About battens

[olivir]

Hi everybody,

I have a, interrogation, it's about hygrothermal simulation but also about DIN 4108.

In France, it's not a so usual to make breathable composition. Until today, vapor barrier were the norm. Now, Glaser-like studies become more frequent but, because people considers condensation behind battens, the conclusions are the same than yesterday : use a vapor membrane with a big Sd !



But, if we test this type of wall in WUFI, we see no problem. Nonetheless, WUFI ignore that battens are highly localized.

So, two questions :
- Do you know some experiments about battens in real situation ? Are the comportment identical to WUFI simulations or is it more "virtuous" because of the low surface of battens ?
- How the DIN4108 standard takes this situation into account in Germany ? Just calculating drying time or is there a specification for this small elements ?

[olivir]

OK, no success with my question....

[Christian Bludau]

Hi Olivir,
I´m not sure about your question and picture. Your layer 5 are battens? With air gaps in between?
Over here we build such a construction with a moderate or variable vapor retarder or with a barrier. At least something like an OSB-board at the inside used as airtight layer (problem is, that OSB is not always air tight).

The standard DIN 4108 handles such constructions quite conservative. As long as the sd-value inside is higher than 100m and the exteriour one is lower than the higher one, this constructions are free to build. But this does not consider something like infiltration/convection. If that happens in a tight-tight construction, the construction usually gets damaged.

For wooden constructions the standard DIN 68800 directs you to keep a drying reserve in account. For glaser thats 100g/m² for roofs and 250g/m²a, for simulations you have to use an appropriate model. In WUFI we included the IBP infiltration model [1] for that.

[1] Künzel, H. M., Zirkelbach, D., & Schafaczek, B. (2011). Vapour control design of wooden structures including moisture sources due to air exfiltration. In Proceedings 9th Nordic symposium NSB Tampere (pp. 189-196).
http://publica.fraunhofer.de/documents/N-178130.html
Presentation:
http://webhotel2.tut.fi/nsb2011/sites/w ... elbach.pdf

[2] Künzel, H.M., Zirkelbach, D., Schafaczek, B.: Modelling the Effect of Air Leakage in Hygrothermal Envelope Simulation.
Proceedings BEST3 Conference Atlanta, National Institute of Building Science 2012, 13 pp.
http://www.hoki.ibp.fraunhofer.de/ibp/p ... lation.pdf

Regards,
Christian

[olivir]

Hi Christian,

Sorry my picture is not good but it was to show condensation

Layer 5 is very classical 60 mm x 60 mm battens separated 600 mm spacing. In this project it's not air gaps, there is some insulation but I don't think it's very different, is it ?

The other layers are : 1 - plasterboard, 2 - glasswool, 3 - OSB/3, 4 - wood wool panel, 6 - rain screen, 7 - ventilated layer, 8 - cement panel.

In fact, it's what you describe but here there's some big brakes to wall without vapor barrier film, even if there are people to want to avoid tight-tight construction.

Using WUFI, I can prove there's no risk but I am surprised that no standard explains do not take into account the battens in Glaser calculations. Because there are too small (and ventilated generally) to create a risk. No ?!

When you say the the standard DIN 68800 directs you to keep a drying reserve in account (100g/m²a for roofs and 250g/m²a for walls, I presume), you means it permits to evaluate a condensation inferior to those thresholds in wooden construction with Glaser ?! Because it can dry ?!

[Christian Bludau]

Hello Olivir,

In this project it's not air gaps, there is some insulation but I don't think it's very different, is it ?

Depends on the vapor diffusion resistance of the insulation. If its something like EPS, there will probably be an influence, for mineral wool its probably only a thermal change.

Using WUFI, I can prove there's no risk but I am surprised that no standard explains do not take into account the battens in Glaser calculations. Because there are too small (and ventilated generally) to create a risk. No ?!

I think in Glaser you should handle it like a 60mm air layer. The reason why the standards about Glaser do not handle such constructions is probably, that such kind of constructions where not usually built in the 50´s, when Glaser was invented. The only construction a little similar to that is a pitched roof with tiles, where the battens are outside below the tiles. And this construction was free of proof for according to DIN 4108.

When you say the the standard DIN 68800 directs you to keep a drying reserve in account (100g/m²a for roofs and 250g/m²a for walls, I presume), you means it permits to evaluate a condensation inferior to those thresholds in wooden construction with Glaser ?! Because it can dry ?!

Yes, thats a simplified idea to take in account convection effects in Glaser Method. If this additional moisture can dry out (you add that to the dew water in winter period), the construction is proof to build.

Regards,
Christan

[olivir]

Depends on the vapor diffusion resistance of the insulation. If its something like EPS, there will probably be an influence, for mineral wool its probably only a thermal change.

It's a wood wool panel with μ = 5, far enough from EPS vapour diffusion resistance so.

I think in Glaser you should handle it like a 60mm air layer. The reason why the standards about Glaser do not handle such constructions is probably, that such kind of constructions where not usually built in the 50´s, when Glaser was invented. The only construction a little similar to that is a pitched roof with tiles, where the battens are outside below the tiles. And this construction was free of proof for according to DIN 4108.

Oh yes good example the roofs with battens not considered in Glaser method !

Yes, thats a simplified idea to take in account convection effects in Glaser Method. If this additional moisture can dry out (you add that to the dew water in winter period), the construction is proof to build.

OK, understood ! Even with battens like in my pics, I don't exceed the limit.

Thanks a lot, Christian !

[olivir]

Oh, just for curious people like me, there's one page here (from a DETAIL publication) covering several topics lequels was exchanged with C. Bludeau !