) 8,9 11,6 9,0
5 10,9 14,3 (100 %) 9,0 11,8 9,0
6 11,2 14,3 (100 %) 9,0 (ca.61%) 11,9 9,0
7 11,3 14,3 (100 %) 9,0 12,0 (ca.83%) 9,0
8 11,4 (ca.80%) 14,3 (100 %) 9,0 12,0 9,0

It becomes clear that a ventilation-replacement is to be looked very critically at under 0,5 h-1 since the constantly climbing atmospheric humidity cannot be led sufficiently away. The ventilation-replacement should be least so big that the produced humidity doesn't rise further. If the space-volumes are smaller, is so to be increased also the ventilation-part payment. (That also through an easily opened door to the neighbor-space or to the hallway can be, with what all so big temperature-differences should not be available here.) Now, one has not the above named ideal-status but continuous climatic changes and also more moisture-sources in the apartment. Per sorptionsoffener the wall-construction-materials and wall-coatings respectively are, so better are picked up the moisture-apexes and are handed over again on the day. The relative humidity doesn't rise so strongly presented at, as in the above named arithmetic-case in point with it, for example.
Additionally one also must mention, the craftspersons would produce really such airtight houses, as it is challenged after the EnEV, so an in due form poke-ventilation would have to take place in many bedrooms at the latest every 3 hours, will reckon with precipitation theoretically at the morning hours otherwise.

On the basis of the Mollier-h, x-Diagramms and the Isoplethensystems [1] can be checked these statements about the interaction dampness, temperature and Enthalpie as well as the borders of the spore-end-germination of the molds. Through this environment-federation's exchange [2] in a small brochure of named statements about the moisture-statement and the necessary daily ventilation interconnected with it of 7 times daily (corresponds to 0,3 h-1), is not correct. Would proceed so, so the result can be taken in the above named table in the cleft with this low ventilation-part payment.

With two examined cases, it admittedly had not dripped from the bedroom-cover, but the mold grew in every corner. Here too much humidity was simply produced during the night-quiet and through the dense window menus, no sufficient moisture-replacement could take place.
This connection can with the calculation-tool, for example to the mold-formation is checked.

- Calculation -
Atmospheric humidity - dew point - mold-formation

(Instead of comma input decimal point.)

Space-temperature (input value)  °C  
Relative humidity (input value)  % 
Air pressure p  devoid of 
Full-steam HP
(For the calculation necessary.)
 devoid of 
Absolute dampness  kg / kg air
Absolute dampnesscorresponds, for example  g/m3Luft
Dew point of the cool wall-surface °C
Possible mold-formation of the wall-surface * °C

*)This value serves as bearings and is coordinated on a space-temperature with more normally space-dampness between 20 - 15ºC by 50 per cent. With higher space-temperature and a high humidity, already reinforced mold-growth occurs. Therefore, the temperature of the ambient air and the wall-surface is equated. Please also heed that a possible mold-formation of the food-substance (wallpaper) and from the term of the encumbrance depends. They here also under molds and its metabolites

All values are without engagement.

Complementary contributions
Space-climate role of the air-movement
Space-climate role of the atmospheric humidity
Absolute atmospheric humidity
Relative atmospheric humidity

[1] Sedlbauer, K.; Krus, M.; Holzkirchen, Schimmelpilze an Wohngebäuden - Altes Thema, neue Lösungen -, Vortrag auf 3. Dahlberg-Kolloquium, Mikroorganismen und Bauwerksinstandsetzung, Verlag Bauwesen Berlin, 2001, S. 38 - 47
[2] Umweltbundesamt, Fachgebiet II 2.3., Innenraumhygiene, Fachgebiet II 2.3, Mikrobiologie Berlin, Hilfe! Schimmel im Haus, Ursachen -Wirkung- Abhilfe, S. 14
[3] Buss, Harald; Das Tabellenhandbuch zum Wärme- und Feuchteschutz, 2002 WEKA Bauverlag, S. 287
Rauch, Peter; Schimmelpilzbildung und Wärmebrücken - Allgemeine Darstellung und das Aufzeigen konstruktiver Mängel beim Dachgeschoßausbau 1994
Meier, Claus; Der sinnvolle Gebäude - Wärmeschutz - Konzeption und Nachweis, RKW Merkblatt 68, S. 3, in Wirtschaftliche Energienutzung an Gebäuden, RKW-Verlag 1989
DIN 4701 Regeln für die Berechnung des Wärembedarfs von Gebäuden
Bobran, Handbuch der Bauphysik, 7.Aufl. Verlag Vieweg 1994, S. 76

Divide 1  2  3

Ingenieurbüro Baubiologie Peter Rauch

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