Abstract:
An attic tray made from a breathable membrane for use in controlling moisture in a building attic and improving the energy efficiency of the building achieved by installing the tray above the roof rafters thereby providing the presence of an air gap between the breathable membrane and the roof deck such that energy that normally passes from the living space into the attic and out the top of the building is conserved.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an improved building construction material for controlling attic moisture and improving the energy efficiency of a building. 
         [0003]    2. Description of the Prior Art 
         [0004]    Some types of buildings have a space known as an attic located directly underneath the roof structure and above the useful living space. It is common in this type of building to use rafters and decking in the attic space. It is typical to use airflow to control the moisture level in the attic by ventilating air from the eaves of the building to the ridge vent at the highest point of the roof. Air is allowed to flow by means of convection from open spaces along the eaves (between the walls of the building and the bottom of the roofline) to an open space along the ridge(s) at the top of the roof, e.g., a ridge vent. This flow of air purges the attic of moisture before it can build up in the attic. Moisture commonly enters the attic from the living space in the form of vapor. Sources of moisture in the living space include human respiration, use of bathtubs and showers, cooking, houseplants, etc. 
         [0005]    Typically, the attic is open to the flow of air from the living space and from the exterior of the building surrounding the eaves. While this allows for good moisture control in the attic, it is not energy-efficient since the living space is not sealed and energy from the climate-controlled living space leaks to the exterior of the building through the ridge vent along with the airflow. 
         [0006]    Expandable foams have been used to insulate and seal attics. The foams are sprayed under the roof decking and inside the roof rafters, or on the “floor” of the attic. While this can effectively seal the attic, this method does not prevent moisture from building up in the attic since the typical foams are not breathable and do not permit air to flow through the attic, therefore this is not acceptable for many climates. A common method of providing attic ventilation is a vacuum formed plastic tray that has flanges that attach onto the top edge of the rafters. The design of these products does not allow for any variation of space between the rafters, and they are formed from rigid materials such as plastic and cardboard which are not vapor permeable. United States Patent Publication 2006/0260265 to Zatkulak, assigned to E.I. DuPont de Nemours and Company, Wilmington Del. (DuPont) discloses a method for controlling attic moisture utilizing a breathable membrane positioned over the top of the rafters. In order to lay the membrane over the rafters securely, large pieces of membrane must be handled by those installing the materials. This has been found to be cumbersome. It is difficult to attach the membrane to the underside of the rafters as large pieces of membrane are difficult to maneuver in an attic space, especially when trusses are used along with their accompanying cross braces. 
         [0007]    It is desirable to provide construction materials and methods that eliminate the exchange of air between the living space and the attic, while providing good control of moisture in the attic, along with safer and easier installation. 
       SUMMARY OF THE INVENTION  
       [0008]    This invention is an attic tray comprising a breathable membrane having first and second opposing edges and top and bottom opposing edges, with side supports adhesively attached at the first and second opposing edges, and an upper overlap at the top edge, wherein at least a portion is coated with adhesive, and a lower overlap at the bottom edge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is a view of an assembled attic tray folded for installation. 
           [0010]      FIGS. 2A-2C  show cross-sectional and side views of installed attic trays. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Definitions  
       [0011]    The term “active air space” refers to an air space in which air is allowed to move freely both within the air space and in and out of the air space in response to conditions that influence airflow, e.g., thermal gradients. 
         [0012]    The term “roof deck” is used interchangeably with the term “roof decking” and refers to the structural board on which roofing material (e.g., shingles) is installed, such as plywood or oriented strand board (OSB). 
         [0013]    The term “eave” herein refers generally to the intersection between the roof and the wall of a building. 
         [0014]    The term “ridge vent” herein refers generally to the space between differing planes of roof decking along their uppermost edges, typically protected by a cap. 
         [0015]    The term “peripheral building wrap” herein refers to the use of a flexible sheet material to wrap the unfinished walls of a building, such as a weather-resistive barrier. 
         [0016]    The term “rafter” is used herein to refer to discrete structural load-bearing elements that form the upper portion of a building&#39;s attic (also commonly referred to as joists, beams, or trusses). 
         [0017]    The term “rafter opening” is used herein to refer to the space between adjacent rafters. 
         [0018]    The invention provides an attic tray to form an active air space directly below a roof deck for the active flow of air entering the air space at the eaves and exiting the building at a roof ridge. As shown in  FIG. 2A , active air space  6  is the space between the attic tray  1  and roof deck  10 . The active air space removes water vapor as indicated by the arrow from the attic space to avoid moisture building up in the wood of the rafters  12  and roof deck  10 . The invention also seals the attic, thereby minimizing air exchange between the living space and the attic and providing considerable energy savings. 
         [0019]    As depicted in  FIG. 1 , the attic tray of the invention comprises a breathable membrane  100  having side supports  200  attached to the first and second opposing edges, which can be fastened to rafters. The membrane is typically rectangular and may be depicted and described as such herein, but is not limited by shape. In one embodiment, the membrane can be about 20 inches wide by 44 inches long in order to form an attic tray with a width to fit a rafter opening with 16-inch on-center studs. 
         [0020]    The side supports  200  hold the breathable membrane in place and the primary purpose of the supports is to provide a stiffener to the breathable membrane to allow an installer to handle the attic tray without its flopping. The side supports may be constructed from rigid or semi-rigid materials, as some flexibility is found to be helpful in positioning the attic tray. Some suitable materials are corrugated plastic, such as Coroplast® (available from_Coroplast, Inc, Dallas Tex.), cardboard, plastic and wood. A preferred material is corrugated plastic. There are no limitations on the size of the supports but it has been found that a 2.75 inches wide by 44 inches long piece would be suitable. The side support may optionally be provided with perforations  210  as shown in  FIG. 1  to allow a portion of the side support to be bent to form a flange  212 . The flange will form a nailing surface to attach the attic tray to a horizontal surface of a rafter. A large perforation will allow the side support to bend inward or outward, thus allowing the attic tray to be formed in a manner to allow installation from the attic space below or from the rooftop above, as shown in  FIGS. 2C and 2B , respectively. 
         [0021]    Optionally, a dead folding reinforcement  400  as shown in  FIG. 1  may be utilized to maintain the bent position of the side supports. Any material with the ability to take and hold a fold without springing back, known as a dead fold, may be used as a dead fold reinforcement. Suitable materials are metal wire, metal sheets, biaxially oriented polyester and HDPE sheet. The preferred dead fold reinforcement is made of metal wire. The dead fold reinforcement may span across the joints of side supports to cross supports, across perforations, or both. When metal wire is used for the dead fold reinforcement, an optional hook shape  400   a  as shown in  FIG. 1  has been found to prevent the wire from working loose. 
         [0022]    Optionally, cross supports  300  as shown in  FIG. 1  may be provided to span from the side support along one edge to the side support on the opposite edge to provide increased rigidity during installation and prevent the breathable membrane from sagging after installation. The cross supports may be about 2 inches wide by 14.5 inches long. 
         [0023]    The attic tray of the invention is formed by adhesively attaching the supports to the breathable membrane, as depicted in  FIG. 1 . Any adhesive known to bond to nonwoven fabrics may be used; such as hot melt glues and acrylic glues. The preferred adhesive is hot melt glue such as Duro-Tak 4233 hot melt adhesive supplied by Nacan Products Limited, Brampton, Ontario, Canada. The side supports and optional cross supports may be a unitary construction that is cut from a single piece of material, or built up from various pieces. Perforations to allow bending are placed at the folds between side supports and cross supports when the attic tray is formed as a unitary construction, with optional reinforcements to maintain the fold. Cross supports are butted up against the side supports when formed from built-up pieces. Dead fold reinforcements are preferred for the joints between side supports and cross supports when built-up from pieces. 
         [0024]    To allow each attic tray to form a continuous breathable membrane with the other attic trays installed within a rafter opening and the wall below it, a sealing means is required to connect them. It has been found that a length of breathable membrane that extends from each end of the section of breathable membrane framed by the supports provides a suitable means to overlap one tray onto another tray.  FIG. 1  depicts an assembled attic tray with a lower overlap  130  at the bottom of the membrane and an upper overlap  120  at the top of the membrane. The upper overlap incorporates at least a portion which is coated with an adhesive  110  which can be covered with a release paper (not shown). Any adhesive known to adhere to a nonwoven material may be used. 
         [0025]    The attic tray is installed by placing the folded tray into place in a rafter opening and fastening it into place and sealing the joint with any attic tray or wall surface adjacent to it. Attic trays are placed as is typically done in roofing processes by completing a course along one eave of the building structure and then proceeding to install subsequent attic trays in the row above it. The upper attic tray is sealed to the lower attic tray by peeling away the release paper, if present, to reveal the adhesive strip and pressing the lower overlap  130  of the upper attic tray onto the upper overlap  120  of the lower attic tray. In situations where no second attic tray abuts the end of a first attic tray, the overlap is sealed to peripheral building wrap. Roof decking is then constructed using typical roofing materials such as sheathing and asphalt roofing shingles. It has been found especially useful to apply sheathing after each course of attic trays is installed. The subsequent course of attic trays may be safely installed by using the sheathing as a work platform by the installer. The attic tray may also be fastened to the bottom of the rafter. Mounting the attic tray to the bottom of the rafters allows the workman to work from the attic and avoid any falling hazards inherent to roofing. 
         [0026]    In another embodiment of the invention, the attic tray is formed into a roll. The roll is nailed and sealed at the peak of the roof and unrolled to the eave, forming a continuous attic tray. 
         [0027]    The invention utilizes a breathable membrane  100 . The breathable membrane can be any vapor permeable material, preferably having a moisture vapor transmission rate of at least about 20 US perms as tested according to ASTM E96 Method A. The breathable membrane allows moisture to diffuse through it from the attic space into the active air space where moisture is carried by the flowing air to the exterior through the ridge vent. It is found that the chimney effect formed by the active air space enhances the removal of moisture from the attic space. Preferably, the breathable membrane is durable and UV resistant. A preferred membrane has a tensile strength (according to ASTM test method D828) of at least about 34 lb/in (59 N/cm) in the machine direction and about 30 lb/in (52 N/cm) in the cross direction. Preferably, the membrane does not lose strength after exposure to 25 cycles of accelerated aging consisting of oven drying at 120° F. for 3 hours, immersion in water at room temperature for 3 hours and air-drying for 18 hours at room temperature (73° F.). Also preferably, the membrane does not lose strength and shows no visible signs of damage after exposure to UV radiation for 210 hours (10 hours/day for 21 days) with 5.0 Watts/m2 irradiance at a wavelength of 315-400 nm, wherein the membrane is held at a distance of one meter from the UV source at a membrane temperature of 140° F. 
         [0028]    An example of a suitable breathable membrane is a two-layer composite sheet with Tyvek® high density polyethylene (available from DuPont) as the inner layer and a durable spunbond polypropylene sheet as the outer layer. The composite sheet can be made by joining the two layers with an adhesive and subjecting them to a thermal calendering process. The temperature of the calendering process should be sufficient to melt the adhesive, and the nip pressure should be sufficient to force the molten adhesive around the fibers of the two layers to lock the two layers together mechanically and ensure high delamination strength of the composite sheet. 
         [0029]    Other examples of materials suitable for use as the breathable membrane in the invention are spunbond polyolefin nonwoven sheets, including for instance a three-layer spunbonded polypropylene fabric such as the roofing underlayment sold under the trade name Roofshield® (available from the A. Proctor Group, Ltd., UK). Other materials suitable for use as the breathable membrane are a nonwoven sheet comprising sheath-core bicomponent melt spun fibers, such as described in U.S. Pat. No. 5,885,909, herein incorporated by reference; and a composite sheet comprising multiple layers of sheath-core bicomponent melt spun fibers and side-by-side bicomponent meltblown fibers, such as described in U.S. Pat. Nos. 6,548,431, 6,797,655 and 6,831,025, herein incorporated by reference. For instance, the bicomponent melt spun fibers can have a sheath of polyethylene and a core of polyester. If a composite sheet comprising multiple layers is used, the bicomponent meltblown fibers can have a polyethylene component and a polyester component and be arranged side-by-side along the length thereof. Typically, the side-by-side and the sheath/core bicomponent fibers separate layers in the multiple layer arrangement. 
       Description of a Typical Installation of Trays  
       [0030]    1. A flat attic tray was bent along the wire-reinforced junction of the side supports with the cross supports to form a tray. 
         [0031]    2. The side supports were folded along the perforations to form a flange. 
         [0032]    3. The attic tray was placed in a roof rafter opening, starting at one end of an eave. 
         [0033]    4. Staples were driven through the flange to the top surfaces of the roof rafters. 
         [0034]    5. Staples were driven through the side supports to the inside walls of each roof rafter. 
         [0035]    6. The bottom overlap was wrapped around the eave and overlapped onto the wall housewrap and sealed with Tyvek tape. 
         [0036]    7. Steps one through six were repeated for all rafter spaces in the row along the eave. 
         [0037]    8. Roof deck plywood was installed over attic trays using standard nailing protocol. 
         [0038]    9. Using the plywood decking as a working platform, additional attic trays were installed above the attic trays that were installed in the row previously installed along the eaves. 
         [0039]    10. The release tape was removed from the top overlap of the previously installed attic tray and sealed to the bottom overlap of the attic tray installed above it. 
         [0040]    11. Steps 8-10 were repeated for all remaining rafter openings.