Pathology of humidity. Simple wall. Phenomenon of condensation.

In the art of building, the client and/or the project manager always have a duty to adapt constructions to the site, and an obligation to achieve results in the face of climatic conditions.

Adaptation to specific sites remains the domain of architecture.

Whether a building performs well, or deteriorates, generally depends on the construction "technique", and in particular on how it reacts to the aggression of natural agents such as heat and water, in all their forms, acting separately or together.

The theory of "water vapour migration in the mass" provides a qualitative approach to these natural phenomena. This theory also makes it possible to quantify them. The advantage of quantifying this migration is to be able to :

• understanding and solving existing or future humidity problems;

• intervene as far upstream as possible, during project design, and thus be able to prevent, rather than cure, potential pathology(ies).

This approach implies that the owner and/or project manager will have to budget for specific studies, which will be largely offset by the long-term reliability of the forecasts made.

This practical resolution of complex phenomena is based on the scientific approach described in REEF (Volume II) under the title: "Diffusion of water vapor through walls. Condensations" by Jacques Berthier (died 1980), Director of CSTB (Centre Scientifique et Technique du Bâtiment).

In order to move from "theory to practice", the example treated will be a "typical wall", studied in a progressive and didactic way to help you make the most of this method.

The aim is to assimilate this methodology, so that each participant can use the example chosen to solve other concrete cases by analogy.

This method makes it possible to predict and evaluate the physical behavior of components exposed to natural hygrothermal aggression. It also facilitates comparison with the permissible resistances found in official documents (standards, DTU, technical notices, test reports from certifying laboratories, professional rules, etc.).

Ultimately, this approach constitutes a "working tool" intended for all those involved in the act of building (owners, project managers, technical design offices, teachers, contractors, materials merchants, etc.), as well as for professionals who have "to judge the built thing".

In this dossier, we recall the theory of the condensation phenomenon necessary for a "qualitative" understanding of phenomena relating to the migration of water vapour in the mass.