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Definition
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Double Hung Windows
The double-hung window consists of an upper and lower sash that slide vertically in tracks located in the side jambs. In the closed position the upper sash will engage the head of the frame while the lower sash will rest on the sill. To protect against water penetration the upper sash travels in the exterior track and the lower sash travels in the interior track. The sashes operate independently of each other.
Each sash is provided with means to suspend it in various positions along its travel up and down. This is known as balancing the sash and when a device is used it is called the balance or balancer. The most common types are the constant force, block and tackle and spiral.
The area where the bottom of the upper sash aligns with the top of the lower sash is known as the meeting or check rails. This is a critical area for air infiltration and security.
This type of window provides a maximum opening of approximately one-half the total window area for ventilation. For operation of the lower sash a half screen is usually acceptable. If both sashes are used for ventilation a full screen is required.
Double hung windows that have sashes of unequal heights (usually 2/5 of the height for the upper sash and 3/5 for the lower) are known as cottage or oriel windows. They offer less ventilation potential and usually are used for architectural design purposes.
