Field Testing of an Unvented Roof with Fibrous Insulation, Tiles and Vapor Diffusion Venting

Technical Report · Fri Feb 05 04:00:00 EST 2016

DOI:https://doi.org/10.2172/1238328· OSTI ID:1238328

Ueno, K. ^[1]; Lstiburek, J. W. ^[1]

---

1. Building Science Corporation, Westford, MA (United States)

This research is a test implementation of an unvented tile roof assembly in a hot-humid climate (Orlando, FL; Zone 2A), insulated with air permeable insulation (netted and blown fiberglass). Given the localized moisture accumulation and failures seen in previous unvented roof field work, it was theorized that a 'diffusion vent' (water vapor open, but air barrier 'closed') at the highest points in the roof assembly might allow for the wintertime release of moisture, to safe levels. The 'diffusion vent' is an open slot at the ridge and hips, covered with a water-resistant but vapor open (500+ perm) air barrier membrane. As a control comparison, one portion of the roof was constructed as a typical unvented roof (self-adhered membrane at ridge). The data collected to date indicate that the diffusion vent roof shows greater moisture safety than the conventional, unvented roof design. The unvented roof had extended winter periods of 95-100% RH, and wafer (wood surrogate RH sensor) measurements indicating possible condensation; high moisture levels were concentrated at the roof ridge. In contrast, the diffusion vent roofs had drier conditions, with most peak MCs (sheathing) below 20%. In the spring, as outdoor temperatures warmed, all roofs dried well into the safe range (10% MC or less). Some roof-wall interfaces showed moderately high MCs; this might be due to moisture accumulation at the highest point in the lower attic, and/or shading of the roof by the adjacent second story. Monitoring will be continued at least through spring 2016 (another winter and spring).

• Research Organization: NREL (National Renewable Energy Laboratory (NREL), Golden, CO (United States))
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (EE-5B)
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1238328
• Report Number(s): NREL/SR--5500-64999; DOE/GO--102016-4764
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
BSC
Building America
Building Science Corporation
cathedralized roof
diffusion vent
hot-humid
moisture damage
moisture risks
residential
residential buildings
tile roof
unvented roof