Underground Concrete structure

[Nidhi]

Hello we are building an underground concrete structure that I have been testing details in WUFI. The project can be seen here - https://www.youtube.com/watch?v=fc9kyEWZ-f8

The build up at the top of the arch or ceiling is from inside to outside - Concrete, waterproofing, 1-2 inches of foam and 24 inches of Earth.

hen I model I am seeing that the local hygrothermal load graph shows values at the point the water proofing touches the concrete so essentially there is mould growth there. But when I open the Wufi bio it is always green. It says there is no mould risk. I feel like I am doing someting incorrectly but not sure what?

I also have another situation where we are putting a radon barrier in the crawl space and then the client wants us to insulate the crawl space and bring it in the conditioned space. But when I did the WUFI analysis of that detail I also get similar readings. where wufi bio shows no risk but the local hygrothermal graph shows that the mould will be present. Am I reading it incorrectly?

[Christian Bludau]

First of all, I would recommend having a look at the WUFI guideline on typical constructions, which also explains the correct handling and interpretation of simulations (including boundary conditions and evaluation). There you can find a basement example:
https://wufi.de/en/service/downloads/#t ... structions

Regarding your first question (local hygrothermal load vs. WUFI Bio)
You are comparing two different evaluation methods:

• The local hygrothermal load graph shows temperature and relative humidity at a specific point. This can indicate conditions where mould could be possible in principle.

• WUFI Bio, on the other hand, represents a more advanced evaluation of the local hygrothermal conditions, taking into account not only temperature and relative humidity, but also the duration, dynamics and material sensitivity.

So it is possible—and not contradictory—that:

• the local RH temporarily reaches high values,

• while WUFI Bio still shows no mould risk, because the conditions are not critical long enough or not relevant in terms of growth kinetics.

About your underground / earth-contact construction
For constructions with soil contact (like your 24 inches of earth), it is especially important to ensure:

• correct exterior boundary conditions (often using appropriate climate data or simplified assumptions),

• and realistic interior conditions.

Again, the guideline for typical constructions gives good orientation here.

Crawl space / conditioned space case
For your second question:
In WUFI, there is already a predefined indoor climate template for such situations:
Under User-defined indoor climates, you will find a template called “Crawlspace”.
This can be used as a starting point for modelling crawl spaces as a boundary condition.

Christian