Masonry Magazine June 1978 Page. 18
States for urea-formaldehyde based foams; thus, at present, there are no means available of assuring a minimum level of quality of urea-formaldehyde based foams.
The NBS report, in addition to determining the advantages and disadvantages, also identifies two major problem areas: (1) shrinkage of the foam, and (2) its resistance to high temperature and high humidity. Preliminary tests conducted at NBS raise serious questions concerning the durability of the foams when used under certain conditions. These preliminary tests support information from the literature that these aspects of the performance of the foams may be suspect.
To date, BIA has not undertaken a complete investigation of the use of foamed-in-place insulations in brick masonry cavity walls. Such materials may have properties suitable for a particular job, and their use could prove satisfactory, but until such time as more information becomes available, BIA cannot recommend their use as insulation in brick masonry cavity walls.
INSTALLATION PRACTICES
# General
The diversity of types of insulation and manufacturers make it virtually impossible to give explicit instructions for the installation of all insulation materials. Therefore, this Technical Notes will discuss general installation practices. It is suggested that the manufacturers' literature be consulted for specific information prior to specification and construction.
# Granular Fills
Granular fill insulation is usually poured directly into the cavity from the bag or from a hopper placed on top of the wall. Pours can be made at any convenient interval, but the height of any pour should be kept below 20 ft (6 m). Rodding or tamping is not necessary, and could possibly reduce the thermal resistance of the material. The insulation in the wall should be protected from weather during construction.
Special care, such as the use of screening, should be taken when designing weep holes so that provision is made to keep the granular fill from leaking out of, or interfering with, the natural drainage of the cavity. See Technical Notes 21B for suggested details.
# Rigid Boards
There are probably as many different types of installation procedures as there are types of rigid board insulation, but the following is a generally accepted method.
Rigid board insulation is installed horizontally within the air space against the cavity face of the back-up wythe. A minimum of 1 in. (25 mm) should be left between the cavity face of the external wythe and the insulation board. The 1-in. (25 mm) space between the outer wythe and the insulation board facilitates the wall construction and allows for drainage of the cavity. Care should be taken during installation to insure that all boards are abutted and installed between ties, and fit flush against the inner wythe. An adhesive should be used to hold the insulation in place.
Vapor Barriers
Sheets or layers of material which effectively retard or stop the flow of water vapor are called vapor barriers. An acceptable vapor barrier is one which has a moisture vapor permeance not exceeding 1 perm (1 grain of vapor transmission per square foot per hour per inch of mercury vapor pressure difference). They are properly used on the warm side of the insulation. They may take the form of asphalt-coated paper, continuous aluminum foil surfaces or continuous polyethylene films. They may be attached to the insulation as part of the fabricated product, or they may be incorporated separately in or on the warm side of the wall. For greatest effectiveness, they must be continuous and without openings through which vapor may pass.
ADVANTAGES OF INSULATED CAVITY WALLS
# General
Insulated cavity walls have certain advantages over plain cavity walls. The following is a discussion of the major properties of cavity walls and how the introduction of insulation into the cavity affects these properties.
# Resistance to Moisture Penetration
One of the principal considerations in the development of the cavity wall was the elimination of moisture penetration to the interior of the building by the inclusion of an air space across which the moisture could not travel. When the cavity wall is properly built, with flashing and weep holes provided for the collection and drainage of moisture, this theory is sound. On the basis of many tests and inspections of cavity walls built in almost every type of exposure condition, it is evident that such walls remain dry under the most severe exposures, even with average workmanship. The mechanism for moisture removal in cavity walls is explained in detail in Technical Notes 21 Revised.
The addition of an insulation material into the cavity raises the question of whether this important advantage of the cavity wall is preserved. During the earlier testing programs using granular fill insulation, water under pressure was sprayed on the outside of a full size wall panel. The test conditions, lasting 6 days, represented a rainfall amounting to 512 in./h (140 mm/h) for 120 h, accompanied by a continuous 50-mph (80 km/h) wind. Despite the severity of the test, no damp spots appeared on the interior exposed surface of the wall. The insulation permitted the cavity to act as a barrier to moisture penetration and still allowed the weep holes to perform their intended function.