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Insert Replacement Window

Scope

Vinyl frame window replacement detail
Vinyl frame window replacement detail

As summarized within the Ensuring 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.

Remove the existing window sash. 

Remove the existing sash-weight and balance system and air seal and insulate the cavity.  Windows must be custom ordered to size; however, they do not require as tight an installation tolerance as the replacement sash option.

Insulate and seal all voids and cracks between the replacement window assembly and the original window jambs, sill, and head.

Install the window insert 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 Certified Homes, and Indoor airPLUS.

Description

Before beginning this work, the window should be assessed as outlined within the Ensuring Success tab.

In this measure, the existing wood window frame should be considered to be the new window rough opening, and treated in a similar manner following current industry recommended practice for waterproofing and draining. The window frame should be cleaned of any dirt and loose paint. The parting beads and interior stops at the head and jambs should be removed from the frame. The weight pocket pulleys should be removed and the openings left by the pulleys in-filled. All corners between head, jambs, sill, and exterior casings should be sealed with caulking. This is recommended for both water management performance as well as for air tightness performance. The rough opening should then be coated on all sides with a liquid applied waterproof membrane. A membrane product is recommended in this application because the area will no longer be accessible for maintenance once the replacement window is installed.

The existing sash-weight and balance system will be abandoned. Remove the weights and air seal and insulate the cavity. Insulate and seal all voids and cracks between the replacement window assembly and the original window jambs, sill, and head.

Install the window insert according to manufacturer’s instructions.

It may be beneficial to build out the casing to cover large gaps between the casing and the new insert.

Frame preperation
Figure 1 - Frame preparation for inserting a replacement window

 

Examples of membrane installation in a wood window frameExamples of membrane installation in a wood window frame
Figure 2 - Examples of membrane installation in a wood window frame

The replacement window is typically installed from the interior: it is normally set on the sill, tilted up into the rough opening, and pushed up against the exterior casing of the window. An interior backer rod and sealant joint should be installed around the interior perimeter of the rough opening. New interior stops are then installed (or the originals could be re-installed if still in a usable condition). The joint between the window and stops is caulked for aesthetics.

On the exterior the window should be caulked to the casing on the head and jambs. However, the sill should be left to drain to the exterior.

Example sill detail of insert replacement window
Figure 3 - Example sill detail of inserting a replacement window

 

Ensuring Success

Wood window options for existing homes

Identifying Risks
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

Contractor/Homeowner Safety

US EPA: Lead in Paing, 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):

  1. Between the window frame and rough opening
  2. Through the joints in the window frame
  3. Between the window frame and the operable sashes
  4. Through the joints between the glass and the sash frames
Common window water infiltration pathways
Figure 1 - Common window water infiltration pathways

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.

Failed window sill with replacement window installed
Figure 2 - Failed window sill with replacement window installed

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.

Failed window sill with replacement window installed
Figure 3 - Failed window sill with replacement window installed 

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.

Insert Replacement Window

For window sashes that are in poor condition and/or the cost of sash rehabilitation, retrofit, or replacement is too high, a common retrofit approach is to install a replacement window in the existing wood window frame. The benefit to this is the speed of installation (very little rehabilitation of the existing window frame is needed), low disruption to the homeowner (the installation does not overly affect interior or exterior trim and finishes), and adjustment ability (while the windows do need to be custom ordered to fit the existing window frames, the tolerances do not need to be as tight or the measurements as precise as the replacement sash option). The result is a completely new window assembly. A down side to this approach is that the amount of vision area of the windows is reduced by the addition of an additional window frame with sashes. For already small window openings, this reduction may be significant and undesirable. For larger windows, the impact will be less noticeable.

Key points to consider when selecting to insert a replacement window are as follows:

  1. Affects the interior and exterior appearance of the building. Typically not an acceptable approach for historic zoned projects.
  2. The measure is not reversible.
  3. This work should be done in conjunction with a partial rehabilitation (window frame only) as set out in the measure guide Window Rehabilitation.
  4. This work will improve the energy performance of the assembly by reducing air infiltration, as well as thermal conductance through the assembly. The replacement windows can be high performance units (e.g., U < 0.25, such as triple glazed with high performance protruded fiberglass frames), allowing for significant improvements in thermal performance.
  5. This work will reduce the potential for interior condensation problems on the window system.
  6. Existing sash weight and balance system will be abandoned, allowing for an air sealing and insulation retrofit of the weight pockets and voids around the window frame.
  7. Windows must be custom ordered to size; however, they do not require as tight an installation tolerance as the replacement sash option.
  8. Vision area is reduced.
  9. Expensive option.

Climate

No climate specific information applies.

Training

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Presentations

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Videos

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CAD Images

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Compliance

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.

ASTM E-2112-07

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 IECC

Section 101.4.3 Additions, alterations, renovations or repairs. Additions, alterations, renovations or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code as they relate to new construction.  Unaltered portions do not need to comply. Exceptions are included for storm windows installed over existing fenestration and glass-only replacements in an existing sash and frame. 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.

2012 IECC

Section R101.4.3. Additions, alterations, renovations or repairs. Additions, alterations, renovations or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code as they relate to new construction.  Unaltered portions do not need to comply. Exceptions are included for storm windows installed over existing fenestration and glass-only replacements in an existing sash and frame. 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.

2015 IECC

Section R501.1.1. Additions, alterations, or repairs:  General.  Additions, alterations, or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code.  Section R503.1.1 Building envelope.  Exceptions are included for storm windows installed over existing fenestration and surface-applied window film installed on existing single pane windows.  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.

2018 IECC

Section R501.1.1. Additions, alterations, or repairs:  General.  Additions, alterations, or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code.  Section R503.1.1 Building envelope.  Exceptions are included for storm windows installed over existing fenestration and surface-applied window film installed on existing single pane windows.  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: 200920122015, and 2018 IECC

Section R101.4.3 (Section R501.1.1 in 2015 and 2018 IECC). 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.)

2009 IRC

Section N1101.3 Additions, alterations, renovations or repairs. Additions, alterations, renovations or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code as they relate to new construction.  Unaltered portions do not need to comply. Exceptions are included for storm windows installed over existing fenestration and glass-only replacements in an existing sash and frame. 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.

2012 IRC

Section N1101.3 (R101.4.3) Additions, alterations, renovations or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code as they relate to new construction.  Unaltered portions do not need to comply. Exceptions are included for storm windows installed over existing fenestration and glass-only replacements in an existing sash and frame. 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.

2015 IRC

N1107.1.1 (R501.1.1).   Additions, alterations, or repairs:  General.  Additions, alterations, or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code.  Section N1109.1.1 (R503.1.1) Building envelope.  Exceptions are included for storm windows installed over existing fenestration and surface-applied window film installed on existing single pane windows.  Section N1109.1.1.1 (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. 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.

2018 IRC

N1107.1.1 (R501.1.1). Additions, alterations, or repairs:  General.  Additions, alterations, or repairs to existing buildings, building systems, or portions of buildings or systems must meet the requirements of the code.  Section N1109.1.1 (R503.1.1) Building envelope.  Exceptions are included for storm windows installed over existing fenestration and surface-applied window film installed on existing single pane windows.  Section N1109.1.1.1 (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. 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.

Retrofit: 200920122015, and 2018 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018 IRC). 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.)

Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

More Info.

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.

Case Studies

None Available

References and Resources*

  1. Author(s): American Society for Testing and Materials
    Organization(s): American Society for Testing and Materials, ASTM
    Publication Date: January, 2018

    Standard covering the installation of fenestration products in new and existing construction.

  2. Author(s): Wilson
    Organization(s): National Research Council Canada
    Publication Date: May, 1960
    Document about condensation between the panes, on the inside surface of the outer glass of double pane windows.
  3. Author(s): EIA
    Organization(s): EIA
    Publication Date: January, 2009
    Federal statistics about national energy consumption in residential homes.
  4. Author(s): Davis
    Organization(s): Fine Homebuilding Magazine
    An article about double-hung windows.
  5. Author(s): National Fenestration Rating Council
    Organization(s): National Fenestration Rating Council
    Publication Date: January, 2010
    Standard providing a procedure for determining fenestration attachment product U-factors.
  6. Author(s): National Fenestration Rating Council
    Organization(s): National Fenestration Rating Council
    Publication Date: January, 2010
    Standard for determining fenestration attachment product SHGC and visible transmittance.
  7. Author(s): Brown
    Organization(s): National Research Council Canada
    Publication Date: January, 1997

    Research study dcribing an evaluation of selected windows undertaken by IRC researchers at Ottawa’s Laurier House (now being used as a museum) to determine their effectiveness in controlling condensation.

  8. Author(s): Baker
    Organization(s): Building Science Corporation
    Publication Date: December, 2012

    Document providing information and guidance about rehabilitating, retrofitting, and replacing wood window assemblies in residential construction.

Contributors to this Guide

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

Last Updated: 10/02/2013