Field Testing Unvented Roofs with Asphalt Shingles in Cold and Hot-Humid Climates

Ueno, Kohta; Lstiburek, Joseph

doi:10.2172/1225496

Cited by 5 publications

(20 citation statements)

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“…Figure 17 Images showing results of deconstructive assessments of sealed and insulated attic assemblies in a test roof in a cold climate after one year of stress testing (high indoor moisture gains at 50% RH, intended to lead to failure). Source: Ueno & Lstiburek, 2015 Figure 25 Projected energy savings (heating, cooling and combined time-dependent valuation (TDV)) for ducts in conditioned space across California climate zones compared with the 2013 prescriptive code path to compliance with Title 24 Building Energy Code. Projected savings vary substantially by climate zone and conditioning type.…”

Section: Moisture Performance Of Sealed and Insulated Atticsmentioning

confidence: 99%

“…The Hoeschele et al (2015) results represent the only data obtained for modern, new homes built to California's Title 24. All subsequent literature added a total of only 12 additional homes, with homes located in cold (Prahl & Shaffer, 2014), mixed-humid (Boudreaux, Pallin, & Jackson, 2013;Salonvaara, Karagiozis, & Desjarlais, 2013), hot-humid (Ueno & Lstiburek, 2015) and hot-dry climates (Rudd & Lstiburek, 1996;Sherman & Walker, 2002). Nearly all testing in sealed and insulated attic homes comes to the same conclusion: sealed and insulated attics remain somewhat leaky to both outside and the house, and they are likely leakier than the houses they are attached to when normalized by surface area.…”

Section: Measured Airtightness Of Sealed and Insulated Atticsmentioning

confidence: 99%

“…Consistent with this, thermographic inspection of a sealed and insulated attic in a Houston, TX home, showed evidence of air leakage around gas appliance exhaust and intakes. Roof peaks had no sign of leakage, but leakage often occurred at transitions and connections between roofs and walls, especially at complicated areas with multiple intersecting planes, namely roof-wall connections, dormers and gable ends (Ueno & Lstiburek, 2015). Siegel & Walker (2003) noted poor attic air sealing due to difficulty in getting crews used to new activities and a lack of oversight/inspection.…”

Section: Observed Construction Defectsmentioning

confidence: 99%

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A Literature Review of Sealed and Insulated Attics—Thermal, Moisture and Energy Performance

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Walker

Levinson

2016

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In this literature review and analysis, we focus on the thermal, moisture and energy performance of sealed and insulated attics in California climates.Thermal. Sealed and insulated attics are expected to maintain attic air temperatures that are similar to those in the house within +/-10°F. Thermal stress on the assembly, namely high shingle and sheathing temperatures, are of minimal concern. In the past, many sealed and insulated attics were constructed with insufficient insulation levels (~R-20) and with too much air leakage to outside, leading to poor thermal performance. To ensure high performance, sealed and insulated attics in new California homes should be insulated at levels at least equivalent to the flat ceiling requirements in the code, and attic envelopes and ducts should be airtight. We expect that duct systems in well-constructed sealed and insulated attics should have less than 2% HVAC system leakage to outside.Moisture. Moisture risk in sealed and insulated California attics will increase with colder climate regions and more humid outside air in marine zones. Risk is considered low in the hot-dry, highly populated regions of the state, where most new home construction occurs. Indoor humidity levels should be controlled by following code requirements for continuous whole-house ventilation and local exhaust. Pending development of further guidance, we recommend that the air impermeable insulation requirements of the International Residential Code (2012) be used, as they vary with IECC climate region and roof finish.Energy. Sealed and insulated attics provide energy benefits only if HVAC equipment is located in the attic volume, and the benefits depend strongly on the insulation and airtightness of the attic and ducts. Existing homes with leaky, uninsulated ducts in the attic should have major savings. When compared with modern, airtight duct systems in a vented attic, sealed and insulated attics in California may still provide substantial benefit. Energy performance is expected to be roughly equivalent between sealed and insulated attics and prescriptive advanced roof/attic options in Title 24 2016. System performance can also be expected to improve, such as pull down time, performance at peak load, etc. We expect benefits to be reduced for all advanced roof/attic approaches, relative to a traditional vented attic, as duct system leakage is reduced close to 0. The most recent assessments, comparing advanced roof/attic assemblies to code compliant vented attics suggest average 13% TDV energy savings, with substantial variation by climate zone (more savings in more extreme climates). Similar 6-11% reductions in seasonally adjusted HVAC duct thermal losses have been measured in a small subset of such California homes using the ducts in conditioned space approach.Given the limited nature of energy and moisture monitoring in sealed and insulated attic homes, there is crucial need for long-term data and advanced modeling of these approaches in the California new and existing home contexts.

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Section: Moisture Performance Of Sealed and Insulated Atticsmentioning

confidence: 99%

Section: Measured Airtightness Of Sealed and Insulated Atticsmentioning

confidence: 99%

Section: Observed Construction Defectsmentioning

confidence: 99%

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A Literature Review of Sealed and Insulated Attics—Thermal, Moisture and Energy Performance

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Walker

Levinson

2016

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“…Almost as soon as sealed and insulated attics gained popularity, their potential to lead to moisture and mold problems became evident (Rudd, 2005;Ueno & Lstiburek, 2015).…”

Section: Introductionmentioning

confidence: 99%

Sealed and Insulated Attic Hygrothermal Performance in New California Homes Using Vapor and Air Permeable Insulation—Field Study and Simulation

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Walker

Slack

et al. 2019

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Company -were selected to administer the EPIC funds and advance novel technologies, tools, and strategies that provide benefits to their electric ratepayers.The Energy Commission is committed to ensuring public participation in its research and development programs that promote greater reliability, lower costs, and increase safety for the California electric ratepayer and include:• Providing societal benefits.• Reducing greenhouse gas emission in the electricity sector at the lowest possible cost.• Supporting California's loading order to meet energy needs first with energy efficiency and demand response, next with renewable energy (distributed generation and utility scale), and finally with clean, conventional electricity supply.• Supporting low-emission vehicles and transportation.• Providing economic development.• Using ratepayer funds efficiently. ABSTRACTThis project investigated the thermal and moisture performance of a low-cost approach to sealing and insulating attics using glass fiber insulation. The work included a combination of:(1) field measurements of attic and HVAC system performance in two new, high performance homes in California's Central Valley (Fresno), and (2) hygrothermal simulations of attic performance. Each field study attic was continuously monitored at multiple locations for over a year for wood moisture content, air humidity, condensation, temperature, and heat flux, together with on-site weather and solar conditions. The Fresno test home showed periodic condensation and high surface wood moisture content, but no surface mold or degradation upon visual inspection at the end of the test period. The Clovis test home showed less indication of high moisture levels-either from surface condensation or wood moisture content-but did have visible suspected mold growth on the inside of the North sheathing at the end of the field testing. These results show the limitations of current moisture measurement techniques focused on wood moisture content, rather than potential for mold growth. From a thermal/energy perspective the attics were close to indoor conditions thereby realizing the design intent for reducing duct system losses. Simulated site HVAC energy savings for sealed vs. vented attics averaged 18% across California climate regions (8% TDV energy savings). Savings were dominated by heating energy reductions; cooling savings were substantially lower. The moisture issues are investigated in greater detail in the simulations.First, we identified the climate regions and house characteristics that are associated with increased risk of mold growth or wood rot in new CA homes. Climate region was very important in determining risk, as were house features that reduced outside air exchange (e.g., 1story homes, very tight envelopes, very tight attics, no IAQ fan), along with those that increased flow of moist air from the living space to the attic (e.g., supply ventilation fans, larger ceiling leaks, duct leakage). Second, we investigated several approaches to reduce moisture risks, and the best appr...

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“…Heat and moisture models were provided by Burch and Luna (1980), Ford (1982), Cleary (1984) and Gorman (1987).These references represent the work completed up to 1990. Several attic performance models have appeared since then: Straube et al (2010), Salonvaara et al (2013), Roppel et al (2013) and Ueno and Lstiburek (2015).…”

mentioning

confidence: 99%

Must attic ventilation be preserved in energy retrofits?

Rose

2019

IJBPA

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Purpose The addition of thermal insulation into attics along with air-tightening of the ceiling plane is a common first step in making homes more energy efficient. Attic ventilation was introduced decades ago on the assumption that air leakage across the ceiling was inevitable and not correctible – this was before the era of spray-applied foams. Often attic ventilation is provided at roof eaves, and ensuring good insulation in their location is critical to avoid cold corners in the rooms below. So may vents be blocked in the course of energy retrofits? The paper aims to discuss this issue. Design/methodology/approach This study consists of a simple spreadsheet model of attic performance. The model is built using material from ASHRAE Handbook Fundamentals and ASHRAE Standards. It includes: Glaser calculations for temperature, vapor pressure and vapor pressure excess; radiation exchange – solar and sky; buoyancy flow assumption for leakage from indoors; wind flow assumption for leakage from outdoors; and change in attic air RH as assumed indicator of change in sheathing moisture performance. Findings The model results show that lowered moisture contributions across air-tightened ceilings may compensate effectively for added insulation (which lowers the attic air temperature) and reduced moisture dilution from attic ventilation. Originality/value These results provide support for the policy of allowing attic ventilation reductions that are proportionate to ceiling air leakage reductions as part of weatherization efforts. Given the limitations of the model, continued field observations remain critical.

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Field Testing Unvented Roofs with Asphalt Shingles in Cold and Hot-Humid Climates

Cited by 5 publications

References 0 publications

A Literature Review of Sealed and Insulated Attics—Thermal, Moisture and Energy Performance

A Literature Review of Sealed and Insulated Attics—Thermal, Moisture and Energy Performance

Sealed and Insulated Attic Hygrothermal Performance in New California Homes Using Vapor and Air Permeable Insulation—Field Study and Simulation

Must attic ventilation be preserved in energy retrofits?

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