capillary break

Capillary ActionˇŞThe flow of liquid moisture through small interconnected pores or spaces due to adhesion and surface tensionˇŞ commonly referred to as ˇ°wicking.ˇ± This is a very powerful mechanism and depending on pore size and available water the moisture can rise many feet against the force of gravity. Capillarity can be controlled by sealing the pores or making the pores very large, such as washed aggregate. Common problems include capillary rise from the footing into the foundation wall and capillary suction of water behind siding.

To provide protection against rain, air gap with weather barrier and flashings provides capillary break and leads water away. (see IRC Construction Practice series, #8: Heat, Air and Moisture Interactions)

Foundation Waterproofing against Capillary rise through Concrete Footing

Concrete underslab vapor retarders are designed to intercept and block moisture vapor before it can reach the slab. As the term ˇ°underslabˇ± implies, they are always installed below the slab, either below or on top of the capillary break. This positioning is critical, as no concrete top coat can protect slabs from moisture migrating from beneath the concrete. (see: Specifying Concrete Underslab Vapor Retarders)

EIFS: have some sort of requirement for creating an air space or capillary break between the EPS board and the drainage material covering the wall (from JLC)

Articles

A drainage cavity is a more elaborate feature that introduces an airspace between the cladding and the drainage plane/sheathing . The airspace serves as a capillary break to prevent water from excessively wetting the drainage plane. The airspace, particularly when it provides a pressure-equalization function, can also be seen as another means of deflection, in that pressure-equalization neutralizes the primary driving force behind rain penetration (air pressure differential), and thereby reduces the amount of moisture being driven through the cladding into the drainage cavity. [Moisture and Wood-Frame Buildings Building Performance Series No.1 (by CWC:)]

National Building Code Canada: capillary break for cladding section 9.27.2.2.

A minimum air gap of 30mm is required by DIN between the outer face of the insulant and the inner face of the tile in the cavity. - http://www.telling.co.uk/trpage4.html

Heat, Air and Moisture Interactions

"Building Envelope and Environmental Control: Part 1- Heat, Air and Moisture Interactions" by M.T. Bomberg and W.C. Brown in Construction Practice

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Adsorption, surface area and porosity, 2ed, by Gregg, S.J. and K. S. W. Sing, 1982

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Description of the moisture capacity of building materials, by Carmeliet, J. and S. Roels, 2002

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Determination of the moisture capacity of porous building materials , by Carmeliet, J. and Roels, S., 2002

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Drying of walls with ventilated stucco cladding parametric analysis, by DMO Associates, 1999

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Housewraps, felt paper and weather penetration barriers, by Fisette, P., 1999

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Infrared thermography as a tool for studying the movement of water through some building materials. Part 1. Capillary moisture, by Gayo, E., Palomo, A. and Macias, A., 1993

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Interfacial mass and heat transfer during evaporation. I. An experimental technique and some results with a clean water surface , by Navon, U. and Fenn, J. B., 1971

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On the influence of cavity ventilation on moisture content in timber frame walls, by Hansen, M. H., Nicolajsen, A. and Stang, B. D., 2002

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Surface temperatures of window specimens: infrared thermography laboratory measurements, by Griffith, B.T., H. Goudey and D. Arasteh, 2002

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Water flow by means of capillary action, by Air-Ins inc, 1997