Bonjour,
J'étudie actuellement une toiture avec des tuiles terre cuite, posées sur une lame d'air ventilée (3 vol/h). La toiture est isolée par de la ouate de cellulose et un pare-vapeur Sd20 est prévu devant cet isolant (côté chaud).
Lorsque je lance l'étude avec les tuiles, l'isolant et le panneaux bois se saturent en eau. Lorsque je retire les tuiles (tout en laissant la lame d'air), ils présentent des valeurs d'hygrométrie tout à fait convenables.
D'où vient cette différence ? Car je ne vois pas comment les tuiles pourraient empêcher la vapeur d'eau de migrer...
Merci d'avance
Toiture tuiles
-
Christian Bludau
- WUFI SupportTeam IBP
- Posts: 1270
- Joined: Tue Jul 04, 2006 10:08 pm -1100
- Location: IBP Holzkirchen, the home of WUFI
- Contact:
Re: Toiture tuiles
Dear Guillaume,
the behaviour you observe is mainly related to how the roof covering is represented in the model.
In WUFI, roof tiles do not simply act as a vapor diffusion resistance layer. Instead, they modify the exterior boundary conditions acting on the underlying construction. In particular, the roof covering reduces solar radiation and drying potential, and it also changes the rain exposure and long-wave radiation exchange. As a result, the drying potential of the assembly can be significantly reduced, which may explain the higher moisture contents in the insulation and wood-based layers.
If the tiles are removed, the model assumes much more favorable drying conditions at the exterior surface of the air layer, which explains why the results improve significantly. This modelling approach is described in detail in the WUFI guideline for pitched roofs. We recommend following the boundary condition settings given there:
https://wufi.de/en/service/downloads/#pitched_roofs
In particular, please check:
the definition of the ventilated air layer (e.g. air change rate),
the applied exterior surface coefficients,
and whether the recommended simplified modelling approach for tiled roofs is used consistently.
Best regards
Christian
the behaviour you observe is mainly related to how the roof covering is represented in the model.
In WUFI, roof tiles do not simply act as a vapor diffusion resistance layer. Instead, they modify the exterior boundary conditions acting on the underlying construction. In particular, the roof covering reduces solar radiation and drying potential, and it also changes the rain exposure and long-wave radiation exchange. As a result, the drying potential of the assembly can be significantly reduced, which may explain the higher moisture contents in the insulation and wood-based layers.
If the tiles are removed, the model assumes much more favorable drying conditions at the exterior surface of the air layer, which explains why the results improve significantly. This modelling approach is described in detail in the WUFI guideline for pitched roofs. We recommend following the boundary condition settings given there:
https://wufi.de/en/service/downloads/#pitched_roofs
In particular, please check:
the definition of the ventilated air layer (e.g. air change rate),
the applied exterior surface coefficients,
and whether the recommended simplified modelling approach for tiled roofs is used consistently.
Best regards
Christian