Construction Today - October/November 2011 - (Page 18)

Institutional BUILD TIGHT, By Jason Smith VENTILATE RIGHT W hile building energy-efficient, high-performance buildings requires some change, it is not as difficult as one might think. High quality mechanicals, smart control strategies and efficient lighting strategies are all key pieces to this puzzle, but energy efficiency really starts with the building envelope. When people think of the building envelope, they tend to think in terms of R-value, construction types, aesthetics and more recently in terms of total Uvalue and continuous insulation as well. There is an important aspect to a building envelope that is just now getting the credit it deserves – air tightness. Until recently, the specifications for wall and roof assemblies rarely required an assembly to be tested for air tightness, air barrier materials to be detailed in drawings and inspected in the field or a building to undergo a whole-building air tightness performance test. Yet, moving forward these types of specifications are going to become more commonplace as the U.S. Army Corps of Engineers (USACE) as well as several states and municipalities adopt air tightness requirements. There are four reasons to build tight: energy efficiency, comfort, moisture management and indoor air quality. son is simple: every bit of outside air that enters the building through air infiltration must then be heated, cooled and/or dehumidified to get back to a thermostat’s set point. In residential construction, air tightness is typically expressed as air changes per hour (ACH). According to studies performed by Lawrence Berkeley National Laboratory, typical existing American homes built in the last 20 years have rates of 0.5 to 1 ACH. This means that every one to two hours on average, the entire volume of air within the homes is exchanged with air from the outside. If the thermometer reads 10 degrees Fahrenheit outside, leaky buildings are not only uncomfortable, but expensive. Moisture Management Moisture transfer happens in two ways: diffusion and via air leakage. Diffusion is a slow process by which water molecules move from areas of high humidity to areas of low humidity. Vapor retarders are specified in buildings to control this process. Air leakage, on the other hand, is a very fast process and presents a much higher potential for condensation, mold and rot than diffusion. In this mechanism, moisture, as measured by humidity, is transferred into wall assemblies via air movement. It could be hot, humid air infiltrating on a hot New Orleans summer day, only to condense on the cold back surface of the interior gypsum board. Alternatively, it could be warm, 50 percent relative humidity air leaving a heated New England home on a winter day to condense on the cold back surface of the exterior sheathing. While vapor retarders are important contributors to moisture management, air barrier materials and tight buildings are the first line of defense against moisture problems. Indoor Air Quality The notion that one does not want to build a building too tight is largely grounded in the fact that building occupants need fresh air. While it is true that occupants need fresh air to maintain a healthy, comfortable space, the concept of “build tight, ventilate right” is changing the misconception that a tight building is bad for indoor air quality. The key difference with a tight building is that ventilation is controlled mechanically. Rather than allowing fresh air to enter whenever Energy Efficiency and Comfort According to the Department of Energy (DOE), uncontrolled air leakage in a typical building can account for as much as 30 to 50 percent of a building’s heating and cooling costs. The rea- 18 CONSTRUCTION-TODAY.COM OCTOBER/NOVEMBER 2011 http://www.CONSTRUCTION-TODAY.COM

Table of Contents for the Digital Edition of Construction Today - October/November 2011

Construction Today - October/November 2011
Energy Efficiency
Green Building
Executive Perspective
Best Practices
Bernards Construction – El Capitan High School
Bogner Construction Co. – College of Wooster Scot Center
Jean McClung Middle School
Hellas Sports Construction
The Walsh Group – NOAA Pacific Regional Headquarters
Haskell Co. – Scripps Proton Therapy Center
Robert A. Bothman Inc. – Stockton Unified School District
JE Dunn – Energy Systems Integration Facility
Rosendin Electric – AVUHSD Solar Project
Ratcliff Construction Company – Crossroads Church
University of Texas Southwestern Medical Center
Flintco Pacific – Calaveras County Adult Detention Facility
Lee Lewis Construction – Angelo State University’s Plaza Verde Student Housing
Manhattan Construction – First Baptist Church of Dallas
Market & Johnson – Eau Claire County Courthouse project
McTech Corp – 97th Military Police Battalion Headquarters
Parkland Health & Hospital System
RBC Construction
Central Building and Preservation – Randolph Tower City Apartments
Scaparotti Construction Group
Trinity Properties – Trinity Place
Advanced Real Estate Services
Lawrence B. Wohl Inc./Wohl Diversified Services
TN Ward and Commercial Interiors – Maryland Live
ASX Construction – Parc Lafayette
Bayland Buildings Inc.
Dependable Mechanical Systems
New Dawn Developments
DSLD Homes
Aquilini Development and Construction Inc.
Cobalt Construction – Meta Housing
Lifestyle Communities
Pratt and Associates LLC
Miramonte Homes
MP J.J. Duffy Joint Venture/Pathway Senior Living LLC – Victory Centre Vernon Hills
Woodland Homes
Aecom/Inima Joint Venture – Hialeah, Fla., Water Treatment Plant
MWH Constructors – Austin Water Treatment Plant No. 4
Pepper-Lawson Construction – Missouri City Surface Water Treatment Plant
MWH Constructors – AWT Improvements
Blount Contracting Inc.
Harbor Offshore Services
Cruz Construction Inc.
Humble Construction
Nova-Con Projects Ltd.
Trimen Electric
EllisDon Corp. – Atlantic Region
EllisDon Corp. – St. Joseph's Regional Mental Health Care
Focus Equities
Intercom Services Immobiliers
George Brown College – New Waterfront Campus
Seaside Transportation Services
Last Look

Construction Today - October/November 2011