weight pockets example

Repairing and Revamping Sash Window Pulleys

If you live in a historic or older home with double-hung windows, it’s possible that your windows are fitted with weight pockets. You may also know them as sash window pulleys.

A weight pocket is a counterbalance system of cast iron weights in older windows that allow the windows to be opened and closed. The cast iron weights are attached to the window sash via chains or ropes, and move up and down in the weight pockets - hollow channels on either side of the window - as the window sash is lowered and raised. In newer homes, the weight pocket system has been replaced by spring loaded balances, which eliminates the need for this older system.

While weight pockets provide an interesting glimpse into the window technology of the past, modern homeowners may be concerned about the energy efficiency issues caused by having two hollow spaces on either side of all their windows. Some homeowners have reported drafts around their older windows, which can also result from the hollow weight pockets. Luckily, addressing this problem while preserving the look of your original historic windows is fairly straightforward, and can save you money on your energy bill.

Typically, the best practice when dealing with sash pulley systems is to remove the old weight mechanism, insulate the weight pocket, and then install a spring loaded balance as a replacement. Our expert installers address this when doing a window installation.  


The experts of This Old House have laid out the basic steps in their short but effective video on the topic. In essence: 


  1. Remove the window sash and the stop bead
  2. Remove the pulleys, cords or chains, and weights from the weight pockets
  3. Weigh your sash to ensure that it doesn’t exceed the rating of your spring loaded balance
  4. Insulate the weight pocket void (more on that below)
  5. Screw spring-loaded balance to each jamb and attach to hooks on sash
  6. Set sash back in window and replace stop bead
  7. Test new window!

Not so bad, right? Still, it can be a complex project, and is best to have a professional deal with it.


The biggest question you probably have now is insulation - what is the best material to fill your now empty weight pocket? While fiberglass or expanding foam may be tempting options, they are not the industry recommendation. Instead, you should use foil-faced rigid foam insulation cut to the size of your window’s weight pockets, and foil duct tape to seal the edges. Get an expert to help you with this as well, as proper insulation for your empty weight pocket is extremely important for energy efficiency and comfort. 


As Tom Silva so succinctly explains, rigid foam insulation provides the appropriate insulation density as well as ease of installation. Sometimes, if you have had older windows in your home replaced, hollow weight pockets still exist on either side of the window, so it would be wise to make insulating them a priority, even if the original sash window mechanism is long gone. 


Let the experts here at Renoviso help replace and fill your old weight pockets!