Mulling system for plural fenestration units with stiffener member and cover member

1 . A mulling system for mulling together a first fenestration unit and a second fenestration unit at a mull joint to define a fenestration assembly with the fenestration assembly including a first side and a second side that are cooperatively defined by the first fenestration unit and the second fenestration unit, the first fenestration unit including a first frame member with a first mull seating strip and a backing strip, the backing strip being offset from the first mull seating strip so as to define a channel of the first frame member, and the second fenestration unit including a second frame member with a second mull seating strip, the mulling system comprising:

a stiffener member that is disposed within the mull joint along a first axis extending between the first fenestration unit and the second fenestration unit, the stiffener member extending along a second axis between the first side and the second side of the fenestration assembly, the stiffener member including a seating strip abutting the first frame member and abutting the second frame member, the seating strip having a solid cross section in a plane defined by the first axis and the second axis, the seating strip, the first mull seating strip, and the second mull seating strip being layered together in sequence along the first axis in abutting contact;

a cover member that attaches to the stiffener member on the first side, the cover member covering over the first frame member, the second frame member, and the stiffener member to conceal the mull joint on the first side; and

a fastener that is partly received in the channel and that extends through the seating strip of the stiffener member, the first mull seating strip, and the second mull seating strip.

2 . The mulling system of claim 1 , wherein the cover member is a first cover member and further comprising a second cover member that attaches to the stiffener member on the second side, the second cover member covering over the first frame member, the second frame member, and the stiffener member to conceal the mull joint on the second side.

3 . The mulling system of claim 1 , wherein the stiffener member includes a first side portion proximate the first side, a second side portion proximate the second side, and a thermal break member that attaches the first side portion and the second side portion, the thermal break member having lower thermal conductivity than at least one of the first and second side portions.

4 . The mulling system of claim 1 , wherein the cover member is removably attached and received in the stiffener member.

5 . The mulling system of claim 1 , further comprising a seal member that is attached to the stiffener member and that substantially seals against one of the first frame member and the second frame member.

6 . The mulling system of claim 1 , further comprising a seal member that is attached to the cover member and that provides a seal between the cover member and one of the first frame member and the second frame member.

7 . The mulling system of claim 1 , wherein the seating strip of the stiffener member includes a face that faces the first frame member, and wherein the seating strip of the stiffener member includes a ridge that projects from the face, the ridge abutting against the first mull seating strip.

8 . The mulling system of claim 1 , wherein the cover member defines a first width measured along the first axis across the mull joint;

wherein the cover member is a first cover member and further comprising a second cover member that attaches to the stiffener member on the second side, the second cover member covering over the first frame member, the second frame member, and the stiffener member to conceal the mull joint on the second side;

wherein the second cover member defines a second width measured along the first axis across the mull joint;

wherein the first frame member has a first inner side facing away from the mull joint and the second frame member has a second inner side facing away from the mull joint in a direction opposite the first inner side;

wherein the first frame member and the second frame member cooperatively define a third width measured along the first axis across the mull joint from the first inner side to the second inner side; and

wherein the first width and the second width are at least equal to the third width.

9 . A fenestration assembly comprising:

a first fenestration unit including a first frame member with a first mull seating strip and a backing strip, the backing strip being offset from the first mull seating strip so as to define a channel of the first frame member;

a second fenestration unit including a second frame member with a second mull seating strip;

a mulling system that mulls together the first fenestration unit and the second fenestration unit at a mull joint, the fenestration assembly including a first side and a second side that are collectively defined by the first fenestration unit and the second fenestration unit, the mulling system including:

a stiffener member that is disposed within the mull joint along a first axis extending between the first fenestration unit and the second fenestration unit, the stiffener member extending along a second axis between the first side and the second side of the fenestration assembly, the stiffener member including a first side portion proximate the first side, a second side portion proximate the second side, and a thermal break member that attaches the first side portion and the second side portion, the thermal break member having lower thermal conductivity than the first side portion and the second side portions, one of the first side portion and the second side portion including a seating strip abutting the first frame member and abutting the second frame member, the first side portion and the second side portion being non-hollow to respectively have a solid cross section in a plane defined by the first axis and the second axis, the seating strip, the first mull seating strip, and the second mull seating strip being layered together in sequence along the first axis in abutting contact;

a cover member that attaches to the first side portion of the stiffener member on the first side, the cover member covering over the first frame member, the second frame member, and the stiffener member to conceal the mull joint on the first side; and

a fastener that is partly received in the channel and that extends through the seating strip of the stiffener member, the first mull seating strip, and the second mull seating strip.

10 . The fenestration assembly of claim 9 , wherein the cover member is a first cover member and further comprising a second cover member that attaches to the second side portion of the stiffener member on the second side, the second cover member covering over the first frame member, the second frame member, and the stiffener member to conceal the mull joint on the second side.

11 . The fenestration assembly of claim 9 , wherein the cover member is removably attached and received in the first side portion of the stiffener member.

12 . The fenestration assembly of claim 9 , further comprising a seal member that is attached to the stiffener member and that substantially seals against one of the first frame member and the second frame member.

13 . The fenestration assembly of claim 9 , further comprising a seal member that is attached to the cover member and that provides a seal between the cover member and one of the first frame member and the second frame member.

14 . The fenestration assembly of claim 9 , wherein the seating strip of the stiffener member includes a face that faces the first frame member, and wherein the seating strip of the stiffener member includes a ridge that projects from the face, the ridge abutting against the first mull seating strip.

15 . The fenestration assembly of claim 9 , wherein the cover member defines a first width measured along the first axis across the mull joint;

wherein the cover member is a first cover member and further comprising a second cover member that attaches to the stiffener member on the second side, the second cover member covering over the first frame member, the second frame member, and the stiffener member to conceal the mull joint on the second side;

wherein the second cover member defines a second width measured across the mull joint;

wherein the first frame member has a first inner side facing away from the mull joint and the second frame member has a second inner side facing away from the mull joint in a direction opposite the first inner side;

wherein the first frame member and the second frame member cooperatively define a third width measured along the first axis across the mull joint from the first inner side to the second inner side; and

wherein the first width and the second width are at least equal to the third width.

16 . A method of mulling together a first fenestration unit and a second fenestration unit at a mull joint to define a fenestration assembly, the first fenestration unit including a first frame member with a first mull seating strip and a backing strip, the backing strip being offset from the first mull seating strip so as to define a channel of the first frame member, the second fenestration unit including a second frame member with a second mull seating strip, the method comprising:

positioning a stiffener member along a first axis extending between the first fenestration unit and the second fenestration unit, the stiffener member extending along a second axis between a first side and a second side of the fenestration assembly, the stiffener member including a seating strip, the seating strip having a solid cross section in a plane defined by the first axis and the second axis;

layering the seating strip of the stiffener member, the first mull seating strip, and the second mull seating strip together in sequence along the first axis in abutting contact;

extending a fastener through the seating strip of the stiffener member, the first mull seating strip, and the second mull seating strip, the fastener being partly received in the channel; and

attaching a cover member to the stiffener member on the first side, the cover member covering over the first frame member, the second frame member, and the stiffener member to conceal the mull joint on the first side.