BobVila.com

8' tall windows

Now, if as suggested by a previous poster, you mean two mulled double hung windows, by special order it *might* be possible.

There would likely be some architectual/engineering sign-offs required, and it would likely have to be designed to be that the upper sash was FIXED in place. Safety glass or tempered would also be required, by numerous life, building, safety, fire, etc. codes. Elevation, sheer, huricane and/or seismic ratings/restrictions may also apply.

Keep in mind that a two-sash window is not called double-hung if the sashes (operable or not) are not equal in size - usually such older windows are not always equal in sash dimmensions (larger on top, larger on bottom, etc.) please specify if this is the case.

Also depending on where such window is located, the glazing might be required to be "fire-heat shatter proof" or similar (for example a NYC apartment fire-escape window, or one located in close proximity to a narrow alley, etc.).

Do you really need a complete window or a replacement sash, replacement window (full-frame or insert) or a new construction type window?

Sometimes an alternative is to use a pivot window for loft/converted comercial/industrial spaces.

This is not the type of thing you'll find cost-effectively via your big-box stores.

The type of structure/support required for such a large operable window would be enormous and likely require significant beefing up to meet current code requirements also (you lose any grandfathering in as you seek to replace the existing). For such a large opening you might even require cabling or strapping or cantilliever support for the weight of the window frame, the window itself and the stresses of operation in addition to variable stresses to the overall wall - read: screws/nails alone wouldn't make it.

Your first best consult might be with a certified (qualifed to produce stamped plans) architect or structural engineer, the later being your best resource, including specifics as to forces, stresses, support, sheer, load, etc. calculations which will be required to begin to specify a safe/legal replacement window.