Bas A. Baskaran

Performance of Pressure Equalized Rainscreen Walls under Cyclic Loading

WIND-INDUCED PRESSURE difference is one of the forces that contributes to rain penetration of walls. It can be attenuated by using the pressure equalized rainscreen (PER) approach to wall design. In such a wall an air space that is located mside the exterior cladding is vented to the outside so that the pressure on the inside of the cladding equalizes to the pressure on the outside. As pressure equalization is the key element of the process, it is important that the system be fast enough to respond to most changes in exterior pressure. In 1963, Garden introduced the concept of the &dquo;open rainscreen&dquo; to building designers. The significance of this work lies in the formulation of basic design guidelines. These have subsequently been modified on several occasions in order to address the complicated nature of the interaction between wind-driven rain and wall systems. Kilhp and Cheetham (1984) reviewed the process of rain penetration through walls. They also performed simplified experiments to measure the pressure drop in the cavity for various venting and leakage conditions. Field measurements on PER walls were undertaken by researchers at the Institute for Research in Construction of the National Research Council 3f Canada (IRC/NRCC). From June 1983 to October 1984, the Place Air

Critical Evaluation of Existing Specifications for Polyisocyanurate (ISO) Foam Insulation Boards in Roofing Applications

In North America, more than 50 % of low slope roofing applications uses faced rigid cellular polyisocyanurate (hereafter abbreviated as ISO) board as thermal insulation. Long-term performance of a roof assembly is critically dependent on the ISO characteristics during the service period in various environmental conditions. For this reason, the ASTM C 1289-02, “Standard Specification for Rigid Cellular Polyisocyanurate Thermal Insulation Board,” outlines the physical and thermal property requirements for the ISO boards. However, these requirements are based on the available knowledge, information, and consensus at the time of drafting and balloting of the ASTM standard. Nevertheless, the standard gets updated and revised when more credible data are available that solicits revisions of the current standard. This paper presents experimental results from an ongoing pilot research study that critically evaluates the ASTM C 1289-02 specification requirements for the ISO on three engineering properties: (1) dimensional stability, (2) thermal resistance, and (3) compressive strength. Preliminary results from this study reveal many unknown phenomena, particularly regarding the dimensional stability and compressive strength of ISO boards.

Dynamic Evaluation of the Building Envelope for Wind and Wind-Driven Rain Performance

The building envelope should be designed to provide a comfortable indoor environment irrespective of changes in the weather. Therefore, to provide a functional and durable building envelope, the dynamic character of the driving forces must be recognized by the envelope designer. The dynamic performance of the building envelope can be evaluated in laboratories in which the design details and most of the dynamic properties of the driving forces are simulated. This paper dis cusses the dynamic processes and the need for dynamic evaluation of structural per formance under wind loading and of rain penetration performance under wind driven rain conditions. Three research facilities are examined for their approach to dynamic evaluation of structural performance and rain penetration performance. Ad ditional information on dynamic evaluation of the building envelope was gathered from standards and the literature. Based on this information, procedures for dynamic evaluation under wind loading and wind driven rain conditions are proposed.

Development of a New Test Method for Air Intrusion Quantification of Roofing Assemblies

In North America, approximately one-fourth of low-slope buildings are roofed with a mechanically attached assembly (MAA) with a single-ply membrane. During wind suctions, the membrane can lift and billow. This creates localized suction under the membrane. If design provisions are not made to control the air intruison at the deck level, this suction pressure can draw the indoor conditioned air into the assembly. Two main factors influence the air intrusion: the air permeability of the components and shape or volume changes during the wind uplift. Available standard test procedures can quantify the former for roof materials. However, there is no widely accepted standard specification or test to address the air intrusion characteristics of roofing assemblies. Air leakage measurement techniques used for walls are also not applicable for roof assemblies due to the membrane shape and volume changes in the roof assembly. Research efforts are under way at the National Research Council of Canada to quantify the air intrusion rate of roof assemblies. This paper presents the details of the experimental setup, test procedure, and validation effort of this newly developed test method.

Impact of Fastener-Deck Attachment on the Wind Uplift Resistance of Mechanically Attached Roofing Systems

A roofing system (RS) consists of a waterproof membrane, mechanical attachments, cover board (if present), insulation, and vapor or air barrier (retarder — if present). A roof assembly (RA) is defined as an RS that includes a structural deck. Wind uplift ratings are obtained by subjecting RA mockups to dynamic wind loading. Mechanically Attached Roofing Systems (MARS) are one particular type of roof assemblies in which the membrane is attached to the structural deck using mechanical fasteners. The strength of the fastener-deck interface is an important aspect in the successful design of the wind uplift resistance of mechanically attached roof systems. To quantify the fastener-deck interface influence on the wind uplift performance of MARS, seven different roofing assemblies were constructed and tested under dynamic conditions. The experimental investigation identified three parameters namely deck grade, deck gauge and fastener type that have influence on the wind uplift resistance of MARS. Based on this component characterization, fastener pullout resistance (FPR) is identified as a verification factor for system wind resistance estimation.

Effect of Fastener-Deck Strength on the Wind-Uplift Performance of Mechanically Attached Roofing Assemblies

A roofing system consists of a waterproof membrane, attachments, cover board (if present), insulation, and vapor or air barrier [retarder (if present)]. A roof assembly is a roof system that includes the structural deck. Wind-uplift ratings are reported by subjecting roof assembly mockups to wind dynamics. Most of the time, technical reports clearly document the properties of membranes and attachment systems (fasteners, plates, and seams) and only briefly mention the strength of the fastener-deck interface. Research by a North American roofing consortium established at the National Research Council of Canada, the Special Interest Group for Dynamic Evaluation of Roofing Systems, has demonstrated the significant influence of fastener-deck parameters on the wind-uplift resistance of mechanically attached roofs. This paper presents data and information from this ongoing investigation. Seven different roofing assemblies using three widely used roofing membranes with different fastener-deck combinations were co...