WestCon Tribune

In September's presentation, Theodore Vornicu of Saarman Construction, Ltd. gave a very brief outline of his incredibly detailed report on moisture control practices. Trying to condense and capsulize a multitude of research and many ours of work into a forty-minute meeting was not an easy task. Mr. Vornicu started with covering the following basic issues on heat transfer and water vapor diffusion which are covered in his report:

Conduction Heat Transfer: Thermal conductivity represents the phenomena of heat transfer from molecule to molecule or atom to atom through one of three ways. First there is the elastic colliding of molecules in their continuous random movement, exchanging energy and momentum which are characteristic for liquids and gases. Secondly there is the phonons that transfer the thermal energy from the warmer surface of a crystalline structure (for nonmetallic and dielectric materials) to cooler surface through acoustical radiation. This energy transfer may be encountered also as vibration energy in the lattice structure of the material. Thirdly you there are free electrons (considered a perfect mono-atomic gas) that transfers the energy of metallic and semi-conductive materials and the contribution of free electrons is 10-30 times higher in that of phonons.

Convection Heat Transfer: Convection heat transfer represents the phenomena of heat transfer accomplished through the moving of a mass (quantity) of fluid (gas of liquid) between the areas with different temperatures. Convection heat transfer is very important at the contact surface between a solid and a fluid (gas or liquid).

Radiation Heat Transfer: In contrast to the mechanisms of conduction and convection heat transfer, where energy transfer through a material is involve, heat may also be transmitted through areas where a perfect vacuum exists. The mechanism in this case is electromagnetic radiation which is transmitted as a result of temperature difference and is termed "thermal radiation". The Stefan-Boltzmann law shows that an ideal thermal radiator, or a black body, will emit energy at a rate proportional to the fourth power of the absolute temperature of the body and in direct proportion to its surface area.

Water Vapor Diffusion: If a medium has one or more areas in which the pressure or concentration vary, there is a natural tendency to even the pressure by moving the mass toward the area with lower pressure. This process is called mass transfer, being analogues to heat transfer. For vapor diffusion in construction, the main factors of interest are the air which is a combination of gases, including water vapor and the construction materials that have pores and capillaries filled with air. The amount of moisture that air can hold - the air's vapor pressure, or absolute humidity, is dependent on the temperature of the air. The warmer air is the greater the amount of moisture it can hold. The air is saturated when it contains the maximum amount of moisture possible at a specific temperature.

After explaining the above, Mr. Vornicu used graphs to show the moisture movement in construction. Included topics were:

á The liquid flow due to gravity and/or an air pressure difference

á The moisture transport due to capillary suction

á Air movement and vapor diffusion

á Controlling air pressure

á Moisture balance

á Moisture redistribution and accumulation within wall assemblies

á Air movement in wall assemblies

Control strategies for alleviating moisture problems in wall assemblies fall into three groups: control of moisture entry, control of moisture accumulation, and removal of moisture. Of these three groups, control of moisture entry has traditionally proven to be the most effective. Control of moisture entry strategies include installing interior vapor diffusion retarders, eliminating inlet and outlet openings, controlling moisture in the interior air and controlling the air pressure differential.

Control of moisture accumulation strategies include the control of temperature of the interstitial condensing surface and replacing plywood sheathing with insulating sheathing.

Strategies for the removal of moisture include moisture elimination by vapor diffusion and replacing exterior plywood sheathing with vapor permeable, asphalt-impregnated fiberboard which allow the transfer of moisture to the building paper, utilizing ventilation to remove moisture from the wall assembly and providing drainage of condensed moisture.

The overall presentation showed a great deal of technical knowledge which is covered in Mr. Vornicu's report. Copies were circulated prior to and during the meeting with a sign-up sheet for orders. Anyone who missed the meeting and would like to obtain a copy of the report, you may send a check to Saarman Construction for $25.00, attention Ted Vornicu, 683 McAllister Street, San Francisco, CA 94104. If you have questions or need additional information, you can reach Mr. Vornicu at (415) 749-2700.