If the drapery is full working, determine if the drapery is to clear the window when open or if coverage of some of the glass is acceptable. This is usually a matter where the client will want to have input since the loss of light or view from a window covered by drapery is an emotional decision.
Draperies that stack off the glass or opening and stack over the wall will make the room appear larger and more open while gaining maximum benefit from the light and view the window allows. The drawback of this is that drapes stacked on the wall require longer rods, more fabric, are therefore more expensive and can cover valuable wall space.
Draperies that stack over the widow or glass tend to be less desirable as they will often obstruct views and block light. If the drapery is to clear the window, an allowance for "stack back" must be made. It is the designer's job to determine the client's preferences and strike an acceptable balance between the client's wishes and the stack requirements outlined below.
Use the following stack back formula to find the approximate stack back width. Once this is determined, add it to the width of the window opening. After applying the formula, ensure that the finished width includes the stack back on each side of the window.
Stack back formulas
For pair: rod width ÷ 6 = approximate stack back width per side.
For panel: rod width ÷ 3 = approximate stack back width per panel.
If rod width = 100, then 100 ÷ 6 = 16.66. This is the approximate stack back width on each side of the window. The rod width needed to clear the window would be the window width plus 16.6" on each side.
If rod width = 100, then 100 ÷ 3 = 33.33. This equals the approximate stack back width when the drape is fully open. The approximate rod width needed would be the window width plus the stack back plus the extension of the rod past the window on the stack side.
These general formulas work in most cases. Figuring drapery stack is not an exact science, and it is necessary to keep in mind a few variables such as thickness of fabric, interlining, type of heading, and type of hardware, and to adjust the results up or down accordingly.
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