attic

A large-scale model of an attic construction has been built in a climatic chamber. The purpose of the attic test model is to investigate hear transfer-in particular, heat transfer by convection-in loose-fill attic insulation. The influence of a number of factors on heat flows can be investigated using the attic test model; for example, insulation thickness, attic ventilation, ceiling construction, roof slopes, and the quality of installation workmanship. The heat flow through the attic ceiling construction is measured with a metering box.

     Nothing highlights construction shortcomings like severe winter storms. Too often, possible problems are neglected during the construction season when winter and its bad weather seem far removed. The winter of 1999 produced many ice dams on shingle roofs in central and eastern Canada. The resulting leaks caused widespread damage to ceilings, walls and interior .furnishings of many homes.     

Current model building codes require attic ventilation in all U.S. climates. Originally, these requirements were strictly based on concerns for condensation in attics during winter in cold climates, and they were based on limited technical information. Nevertheless, attic ventilation has become the uncontested strategy to minimize condensation and ice dams during winter and extreme attic temperatures during summer. However, other strategies exist that address each of these problems as well as or better than attic ventilation.

Canada Mortgage and Housing Corporation (CMHC) conducted a series of attic research projects from 1988to1997. Initially, there were few field test data to substantiate how attics dealt with air and moisture transfer. The CMHC research developed a test protocol for attic airtightness and air change testing and then proceeded to field testing of a variety of attics in different climatic areas. An attic model, ATTIX, was referenced against test hut data and used to simulate attic performance across Canada.

While monitoring the comparative performance of two test houses in Pittsburgh, Pennsylvania, it was noticed that the attic air temperature of one house with a plastic shake roof was consistently 20°F ( 11°C) cooler than its twin with asphalt shingles during peak summer cooling periods. More detailed monitoring of the temperatures on the plastic shake, the roof deck, and the attic showed this effect to be largely due to the plastic shake and not to better roof venting or other heat loss mechanisms.

This paper describes a residential research facility built for the experimental measurement of the relative energy and moisture performance of various residential building envelope components and systems. The building comprises 12 test bays on an east/west axis bounded on each end by a guard bay. The eastern six test bays are framed in steel, and the western six bays are framed in wood. Each half of the building contains a symmetrical mix of vented and unvented cathedral and attic roofing systems and is built above a heated basement.

In the last decade, public awareness of the greenhouse effect has pushed the building sector toward higher energy efficiencies. This move has had consequences for roofs with a cathedral ceiling. AU-factor in the vicinity of 0.2 W/(m2·K) instead of 0. 6 W/(m2· K) became the new target value. The move toward such a low U-factor for cathedral ceilings was evaluated in an extended test house program.