kg/m² criteria

[olivir]

Hi and hppy christmas to everybody,

WUFI resumes criteria from DIN4108 which are about amount in moisture in kg/m².

German standard DIN 4108-3 adds the following criteria:

The amount of condensing moisture in roof or wall assemblies must not exceed a total of 1.0 kg/m².
This is a more or less arbitrary criterion. In order to test it with WUFI, start the calculation with the normal equilibrium moisture (corresponding to 80% RH) and see if the total water content exceeds the starting value by more than 1 kg/m².
At interfaces between materials that are not capillary-active, no moisture increase exceeding 0.5 kg/m² is permissible.

How we proceed to apply ?

I take an example :




For mineral wool (45 mm thick), max condensing moisture (2019) = (0.754 - 0.433)/1000*45 = 0,014 kg/m²
0.014 kg/m²< 1 kg/m² OK
0.014 kg/m²< 0,5 kg/m² OK (because mineral wool is not capillary active)

Is it correct ?

I think WUFI must help us more, it's not easy enough too obtain, there are not enough direct readable informations (even in Status:Last results) :/

[Christian Bludau]

Hello Olivir,

you are on the right way, but what you are doing is to access the water content as a mean value over the whole mineral wool.
The standard 4108 is talking about the formation of dew water at the contact surfaces between two materials.

There is an easy way to get the amount of water for this region:
Split the mineral wool in two layers, one close to the surface you like to access with 1-5 millimeters and the rest. As the connection between the materials is assumed to be ideal, this will cause no change in the results. Now you can let you show or export the water content for this small layer of mineral wool. If you use 1 mm, the kg/m³ is the same like kg/m². If you use other thicknesses (may be necessary if whole layer gets filled by dew water) you have to transform as you described it above.

For mineral wool (45 mm thick), max condensing moisture (2019) = (0.754 - 0.433)/1000*45 = 0,014 kg/m²
0.014 kg/m²< 1 kg/m² OK
0.014 kg/m²< 0,5 kg/m² OK (because mineral wool is not capillary active)
Is it correct ?

Yes, except your conclusion. The critical value is set because of water could run out of the insulation on the surface it forms. So here you have not to look on the insulation, but on the connected layer. In your case probably the OSB3? It is not really a capillary active material, so I would use the 0,5 kg/m² here.

Also important is, that your OSB3 layer does stay below a critical value of 18 M.-% (according to the German standard. I´m not sure if you use that in France).

I recently wrote a German FAQ about the DIN 4108 criteria and a HowTo in German and English will follow soon.
I also would like if WUFI could see, where the critical layer is and than automatically give you the relevant results, but unfortunately WUFI does not know which material is the critical and how to access. The user should know that. But we are permanent trying to improve and simplify WUFI, so if you have any ideas about that please tell me, we will discuss that and see if we can implement that.

Christian

[olivir]

Hi Christma... Christian !

you are on the right way, but what you are doing is to access the water content as a mean value over the whole mineral wool.
The standard 4108 is talking about the formation of dew water at the contact surfaces between two materials.

Oh, I understood the interface term but I wasn't able to apply

There is an easy way to get the amount of water for this region:
Split the mineral wool in two layers, one close to the surface you like to access with 1-5 millimeters and the rest. As the connection between the materials is assumed to be ideal, this will cause no change in the results. Now you can let you show or export the water content for this small layer of mineral wool. If you use 1 mm, the kg/m³ is the same like kg/m². If you use other thicknesses (may be necessary if whole layer gets filled by dew water) you have to transform as you described it above.

OK, it's just clear !

Yes, except your conclusion. The critical value is set because of water could run out of the insulation on the surface it forms. So here you have not to look on the insulation, but on the connected layer. In your case probably the OSB3? It is not really a capillary active material, so I would use the 0,5 kg/m² here.

I have to look at where the water may overflow so I must create a very small layer in OSB only, right ?
But if I put a capillary-active insulation, I do not have to check the 0.5 kg/m² criteria ?! With a wood wool for example ?

Also important is, that your OSB3 layer does stay below a critical value of 18 M.-% (according to the German standard. I´m not sure if you use that in France).

Well, I never had this problem because I want my OSB to dry and its water content begins under 18 %. But thanks !

I also would like if WUFI could see, where the critical layer is and than automatically give you the relevant results, but unfortunately WUFI does not know which material is the critical and how to access. The user should know that. But we are permanent trying to improve and simplify WUFI, so if you have any ideas about that please tell me, we will discuss that and see if we can implement that.

What about a specific monitor : "risky not capillary-active product" ?
It would be great to have some % results in the water content last results interface too

[Christian Bludau]

Hello Olivir,

I have to look at where the water may overflow so I must create a very small layer in OSB only, right ?

No, not the OSB. Your construction should look like that:
From outside:
Concrete
Air
Pare vent
Bois
Pavaflex
OSB3
1 to 5mm Mineral Wool (the dew water is forming on the OSB in the mineral wool)
Mineral Wool minus 1 to 5mm
Air
Cartonee

Then access the water content in the thin layer of mineral wool.

Thanx for your ideas, we will discuss that over here.
Have a nice Christmas time and a happy new year ,
I´m off till jour des Rois.
Christian

[olivir]

Wow, thanks for this ultimate message very critical for me, I hope that Father Christmas will be generous with you.
Have a nice Christmas time and a happy new year too !

[olivir]

OK, cool, no issue