Scientific Research Reports

The addition of insulation to the exterior of buildings is an effective means of increasing the thermal resistance of both wood framed walls as well as mass masonry wall assemblies. For thick layers of exterior insulation (levels > 1.5 in.), the use of wood furring strips attached through the insulation back to the structure has been used by many contractors and designers as a means to provide a convenient cladding attachment location.

The yield limit equations specified in the National Design Specification® (NDS®) for Wood Construction for bolt, lag screw, wood screw, nail, spike and drift pin connections represent a mechanics-based approach for connection design. This approach, which was incorporated in the 1991 NDS, permits the designer to determine effects of member thickness, member strength, fastener size, and fastener strength on lateral connection values for the majority of connections found in wood construction.

This guide provides information and recommendations to the following groups: insulation contractors; general contractors; builders; home remodelers; mechanical contractors; and homeowners, as a guide to the work that needs to be done. The order of work completed during home construction and retrofit improvements is important. Health and safety issues must be addressed first and are more important than durability issues. And durability issues are more important than saving energy. Not all techniques can apply to all houses. Special conditions will require special action.

When insulating a steel-framed exterior wall in cold climates, it is usually necessary to provide continuous insulation on the exterior of the studs to reduce the effect of thermal bridging. As energy codes continue to become more stringent, the thickness of the continuous installation has increased. The increased insulation thickness, however, introduces several problems for building designers, such as window and door jambs needing to be extended, siding manufacturers’ warranties being voided when more than one inch of continuous insulation is used, and heavier siding products causing fast

Building science studies have recognized the importance of the proper installation of flashing and its integration with the water resistive barriers as very important to the success of a wall assembly. The roll of flashing is to direct water away from the opening to the water resistive barrier, which in turn directs the water to the exit point in the wall. The integration of these two elements and the quality of their installation is ultimately important to the success of the wall system. It is equally important to select products, which perform as intended after installation.

An effective and durable window installation demands good airtightness and proper water management. This Report explains how the degree of airtightness and the location of the plane of airtightness of the wall-window interface affect water entry. It is the second in a series of Updates presenting results from studies of window installation details.