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Air Seal and Insulate Wood Single-Pane Windows

Materials Cost: 1
Difficulty Level: 1

Introduction

Air seal and insulate around old wooden windows to remove or renovate pocket weights, decrease heating and cooling losses, and make your home more comfortable.

Why

Old wooden double-hung windows use an intricate system of weights and pulleys to counterbalance the weight of the window sash, allowing it to slide up and down smoothly and stay open in any position. These weights, made of lead or cast iron, hang in a hidden cavity next to the window. A rope or chain runs through a pulley at the top of the frame, connecting the weight to the sash. As the window is raised, the weight lowers, and as the window is lowered, the weight is raised, providing a consistent counterbalance. Newer windows use a high-tension spring built into the frame to serve the same purpose. Because the cavity needs to remain open so that the weight can move, there is no insulation in this section of the wall and the location of the pulley is often in a small opening in the window frame which means cold or hot air can easily flow into the room. So, while they may be nostalgic, these window weight pockets are also likely a big source of air leakage and discomfort during hot summers and cold winters. There are several options for replacing or renovating these weight pockets, some of which are discussed here.

What You'll Need

  • Tape measure
  • Weatherstripping material (styles including felt, reinforced foam, vinyl, or silicone, tape, magnetic, tubular rubber or vinyl, and others)
  • Caulk or caulking tape
  • Rigid foam insulation
  • Canned spray foam
  • Window balance hardware (such as spring balances or jamb liners)
  • Utility knife
  • Putty knife
  • Prybar or hammer
  • Screw driver

1. Determine your strategy.

You have several options for treating old wooden windows with window weights, including the following:

  1. Keep the window weights and restore the window to original operation.
  2. Keep the window but replace the weights and pulleys with spring balances.
  3. Replace the window, and seal and insulate the weight pockets.

These options may require advanced carpentry skills. Consider the condition of the windows. The pulley chains or ropes may be missing (Figure 1) or painted over. If the windows are loose or water damaged, or if you see signs of water damage around them, you may need to replace the windows. If the home is older than 1978, it may have lead paint. Lead safety precautions should be followed when conducting renovation activities like sanding painted surfaces. Depending on the condition of the windows, it may be best to hire a professional contractor.

2. Option 1. Keep the window weights.

If you want to keep the window weights and pulleys to maintain the historic nature of your home, it will typically involve replacing the pulley chains or ropes and cleaning and lubricating the pulleys. This requires opening the access panels on the sides of the windows, which typically  involves removing the window stop along the jambs. You may also need to remove the interior window trim to access the weight cavities so you can replace the ropes or clean the chains. This might give you the opportunity to use caulk to air seal the seams in the back of the cavity along the exterior sheathing, but there still likely won’t be room to add any insulation. Restoring these window pockets and window frame may take advanced carpentry skills depending on their current condition. Detailed instructions for doing this renovation are beyond the scope of this guide. Find resources on line. 

Figure 1. The pulleys in this old window frame were once used for counterbalancing weights to help raise and lower the window; this window can be restored with new pulley ropes or the weight pockets can be insulated with caulk and rigid insulation and new spring balancing hardware can be installed. (Source: PNNL).

3. Option 2. Remove the weights.

You can keep the window but remove the weights and pulleys and replace with spring balances:

  1. There are typically access panels in the sides of the window that are held in place with screws or nails to access the weight pocket but these give limited access to the pocket (Figures 2 and 3). Another option for accessing the pockets is to remove the interior window trim which should expose the full pocket (Figure 4).
  2. Pull the weights and ropes out of the pockets. Cut the ropes and remove the weights (Figure 3).
  3. Remove the pulley located at the top of the opening. Caulk the corners and seams in the back of the pockets, then fill the space with strips of rigid foam. Use foil-faced foam if you are in a colder climate that requires a vapor barrier in exterior wall insulation. The foil should face toward the room. Seal the edges with caulk or metal tape.
  4. Re-install the trim. 
  5. Install new jamb liners and new spring balances.
Figure 2. Old window weights can be removed and the cavities on each side of the window can be filled in with rigid foam, then new jamb liners and spring balance hardware can be installed (Source: PNNL).
Figure 3. Window weights can be taken out of cavities to allow for air sealing (Source: PNNL).
Figure 4. The exterior trim was removed around this window revealing the weight pockets (Source: PNNL).

4. Option 3: Install new windows.

In addition to air sealing and insulating the weight pockets, if the windows themselves are in bad shape (loose or cracked panes, evidence of water damage) and/or if they are single-pane only, you may want to replace the old window unit with a new double- or triple-pane replacement window. See the Building America Solution Center Guide Insert Replacement Window for details.

Instead of installing a replacement window, if the window is single-pane but otherwise in good shape, another option for improving the overall window performance is to install weatherstripping and storm windows. See the DIY guides Add Weatherstrip to Windows and Doors, Install Interior Storm Windows, and Install Exterior Storm Windows.

Additional Info

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Disclaimer

This content is a work created with funding provided by the United States Department of Energy under Contract no DE-AC05-076RL01830 for the operation of Pacific Northwest National Laboratory. The information and guidance provided by Pacific Northwest National Laboratory (PNNL) in the content are intended solely for educational purposes only and do not constitute formal training or certification. It is provided with the explicit understanding that neither the United States Government nor the United States Department of Energy, nor the Contractor, nor any or their employees, nor any jurisdiction or organization that has cooperated in the development of these materials, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness or any information, apparatus, product, software, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Viewers assumes full responsibility for all actions that they may take from information provided in this content including ensuring the safety, code compliance, and proper functionality of any products they choose to install. Installation and use of such products should be performed in accordance with local regulations and manufacturer instructions.