DensElement™ BARRIER SYSTEM

[johannbjorn]

Dear forum,

I want to simulate the a roof with roofing felt as DensElement™ BARRIER SYSTEM from wufi database.

The DensElement™ BARRIER SYSTEM is in the WUFI material database and should be watertight but lets vapour out through the construction according to its technical guide.

1. I need the Sd-value [m] or the vapour transfer coefficient [kg/m2sPa] for the barrier system in WUFI2D. In the technical guide of DensElement the vapour transfer coefficient is given as:
   Permeance: US perms (ng/m2•s•Pa) ≤24 (1823).
   Does that mean I can use the vapour transfer coefficient at the exterior surface as: 1.823e-9 kg/m2sPa ?
2. As seen in the figure below the thickness of the den-element should be 0.01588m. If I want to include the dens in my simulation is it neccessary to adjust the thickness of the dens element to 0.01588m?
3. Is it reasonable to use this material as a roofing felt on top of a gypsum roof board air tight roof.

Technical guide:
https://denselement.com/wp-content/uplo ... _Guide.pdf

[Manfred Kehrer]

1. I think you mixed up US perm, Metric Perm, and ng/sm2Pa
2. I am not sure what you want to do.
3. Not sure what you want to do. If you are designing a roof, Georgia Pacific will likely say to you this is not a roofing board

[johannbjorn]

Hi Manfred,

i. I want to simulate a roofing felt. The roofing felt should be open. That is, vapour can pass out of the construction but liquid will not pass through it into the construction. Is this doable in WUFI?

1. So what is the vapour transfer coefficient if the permeance is 1823 ng/m2•s•Pa (is ng not the same as nano gram? i.e. 1 ng = 1e-12 kg?)
2. in the material data base of denselement there is window down below that says thickness 0.01588m (see figure above, red circle) Does this mean that the dens-element I create in my construction in WUFI should be 0.01588m?
3. Ok.

Warm regards, Jóhann

[Manfred Kehrer]

1. Of course this is possible set liquid transport coefficient to zero and fill in a my value for your material
2. If you mean "Vapor Transport Coefficient" then the my value = sd value [m] / Thickness [m]. The sd value is roughly 200 ng/smPa / 1823 ng/sm2Pa =0.11m.