Understanding Pressure and Thermal Boundaries for Efficient Weatherization
This training session focuses on the critical concepts of pressure and thermal boundaries in building science. Participants will learn to differentiate between air and thermal barriers, recognize their locations, and identify common breaks that can impact efficiency and comfort. Insights on using blower door tests to assess air barrier integrity will be provided, along with strategies for effective air sealing. Emphasizing the importance of continuous barriers, this session ensures participants understand the significance of proper boundary alignment in weatherization efforts for improved dwelling performance.
Understanding Pressure and Thermal Boundaries for Efficient Weatherization
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Presentation Transcript
Overview • Introduction to the Weatherization Assistance Program • Communication Skills • House as a System • Building Science Basics • Blower Door Basics • Pressure and Thermal Boundaries • Combustion Safety • Worker Safety • Materials, Tools, & Equipment • Typical Weatherization Measures • Mobile Home Basics • Multifamily Basics
Learning Objectives PRESSURE & THERMAL BOUNDARIES By attending this session, participants will: • Understand the difference between the thermal boundary and the air or pressure boundary, and the behavior and function of each • Know the proper location of the pressure and thermal boundaries • Know common sites for breaks in the pressure and thermal boundaries • Understand what is meant by inside and outside in terms of air barrier, and how a blower door is used to determine that
Thermal & Air Barriers PRESSURE & THERMAL BOUNDARIES For maximum efficiency and comfort, the thermal and air barriers must be continuous and in contact with each other.
Thermal & Air Barriers PRESSURE & THERMAL BOUNDARIES An uninsulated attic hatch is a gap in the attic’s thermal barrier Air Barrier Thermal Barrier
PRESSURE & THERMAL BOUNDARIES A mechanical chase containing ducts can break the attic’s air barrier Air Barrier Thermal Barrier
Moisture PRESSURE & THERMAL BOUNDARIES Moisture flows with warm air through breaks in the air barrier, causing damage when it condenses on cool surfaces. Air Barrier Thermal Barrier
Blower Door Test PRESSURE & THERMAL BOUNDARIES ΔP = -50 Pa Blower Door
Zone Pressure Diagnostics PRESSURE & THERMAL BOUNDARIES Pressure difference of attic with reference to the house should be close to -50 Pa ΔP = -50 Pa Blower Door
Zone Pressure Diagnostics PRESSURE & THERMAL BOUNDARIES Pressure difference of interior wall with reference to the house should be close to 0 Pa ΔP = 0 Pa Blower Door
Where Is the Air Barrier? PRESSURE & THERMAL BOUNDARIES Cape Cod1½ Story House
Where Is the Air Barrier? PRESSURE & THERMAL BOUNDARIES Pressure difference of the floor cavity with reference to the house should be 0 Pa. But, is it?
Where Is the Air Barrier? PRESSURE & THERMAL BOUNDARIES Targeted air sealing defines air barrier
Where Is the Air Barrier? PRESSURE & THERMAL BOUNDARIES Pressure and thermalboundaries are now aligned
Summary PRESSURE & THERMAL BOUNDARIES • For maximum efficiency and comfort, the thermal and pressure boundaries must be continuous and in contact with one another • Electrical and mechanical chases, missing top plates, knee walls and dropped ceilings are common trouble spots • Pressure diagnostics determine location and condition of air barrier • Zonal pressure readings in conditioned spaces should read close to 0 WRT inside • Targeted air sealing defines the pressure boundary
