Page 25 - Zero Net Energy Case Study Homes-Volume 2

PASSIVE HOUSE LOS ANGELES (PHLA+) CASE STUDY NO. 6
Sidebar: Airtightness
One of the keys to minimize energy use in residential construction is airtightness. Building sci- entists confirmed this in the 1970s, and it led to many construction techniques, products and testing methods that are used today. These are essential in ZNE residential structures, as will be discussed in all the case studies in this book.
One of the principal techniques to develop airtightness is to seal the wall and roof planes using air/vapor barrier tapes and sheet material, plus carefully seal the joints at exterior windows and doors.
Another important technique is to seal the joint between the framing and the foundation system. This is achieved by using gaskets between the foundation and the framing to seal that common source of air leakage. The gaskets are typically compressed down to 1/16”, which create an airtight seal.
Good quality (airtight sealing) windows and doors are essential. It is important to seal around these openings between the frames and the flashing material.
With “airtight” construction techniques employed to the appropriate degree, the house is then tested using a Blower Door1 and associated testing meters and recording devices.
The result of the test is a number that gauges the airtightness of the house, typically reported as ACH50, the number of times that the volume of the indoor air would be replaced during an hour, or air changes per hour, at 50 pascals of pressure. The house is pressurized using the blower door and then the pressure difference is measured between inside and outside (after any leak points are located and sealed).The benchmarks for airtightness of a house can be described as follows:
• >20 ACH50: poor airtightness (i.e., leaky) house
• • •
5 ACH50: adequate tightness per California Title-24 energy standards 2.5 ACH50: “stuffy” house—needs fresh air ventilation system
0.6 ACH50: Passive House2 standard
1 For a description of the Blower Door Test, see https://www.energy.gov/energysaver/blower- door-tests.
2 https://passipedia.org/planning/airtight_construction/general_principles/blower_door_test
(Above, left) An installed Blower Door with pressurizing fan; (Above, center) Close-up view of the pressurizing fan; (Above, right) Air- tightness measurement device, called a manometer, for testing the number of air changes per hour at a certain air pressure created by the Blower Door. (Photos by Christian Kienapfel)
Zero Net Energy Case Study Homes: Volume 2
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