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A Deeper Dive . . .
Cladding Attachment Systems: The Effects of Fasteners on Thermal Performance
ABSTRACT -Three-dimensional thermal modeling was employed to compare effective R-values of cladding attachment systems. Particular emphasis was placed on the effects of fasteners and their connectivity with other thermal bridges. Thermal degradation attributed exclusively to fasteners ranged from 2 to 16%. When considering all bridging elements and an exterior insulation layer of three inches, the most efficient systems were Structural Insulated Sheathing (SIS) and composite z-girts. These systems achieved the true intent of the R-20 wall with effective R-values of 21.5 and 20.1, respectively. Other means for mitigating thermal degradation such as thermal isolation pads and punched engineered z-girts offered limited effectiveness.
The Face Column: A Systems Approach for WRB Evaluation
ABSTRACT – A novel test apparatus is described for evaluating Water-Resistive Barriers (WRBs) and their system components. The ‘Face Column’ represents a thin layer of water expressed vertically against a continuous surface or interfacing component planes. It is designed specifically to convey a range of hydrostatic pressures simultaneously along a single vertical gradient. The concept is highly adaptable to accommodate preferred specimen size, column heights, and multiple component interfaces such as fasteners, joints, tapes, sealants, and liquid flashing. Applications are discussed in context with a proposed shift from current single-component testing to WRB System evaluation.
Mineral Wool and Polyisocyanurate: A Comparative Study of Water Absorption, Drying and Rewetting
ABSTRACT – Wetting behaviors of common insulation products were assessed by standard two-hour water immersion. Mineral wool slabs absorbed 8 to 38 times more water than foil-faced polyisocyanurate (PIR) and 4 to 19 times more water than coated glass-faced PIR. Drying within vented benchtop assemblies required 2 to 6 days longer for mineral wool as compared to PIR. Rewetting of mineral wool specimens increased water absorption by 130% to 190% and extended dry times by an additional four days. In comparison, sorption behaviors of PIR remained unchanged. Repeated wetting of mineral wool revealed dynamic holding capacities that varied on the basis of pore structure and slab macrostructure.
Water Resistance of Integrated WRB Panels
ABSTRACT – Two integrated sheathing systems were assessed for water resistance under prolonged hydrostatic pressure. Findings revealed stark contrasts in moisture performance based largely on material composition of exterior overlays, one representing a glass mat facer and the other a factory-applied fluid membrane. Water staining through glass mat-faced panels occurred at 18 to 24 hours in association with sealed wall interfaces and as a function of hydrostatic pressure. Conditions progressed over a typical seven-day test period culminating with panel saturation and uncontrolled water entry. Membraned-based panels showed no evidence of moisture accumulation or liquid water penetration after 30-days.
Simulation of Convective Heat Loss Through Mineral Wool in a Rainscreen Facade
ABSTRACT -This study applied Computational Fluid Dynamics (CFD) to determine the effects of wind-induced convection through mineral wool in a ventilated rainscreen system. Wind studies of a conceptual low-rise building subject to a wind speed of 6.7 m/s demonstrated dynamic airflows and rainscreen velocities ranging from 0.1 to over 3 m/s. Localized pressure fields near cladding support framing increased air velocities within the mineral wool by one to two orders of magnitude. These high pressure regions, together with increased surface flows at corner domains, represented the primary pathways governing convective heat loss. Simulated convection through mineral wool slabs showed that even high density materials are prone to increased heat transfer due to air permeability into the open pore volume. Vertical and horizontal flow regimes at 1 to 2 m/s increased heat transfer by 4 to 42% over the range of simulated mineral wool densities. Gaps between and behind insulation slabs further increased the convective effects, resulting in heat flux densities that were up to 62% higher than non-gapped, impermeable insulation. The results of this study support growing recognition that exterior mineral wool must be protected from the detriments of convective forces. Alternatively, adjustments in effective R-values should be made when using un-faced mineral wool slabs.
