As summarized within the Success tab, before beginning this work, inspect the interior and exterior of the building, including each window, to identify impacts and potential risks with completing the work. Diagnose water and air infiltration pathways, and choose strategies most appropriate to address each leak.
Replace the existing window sash with a new sash including an insulated glass unit appropriate for the climate and containing a low-E coating. Completely remove and dispose of or recycle the old window sashes. Remove existing sash weights. Recycle the cast iron weights. Air seal and insulate the sash weight cavities. Air seal the existing window frame casing and install a liquid applied waterproof membrane to the window jamb. Install replacement sashes according to manufacturer’s instructions.
See the Compliance tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Single-Family New Homes, and Indoor airPLUS.
Before beginning this work, the window should be assessed as outlined within the Success tab.
In this measure, the window frames are typically retrofitted with new jamb liners that provide the tracks for the sashes to ride in, and eliminate the need for sash weights. Prior to the installation of the jamb liners, it is recommended the frame be cleaned and the corner interfaces between the head, jambs and sill caulked. When large window sashes are being replaced it may be beneficial to build out the casing or sash stop to cover the liner.
Coat the jambs with a liquid applied waterproof membrane, or at minimum, high quality paint (such as an elastomeric paint). The membrane should extend down onto the sill. Where exposed it can be painted to match the rest of the sill and trim color. These measures are water control improvements, which increase the water resistance of the existing sloped wood sill, and allow any incidental leakage to drain to the exterior.
The space between the jamb liners and window frame should be sealed at the jambs and head on both the interior and exterior, for air barrier continuity. Where the jamb liners interface with the sill, they should be left unsealed to allow the space to weep out at the bottom.
Install the jamb liner and replacement sash according to manufacturer’s instructions.
Prior to any retrofit work being conducted, it is important that the following conditions of the building systems be reviewed:
- Lead and other hazardous materials
- Site conditions and project staging
- Identification of water infiltration concerns
- Identification of deteriorated or damaged materials
- Identification of user comfort concerns
US EPA: Lead in Painting, Dust and Soil: Renovation, Repair Painting
OSHA: Fall Protection (if window work is to be done at height, from the exterior)
Lead and Other Hazardous Materials
Old wood windows and trim are a common location of lead paint in homes. Any work being completed on the window systems should follow all appropriate state and federal laws regarding handling of hazardous materials.
Site conditions and Project Staging
The home and site should be reviewed to identify impacts and potential risks with completing the work.
If the work is to be done for the exterior, scaffolding, lifts, ladders, or other means to access work areas may be needed. Work done at height may require fall protection be used. Proximity to adjacent property or vegetation may limit access or create unsafe work areas. Exterior staged work may also damage existing landscaping or vegetation.
If the work is intended to be completed from the interior, consideration should be given to disruption of the occupant and clearances for moving equipment and materials into and out of the space. With any interior work there is always a chance of damage to interior finishes. Appropriate planning and protection is required.
Identification of Water Infiltration Concerns
Windows, above all other enclosure systems, are a common location of water infiltration issues. It is important to understand the various pathways for potential water infiltration, and identify current water leakage problems. While the details presented in this document are all intended to improve the moisture performance of the window assemblies, it is not intended to address all possibilities, and is not a replacement for inspection and evaluation of the performance of an individual window. Existing problems should be identified, and the strategy chosen that will be most appropriate to address the concern. Window systems water leaks can be grouped into four general categories (Figure 1 below):
- Between the window frame and rough opening
- Through the joints in the window frame
- Between the window frame and the operable sashes
- Through the joints between the glass and the sash frames
Prior to any work being done, interior and exterior inspection and monitoring of the conditions of the building should be completed. Water staining, peeling paint or wall paper, and staining on trim or floor assemblies below window systems are indications of water infiltration and/or condensation. Leakage between the sashes and the frame and between the glass and the sash is usually marked by water staining on the interior window frame itself. Condensation on the window frames can also lead to staining of the interior finishes. It is important to monitor the questionable area to prevent a false diagnosis of the water management problem being experienced.
Leakage between the window and rough opening or through the joints in the window itself are typically contained within the wall assembly and may go unnoticed, or could manifest as staining and peeling paint below the window or damaged flooring.
Other problems such as water infiltration at the window head may be indications of failed or missing head flashing. However, other problems not associated with the window system may in fact be the cause of the water infiltration. Care must be taken to properly diagnose the infiltration pathway.
If it is a known recurring problem, then the infiltration problem must be addressed prior to or in conjunction with the window retrofit work.
If no obvious signs of water infiltration problems exist and the window elements and connection wall components are in good condition, no additional work may be needed. However, as stated above, water infiltration problems are often concealed within wall cavities with no outward signs. This becomes more of a concern if the window retrofit work is being done in conjunction with the addition of cavity fill insulation. With the addition of insulation to the wall cavities, water infiltration problems that previously may have had sufficient drying ability, may now lead to prolonged moisture accumulation. Prolonged moisture accumulation can lead to material deterioration. If there is suspected leakage, then further investigation, including but not limited to thermal scans, moisture content measurements, and cutting of investigation holes below window assemblies to look for signs of moisture problems would be recommended.
Unless the problem is obvious, it may be prudent to contact someone with experience with diagnosing water infiltration problems prior to proceeding.
Identification of Deteriorated or Damaged Materials
If damage to existing elements is noted, the materials should be removed and replaced as part of the retrofit. Certain elements will be more critical to the proper implementation of the chosen strategy.
The window sill is arguably the most important element of the window assembly, as water will drain downward by gravity either into the wall (e.g., hole through sill) or directly onto the wall (failure of the sill extension). For all proposed measures in this document excluding complete window replacement, the condition of the sill is critical to the performance of the measure. Cracked or rotting sills need to be replaced prior to any work being done.
The window frame including the exterior casings is the next most critical element. If the casing is deteriorating, its replacement may be warranted. This should not be confused with the exterior trim, which is often installed as a decorative element on top of the casing.
Deteriorating trim may not affect the water management performance of the window however; it may be an indication of other problems and generally creates an aesthetic problem.
Depending on the measure being examined, the condition of the window sashes may or may not be a concern to the performance of the measure taken. For window rehabilitation, sash retrofit, or interior storm retrofit, the condition of the sashes is critical to the performance of the window. For exterior storms, the sashes are more protected from the elements, and the condition is less important from a water management perspective, yet still critical from an energy and condensation resistance perspective. For sash replacement, window insert, or full window replacement, the condition of the sash is irrelevant, as they will be removed. For this reason, windows with severely deteriorated sashes may be better candidates for the latter retrofit measures.
Identification of User Comfort Concerns
As part of the initial review, associated comfort concerns relating to the window systems should be evaluated. Window air leakage is a significant source of occupant comfort problems. Unlike other common enclosure leakage pathways, window air leakage is commonly very direct, resulting in distinct drafts.
Radiation effects from cool glass surfaces are another common comfort problem. This is more difficult to identify, as the tendency is to assume that the discomfort felt when near a window is from air leakage or drafts. This results in some misdiagnosis of the dominant function. A general recommendation is to increase the interior surface temperature of the window system to reduce the radiant heat transfer from the occupant to the window. This is commonly done by adding additional panes of glass (or films) to create an insulating air (or other gas) space between the layers.
Window Sash Replacement
Window Sash Replacement is an option to replace the window sashes while leaving the existing frame in place. This is a good option if there is a desire to maintain the original appearance, but the existing sashes cannot accommodate new insulated glass units (IGUs), or are in sufficiently poor condition to warrant replacement in lieu of rehabilitation. The replacement sashes must be custom built for the frame opening, as there is very little opportunity for adjustment. Window frame condition and geometry can be a factor. The window jambs however need to be very close to parallel to allow for smooth operation and to prevent unwanted air leakage between the frame and sash. If the replacement sashes are made from wood, the windows can be out of square to a certain degree since the top and bottom of the sashes can be cut to match the angles.
Key points to consider when selecting the Window Sash Replacement option are as follows:
- The measure is not reversible and affects the interior and exterior appearance of the building. Typically, historic review boards prefer preservation of existing windows. (The visual effect could be minimal depending on how closely the replacement sashes and muntins (grilles) match the existing sashes and muntins).
- This work should be done in conjunction with a partial rehabilitation (window frame only) as set out in the Window Rehabilitation Measure Guide.
- This work will improve the energy performance of the assembly by reducing air infiltration, as well as thermal conductance through the assembly. The replacement sashes can accommodate up to triple glazed IGUs, and low-E coating, allowing for significant improvements in thermal performance.
- This work will reduce the potential for interior condensation problems on the window system.
- Replace the sash weight and balance system (with a spring-loaded jamb liner), allowing for retrofit of the weight pockets and voids around the window frame.
- Work requires tight tolerances and is workmanship sensitive; significant air leakage can result if tolerances are too loose. Side jambs can be built out to accommodate a slightly narrower replacement sash.
- In large windows the spring-loaded jamb liner can be up to an inch thick. This may require modifications to the casing to hide the liner. The added width may reduce the visible window area.
No climate specific information applies.
The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
American Society for Testing Materials (ASTM) E2112-07
Standard Practice for Installation of Exterior Windows, Doors and Skylights. Available from ASTM. The standard covers fenestration product installation from pre-installation through post-installation procedures in new and existing construction.
2009-2021 IECC and IRC Window U-Factor Requirements Table
The maximum U-Factor and Solar Heat Gain Coefficient (SHGC) requirements for fenestration (windows) and skylights in new homes, as listed in the 2009, 2012, 2015, 2018, and 2021 IECC and IRC, can be found in this table.
2009 International Energy Conservation Code (IECC)
Section 402.3.6 Replacement fenestration. When some or all of an existing fenestration unit is replaced, including sash and glazing, the replacement unit must meet the U-factor and SHGC requirements in Table 402.1.1.
Section R402.3.6 Replacement fenestration. When some or all of an existing fenestration unit is replaced, including sash and glazing, the replacement unit must meet the U-factor and SHGC requirements in Table R402.1.1.
Section R503.1.1.1 Replacement fenestration. When an existing window is replaced, including the sash and glazing, the replacement unit must meet U-factor and SHGC requirements in Table R402.1.2.
Section R503.1.1.1 Replacement fenestration. When an existing window is replaced, including the sash and glazing, the replacement unit must meet U-factor and SHGC requirements in Table R402.1.2. Where more than one replacement fenestration unit is to be installed, an area-weighted average of the U-factor, SHGC or both of all replacement fenestration units shall be an alternative that can be used to show compliance.
Retrofit: 2009, 2012, 2015, 2018, and 2021 IECC
Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)
Chapter 5 (in 2015, 2018, 2021). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.
2009 International Residential Code (IRC)
Section N1102.3.6 Replacement fenestration. Where some or all of an existing fenestration unit is replaced with a new fenestration product, including the sash and glazing, the replacement unit must meet the U-factor and SHGC requirements of Table N1102.1.1. AJ102.4 Replacement windows. When an existing window is replaced, including the sash and glazing, the replacement must meet Chapter 11 requirements. AJ401.2 Door and window dimensions. Minor reductions in the clear opening dimensions of replacement doors and windows that results from using different materials are allowed.
Section N1102.3.6 (R402.3.6) Replacement fenestration. Where some or all of an existing fenestration unit is replaced with a new fenestration product, including the sash and glazing, the replacement unit must meet the U-factor and SHGC requirements of Table N1102.1.1. AJ102.4 Replacement windows. When an existing window is replaced, including the sash and glazing, the replacement must meet Chapter 11 requirements. AJ401.2 Door and window dimensions. Minor reductions in the clear opening dimensions of replacement doors and windows that results from using different materials are allowed.
Section N1184.108.40.206 (R503.1.1.1) Replacement fenestration. When an existing window is replaced, including the sash and glazing, the replacement unit must meet U-factor and SHGC requirements in Table N1102.1.2.
Section N1220.127.116.11 (R503.1.1.1) Replacement fenestration. When an existing window is replaced, including the sash and glazing, the replacement unit must meet U-factor and SHGC requirements in Table N1102.1.2. Where more than one replacement fenestration unit is to be installed, an area-weighted average of the U-factor, SHGC or both of all replacement fenestration units shall be an alternative that can be used to show compliance.
Retrofit: 2009, 2012, 2015, 2018, and 2021 IRC
Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)
Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.
Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
NFRC 200A-2010 - Procedure for Determining Fenestration Attachment Product Solar Heat Gain Coefficient and Visible Transmittance
The following authors and organizations contributed to the content in this Guide.
Building Science Corporation, lead for the Building Science Consortium (BSC), a DOE Building America Research Team
High-R Window = High-Efficiency Window
There are two levels of window efficiency relative to standard windows: high-efficiency (e.g., ENERGY STAR Certified windows), which perform at least 15% better than standard windows, and ultra-efficient (e.g., most triple-glazed windows) which perform at least 50% better. These windows use a combination of features to reduce heat loss or gain including two or three glass panes separated by insulating spacers, nontoxic gas (e.g., argon or krypton) in the spaces between the glass panes for better thermal resistance, a nearly invisible low-emissivity coating on the glass that keeps heat in during the winter and out in the summer. They also block damaging ultraviolet sunlight (e.g., fading curtains and furniture), and insulate frames.