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TIGHTEN YOUR BUILDING SHELL TO KEEP YOUR MONEY FROM ESCAPING!


Your building shell (or building envelope) consists of your building’s roofing, walls, doors, windows and foundation, and it is one of the first places you should look for savings when upgrading your facility.  The building shell plays a critical role in controlling heat flow into and out of your building and in helping to minimize the energy consumed by your heating, ventilation and air conditioning (HVAC) system to provide comfort to occupants.  The main types of heat flow through the building envelope are conduction, infiltration and solar radiation.  Conduction is the flow of heat from hot to cold through materials (such as windows and walls).  Infiltration refers to a form of convection where heat flows via air movement.  During the winter, the temperature gradient between the inside of a building and the outside air can be significant, and you may notice drafts where heat is flowing out of your building.  Finally, solar radiation can add significant amounts of heat to your building during all seasons, potentially decreasing heating loads in the winter or increasing cooling loads in the summer.

Insulation, building sealing materials and techniques, and proper maintenance are used to try to control these heat flows for your benefit.  The answers to the following questions will help get you started in identifying opportunities for upgrading all aspects of your building shell to save energy and money while increasing occupant comfort.  A separate energy savings guide is available for specifically addressing your HVAC System.

Building Shell FAQ

  1. How can I evaluate the performance of my building shell?
  2. What are some simple steps I can take to tighten my building’s shell?
  3. How does insulation impact the performance of my building’s shell?
  4. What should I look for if I am upgrading my building’s roofing materials?
  5. Are there any steps I can take to improve the performance of my windows without replacing them?
  6. I am ready to replace my windows.  What should I consider in selecting my new windows?
  7. How can adding insulation to my building’s foundation affect the performance of my building’s shell?
  8. What incentives and rebates are available to help reduce the cost of my building shell upgrades?

1. How can I evaluate the performance of my building shell?

Consider hiring a contractor to perform a commercial energy audit to evaluate your building shell and internal systems. Check out our listing of contractors in your area. Blower door tests can be used to identify gaps in your building shell that are contributing to infiltration.  Thermal scans of your building can identify areas that would benefit from increased insulation.  Your utility may offer low or no cost commercial energy audits to get you started with the process.  Check the Energy Action Planner to view the options available in your area.

2. What are some simple steps I can take to tighten my building’s shell?

There are fewer easy opportunities for upgrading the shell of existing buildings that are available for new construction.  For example, adding wall insulation in new construction can be a relatively easy process, while adding wall insulation in an existing building can be expensive since it can require renovation. However, some simple opportunities may be available:

  • Fill gaps around doors and window frames with caulk, spray foam or insulative batting.
  • Check the weather stripping around windows and doors.  If weather stripping is missing, hard or cracked, replace it.  If there are significant gaps under exterior doors (i.e., you can see daylight), consider installing a door sweep.
  • Roofs and attics should be prioritized during insulation retrofits due to excellent opportunities for easy installation and significant energy savings during both the heating and cooling seasons.
  • If engaging in new construction, select materials that have a lower rate of thermal conductance (i.e., a high “R-value”) in order to minimize heat escaping.  For example, wood and masonry will conduct heat at a significantly lower rate than metal framing.  If you are using a high thermal conductivity framing material, like aluminum studs, consider using insulating materials or wraps to enclose wall and ceiling assemblies to reduce heat conduction.

3. How does insulation impact the performance of my building’s shell?

  • Insulation slows the transfer of heat through the building shell.  Higher R-values for insulation indicate that less heat will be conducted through the material in a given amount of time.  Improved insulation combined with better air sealing can cut your energy bill by up to 20%.
  • In selecting insulation, check for the R-value (the higher the value the better!), the types of spaces in which the selected material can be used, and any safety precautions or fire hazard related restrictions prior to installation.
  • Note that insulation placed between framing materials does not reduce heat transfer through framing materials.  Framing materials can act as thermal bridges, or connections between the outside and the inside of the building, that reduce the overall R-value of the building shell (walls and roof) by allowing more heat transfer.  Framing materials need to be wrapped or enclosed with insulation or other barriers in order to reduce the heat conduction through these thermal bridges.
  • If exterior walls or walls connected with unconditioned spaces (e.g. garage) are exposed during a renovation or new construction, consider installing a quality building wrap or high R-value insulation to significantly reduce air and moisture infiltration into the conditioned (i.e., heated/cooled) space.

4. What should I look for if I am upgrading my building’s roofing materials?

  • Purchase ENERGY STAR® qualified roofing products.
  • If replacing your roof, consider specifying installation of insulation under the roof.  Two inches of rigid board insulation can be applied to the outside surface of the roof prior to installing the roof covering.  For most commercial building attics in Colorado, an R-value of at least 38 is recommended.
  • In addition to installing insulation, add radiant heat barriers to the underside of your roof (i.e., in your attic) to save additional energy in the summer and winter.
  • If your roof has a vented attic or crawlspace, fiberglass blanket or blown-in loose insulation can be applied to the attic floor to increase the R-value.  Avoid the use of attic floor insulation if water pipes rely on heat from the conditioned space in your building to prevent potential freezing.  Insulate the attic ceiling instead of the floor if this is the case with your building.
  • If the attic is unvented or if there is frequent foot traffic on the attic floor, rigid board or spray-on foam insulation can be applied to the inside of the roof surface.
  • The effectiveness of roof insulation can be reduced by up to 20% if structural members (i.e., joists) are left uninsulated.
  • Built-up roofing systems can be used to retrofit flat or low-sloped commercial or public buildings to add multiple layers, including a roof deck, vapor retarder, insulation, membrane and surfacing material, in order to reduce wasteful heat flow through your building’s roof.
  • “Cool roofs” are light-colored roofing options that reflect much of the heat otherwise absorbed in darker color roofing shingles. Discuss with your roofing or HVAC professionals whether cool roofing is a viable option for reducing the solar heat gain in your facility to save on air-conditioning costs.  ENERGY STAR® qualified cool roofing products can reduce the temperature of your building’s roof by 50-70°F on a sunny day.  Cool roofs are most cost effective when:
    • Installed as part of new construction or major renovations
    • Old HVAC systems need to be replaced
    • The building has three or less floors, has a flat-roof and is air conditioned
    • Little or no roof insulation is present, and
    • The climate is hot and sunny in the summer
  • The ENERGY STAR® Roofing Comparison Calculator can help you make better informed roofing decisions.
  • For additional discussion on roofing options, including information on green roofs and photovoltaic systems, see the roofs section of the Reducing Supplemental Loads chapter of ENERGY STAR®’s building upgrade manual.

5. Are there any steps I can take to improve the performance of my windows without replacing them?

  • Retrofittable window films can be used to significantly improve the performance of windows without requiring the expense of window replacement by limiting both the amount of solar radiation entering and the amount of internal heat escaping through a window.  They are applied directly to the interior surfaces of existing windows and have lifetimes of 5-15 years.
  • During the heating season in colder climates, more heat generally escapes through windows than enters the building through solar radiation.  Window films can reflect radiant heat back into the room to reduce heating loads.
  • During the cooling season, window films can reduce solar heat gain at the window prior to the heat entering the room in order to reduce cooling loads.
  • According to the Reducing Supplement Loads chapter of the ENERGY STAR® Building Upgrade Manual, window films may be cost effective where any or all of the following are true:
    • Windows account for greater than 25% of the building’s outer surface area.
    • The building is not well shaded by vegetation and is in a sunny climate.
    • Direct sunlight hits windows on the west and south sides of the building.
    • The building has single-pane windows.
    • Windows are not already tinted, colored or designed with reflective coatings.
    • Reducing peak cooling demand in the summer can save the building significantly on utility peak demand charges.
    • Fan and cooling systems can be potentially downsized if peak cooling load is reduced, thereby reducing your electricity bill.
  • Window films typically cost between $1.35 and $3 per square foot installed.  It may be more economical to only install films on south or west-facing windows or to completely replace old, drafty, single-pane windows.
  • In addition to window films, interior or exterior window coverings such as shades, blinds, curtains and louvers can be used to reduce solar heat gain through windows.

6. I am ready to replace my windows.  What should I consider in selecting my new windows?

  • Windows tend to represent the largest source of unwanted heat gains or losses in a building as even high performance windows have lower R-values than walls and roofs, and they are often sources of air leakage.
  • Full window replacement can be economical as part of a major renovation.
  • If your building was built in the 1960s or 1970s, you probably have very inefficient single-pane windows and should consider replacing with modern windows.
  • For selecting windows and frames consider:
    • Purchasing ENERGY STAR® qualified windows.
    • Selecting double or triple-paned glass that is advertised as Low-E (low-emissivity) and has appropriate tinting for your building’s orientation.
    • Using windows with insulated frames that use low-conductivity materials and have glass panes filled with inert gases (e.g. krypton, argon or nitrogen)
    • Computer modeling can be used to determine the most appropriate window and glazing system for your climate.  Consult with a window installation professional for your options and pricing.

7. How can adding insulation to my building’s foundation affect the performance of my building’s shell?

  • Insulating foundations can result in warmer above grade floors in winter months, increasing occupant comfort.
  • Increasing basement insulation levels can make the space more usable for a variety of purposes.
  • The structural integrity of a foundation can be potentially compromised if there is inadequate insulation and moisture control.
  • Insulating and sealing a foundation can save energy but also leads to a tighter building with fewer air exchanges.  Be sure that radon is tested for, and is properly mitigated if present, as greater accumulation of radon levels can occur as a result of fewer natural air exchanges.

8. What incentives and rebates are available to help reduce the cost of my building shell upgrades?

Incentives and rebates may be available to help your business with its building shell upgrade efforts.  Use Recharge Colorado’s Energy Action Planner to identify opportunities that match your needs.