Your historic house may have a double-hung window that does not operate properly because it has a broken or rotten sash cord. If you are faced with this issue, you do not need to spend hundreds or thousands of dollars to replace your window. Instead, you can make your historic window operational again simply by replacing the sash cord.

In a double-hung window, each of the two window sashes move up and down with a counter balance system. The counter balance system consists of a cast-iron weight, a pulley and a sash cord. The sash cord connects the weight to the sides of the window sashes through the pulley. Each weight is half the weight of the window sash. Over time, a sash cord can rot or break.

Choose a New Sash Cord

Before you get started with the steps to replace a broken sash cord, you should buy a new sash cord. Most hardware stores sell sash cord. Be sure to buy a product that is called "sash cord" to ensure that it will be strong enough to handle a heavy cast-iron sash weight. A 100% cotton sash cord will last longer and stretch less than nylon cord as long as you do not get paint on it.  The standard residential size of sash cord is ¼-inch diameter.

To determine how long your sash cord needs to be, measure the height of the entire window opening from the sill area to the top of the jamb. Add 6 inches to this height to get the needed length.

Gather Your Tools and Supplies

To replace a broken sash cord on your double-hung window, you will need to gather the following tools and supplies:

• New sash cord
• Spray bottle containing water
• Putty knife
• Utility knife
• Pliers or end cutters
• 3 x 16 inches pieces of cardboard
• Flat-blade screwdriver
• Shop vacuum
• Tape measure
• Pencil
• Felt marker
• Small metal link chain, about 12 inches long
• Thin piano wire, about 6 inches long
• #6 finishing nail(s)
• Hammer and nail set
• Drywall screw, 1-5/8 inches long
• Wood filler epoxy
• Paint for touch-up finishing

Steps to Replace a Broken Sash Cord

Here are the steps to replace a broken sash cord on the sash of a double-hung window.

Step 1: Remove the Interior Sash Stops

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Step 1

Source: Bob Yapp

The interior sash stops create a track on the interior side of the bottom window sash. Before you try to remove the interior stop, use water in a spray bottle to lightly mist the painted edge of the stop. After misting the stop, use a utility knife to lightly score the paint line. Pry the interior stops off of both sides of the window from the back edge of the stop. Use a pair of pliers or end cutters to remove the nails from the back side of the interior stops. If you attempt to pound them through the finished side of the molding, the nail heads will damage the surrounding wood. 

Step 2: Remove the Sash

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Step 2

Source: Bob Yapp

Lift the bottom sash up just enough to clear the stool (interior sill) and remove the window sash from the jamb opening (the frame the window sashes move up and down in). Set the window down in an out-of-the-way spot.

Step 3: Remove Weatherstripping

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Step 3

Source: Bob Yapp

If weatherstripping exists, this will need to be removed by unscrewing or pulling the nails.  The weatherstripping may also have been painted over in which case a utility knife may be needed to score through this joint.

Step 4: Remove the Weight Pocket Access Panel

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Step 4

Source: Bob Yapp

Look at the lower portion of each side of the jamb. You will see a small weight pocket access panel held in place with a screw on each side. Remove the screws. Insert the blade of a small putty knife into the narrow gap at the top of the access panel and pry off the access panel. Mark the backside of the access panel with a marker, pen or pencil so you'll know which side it came from. Put the screw back into the screw hole in the jamb so you don't lose it.

Step 5: Remove Sash Weights

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Step 5

Source: Bob Yapp

With the access panel removed, you should be able to see two cast-iron sash weights in the pocket. The sash weight in the rear of the pocket is for the upper sash, and the sash weight in front (to the interior side of the pocket) is for the bottom sash. Pull the sash weight for the bottom sash out of the pocket and set it on some cardboard on the floor below the window. Repeat for the other side of the window if that sash cord is broken as well. Remove any loose sash cord sitting in the pocket.

Step 6: Remove the Old Sash Cord and Knots

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Step 6

Source: Bob Yapp

Remove the old sash cord that's still attached to the sash weights. Observe both sides of the window sash and find the groove that starts at the top on each side of the sash. This sash cord groove runs down the sides from 8 to 18 inches to the knot hole, depending on the size of the window sash. The sash cord groove ends with a ¾ inch to 1 inch hole. If the old sash cord knots are still in the hole, remove them. Occasionally these knots are nailed or screwed into the hole. Be sure to remove any nails or screws you find.  Use a narrow tip on a vacuum hose to vacuum out any debris on the bottom of each weight pocket. Vacuum off the sill area at the same time.

Step 7: Prepare the Sash Cord

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Step 7

To determine how long your sash cord needs to be, measure the height of the entire window opening from the sill area to the top of the jamb. Add 6 inches to this height to get the needed length. Source: Bob Yapp

If your sash cord is not yet cut to the appropriate length, cut the cord and tie a square knot on one end of each sash cord.

Step 8: Attach Piano Wire to the Metal Chain and Sash Cord

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Step 8

Source: Bob Yapp

Cut a 12-inch long piece of metal link chain that is small enough in diameter to fit through the top hole above the pulley. Bread tie (twist) a small piece of thin piano wire to the link at one end of the chain. Poke the other end of the wire through the sash cord about 1 inch from the end and bread tie this end as well.

Step 9: Feed the Chain and Cord through the Pulley Hole

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Step 9

Source: Bob Yapp

Feed the chain through the hole at the top of the pulley. The weight of the chain will help the lighter-weight sash cord fall to the bottom of the weight pocket. The knot on the other end of the sash cord will prevent it from pulling through the sash pulley. Later in the process you will insert this knot into the knot hole on the sides of the sash. Remove the chain and piano wire from the sash cord.

Step 10: Measure the Side of the Sash

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Step 10

Source: Bob Yapp

Use a tape measure to measure from the top of the sash down the side sash cord groove to the center of the knot hole at the bottom of the groove. This distance can vary from 8 to 18 inches depending on how tall the sash is. Measure down from the top of the jamb the same distance and use a pencil to mark this distance on the side of the jamb just below the sash pulley.

Step 11: Feed the Sash Cord through the Sash Weight

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Step 11

Source: Bob Yapp

Put a piece of cardboard on the stool (interior sill) and set the first sash weight on the cardboard. Feed the end of the sash cord through the hole at the top of the sash weight. Lift the sash weight into the weight pocket with the sash cord still running through the sash weight top hole. Do not tie a knot in the cord.  

Step 12: Screw the Knot to the Jamb

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Step 12

Source: Bob Yapp

Pull the knot on the other end of the sash cord down to the mark you made on the jamb just below the pulley. Use a drywall screw to screw the knot to the jamb at the pencil mark.

Step 13: Mark the Sash Cord

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Step 13

Source: Bob Yapp

Take the loose end of the sash cord that you fed through the sash weight and pull upwards until the sash weight is hanging freely 2 to 3 inches above the floor or the bottom of the weight pocket. Use a felt marker to mark the sash cord at the location where it goes through the hole in the top of the sash weight.

Step 14: Make a Knot in the Sash Cord

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Step 14

Source: Bob Yapp

Pull the sash weight out of the weight pocket and set it back on the cardboard. Tie a tight and solid square knot in the sash cord at the sash weight, and make sure the mark in the cord is in the same place it was when you had the weight 2 to 3 inches above the weight pocket floor or bottom. Slip the sash weight back into the weight pocket. Check to make sure the sash weight is still hanging freely 2 to 3 inches above the weight pocket floor or bottom. Follow this procedure for the other side if you're replacing that sash cord as well.

Step 15: Remove the Drywall Screw and Slide the Sash Cord in Place

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Step 15

Source: Bob Yapp

Remove the drywall screw in the knot from the jamb while holding the sash cord just above the knot. Carefully slide the knot toward the sash pulley until the sash weight touches the floor or bottom of the weight cavity.

Step 16: Reinstall the Weight Pocket Access Panel

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Step 16

Source: Bob Yapp

Reinstall the weight pocket access panel using the screw you left in the jamb.

Step 17: Insert the Knot into the Knothole

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Step 17

Source: Bob Yapp

Set the window sash on the stool (interior sill) with the inside of the sash facing inward. Pull down the knot at the pulley and insert it into the knot hole at the end of the sash cord groove. Do this to both sides, and then slip the sash back in its opening.

Step 18: Reinstall and Finish the Interior Stop

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Step 18

Source: Bob Yapp

Reinstall the interior stop, making sure it is not too tight to the window sash. Nail the stop with a #6 finishing nail and use a nail set to set the nail head below the surface. Finally, fill the nail holes with wood epoxy and touch up the paint on the interior stop.

The information presented here is not intended to provide comprehensive technical advice or instructions on solving historic preservation issues. Any information contained or referenced is meant to provide a basic understanding of historic preservation practices. Read full disclaimer.