Window seal construction

Details Window seal construction Window seal construction

2001-03-21

2004-04-27

Canfield, Robert (Department: 3635)

Static structures (e.g., buildings)

Exterior-type flashing

C052S204100, C052S204500, C052S741400, C052S745150

Reexamination Certificate

active

06725610

ABSTRACT:

This invention relates to a window or door construction for sealing window or door frames to a wall.
Development of nail-on windows occurred in the 1970's and originally incorporated aluminum frames and then vinyl frames, which comprise the majority of residential windows.
The window assembly must be water tight within the exterior wall and must be flashed. The flashing seals the window into the exterior wall opening to establish resistance to air and water infiltration. The degree of water resistance should match that of the adjoining wall cladding while the material must breath to allow for outward migration of moisture vapor.
Windows are prefabricated assemblies that are installed into typical frame or other construction walls. The problem of installation of such assemblies is to provide seals for resisting water and moisture penetration at the transition between window frame and the wall structure's ‘rough opening’. Windows typically are sealed to the frames with flashing materials in combination with adjoining weather resistive barrier (WRB) materials. Asphalt-based flashings and laminated flashings and building papers do not resist constant exposure to water or continuous cycles of wetting and drying commonly associated with the subject portion of the building envelope.
Window assemblies of recent design have integral nailing flanges which are used to nail the assemblies to the wall frame construction. The altered methods of window installation inherent to these ‘nail-on windows’ require an altered method of flashing the window to the exterior wall weatherproofing.
Nailing flanges provide a method of securing the window to the exterior wall framing. They also provide a flat surface onto which a flashing component and sealant can be applied and compressed to create a waterproof seal. Typically, the nailing flange is used as a transition point for the weather resistive barrier installed at adjoining wall areas.
In
FIG. 1
, a typical nail-on window frame assembly
6
is shown. The assembly
6
includes a glass pane
94
set in a frame
96
. Flashing materials
98
,
99
and
100
overlap the nailing flanges on the respective head
102
, jamb
104
sides of the frame
96
and under the sill flange
106
. The flashing materials
98
,
99
and
100
are typically of polyethylene material or the like of low permeance, e.g., about 0.30 perms, exhibiting negligible moisture vapor penetration therethrough. The flashing materials
98
,
99
and
100
are applied sequentially as separate strips resulting in overlap at regions A, B and so on at each of the corners. The flashing materials are applied with an adhesive to the mating wall construction. Such barriers are available as Moistop E-Z Seal from Fortifiber of Los Angeles, Calif. The material has a vapor permeance of less than about 0.3 perms, as determined following ASTM E96 procedures. This material also is not heat weldable. Other flashing materials may utilize modified bitumen membranes such as Blueskin and Vycor, trademarks for materials used for such membranes as known in this industry.
Due to construction sequencing, the window assembly
6
is typically installed before the flashing materials
98
,
99
, and
100
. In many instances, the flashing materials are improperly lapped onto the nailing flange resulting in leakage. As an improvement, strips of weather resistive barrier or special flashing material (not shown) are installed under the nailing flange on three sides (sill and both jambs) at the time of the window installation. This provides a large area of transition and a material assisting in the formation of a compression seal under the window nailing flange. The seal is, in some applications, augmented by the use of a sealant bead between the underside of the nailing flange and top side of the flashing material. Since the window assemblies
6
are installed during the framing and sheathing process, the flashings are exposed to the weather and can be damaged by weather/exposure.
Once a window assembly with an integral window flange is installed, it is difficult to install a workable flashing without the removal of the window from the opening. The removal can damage the interior window trim and the insulation installed in the framing void between the window profile and the wood framing.
In an effort to design assemblies that can be installed to the outside of a window profile, self-adhering membranes such as the Moistop E-Z Seal noted above have been employed to provide a waterproofing seal. These membranes typically have a very low perm rating trapping moisture vapor at the window perimeter. This can result in deterioration of the wood framing and of the window profile if constructed of wood.
Flashing materials have been developed to wrap the wood framing to the building interior to protect the wood framing from leakage and from the effects of moisture vapor entrapment and condensation accumulation. These materials typically are joined by overlaps, and, in some cases, with a tape to seal the overlaps.
The evolution of both methods of application and materials offered to the market has resulted in the lack of a standardized method of installation and a variety of materials, not all of which are compatible with various weather resistive barriers.
All windows do not provide closed assemblies, and water can leak through the frame that is constructed of individual components mechanically secured at the interior corners. Flashing plays an important role in moisture control of such windows.
Windows are fabricated with mullions, both horizontal and vertical, that are mechanically secured to the window profile and which can leak water. Thus a strong durable seal is needed that can form a full weather tight seal over the entire window opening tying the exterior weather resistive barrier to the interior vapor barrier retarder with an effective flashing seal. While overlaps of prior art strip seals shown in
FIG. 1
will shed water, they do not keep water from entering due to pressure differentials. Moreover, joints at the sill create pinholes where the strips intersect at changes of plane. These pinholes are sources of water entry both by gravity flow of water as well as due to pressure differentials. Typically such pinholes may be sealed with dabs of sealant which is not a reliable permanent seal.
Most current flashing assemblies require removal of the window for installation. A flashing material that can be applied to the installed window is a self adhering membrane that is bonded to the outer flange of the window and to the exterior sheathing. That sheathing is usually exterior grade gypsum or engineered wood such as plywood or oriented strand board. Self adhering membranes are usually made of modified bitumen. The combination of the modified bitumen and the adhesive creates a very low perm rating at the seal. This can result in the collection of condensation under the flashing transition and can damage the underlying moisture sensitive components.
Prior to the development of nail-on windows, windows were typically flashed with a metal pan under the window or door. The pan was formed typically of metal or some other rigid material forming a tray. The jamb edges and the back of the sill were turned up to form end dams. The vertical joints were sealed with a sealant or were soldered or welded. The so called tray was especially fabricated to conform to the dimensions of the associated opening. The tray is installed at the ends of the jambs (vertical) or with clips on the rear side. Flashing strips were installed at the jambs running into the tray. Water entering at the head or jambs was directed to the sill tray. The sill tray remained open at the bottom to allow water that enters the assembly to drain out.
Sill trays cannot be used with nail on windows without modification by removing a bottom flange to allow water to exit the assembly. This reduces the strength of the attachment with one plane not attached. Due to potential of compression of wood frame construction, the head of the window is not attached to allow

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