Exterior Tiles

[David Lam]

I haven't been able to find a satisfactory post on this forum. I may have missed it so please direct me if it exists.

I am attempting to model a building with external tiles (unknown material - I have asked). There is no material in WUFI for this. The exterior surface option of using 2m sd doesn't make sense as I would expect the tiles to keep the rain off pretty well.
I'm using WUFI Pro so can't model the grout (that's the bit between tiles) well, but I'm less concerned about that.
What I need is a sensible way to model the tiles, and there doesn't appear to be one.
Can you help please?

[Manfred Kehrer]

Hello David,
the sd value of 2m refers to the vapor permeance and has nothing to do with the rain absorption/deflection, but you can use a user defined sd value to account for any painting if exists.
I suggest to use a brick material to address the water sorption characteristics.
Best,

[Thomas]

Hi David,

the tiles in the drop-down list are supposed to be glazed and thus impermeable to vapour transfer. However, the mortar in the joints between the tiles is vapour-permeable, and the "2 m" suggested by the drop-down list refer to the vapour permeability of those joints, taking their fractional area on the wall into account (in other words, it is a weighted average of the impermeable glazed tiles and the permeable mortar in the joints).

See here for a short earlier discussion: Perm ratings for ceramic and porcelain tiles

Regards,
Thomas

[David Lam]

Thanks both

So there's two options for this:

Option 1 - model eg 6mm brick to represent the tiles. Textured Coated Clay brick looks like a good candidate with a low A-value. This should represent the 1 dimensional view through the glazed tile. The results are likely to be that the brick protects the facade from wind-driven rain.
Should I also use the 2m sd on the exterior surface?

Option 2 - don't model the tile except for 2m sd on exterior surface. This should represent the combination of glazed tile and joint though it ignores the rainwater uptake in the grout (joint)
Presumably the water uptake is influenced strongly by the adhesive material and backing substrate (cement and concrete in my situation). Assuming this is similar to the grout material I'm assuming this is reasonable.

Any further comments or recommendations please?

[Christian Bludau]

Hi David,

I would be cautious about using an additional sd-value at the exterior surface transfer. While it may represent a reduction in vapor permeability, it does not prevent wind-driven rain from reaching the surface. At the same time, it reduces drying to the exterior, which is not always desirable and may even lead to a less realistic assessment of the assembly's drying potential.

Therefore, in my opinion, Option 1 is the better solution, but I would implement the vapor resistance within the exterior layer itself rather than as an additional surface resistance. This allows both the moisture storage and drying behavior of the tile system to be represented more realistically. If sufficient data are available, I would therefore recommend creating a custom material with effective properties and including the sd-effect in that layer.

I would probably take a slightly different approach.
One option would be to create a custom material for the exterior layer that represents the effective µ-value, thermal conductivity, and water absorption coefficient (A-value) of the glazed tile and joint system as a whole. However, this is not entirely straightforward, as some assumptions will inevitably be required regarding the interaction between the tiles, joints, adhesive, and substrate. Nevertheless, it is often a more realistic way to represent the overall hygrothermal behavior of the system rather than modeling only one of its individual components.

As a conservative (worst-case) approach, you could also model only the mortar/joint material, since it is typically the more moisture-active component and may dominate moisture uptake.

Best regards
Christian