Wayne Tobiasson

Ventilating attics to minimize icings at eaves

Abstract In cold regions, icicles and ice dams may develop on roofs that slope to cold eaves. Ventilating the space below the snow-covered roof with outdoor air to create a ‘cold’ ventilated roof is often an effective way to avoid such problems. Several buildings in northern New York were instrumented to determine how their attic temperature influenced icing. We observed that problematic icings developed very slowly, if at all, when the outside temperature was above −5.5 °C. It appears that icings can be avoided by sizing natural, and if necessary, mechanical attic ventilation systems to maintain an attic temperature of −1 °C when the outside temperature is −5.5 °C.

A Method For Conducting Airborne Infrared Roof Moisture Surveys

Airborne infrared roof moisture surveys can be conducted by using the following method. Maps of the area and plans showing the location of buildings to be surveyed are studied prior to the flights. Permission for the flights is secured and local authorities are notified of the work. An infrared imaging system is mounted on the helicopter and headsets are installed to ensure that all members of the team can communicate. Color airphotos are obtained of each roof early in the afternoon. The flight crew and the spotter are each provided with maps of the installation, with numbers and highlighting used to indicate each building to be surveyed. The spotter has a clear plastic overlay on his copy that he marks to indicate buildings completed. The daytime photographic flight serves to train the team for the more difficult thermographic survey that evening. The color film is submitted to an over-night print processor just after the flight.

Roof Moisture Surveys: Current State Of The Technology

Moisture is the big enemy of compact roofing systems. Non-destructive nuclear, capacitance and infrared methods can all find wet insulation in such roofs but a few core samples are needed for verification. Nuclear and capacitance surveys generate quantitative results at grid points but examine only a small portion of the roof. Quantitative results are not usually provided by infrared scanners but they can rapidly examine every square inch of the roof. Being able to find wet areas when they are small is an important advantage. Prices vary with the scope of the investigation. For a particular scope, the three techniques are often cost-competitive. The limitations of each technique are related to the people involved as well as the equipment. When the right people are involved, non-destructive surveys are a very effective method for improving the long-term performance and reducing the life-cycle costs of roofing systems. Plans for the maintenance, repair or replacement of a roof should include a roof moisture survey.

Locating Wet Cellular Plastic Insulation In Recently Constructed Roofs

Infrared scanners are quite successful in finding wet roof insulation, especially boards of rapidly absorbing insulations like perlite, wood fiber and fibrous glass. But wet areas develop more slowly and nonuniformly in the cellular plastic insulations, such as urethane, which are commonly used in new roofs. These differences can affect the outcome of an infrared survey of new roofs. To determine the feasibility of detecting incipient wet insulation, several recently constructed roofs were examined thermographically. It was usually more difficult to find moisture in new roofs containing cellular plastic insulations than in new roofs with more-absorbent insulations. This increased difficulty is due to the slower rate of wetting and to the nonuniform manner of wetting of some of the cellular plastics. Perlite, wood fiber and fibrous glass insulations tend to become uniformly wet throughout an entire board, whereas moisture initially concentrates at the perimeters of boards of some cellular plastic insulations. However, eight to ten months after construction, enough moisture can accumulate in most cellular plastic insulations to be visible to aninfrared scanner. Since this moisture is concentrated in a small portion of each insulation board, much of it would probably be overlooked by a nuclear or capacitance grid survey.

Maintaining buildings in the Arctic

Close interest in the work of CIB working commission W 40 on heat and moisture transfer has prompted the authors, who are scientists working with the US Army Cold Regions Research and Engineering Laboratory, to send us these two summaries of remedial work on houses in Alaska. The first indicates the scope for simple injection of urea formaldehyde foam to improve thermal insulation of old wood-frame buildings; the second shows how infra-red photography can cut the cost of repairs to leaking roofs.