In my newsletter articles this year, we have been discussing new trends in energy codes along with energy-saving initiatives that Owners could take right now as part of their normal operating procedures and capital replacement plans. The last article focused on retro and recommissioning of HVAC systems to correct poor performance of equipment and controls. In this article, we will explore some other options that will improve system performance and lower operating costs as a result of improved and more energy efficient building envelope systems.
The term “building envelope” refers to all of the elements of the outer shell of a building that maintain a dry, heated, and cooled indoor environment and facilitate climate control. For design of new buildings, there are both updated codes and new building codes that affect the design and construction as it relates to the building envelope, and many of the recommendations discussed below will be incorporated into the design. These recommendations can also be implemented during capital replacement of older building roofs; exterior finishes, including siding, stucco, EIFS, or masonry; windows; and doors.
Building roofs, whether low slope asphalt-based systems, single-ply synthetic systems, high slope shingles or tile, or metal, have definite effective useful lives based on the materials used, workmanship of the original installation, routine maintenance, and exposure to sunlight and rain over the years. Your capital replacement plan most likely details a predicted replacement date and cost for these major capital re-roofing projects.
We are all well aware of the problems that leaky and outdated roofs present, but they can also be a major source of energy loss in buildings. Roof systems include not only the waterproofing membranes, but also thermal insulation for the building. Wet insulation and roofing materials due to leaks lose their insulating properties and actually become heat conductors rather than an insulator.
Often it is tempting just to place a new roof over an existing membrane for price considerations, but evaluation of the condition and amount of roof or attic insulation should also be considered. A thermal infrared scan of your roof can highlight areas of inadequate or wet insulation and areas of gaps in the individual insulation boards that are areas of heat loss. If the infrared scans reveal these problems, the re-roofing project scope can be expanded to include replacement of poor performing wet and/or missing insulation. By doing this, you will improve not only your building’s water tightness at the roof level, but upgrade and improve the building’s energy efficiency.
In future articles, we will discuss in more detail various roofing options, including newer green roofs that incorporate vegetation to the roof system, cooler reflective roofing membranes, use of solar panels, and solar shingles and tiles in your re-roofing projects.
Various elements of the exterior building façade make up the building envelope. These elements include batt wall insulation between the wall studs and cavity wall insulation for masonry, exterior sheathing, house wrap weather barrier membranes (e.g. DuPont Tyvek®), and/or building felts, which are behind the actual exterior wall finishes such as siding, brick, stucco, and stone. Windows and doors also form a part of the building envelope. All of these items – from the materials used to the quality of the installation – affect energy efficiency.
As buildings age, it is necessary to replace the exterior façade. This is an opportunity to incorporate some energy efficient items into these projects. Some older buildings may not have had any air or water barriers behind the siding or stucco/EIFS that is in need of replacement, and installing these items during siding replacement can yield significant energy savings.
There are numerous weather barrier membranes on the market that are relatively easy to install and are not excessively costly. These membranes are breathable, allowing moisture vapor to pass through while blocking bulk water penetration into the wall system, which helps promote drying in wall systems to help prevent mold and water damage. DuPont also produces a weather barrier similar to the standard Tyvek® membranes, but now adds a layer of insulation equal to R-5. This new technology provides additional exterior wall insulation as a continuous barrier, which also serves to reduce thermal bridging that studs create.
Adding weather and air barriers in addition to replacement of wet and rotted sheathing and replacement and upgrade of interior wall insulation during these re-siding projects can greatly increase the energy efficiency of your building in addition to providing a new and attractive water resistant exterior finish.
Proper detailing and installation of the weather barriers along with installation of proper flashings and caulk around windows, doors, and other penetrations also helps keep water out of the wall system and building interiors. If total siding or exterior façade replacement is not in order at this time, re-caulking of the building exterior, including expansion and control joints, windows, doors, and other penetrations, with a high-quality polyurethane sealant (such as NP-1 by BASF) will not only provide enhanced protection against water penetration, but will increase energy efficiency by reducing the leakage of air from conditioned spaces through the building envelope.
Replacement of older windows and exterior doors is also a normal capital replacement budget expense. Advances in window technology over the years has led to increased energy efficiency and performance of windows and glazing. Older single-pane windows can be replaced with newer windows that have energy efficient upgrades, such as insulated or double/triple-pane glass with inert gas or a vacuum between the panes of glass, which cuts down heat flow through the glazing. Replacement windows should also have low emissivity glass (low-E) that will reflect infrared radiation, which reduces heat transfer without affecting the natural lighting coming through the window. Thermal breaks, which are plastic or rubber separator materials that minimize heat transfer and conduction across inner and outer window frames, are also often included in high-quality windows.
If total window replacement is not a possibility or immediate need, then repairs of broken and failed window seals, gaskets, and thermal breaks will aid in reducing heat transfer across the window elements and save energy. Installation of solar films or tinting on existing windows will help keep rooms cooler in bright sunlight and heat, and will cut down glare. These repair and maintenance recommendations also apply to storefront and glass curtain wall systems as well as individual window units.
If you have any questions about the details of implementing building envelope energy-saving initiatives or incorporating other energy efficient projects into the overall capital plans for your community, please contact us for more information.
About the Author:
Doug McMillan, P.E., is President of zumBrunnen, Inc. He began his engineering career in 1980, and he joined zumBrunnen, Inc. in 1998. McMillan received his Bachelor of Science degree in Civil Engineering from the Georgia Institute of Technology in Atlanta, GA. He is a former Resident Engineer with the U.S. Army Corps of Engineers, and he is a member of the Society of American Military Engineers (SAME) and the American Society of Civil Engineers (ASCE). McMillan is a licensed professional Civil Engineer in the state of California.
