Refurbish your windows for energy efficiency

How to fix your old box sash windows to seal the cracks that waste energy

By Iain Mitchell


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Homeowners today are constantly bombarded with the message that their old windows are a huge liability when it comes to energy efficiency. The notion that you should just rip them out and put in new ones is reinforced by the often shabby appearance of old windows: peeling paint, weak joinery, glazing putty that’s flaking and falling out; the list goes on. And if you have old-fashioned box sash windows, you may have another reason for considering their removal: counterweights that have long-since disappeared. Compounding this is the idea that single-pane glass is murder on heating costs.

But not so fast! Did you know that adding up all the cracks around all the window openings in your house will likely add up to the equivalent of a 3 sq. ft. hole in your wall? Sealing all these cracks and refurbishing your windows is your quickest route to energy efficiency. Of course there are those windows that are so far gone–cracked, rotted, and in some cases simply ugly–that brand-new windows are entirely justified. But most of the time, a repair is all that’s needed.

The Fix

Box sash windows operate by counterbalancing the weight of the sash with weights that run up and down a box hidden within the window frame. The sash is attached to the weights with a cord that runs over a pulley mounted within the vertical surface of the frame. If the window is double-hung, meaning both top and bottom sashes can open, there will be a strip running through the box to ensure the upper and lower sash weights don’t interfere with each other.

In many older homes box sash windows no longer function properly, usually because the weights are no longer attached to the sashes. Often this is because the cords frayed over time, or were painted and had to be cut in order for the window to open and close. Most homeowners simply left the windows as they were and resigned themselves to propping the window open with a piece of wood or a book, with the ever-present danger of crushing their fingers each time the window was opened or closed.

Box sash windows were designed with lost weights in mind, and these steps will show you how to get yours working again. And while you’re making sure your window opens and closes properly, you can also seal around it to ensure it will provide many more years of making your house look good, and protecting you from the elements.

What you’ll need:

This project doesn’t take a lot of time or a lot of tools. Get yourself a sharp utility knife, a 1″ paint scraper, a tube of latex window caulk, a pry bar and a tack hammer and you’re all set. New sash cord is available from most hardware stores.

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