Long term measurements of attic wood moisture content have shown that at least fifty kilograms of water may be stored in roof sheathing members over the course of the winter, to be released in the spring. Overlaid on this seasonal cycle there is a daily variation driven by temperature changes in the attic. A dynamic model is required to predict the resulting attic air humidity ratio. Hourly moisture flows in a typical attic - from ventilation and from the wood - are examined, and a simple first-principles dynamic mathematical model to relate them is developed.
Investing in insulation is a good way to reduce energy consumption in the home. The homeowner must determine where adding insulation will be most cost effective. Attics are usually the place to start, followed by floors and walls. Since there is a wide variety of material on the market, thedo-it-yourselfer must choose carefully and install them with proper regard for ventilation and vapour barriers. Even if the work is performed by a contractor, the informed homeowner will benefit by his knowledge of materials and procedures.
A brief synopsis of recent analytic and experimental studies is given. Conclusions are that convective transfer of water vapour into an attic from the living space below often transports more moisture than diffusive transfer through the ceiling construction. Large quantities of moisture are stored in the roof sheathing during warm spring and summer periods. Solar loading during mild winter periods can produce desorption of moisture from the sheathing. This paper reviews the formulation of mathematical relationships among physical parameters governing moisture transfer within attics.
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