A window structure for a wall opening having a perimeter frame said perimeter frame having a first frame portion and having a second flange plate portion, said window structure comprising:
- a grid network placed in and fixedly secured to said perimeter frame, said grid network including at least a first and second meeting rail, each of said first and second meeting rails having a first frame portion and having a second flange plate portion, said first meeting rail interposed between two opposite segments of the first frame portions of other meeting rails in said grid network, or interposed between two opposite segments of the first frame portion of said perimeter frame, or interposed between two opposite segments of the first frame portions of another meeting rail and said perimeter frame, said second meeting rail interposed between a segment of the first frame portion of said first meeting rail and another meeting rail or said perimeter frame, said connecting first and second meeting rails forming at least a part of said grid network whereby said grid network has a minimum of three window receiving openings;
- at least three exterior frame members hingedly or fixedly connected to corresponding portions of said meeting rails or said perimeter frame, said exterior frame members positioned in said window receiving openings, those of said exterior frame members which are fixedly connected to corresponding portions of said meeting rails or said perimeter frame hereinafter referred to as exterior fixed frame members, those of said exterior frame members which are hingedly connected to said meeting rails or said perimeter frame being operably connected whereby each said operable exterior frame member outswings from said corresponding window opening;
- said exterior frame members exposed to the environment outside the wall opening, such that they acquire the temperature of the outside environment, said first frame portions of said perimeter frame and said interior meeting rails exposed to the environment inside the wall opening, such that they acquire the temperature of the inside environment;
- means for thermally isolating said exterior frame members from said first frame portions of said perimeter frame and of said interior meeting rails;
- a two-piece fixed insulating glass unit mounted between the exterior fixed frame and the first frame portions of the perimeter frame and the meeting rails;
- a two-piece operable insulating glass unit mounted on the exterior operable frame members;
- each of said exterior operable frame members including an inwardly directed extension member;
- a first continuous primary seal member supported by the first frame portions of said perimeter frame and the interior meeting rail members for engaging the two-piece fixed insulating glass unit mounted on the corresponding exterior fixed frame;
- a second continuous primary seal member engagingly disposed between the inwardly directed extension member and corresponding portions of the first frame portions of said perimeter frame and said interior meeting rails;
- respective secondary seal members supported by the first frame portions of the perimeter frame and the interior meeting rail members for engaging said operable glass unit;
- and,
- locking hardware means for securing in a closed position said exterior operable frame members including a portion secured to a respective one of said first frame portions and including a portion engaging said perpendicular extension member and extending past a closely proximate secondary seal member into the interior where it can be operated by the user to engage the portion secured to the first frame portion,
- said interior meeting rail having a minimum section modulus and a minimum moment of inertia so that acting as a simple beam, with its ends connected, each said meeting rail provides the necessary windload resistance for a particular application while permitting a total sight line of three inches glass to glass and two inch sight line glass to building at the perimeter frame.