Patent Application
20200208399
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The existing problem is that post-frame construction techniques are not fully weather protected. The application of a high-performance envelope system to a post-frame structure is unpredictable due to concerns about the feasibility, safety, and efficacy thereof.
Post-frame construction has its historic origin in the agricultural sector. As farm outbuildings, these structures were frequently made of rough wood components and were not programmatically required to enclose fully conditioned space. Therefore their construction techniques have excluded details of high-performance envelopes, effectively shortening the lifespan of the building by allowing its components to weather and deteriorate. Historically, wood posts were directly set into the ground. This method drastically shortened the lifespan of the structure, and it has been only recently replaced by other methods of foundation detailing. As such, post-frame construction is poorly received by some builders of non-agricultural buildings due to perceptions of sub-standard quality.
However, post-framing construction techniques provide several advantages over other methods of building erection (e.g. stud framing). Namely, post-frame buildings of simple geometries can be erected more rapidly and with less cost in both labor and material. Therefore market opportunity exists to expand post-framing techniques to other building typologies, and especially to pair them with costly programs demanding conditioned spaces and high-performance envelopes. Despite this, post-framing has remained largely bound within the agricultural sector with limited exposure to the residential sector due to problematic envelope practices. Innovations of more robust envelope technologies for post-frame structures, such as the present invention, have been stifled by the following factors of unpredictability:
Structural Connections: In the current state of technology, thick exterior-insulated envelope systems applied to framing rely on construction types that provide vertical studs, posts, or continuous thick sheathing to mechanically fasten insulation and siding. These vertical members are at their smallest a nominal 2×4 wood stud, allowing fastener embedment to nearly the fullest depth of the member. On the other hand, the girt and purlin spacing of post-frame structures and their structural capacity to bear fasteners that hold thick exterior insulation, siding, and roofing in place are untested, to my knowledge. The horizontal orientation and structural depth of girts create safety and feasibility concerns of whether a fastener could secure embedment, thereby raising secondary concerns of wall deflection and ultimate failure under dynamic loading conditions. Further, girts span from post-to-post and are often secured at wide intervals relative to their size and orientation, creating substantial concerns of girt deflection under the loading conditions of exterior insulation and siding. Additionally, the horizontal orientation of the girt raises concerns of efficacy when driving screws obliquely from the exterior of the insulation toward the center of the girt.
Weather barrier: The current state of post-frame technology does not fully climate-protect its buildings, thereby exposing components to degradation. Specifically, buildings fail to thermally protect the weather barrier. They also fail to continuously protect all sheathing and structural framing from thermal, water, vapor, and air infiltration and fluctuation.
Interior Finish: The current state of post-frame technology utilizes an interior finish to create conditioned spaces. Interior finishes are subject to mold growth, and water and vapor infiltration due to membrane problems mentioned above. They also add cost, labor, and time.
This invention overcomes the problems of related art and provides an envelope-structure interface that continuously protects a post-frame structure from thermal, water, vapor, and air infiltration and fluctuation. The breadth of this interface extends from the structural girts and purlins out to the wall and roof strapping, including all layers contained within.
A series of girts and purlins are regularly configured atop the underlying post and truss framing, in order to receive long, double-threaded screws that are driven from the exterior strapping through the thick insulation at intervals required to structurally support the wall assembly. The depth of the girts and purlins allows a minimum screw embedment that is sufficient to bear the dead and live loads of the wall under varying conditions. The girts, purlins, sheathing, insulation, screws, and strapping are, in conjunction, sized and configured to meet code-established deflection criteria when dynamically loaded from the exterior. These structural innovations support both a continuous sheathing substrate for a fully adhered water, vapor, and air impermeable weather barrier and a thick layer of insulation exterior of said weather barrier. Both the weather barrier and insulation layers are fully continuous from roof to wall, around the entire perimeter of the building. Finally, due to these innovations in climate control and structural systems, the present invention obviates the need for interior finishes at conditioned spaces.
Therefore, it is the purpose of the present invention to enable the construction of a post-frame building with superior envelope characteristics, thereby extending post-frame structure longevity and use in climate-controlled building typologies. The fully adhered continuous weather barrier of the present invention protects all sheathing and structural framing elements from water, vapor, and air infiltration and fluctuation, thereby preserving the structural integrity and longevity of the building. Habitability of the interior is preserved by the restriction of air flows that may carry toxins and allergens from the exterior or from the envelope assembly into the conditioned space. This characteristic of air-tightness also enables high energy performance across the envelope. Further, the layer of thick insulation continuously protects the weather barrier, sheathing, and structural framing from thermal fluctuations. This minimizes the expansion-contraction movement of the weather barrier, sheathing, and structure, and also protects these elements from damaging freeze-thaw cycles. It further ensures that the dew point rests exterior of the weather barrier; condensation therefore dries to the exterior through the vapor-permeable insulation and significantly reduces the potential for condensation-related problems at the interior. The insulation further acts as a provisional barrier to bulk water, preventing water intrusion from reaching the weather barrier itself. Moreover, the method and configuration of securing the exterior insulation minimizes both thermal bridges and aligned seams between insulation panels, thereby rendering it more effective and less prone to point failure. Finally, the removal of interior finishes at conditioned spaces reduces the required cost, time, and complexity of construction.
With reference to
The post-frame structure 10 is erected upon structural footings 11 and may include post bases 12. Posts 13 are anchored to the post bases 12, support roof trusses 15, and may be braced by diagonal bracing 17. Continuous lateral restraints 18 may secure the bottom chords of the roof trusses 15.
The envelope-structure interface 22 begins with girts 14 fastened on-face to the exterior of the posts 13, running the perimeter of the building. At the base of the wall, a skirt board girt 14B fastens to the base of the posts 13 to function as the bottom-most girt, also running the perimeter of the building. Purlins 16 similarly fasten to the top chords of the roof trusses 15 and run the length of the building. A continuous layer of roof sheathing 23 is fastened to the purlins 16 and abuts flush to a continuous layer of wall sheathing 24 that is fastened to the girts 14 and skirt board girt 14B. A continuous roof weather barrier 25 is applied to the roof sheathing 23 and laps over a similar continuous wall weather barrier 26 applied to the wall sheathing 24. Both weather barriers 25 and 26 are self-adhering, polyethylene-faced, polymer-modified, bituminous sheet fully adhered to the substrate in a shingle-lapped configuration from the roof ridge to the bottom of wall. Both weather barriers 25 and 26 in combination form a continuous water, vapor, and air impermeable surface at the wall and roof sheathing 23 and 24 that self-seals when penetrated. Continuous exterior roof insulation 27 is then fastened via roof strapping 29 to the underlying roof components; continuous exterior wall insulation 28 is similarly fastened via wall strapping 31 to the underlying wall components. Both roof insulation 27 and wall insulation 28 are comprised of vapor-permeable mineral wool insulation panels. Roof strapping 29 is preferably applied in-line with wall strapping 31 at regular intervals to achieve an uninterrupted ventilation pathway from the base of the wall to the eave to the ridge.
The pressure-equalized vented roofing system 33 may include roof battens 30 fastened to the roof strapping 29, or may be fastened directly to the roof strapping 29. A roof vent 34 may be secured to the ridge.
The pressure-equalized rainscreen siding system 35 is fastened to the wall strapping 31 and may also include battens (not shown). Metal flashing 32 may be applied to the outside of the exterior wall insulation 28 at grade.
A floor 21 may be bound by the skirt board girt 14B and may sit atop floor insulation 20.
The interior finish may be composed of: girts 14, purlins 16, wall sheathing 24 and roof sheathing 23.
Openings such as windows and doors are not shown for graphic clarity and are not elaborated by this description, but may be installed in a manner compliant with this envelope-interface system 22.
With reference to
With reference to
At the ground condition, a vapor barrier 21A preferably protects the skirt board girt 14B and flooring system 21 from in-ground vapor infiltration, as well as provides an opportunity to insert a thermal break between post 13 and flooring 21. The skirt board girt 14B may be set flush to the top of the flooring system 21; should the flooring system 21 be a slab-on-grade installation, the skirt board girt 14B may function as permanent formwork to bound the slab pour. The height and material of the skirt board girt 14B may vary without affecting the spirit of the present invention, though it must remain equally wide as the typical girt 14 and provide a sufficient fastening surface. The wall sheathing 24 preferably terminates at the bottom of the skirt board girt 14B while the weather barrier 26 preferably laps atop compatible vapor barrier 21A to fully seal the transitional condition. A drain mat 26A is in plane with the weather barrier 26 and wall sheathing 24, and provides a clear drainage path to weep the wall assembly. The bottom extents of the exterior wall insulation 28 and drain mat 26A depend on the flooring 21 assembly, as well as the depth of underfloor insulation 20. Wall insulation 28 may be protected from ultraviolet light and physical disturbance by metal flashing 32, which may be secured behind strapping 31.
The bottom-most typical girt 14 is located above the skirt board girt 14B at a spacing not greater than the maximum allowable for insulation 28 attachment. Typical girts 14 are wood members fastened on-face to the posts 13 and are of sufficient width and depth both to span between said posts and support live and dead loads of said wall assembly without deflecting beyond code-allowed limits, and to allow for required screw embedment. While the typical girt 14 is preferably dimensional lumber, other materials with similar structural properties may be used without affecting the spirit of the present invention. Typical girts 14 are spaced regularly at a distance not greater than the maximum allowable for insulation 28 attachment and for their structural function. Wall sheathing 24 is mechanically fastened to each girt 14 and to the skirt board girt 14B. The wall sheathing 24 is of sufficient thickness and structural properties both to span between girts 14, supporting live and dead loads of the wall assembly without deflecting beyond code-allowed limits, and to allow for required screw embedment; wall sheathing 24 is preferably plywood but may be any other board or sheet material of similar structural properties so long that it provides a continuous substrate suitable for the application of fully adhered weather barrier 26.
Thick exterior wall insulation 28, as described in the context of the present invention, is layered vapor-permeable mineral wool panels with sufficient compressive strength to resist the compression of the fastened wall strapping 31 and siding system 35 dead and live loads. This exterior wall insulation 28 is attached to the post-frame structure 10 by means of driving screws 31A and 31B from the wall strapping 31 through the insulation 28, through the self-sealing weather barrier 26, through the sheathing 24, and into the typical girt 14 or skirt board girt 14B. Screws 31A and 31B are of sufficient length to allow embedment into girt 14 and sheathing 24 to a depth sufficient to support the live and dead loads of the wall assembly, and said screws preferably have heads that allow counter-sinking into the strapping 31 so as not to interfere with rainscreen siding 35. Mechanical fastening preferably uses two lengths and orientations of screws in conjunction: longer screw 31A is driven at an oblique angle upward toward the center of each girt 14, while shorter screw 31B is driven directly toward the centerline of each girt 14. Screws 31A and 31B are preferably dual-threaded to allow simultaneous, even driving into girt 14 and wall strapping 31, while the secondary set of threads under the screw head transfer loads into strapping 31 to avoid over-compression of the insulation 28 and deformation of the wall surface. This preferable screw configuration is intended to reduce deflection under wall assembly loading.
Screws 31B may be used alone, particularly with thin wall insulation 28. Alternatively, screws 31A may be used alone.
The pressure-equalized, vented rainscreen siding system 35 may be mechanically fastened to wall strapping 31, and should include at least one open joint at the wall base of sufficient clear opening area to allow ventilation of the rainscreen cavity. Pest and insect screening (not shown) may be installed at the vent openings of the rainscreen siding 35.
With reference to
At the top of the wall, an atypical girt 14A is located above the previous typical girt 14 at a spacing not greater than the maximum allowable for insulation 28 attachment and for its structural function. This atypical girt 14A runs the length of the building and extends to the bottom of the roof sheathing 23. This condition forms a solid structural corner at the eve to provide for the fastening of roof sheathing 23, wall sheathing 24, and strapping screws 31A and 31B. Not far from atypical girt 14A is the bottom-most purlin 16, with each successive purlin 16 regularly spaced at an interval not greater than the maximum allowable for insulation 27 attachment and for their structural function. Purlins 16 are wood members fastened to the roof trusses 15 and are of sufficient width and depth both to span between said roof trusses and support live and dead loads of the roof assembly without deflecting beyond code-allowed limits, and to allow for required screw embedment. While purlins 16 are preferably dimensional lumber, other materials with similar structural properties may be used without affecting the spirit of the present invention. The roof sheathing 23 is of sufficient thickness and structural properties both to span between purlins 16 (supporting live and dead loads of the roof assembly without deflecting beyond code-allowed limits) and to allow for required screw embedment; roof sheathing 23 is preferably plywood but may be any other board or sheet material of similar structural properties so long that it provides a continuous substrate suitable for the application of fully adhered weather barrier 25. The roof sheathing 23 shingle-laps the wall sheathing 24 and is cut flush to allow continuous adhesion as the roof weather barrier 25 shingle-laps the wall weather barrier 26.
Thick exterior roof insulation 27, as described in the context of the present invention, is layered vapor-permeable mineral wool panels with sufficient compressive strength to resist the compression of the fastened roof strapping 29 and pressure-equalized vented roofing system 33 dead and live loads. This roof insulation 27 is attached to the post-frame structure 10 by means of driving a fastener 29A from the roof strapping 29 through the insulation 27, through the self-sealing weather barrier 25, through the sheathing 23, and into purlin 16. Fastener 29A is of sufficient length to allow embedment into purlin 16 and sheathing 23 to a depth sufficient to support the live and dead loads of the roof assembly, and said fastener may have a head that allows counter-sinking into the strapping 29. Mechanical fastening preferably uses a long screw 29A that is driven at an oblique angle toward the center of each purlin 16 in order to resist roof live and dead loads through tension. Screw 29A is preferably dual-threaded to allow simultaneous, even driving into purlin 16 and roof strapping 29, with the secondary set of threads under the screw head transferring loads into strapping 29 to avoid over-compression of the insulation and deformation of the roof surface. The eave condition of the roof insulation 27 is cut flush to the top of the wall insulation 28 to minimize gaps in the continuous thermal envelope, and shingle-laps the wall insulation 28 in order to assist shedding bulk water from the assemblies.
The pressure-equalized vented roofing system 33 may be mechanically fastened to roof strapping 29, or may be fastened via intermediary roof battens 30. The transition between the pressure-equalized rainscreen siding system 35 and roofing system 33 should include at least one open joint 35A at the eave, of sufficient clear opening area to allow ventilation of the assemblies. Pest and insect screening (not shown) may be installed at the vent openings of the roofing system 33.
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Mineral wool insulation 28 panels may be of varying thickness and dimension. Regardless of size, a minimum of five screws 31B attach each panel, preferably in the configuration noted below. Furthermore, the screws 31B should be located proximately to the edge of an insulation 28 panel. This is preferably achieved through centering the panel seams between screw axes. This concept is shown and noted by equal dimensions W, which indicate that the vertical seams of insulation 28 panels are preferably centered between screw 31B vertical axes. Likewise, the equal dimensions V indicate that the horizontal seams of insulation 28 panels are preferably centered between screw 31B horizontal axes.
Two or more layers of insulation 28 panels are preferable, so that all seams between panels can be offset from the seams of subsequent layers of said insulation, preserving the wall assembly's thermal efficiency. Inner layer insulation panel seams 28A and outer layer insulation panel seams 28B preferably overlap as near as possible to the center of a panel, as shown.
Strapping 31 is partially shown and dashed for graphic clarity. Long screws 31B, along with the strapping 31 whose centers they penetrate, are equally spaced at a regular interval X horizontally along the wall, and at a different regular interval Y vertically up the wall, such that a preferable rectangular screw formation is achieved, where each pair of screws 31A and 31B support a tributary area complying with the loading requirements of the wall assembly. Screws 31A are not shown for graphic clarity, but their location and configuration as described in
