Mulling system for plural fenestration assemblies with joining plates and deflectable seal member therebetween

A fenestration assembly comprising:

• a first fenestration unit with a first frame that supports a first glazing unit, the first frame having a first outer edge;
• a second fenestration unit with a second frame that supports a second glazing unit, the second frame having a second outer edge that faces the first outer edge;
• and
• a mulling system that attaches the first fenestration unit and the second fenestration unit at the first outer edge and the second outer edge, respectively, the mulling system including:
• a first joining plate with a first inner face that faces and overlies the first outer edge to removably attach the first joining plate to the first frame, the first joining plate including a first outer face that faces opposite the first inner face, the first inner face including a first recessed channel;
• a second joining plate that overlies and is removably attached to the second outer edge, the second joining plate including a second outer face, the second joining plate engaging the first joining plate to join together the first frame and the second frame with the first outer face facing the second outer face;
• a deflectable seal member attached to the first joining plate and having a sealing surface that faces away from the first outer face, the sealing surface deflected and sealed against the second outer face of the second joining plate;
• and
• a first sealing strip that is received within the first recessed channel to seal between and abut the first inner face and the first outer edge of the first frame.

A method of assembling a fenestration assembly comprising:

• providing a first fenestration unit with a first fenestration frame that supports a first glazing unit, the first fenestration frame including a first outer edge;
• providing a second fenestration unit with a second fenestration frame that supports a second glazing unit, the second fenestration frame including a second outer edge;
• removably attaching a first joining plate to the first outer edge, the first joining plate including a first inner face that overlies the first outer edge and a first outer face that faces opposite the first inner face, including providing a first sealing strip in a first recessed channel of the first inner face, the first sealing strip sealing between and abutting the first inner face and the first outer edge;
• removably attaching a second joining plate to the second outer edge, the second joining plate including a second outer face;
• and
• engaging the first joining plate and the second joining plate to join together the first fenestration unit and the second fenestration unit with the first outer face facing the second outer face and the first outer edge facing the second outer edge, including, deflecting a deflectable seal member that is attached to the first joining plate and that has a sealing surface that faces away from the first outer face, the sealing surface deflecting and sealing against the second outer face of the second joining plate as the first and second joining plates are engaged.