Patent Publication Number: US-2020284051-A1

Title: Floor Underlayment for Retaining Heater Cable

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional application claiming the benefit of priority from U.S. Prov. Pat. App. Ser. No. 62/268,560, filed Dec. 17, 2015, under the same title, incorporated fully herein by reference. 
    
    
     BACKGROUND 
     Under-floor heating systems arc used to create heated floors in buildings, In some systems, one or more heat-radiating wires, known as “heater cables,” are disposed between a subfloor surface and a main floor surface. Once activated, the heater cables transmit heat to the main floor surface, which may then be heated to a desired temperature. To provide an effective and consistent heating area, the heater cables are arranged in a particular pattern. To that end, one or more wire retaining apparatuses may be utilized to hold the heater cables in a certain orientation and spacing to achieve a desired power output within a given area. In one approach, the wire retaining apparatus is a plurality of strips coupled together and/or attached to the subfloor (or other surface). The heater cables are coupled to the strips to maintain the heater cables in the desired orientation. Adhesive (e.g concrete or mortar) may be poured and the main flooring may be installed on top of the heater cables such that the cables are positioned adjacent and/or are in contact with an underside of the main floor. 
     In another approach, a rigid or flexible underlayment may be laid on the subfloor. The underlayment includes a base that covers all of the area of the floor to be heated. An arrangement of projections extend upward from the base and, depending on the arrangement, can serve multiple purposes. First, the projections can create a primary or secondary bonding, surface, such, that concrete, mortar, or another adhesive contacts both the tops of the projections and the base layer exposed between the projections. This potentially improves adhesion of the adhesive as it dries or cures. Second, the projections can partially decouple the overlaying flooring from the subfloor by creating voids in the adhesive. These voids can facilitate movement of the subfloor without transmitting the movement through to the flooring. This decoupling prevents or reduces cracking (e.g., in tile or grout) and other undesired movement or effects caused by the movement of the subfloor. Third, the projections can be a partially or fully load-bearing surface, distributing loading forces across the surface area of the top and into the surrounding base as desired. 
     Finally, the projections can be shaped, positioned, and structurally configured to retain the heater cables within channels between the projections. In some existing implementations, the projections are spaced close enough together to hold a heater cable of a certain diameter within the channel by friction fit. In other implementations, the heater cable is placed in the channel, and then a flange is placed over the projection to extend over part or all of the channel and retain the heater cable therein. Still other implementations include flanges or recesses integrated into some or all of the projections, creating a channel which is large enough for a heater cable of a desired diameter, but which has an opening that is smaller than the heater cable; the heater cable is thus “snaked” (if the corresponding overhang over the channel is rigid) or “snapped” (if the overhang is flexible and/or resilient) into the channel. 
     A distinct advantage of flexible underlayments comes from manufacturing efficiencies. The base, which is typically polyethylene, is extruded as a thin sheet. The projections are stamped or thermoformed into, but can be bonded to, the base. In some implementations, a fibrous liner is bonded to the underside (i.e., opposite the projections) of the base. This liner allegedly provides additional bonding and/or decoupling properties to the underlayment in existing systems. The flexible underlayment is lightweight and can be rolled, similarly to a carpet, for easy installation. 
     Known underlayments have numerous drawbacks, For example, they are designed for a heater cable with a particular diameter, and it may be difficult or impossible to secure heater cables of different sizes to the underlayment because the retaining element does not grip or otherwise interact with the heater cable in a manner to secure the wire thereto. Thus, when a smaller diameter cable is used, extra care and effort is necessary to keep the cable properly tensioned so as to prevent the wire from lifting away through curling; when a larger diameter cable is used, the retaining elements (i.e., the channel, flanges, recesses, etc.) may not be flexible enough to accommodate the cable. A further drawback of some of the more versatile underlayments described in the existing art is that they have proved to be too difficult or too costly to manufacture, due to overly complicated structuring and arrangement of the projections. For example, projections that are too small or have large or abnormally-shaped flanges cannot be consistently manufactured by an efficient thermoforming process. 
     SUMMARY 
     Described embodiments provide a heater cable retaining membrane for installation between a subfloor and a main flooring to facilitate heating the flooring. The membrane may include a base and a plurality of projections extending outwardly from the upper side of the base. Each retention member includes a perimeter wall defining an outer shape of the projection and a top surface that is substantially parallel to the base. Some or all of the projections may include one or more flange portions. The flange portion extends away from the perimeter wall at a point at or below the top surface of the projection, creating an overhang under which a heater cable may be retained. The arrangement of the projections, with and without the flange portions, facilitates retention by the membrane of heater cables of varying sizes traveling in four or more directions across the membrane. 
     In one described embodiment, the perimeter wall has a long base portion, a left leg portion, a short base portion, and a right leg portion together defining the shape of each projection as substantially a trapezoid. The trapezoid may have rounded corners, allowing a heating cable to maintain contact with the perimeter wall as the heating cable is bent around the projection. The top surface may cover the entirety of the interior of the trapezoid. A hole, slit, or other aperture may be disposed through the top surface, facilitating off-gassing of an adhesive or transmission of the adhesive (or of water or another liquid) from one side of the membrane to the other. With respect to the perimeter wall, the projections may be arranged such that each long base portion of a projection opposes the long base portion of another projection, and each leg portion of a projection opposes the opposite leg portion of another projection, the opposition in each case forming a channel between the opposing portions. The channel may be sufficiently wide to receive any heating cable having a diameter up to a maximum diameter. Each projection may have one flange portion formed into either the long base portion, the left leg portion, the short base portion, or the right leg portion. The projections may be arranged so that no adjacent protrusions have flange portions that either oppose each other or extend in the same direction. 
     In another described embodiment, the perimeter wall may be substantially circular. The projections may be circles of varying sizes. The projections may be annular, having an outer perimeter wall and an inner perimeter wall that are both circular. In one embodiment, the top surface may extend between the outer and inner perimeter walls, leaving a circular recess within each projection. In another embodiment, the outer perimeter wall may be shorter than the inner perimeter wall, and an intermediate portion may extend outward from the base and radially at an angle to the base to meet the top surface. The recess may extend down to the base of the membrane. One described arrangement of the projections includes projections of two different diameters; projections of like diameter align orthogonally with each other and are spaced uniformly along the orthogonal axes, and projections of unlike diameter are oriented at 45 degrees from each other and also spaced uniformly apart. The smaller projections each have at least one flange portion, and the larger projections do not have flange portions. In one embodiment, each small projection may have four flange portions extending from the top surface and/or from the top of the outer perimeter wall. The flange portions may be oriented so that, for each of the smaller projections, none of the flange portions oppose or extend in the same direction as any of the flange portions of the adjacent smaller projections. 
     In another described embodiment, a membrane for decoupling heated flooring from a subfloor includes a flexible base and a plurality of projections formed into the base and extending outward from the base, each projection of the plurality of projections having a perimeter all, a top surface integral with the perimeter wall, and a flange portion extending from the perimeter wall, and a plurality of channels may each be defined by the base and the corresponding perimeter walls of a pair of adjacent projections of the plurality of projections. The plurality of projections may be arranged so that the corresponding flange portion of each projection does not face the same direction or the opposite direction of the corresponding flange portion of any other projection adjacent to the projection. For each channel of the plurality of channels, the corresponding flange portion of at most one of the projections forming the channel may extend over the channel, such that the channel retains a heater cable for heating the heated flooring. The perimeter wall can be circular, or can have a trapezoidal shape. The perimeter wall can include a planar first base portion, a planar first leg portion adjacent to the first base portion, a planar second base portion adjacent to the first leg portion and parallel to the first base portion, and a planar second leg, portion adjacent to the first base portion and the second base portion, and a plurality of rounded corners each disposed between and integral with two adjacent portions of the perimeter wall. 
     The perimeter wall of each projection can define an interior of the projection, and wherein the top surface of each projection is a substantially planar surface extending, over the entirety of the interior of the projection. Each projection of the plurality of projections can further include a slit disposed through the top surface to allow transmission through the membrane of one or more of a gas, a liquid, and a flooring adhesive, the corresponding slits of two or more of the plurality of projections forming a straight line from a first end of the membrane to a second end of the membrane opposite the first end. The perimeter wall of each projection can include a plurality of integral sides that cooperate to define a shape of the projection, a first side of the plurality of sides extending toward the corresponding top surface of the projection at an angle that is oblique to the base to form the corresponding flange portion of the projection. Each side of the plurality of sides other than the first side can be perpendicular to the base. 
     In another embodiment, the present disclosure provides a membrane for decoupling heated flooring from a subfloor. The membrane can include a flexible base and a plurality of projections formed into the base and extending outward from the base, each projection of the plurality of projections having a plurality of sides including a first side extending at an angle that is oblique to the base. The plurality of projections can be arranged into a plurality of pairs of adjacent projections wherein, in each of the pairs, the corresponding first side of a first adjacent projection cooperates with a second facing side, being one of the corresponding plurality of sides of a second adjacent projection other than the corresponding first side of the second adjacent projection, to define a corresponding channel of a plurality of channels for retaining a selected heater cable. Each of the plurality of sides other than the first side can be perpendicular to the base. The corresponding first side of each of the plurality of projections can face neither the same direction nor the opposite direction of the corresponding first side of any other projection adjacent to the projection. 
     The membrane further provides protection against fracture of the flooring by effectively decoupling the flooring from the subfloor. The projections may be essentially uniform in height and may have coplanar (with each other) top surfaces, In this manner, the projections can distribute loading forces and absorb shearing forces more forgivingly than if the flooring were installed on the subfloor. The membrane may further include a fibrous layer bonded to the base opposite the projections. The fibrous layer may be made of fleece or a similar natural or synthetic fiber, and may have a uniform or non-uniform density. The fibrous layer can provide an improved bond of the membrane to the subfloor. Additionally, the fibrous layer can provide decoupling effects between the subfloor and the flooring. Finally, the densityties of the fibrous layer can be selected to provide heat and/or sound insulating properties in the membrane. 
     The membrane, and components thereof, may be fabricated with one or a combination of several efficient manufacturing methods. For example, the membrane can be produced by continuous extruding onto a vacuum roller, roll-forming, or thermoforming in a parallel die-set. Other sheet forming techniques suitable for continuous high volume manufacturing can also be considered. The membrane may be lightweight and sufficiently flexible to be rolled, such as onto a spool on onto itself. To install heated flooring, discrete segments of the membrane may be carried to the installation site by a single installer. Each segment may be rolled out and then cut to the desired shape. Each segment may be laid on an adhesive applied to the subfloor or to another sublayer of the floor (e.g., an insulating layer) to cover the desired area. The installer may install a desired heating cable by placing the cable against the projections along the desired cable path, altering the cable&#39;s direction and pressing the cable beneath abutting flanges as needed to keep the cable in place. The installer may attach the heating cables to the appropriate control modules, and then may apply thinset or another adhesive over the membrane, the adhesive contacting the heater cables and the top surfaces of the projections and filling in the channels and other spaces between and/or within the projections. The installer may then lay the flooring on top of the adhesive. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a first embodiment of a membrane for retaining heater cables in accordance with the present disclosure: 
         FIG. 2  is a top perspective cross-sectional side view of the membrane of  FIG. 1 ; 
         FIG. 3  is a top view of the membrane of  FIG. 1 ; 
         FIG. 4  is a top view of a second embodiment of a membrane for retaining heater cables in accordance with the present disclosure; 
         FIG. 5  is an enlarged cross-sectional side view showing an exemplary installation of the membrane of  FIG. 4  in a heated floor; and 
         FIG. 6  is an isometric view of a third embodiment of a membrane for retaining heater cables in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology arid terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. 
     Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
     Embodiments of the present disclosure provide a system and a method for positioning and retaining one or more heater cables in a desired orientation during construction of a heated floor. The described system includes a flexible, lightweight membrane that overlays a subfloor of a building and serves as an underlayment to a main flooring that provides the exposed floor surface. The membrane is configured to guide the heater cables along multiple and variable paths, and to retain the heater cables within the selected paths as the main flooring is installed over the membrane. Configuring the heater cable paths and orientations is simple and versatile using the membrane, enabling a single installer to lay multiple different sizes of heater cable, within a desired area. The membrane can be used in a number of applications including residential and commercial flooring, roofing, walls, siding, and the like. For clarity of the disclosure, the membrane is described below as being used in a floor. It will be understood that terms such as “upward,” “downward,” “top.” and “bottom” are used with respect to the floor and have obvious corresponding directional terms when the membrane is used in walls, ceilings, and other structures. It is also contemplated that the described membrane may be utilized for retaining different types of cables, such as coaxial and other electrical cable. 
       FIGS. 1-3  illustrate a membrane  100  according to one embodiment. The membrane  100  includes an elongate, sheet-like base  102  and a plurality of projections  112  extending outward (upward, for a floor underlayment) from a top surface  104  of the base  102 . The base  102  may be made of any suitable material, particularly a material that is flexible, lightweight, installable in concrete and other typical flooring adhesives, impermeable to water, and usable in one of the preferred manufacturing methods described herein. While flexible, the base  102  may have a suitable stiffness to accommodate the installer walking and kneeling on the base  102  without collapsing or otherwise damaging the membrane  100 . In some embodiments, the base  102  material may be extrudable, roll-formable, and/or thermoformable, and may be metallic, polymeric, or both, including any suitable alloy, compound, or combination of materials that exhibit the desired flexibility, weight, permeability, and other features and can be formed into a thin sheet. Non-limiting examples of such materials include polyethylene and polypropylene. 
     The base  102  may have any suitable thickness, such as within the non-limiting exemplary range of about 0.5 mm to about 5 mm. In some embodiments, the thickness may be selected to accommodate thermoforming or roll-forming of the projections  112  into the base  102 . The base  102  material may exhibit additional desirable properties, including without limitation: low memory (i.e., rolls out flat); dielectric and other insulating properties; porosity that allows permeation of certain gasses; tear and crack resistance while remaining cuttable by standard hand tools; heat tolerance (e.g., up to 150 degF continuous exposure); arid the like. In some embodiments, the base  102  can include compositions that provide heat insulating and/or sound insulating properties to the membrane  100 . Such properties may be provide by, for example, a layer of heat- and/or sound-insulating material within the base  102 , or by combining, doping, impregnating, or otherwise incorporating a heat- and/or sound-insulating material into the core material (e.g., polyethylene) to form the base  102  material. The base  102  may include features that improve adhesive bonding, cable retention, and/or other functionality. In one example, the top surface  104  may be textured or porous, which can improve adhesion of concrete or thin-set applied over the top of the membrane  100 , and further can increase friction with an abutting heater cable  300  and prevent the cable from slipping. In another example, one or more apertures (not shown) may be disposed through the base  1102  to allow an adhesive to pass through the base  102  or to cure with air contained within or beneath the aperture. 
     The projections  112  may be integral with or bonded to the base  102 . In some embodiments, the projections  112  may be formed into the base  102  via thermoforming, roll-forming, or another suitable technique. In other embodiments, the projections  112  may be formed by cutting away material, such as from a slab of polyethylene. In other embodiments, the projections  112  may be fabricated separately and bonding to the top surface  104  of the base  102  using any suitable bonding agent. The projections  112  may be the same material and may exhibit the same properties (e.g., described above) as the base  102 . The projections  112  may be solid or partially or completely hollow. For example, the thermoforming process may create a projection  112  with a perimeter wall  114  defining the shape of the projection  112 , and a top surface  116  integral with the perimeter wall  114  and defining a cavity  162  (see  FIG. 2 ) inside the projection  112 . The walls and surfaces of the projections  112  may have uniform or non-uniform thickness, and each thickness may be the same as the base  102  or slightly thicker or thinner than the base  102  as a result of the manufacturing process. The top surface  116  may be textured to improve bonding of concrete, thin-set, or another suitable adhesive to the membrane  100 . 
     The illustrated &gt;embodiment of the projection  112  of  FIGS. 1-3  will now be described in detail; it will be understood that various embodiments of a projection  112  may include, omit, or adapt each of the described features according to the desired functionality and/or manufacturability of the membrane  100 . The perimeter wall  114  may be substantially perpendicular to the base  102 , extending upward to define the height of the projection  112 . The height may be selected according to one or more of the following considerations, among others: desired maximum heater cable diameter; base  102  material and thickness; desired minimum bend radius when rolling the membrane  100 ; spacing and orientation of projections  112 ; and the like. A suitable range of perimeter wall  114  height may be up to about 5 mm. In a particular embodiment for retaining heating cable with a diameter of up to 4.75 mm, the projections  112  may be about 3.5 mm tall. Such a membrane  100  retains the heater cables even though the cable diameter is greater than the height of the projections  112  due to the projection  112  configurations described below. 
     The load-bearing and cable-retention functions of the projections  112  may be improved by including an outward-curving portion  140  where the perimeter wall  114  meets the base  102 . An inward-curving portion  142  of the perimeter wall  114  may intersect the top surface  116 . 
     The perimeter wall  114  can define any suitable shape for the projection  112 . The illustrated projection  112  is a trapezoid, the perimeter wall  114  including a long parallel portion  144 , a right leg portion  146 , a short parallel portion  148  that is parallel to the long parallel portion  144 , and a left leg portion  150 . The corners formed by the intersection of two portions  144 - 150  of the perimeter wall  114  may be curved at a radius that allows a suitably sized heater cable  300  to bend around the corner (e.g., at bend  302  of  FIG. 3 ). In some embodiments, the short parallel portion  148  may be so short that it is effectively incorporated into the curvature of the adjacent corners; thus, the trapezoid becomes a triangle with the right leg portion  146  intersecting the left leg portion  150 . 
     One or more of the portions  144 - 150  in each projection  112  may include a flange portion  152 A,  152 B,  152 C,  152 D at or below the top surface  116  and extending outward (i.e., away from the interior of the projection  112 ). In some embodiments, the flange portion  152 A-D may be formed into or otherwise integral with the corresponding portion  144 - 150  of the perimeter wall  114 . Alternatively, the flange portion  152 A-D may be bonded or otherwise attached to the corresponding portion  144 - 150 . In one embodiment, the flange portion  152 A-D may be formed by expanding the perimeter wall  114  outward at the top surface  116 . This may cause the corresponding portion of the perimeter wall  114  to angle outward, rather than be perpendicular to the base  102 , as shown by the cross-section of  FIG. 2 : the long parallel portion  144  incorporating flange portion  152 B, and the left leg portion  150  of an adjacent projection incorporating a corresponding flange portion  202 , are each angled outward from the bottom to the top of the corresponding projection. In other words, the perimeter wall  114  portion incorporating the flange forms a side of the projection  112  that is oblique or slanted with respect to the base  102  and optionally also with respect to the top surface of the projection  112 . In such embodiments, the other sides of the projection (i.e., portions of the perimeter wall  114 ) may be perpendicular to the base  102 . Correspondingly, the corner where the perpendicular sides of the projection  112  meet the base  102  may be rounded with a first radius, and the corner where the oblique (i.e, flanged) side of the projection  112  meets the base  102  may be rounded with a second radius that is less than the first radius. In other embodiments, the perimeter wall  114  may remain perpendicular and the flange portion  152 A-D may “jut” out of the perimeter wall  114 , as described below with respect to  FIG. 6 . Additionally or alternatively, the flange portion  152 A-D may be formed by drawing the perimeter wall  114  inward (i.e. toward the interior of the projection  112 ) near the base  102 . 
     A finishing step of the manufacture of the membrane  100  may include cutting the membrane  100  into segments of a suitable size for the desired application. For example, a segment for residential home installation may be a standard size such as one meter wide and 12.5 m long. The projections  112  may be configured in a prescribed layout on the base  102  in each segment. The layout may determine the size, number, orientation. and spacing of the projections  112 , and may further determine the number and location of the flange portions  152 A-D, if any, on each projection  112 . The projections  112  may be coordinated so that each projection  112  cooperates with its adjacent projections  112  to create channels  120  for retaining, the heater cables along a desired path. A projection  112  is adjacent to another projection  112  if the projections  112  have opposing sides that are parallel and create a channel  120 . For example, in  FIG. 1  projection  112 A is adjacent to projections  112 B,  112 C, and  112 D, and is not adjacent to any other projections  112 . 
     The channels  120  may be the same width or may be varying widths. The heater cables may be retained in the channels  120  via one or more of several mechanisms A heater cable  300  may be held in place within the channel(s)  120  by tension, such as when the heater cable exits the channel  120  and makes a sharp turn, which holds the heater cable against the perimeter wall  114  of one of the corresponding projections  112 .  FIG. 3  illustrates, for example, the heater cable  300  retained in the channel  320  due to the bend  302 . A channel  120  may have a width that retains a heater cable of a certain diameter (e.g., the maximum diameter for the membrane  100  design) by friction fit. Or, a channel  120  (e.g., channel  120 A of  FIG. 2 ) may have an overhang formed by extension into the channel  120  of a flange portion  152 A-D of one or both of the corresponding projections  112 . The flange portion  152 A-D narrow&#39;s the top (e.g., top  122 A) of the channel  120  to a width that is smaller than the diameter of at least one, and preferably all, of the heater cables within a prescribed range of sizes to be used with the membrane  100 . Thus, the range of compatible heater cables may be determine by one or more of the depth of the channels  120 , the width of the channels  120  at the bottom of the channel  120  (i.e., at or near the base  102 ), and the width of the channels  120  at the top of the channel  120 . For example, the illustrated embodiment may accommodate heater cables ranging from about 4.1 mm to about 4.75 mm in diameter. The heater cable may be pressed through the top of the channel  120  or fed under the overhang of the channel  120  and may be loosely (or tightly, if the channel  120  also holds the heater cable by friction fit) retained by the corresponding flange portion(s)  152 A-D. 
     Various arrangements of flange portions  152 A-D may provide effective retention of the heater cables.  FIGS. 1-5  illustrate advantageous embodiments in which each projection  112  has only one flange portion  152 A-D extending from one portion of the perimeter wall  114 . Limiting the flange portions  152 A-D to one per projection  112  provides manufacturing efficiencies over other embodiments that provide multiple flange portions  152 A-D on each projection  112 ; yet, the projections  112  can be arranged so that each channel  120  is overhung by the flange portion  152 A-D of one of the corresponding projections  112 . In one such arrangement, which is illustrated, the following conditions are met: each projection  112  has one flange portion  152 A-D; the flange portion  152 A-D is on the long parallel portion  144 , the right leg portion  146 , or the left leg portion  150 ; and, no two adjacent projections  112  have their respective flange portions  152 A-D on portions of their respective perimeter walls  114  that face the same or opposite directions.  FIG. 1  illustrates the last condition—with the flange portion  152 A of projection  112 A located on the left leg portion: the flange portion  152 B of projection  112 B cannot be on the left leg portion, which faces the opposite direction from the left leg portion of projection  112 A; the flange portion  152 C of projection  112 C cannot be on the right leg portion, which faces the opposite direction from (and also opposes) the left leg portion of projection  112 A; and, the flange portion  152 D of projection  112 D cannot be on the right leg portion, which faces the same direction as the left leg portion of projection  112 A. 
     Since no two opposing portions of adjacent projections  112  can both include flange portions  152 A-D, the illustrated arrangement provides that at most one of the two adjacent projections  112  forming a particular channel  120  has its flange portion  152 A-D overhanging the channel  120 . This makes the channel  120  easier for the installer to use, only having to press the heater cable past one flange portion  152 A-D. Additionally, the conditions of the illustrated embodiment may create channels  120  with no overhangs. These channels  120  can be used to retain a heater cable that cannot fit within the channels  120  that do have overhangs, increasing the range of compatible heater cable sizes. Additionally, when the projections  112  each have multiple flange portions, the flange portions that face in different directions can cause the projection  112  to interlock with the mold during manufacture. The requirement that the projections  112  each have only one flange portion  152 A- 1 ) ensures easy release from the mold. 
     Adjacent and non-adjacent projections  112  may cooperate to create spaces  130 ,  132  of various sizes. The heater cables can pass through these spaces and/or change direction within them. For example, the illustrated smaller space  130  allows the heater cable to pass straight through or to turn 90 degrees to the left or right, while the larger space  132  allows the heater cable to pass straight through or to take left or right turns in 45 degree increments, creating seven possible paths through the larger space  132 . The spaces  130 ,  132  may be large enough to accommodate multiple passes of heater cable through them.  FIG. 3  demonstrates a potential path for a heater cable  300 , extending through multiple channels  120 ,  320 . turning freely at various angles within the provided spaces (e.g, 90 degrees in two spaces  332 ,  334  and 45 degrees in one space  336 ), and abutting a projection (e.g., projection  312 ) to make sharper turns of over 90 degrees (e.g., at bend  302 ). 
     In some embodiments, the layout of the projections  312  may include a repeating pattern of projections  312  in different orientations, sizes, and/or configurations. The illustrated example includes a group  340  of eight uniformly sized projections  312  that each have a combination of orientation with flange portion  152 A-D location that is different from the other projections  112  in the group  340 ; the group  340  is repeated in orthogonal directions to create the two-dimensional layout. 
     In addition to the heater cable retention functionality, the membrane  100  may further provide protection against fracture of the flooring by partially or completely decoupling the flooring from the subfloor and by redirecting, attenuating, and otherwise distributing load and shear forces so such forces do not cause damage to the flooring. In some embodiments, the projections  112  may be essentially uniform in height, and the top surfaces  116  of the projections  112  may be coplanar. The projections  112 , and to an extent the base  102 , may be sufficiently resilient to serve, effectively, as shock absorbers. Referring again to FIGS,  1  and  2 , the membrane  100  may further include a fibrous layer  180  bonded to the base  102  opposite the projections  112 . The fibrous layer  180  may be made of fleece or a similar natural or synthetic fiber, and may have a uniform or non-uniform density. The fibrous layer  180  can provide further decoupling of the flooring from the subfloor, In particular, loose fibers within the fibrous layer  180  can slide past each other in response to loading, shearing, or shifting of the flooring or subfloor, absorbing or attenuating such forces. The fibrous layer  180  may further provide an improved bond of the membrane  100  to the subfloor. The density/ies of the fibrous layer  180  can be selected to provide heat and/or sound insulating properties in the membrane  100 . In some embodiments, the fibrous layer  180  may have multiple varying densities, and may further have other varying properties that contribute to heat and/or sound insulation, such as reflective properties and heat conductivity. 
     As with the base  102 , the top surface  116  of one or more of the projections  112  may be perforated to facilitate transmission of an adhesive through the membrane  100  and/or curing of an applied adhesive. In one embodiment, shown in  FIGS. 1-3 , one or more holes  160  may be formed through the top surface  116 . The holes  160  may be formed during thermoforming or roll-forming, or may be formed by drilling, cutting, or punching the holes  160  after the projections  112  have been formed,. In another embodiment, shown in  FIG. 4 , one or more slits  402  may be cut through the top surfaces  416  of some or all of the projections  412  on a membrane  400 , which is the same as the membrane  100  of  FIGS. 1-3  apart from the perforations. The slit  402  may extend partially or fully across the top surface  416  in a certain direction. The slit  402  may be sufficiently narrow to not compromise the structural integrity of the projection  412 , In one example, the slit  402  is about 1 mm wide. Advantageously, the slit  402  may be formed during a continuous manufacturing process. For example, after the projections  412  are formed, the membrane  400  may be run through a slitter having one or more stationary blades. The slitter can cut the slits  402  continuously in a straight line from one end of the membrane  400  to the other, as shown in  FIG. 4 . 
       FIG. 5  illustrates an exemplary assembled floor using the membrane  400  of  FIG. 4 . One embodiment of an installation method is as follows, As an initial step, or during installation, the installer carries a sufficient number of rolls (i.e., rolled segments) of the membrane  400  to the installation site. The installer may unroll the membrane  400  and cut the membrane  400 , using any suitable hand tool to the corresponding shape of the flooring area to be heated. With die subfloor  502  prepared for installation, the installer applies a layer of thin-set  504  to the subfloor  502 . The installer lays the membrane  400  over the thin-set  504  with the fibrous layer  480  (or the underside of the base  402  if there is no fibrous layer  480 ) contacting the thin-set  504 . After a suitable cure time, the installer installs the heater cable(s)  506  within the membrane  400  as described above. The installer then applies an adhesive layer  508 , which may be thin-set, modified thin-set, concrete, or another suitable adhesive, over the membrane  400  and the heater cable  506 . 
     The adhesive layer  508  may cover the membrane  400 , filling the channels  420  and any empty volume around the heater cable  506 , and settling atop and bonding to the top suffices  416  of the projections  412 . The adhesive layer  508  may pass through the slits  402 , partially or completely filling the cavities  462  within the projections  412  and/or bonding to the top of the fibrous layer  480  or to the thin-set  504  underneath the membrane  400 ; or, as illustrated, the adhesive layer  508  may not pass through the slits  402  and the cavities  462  may remain full of air and/or other gasses. The installer may then install the main flooring (e.g., tile  510  and grout  512 ) over the adhesive layer  508 . 
       FIG. 6  illustrates another embodiment of an anti-fracture membrane  600  for retaining heater cables. The membrane  600  may include a base  602  having the same properties as those described above with respect to the base  102  of  FIG. 1 . Additionally or alternatively, one or more grooves  606  may be formed in the bottom surface of the base  602 . The grooves  606  may direct away outgassing or curing vapors, as well as moisture escaping from the subfloor. Multiple projections  612  extend outward from the base  602  and are arranged in a layout that facilitates heater cable guidance and retention. The projections  612  may be formed and integrated with or attached to the base  602  using any of the techniques described above with respect to the projections  112  of  FIG. 1 . The projections  612  may be annular, as defined by a circular outer perimeter wall  614  and a circular inner perimeter wall  616  offset from the outer perimeter wall  614 . A top surface  618  may extend between the top of the outer perimeter wall  614  and the top of the inner perimeter wall  616 , leaving a circular recess  620  within each projection  612 . The recess  620  may extend partially or fully down to the base  602 . The bottom of the recess  620 , which may be the base  602 , may be perforated and/or textured to facilitate adhesive bonding as described above. The outer perimeter wall  614  may be entirely perpendicular to the base  602 , or may include a perpendicular portion  640  extending upward from the base  602 , and an intermediate portion  642  extending upward from the perpendicular portion  640  and radially inward (i.e., toward the recess  620 ) at an angle with respect to the base  602 , to intersect the planar top surface  618 . 
     In some embodiments, the projections  612  may have different outer and/or inner diameters. The illustrated membrane  600  includes projections  612  of two different, sizes: large projections (e.g., projection  612 A) align orthogonally with each other and are spaced uniformly from adjacent large projections in two directions; similarly, small projections (e.g., projections  612 B,  612 C) align orthogonally with each other and are spaced uniformly from adjacent small projections in the two orthogonal directions; further, the large projections are oriented at 45 degrees from adjacent small projections, and the spacing between adjacent large and small projections may also be uniform. 
     Each projection  612  may have one or more flanges  630 , although some projections  612  may not have any flanges  630 . In the illustrated example, all of the large projections lack flanges  630  and all of the small projections have four flanges  630  each, spaced uniformly around the perimeter of the projection. Each flange  630  may extend from the top surface  618  and/or from the top of the perpendicular portion  640  of the outer perimeter wall  614 . In some embodiments, the flanges  630  may be flush with the intermediate portion  642  of the outer perimeter wall  614 , as illustrated. The flanges  630  extend away from the outer perimeter wall  614 , creating an overhand under which a heater cable may be retained. 
     In some embodiments, the flanges  630  on each projection  612  may be oriented so that none of the flanges  630  extend in the same or in the opposite direction as any of the flanges  630  of the adjacent projections  612 . Thus, for example, one configuration of a small projection  612 B has flanges  630  oriented in the orthogonal directions (i e., toward the adjacent small projections  612 C), and another configuration is used for each of the adjacent small projections  612 C, in which the flanges  630  are oriented at a 45 degree offset from the orthogonal directions. Further, the flanges  630  have a width that is less than the distance between flanges  630 , so that no two flanges  630  on adjacent projections  612  face each other. 
     The membrane  600  provides ample versatility for installing heater cables. An installer may “snake” or “weave” the cable(s) around adjacent projections  612  in any desired path; the flanges  630  combine with tensile forces from bending the cable around the projections  612  to retain the heater cable in place. A heated floor may be installed using the membrane  600  in the same manner described above with respect to  FIG. 5 . 
     It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments arid examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. Various features and advantages of the invention are set forth in the following claims.