Several years ago an alternative moisture analysis method was introduced in the United States.4 Developed in Germany and known as the Kieper method, it has some clear advantages over the traditional moisture profile method, yet has not found widespread acceptance. It allows rapid evaluation of different wall designs under identical environmental conditions. When several transparent overlays are used, response to different environmental conditions also may be quickly determined. The method provides a mechanism for locating the most likely spot for condensation in the wall directly but is not suited for locating more than one such spot. The method is entirely based on diffusion theory, ignoring any air convection effects. At the time of writing, Kieper diagrams or transparent overlays are not commercially available in this country.

Summary of the Kieper method - First, the position of each layer of material is expressed in terms of thermal (x) and vapor flow (y) coordinates. The x-coordinate of a point in the wall is the R-value of all the materials between that point and the inside, divided by the total R-value of the wall. Similarly, the y-coordinate is defined as a fraction of total Rep-value. This definition of x and y makes temperature a simple linear function of x and vapor pressure a linear function of y. It also allows the definition of a condensation boundary curve in the x,y (Kieper) diagram which is independent of the design of the wall and only depends on indoor and outdoor conditions. Below this curve, condensation conditions may occur. Each wall design can be represented by a curve in the diagram. If any section of this curve falls below the boundary curve for condensation, condensation occurs. The location is assumed to be the point of maximum potential moisture accumulation, which can be easily determined with the help of several auxiliary curves which represent different assumed moisture accumulation rates.

• HAM: simplified models - analytical methods : Kieper method