Moisture source Green roof

[Theasjo]

Hi,

I try to investigate the moisture level in a green roof using WUFI Pro and have followed the guideline for extensive green roofs. The guideline says that the moisture source should be added to the lowest 2 cm of the substance, with a fraction of 40%. I have some questions regarding this that I can not seem to find any information about:

1. Why is it necessary to add a moisture source in the green roof? What effect do this have?
2. Why should the moisture source be added to the lowest 2 cm of the substrate? What difference would it make if we, lets say, added it to the lowest 4 cm of the substrate (if the substrate is 8 cm) or even the whole substrate?
3. Why should it be 40% fraction of driving rain? What does this tell us?

Thank you so much in advance for your help.

Best regards,
Thea Johannessen

[Beate Stöckl]

Hi Thea,

in order to take into account that the rainwater is not only absorbed by the substrate through the capillary action, but also seeps or flows through it, an additional moisture sources must be placed in the lower 2 cm of the substrate. Good results in comparison to the measurements were achieved with 40 %. The exact amount is of little importance since the source is used for complete humidification in the event of precipitation and is limited to the free saturation of the material. So a constantly high humidity under the substrate layer can be ensured.

Best regards
Beate