The “building envelope” refers to the external walls, windows, roof, and floor of a building. This barrier between indoors and outdoors is important with regards to ventilation and insulation of a conditioned space. A “tighter” envelope (i.e. one with fewer gaps through which air can flow) more effectively keeps conditioned air in, reducing the load on the HVAC system, and therefore increasing the efficiency at which it operates. Similarly, insulation helps slow the conduction of heat through walls. Improving the efficiency of the building envelope is generally a low-cost, high-return method for increasing efficiency in buildings.
High Performance Features
Air Sealing and Testing
Results of High Performance Envelope design with substantial energy savings are being reported as high as 46% and air barrier design and testing nationwide for over 1 billion dollars of construction across the U.S. in the past 5 years. Air sealing older buildings, which were most likely built with little attention to enclosure tightness, is an essential ingredient to improving their energy efficiency. Air sealing alone can save 10% to 20% of single family home energy use (DOE). Cutting down on heat loss or gain from uncontrolled infiltration is the first step in a retrofit and a prerequisite for implementing other energy savings measures, such as adding insulation or upgrading equipment. The benefits to air sealing and testing your building include:
- Controlling heat loss and/or gain through the envelope in order to save energy
- Improving comfort by eliminating drafts and temperature swings
- Avoiding moisture problems that may form when uncontrolled air leaks bring moisture into building cavities
- Minimizing air movement between apartments and other spaces to prevent transfer of contaminants and improve IEQ
- Improving equipment performance.
The economic impact of air sealing can most readily be measured by energy savings and accounted for in other building influencers such as moisture, indoor air quality, and equipment performance to add benefits to the building owner and occupant.
- Learn more about Air Leakage Testing and Air Sealing from DOE here.
- BSD-040: Airtightness Testing in Large Buildings
Avoiding Moisture and Mold with the Building Envelope
Moisture in envelope assemblies can cause numerous problems affecting the IAQ of a building and the longevity of building components. If elevated moisture levels persist on or inside a wall or roof assembly, these can lead to the growth of microorganisms such as mold and bacteria, as well as infestation by insects. The metabolism of mold and bacteria can create microbiological volatile organic compounds (MVOCs) that adversely affect air quality inside the building. Building materials and construction methods have changed over time from labor intensive uninsulated assemblies of natural materials to labor efficient assemblies of engineered products that result in more comfortable and highly energy efficient buildings. Current construction is much more air tight and highly insulated than those of old. Although, Moisture enters and leaves envelope components. Mold growth and deterioration will be avoided as long as there is a balance between wetting and drying of the component so that the moisture storage capacity is not exceeded. Assemblies with a large amount of storage capacity such as massive masonry construction will be more forgiving of periodic wetting as a result of being able to store moisture. Modern construction generally has less storage capacity so that it is more sensitive to leaks. Visit the FAQ page for additional resources on addressing moisture control.
Performance Practices & Solutions
- Integrity Testing for Roofing and Waterproofing Membranes
Integrity testing is the ‘holy grail’ of building envelope work. To have an assurance that the portions of a building that are expected to get wet due to weather are in a condition to prevent water transmission to the interior is the goal of every contractor, as well as every owner
- What design strategies maximize building envelope performance?
We created a catalogue and teaching tool to help design teams integrate innovative energy, performance, and comfort strategies into building projects earlier and more effectively. Our goal was to provide a strong base of knowledge around building science and physics to serve as a platform to understand both existing low-tech or passive building solutions and new developments in the design of building facades.
- SIP Project Example
Building professionals have used SIPs successfully for decades in all U.S. climate regions and in all types of buildings. An example that illustrates well the panels’ use in educational facilities is the Little Big Horn College Health & Wellness Center in Montana. The College wanted an energy-efficient building targeted to LEED Platinum standards.
- Guide to Better Building Envelopes for Large Buildings – 2016
This Guide is intended to provide an overview of some best practices for the design and construction of more energy efficient building envelopes. This Guide is focused on larger buildings; generally, this means buildings with a footprint over 6,000 sq. ft. that are primarily institutional, commercial or industrial in use. Readers who work in the multi-unit-residential sector may also find some of the Guide’s content useful. The Guide also primarily apples to new construction projects.
As the first Passive House public school in North America, the Center for Energy Efficient Design (CEED) in Rocky Mount, Virginia, is a national model for green school construction. Though initially conceived as an earth sheltered structure, the 3,600 SF high-performance school building evolved to Passive House when Passiv Science founder Adam Cohen and team demonstrated the approach’s superior energy efficiency and lower construction expense. The school cost $26,000 less to build, thanks to a high-performance building envelope that pushed heating and cooling demand so low that expensive mechanical systems could be eliminated and replaced with simpler, smaller equipment.