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Double hung windows

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What are double hung windows?

The classic look of the double hung window is a popular choice for many home owners. This style consists of two sashes that slide past each other within the frame. The frame does not swing out - making double hung windows an ideal choice if you need to limit external projections. By sitting flush with the wall, it is also easy to install security or insect screens to the frame.

As the opening is generally smaller than in sliding windows, a double hung window is considered safer for high rise buildings unless the sill is very low, in which case special safety precautions are required such as window guards or restrictors.

Sashless varieties are available from many manufacturers. This modern alternative features two panes of glass without the bulk of a sash frame surrounding the glass. Sashless windows are useful when uninterrupted views are desired.

 

Sashless double hung. 
A sashless double hung window.

Window operation

Double hung windows comprise of an upper outside sash that slides down and a lower inside sash that slides up. Hidden springs, weights, or friction devices help lift, lower, and position the sash. New designs tend to use more durable spring balances to operate, eliminating the weight and pulley system of older double hung windows. With certain types, the sash can be removed, rotated, or tilted for easy cleaning.

 

Window ventilation

The versatility of double hung windows provides for a wide range of ventilation control. By opening both top and bottom sills you can regulate air flow and temperature within your home. Cool air can enter through the bottom opening with warm air escaping through the top. If there are overhanging eaves or awnings, the upper portion can be kept open in wet weather. However, rattling of double hung windows in windy periods can be of concern, especially with older styles, though anti-rattle devices are available.

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Are double hung windows energy efficient?

Many double hung windows are designed with two panes of glass (double glazing) which includes an air or gas pocket sandwiched between. This provides for better acoustic and energy efficient performance and reduces the need for artificial heating and cooling.

Double hung windows generally have higher air leakage rates than hinged styles. The need for easy sliding can limit their sealing capability, making it a less energy efficient choice. To improve performance It is important that the perimeter weather seals meet at the corners to provide a continuous seal.

 

How to weatherproof

Sealing all openings and joints will improve weatherproofing. Check for features such as double sealed top rails and built in drainage troughs to ensure maximum water resistance.

 

Window security

A cam handle is normally used at the mid-rails which, when rotated, pulls the sashes tightly together. The mid-rails should interlock so that the fastener cannot be forced open from outside. Optional key locks will provide added security.

 

Advantages
  • Good ventilation control
  • Attractive design
  • No internal or external protrusions
  • Easy to install security or insect screens
Disadvantages
  • Air leakage
  • Rattling can occur
  • Less resistant to water infiltration
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