referring to fig1 - 3 , an embodiment of a roof curb 100 configured according to the invention includes four walls 105 interconnected with four connection blocks 110 , defining a roof curb base 112 , for mounting on a roof r . four composite boards 115 mount on walls 105 and support an appliance ( not shown ). in practice , walls 105 are cut into standardized lengths that foster ready packaging in standard shipping containers along with other components described herein for conventional or overnight courier delivery . aluminum extrusion stock permits on - site sizing of the standard pieces without local burning off of corrosion resistant coatings ordinarily required for steel stock . using aluminum stock also eliminates routine rust inhibitor paint coatings that would be required to protect steel stock . referring also to fig4 , each wall 105 is constructed of extruded aluminum having a lower flange 120 and an upper channel 125 . each flange 120 is inwardly - disposed to limit exposure of fasteners and other mounting mechanisms and sealing to the elements . each flange 120 has chamfered ends 130 that promote flushness along the entire contacting surface of flange 120 with roof r . each channel 125 is configured to receive and retain a composite board 115 . channels 125 are inwardly disposed so as to define , in conjunction with wall 105 , a generally uniform vertical wall 127 without ledges or partial enclosures that might find favor with unwanted insects and vermin . flange 120 , vertical wall 127 and channel 125 define a pocket 128 for receiving insulation , as described below . side walls 105 a have an edge 107 a that provides a continuous , water - tight seal with roof r . top and bottom walls 105 b have notches 109 for alignment with and accommodation of seams or ribs f extending from roof r , thus defining an edge 107 b that also provides a continuous , water - tight seal with roof r . referring to fig3 , each connection block 110 is constructed from aluminum and has pre - drilled throughbores 114 at predetermined locations . in practice , a roof curb installer introduces holes at the ends of walls 105 according to a template , as shown in fig8 , that register with throughbores 114 . preferably , composite boards 115 are trex ® boards , which are constructed from a combination of reclaimed wood and plastic . the plastic component shields the wood component from moisture and insect damage , reducing or eliminating rotting or splintering . the wood component protects the plastic component from ultraviolet radiation damage from ordinary sunlight , ensuring integrity longer than would be expected from products constructed from purely plastic or purely wood . as shown in fig2 , unique to roof curb 100 is a top support channel 135 . top support channel 135 is similar to bottom support channel 140 , which is common to roof curb 100 and roof curb 200 , as shown in fig6 . top support channel 135 and bottom support channel 140 each have generally perpendicular ribs 136 and 141 , respectively . ribs 136 , 141 strengthen and enhance top support channel 135 and bottom support channel 140 load bearing capabilities . top support channel 135 has flanges 137 and bottom support channel 140 has flanges 143 that mount onto structural members s supporting roof r . when installed , top support channel 135 and bottom support channel 140 each support a wall 105 b , and support members s support the remaining walls 105 a . referring to fig5 and 6 , another embodiment of a roof curb 200 configured according to the invention provides for diverting water that otherwise might accumulate along the upper , laterally - extending intersection of roof r and roof curb 200 . the water diverting feature of roof curb 200 is intended for larger installationsthat would be susceptible to collecting large amounts of water . roof curb 200 includes four walls 205 interconnected with four connection blocks 210 , defining a roof curb base 212 , that mounts on roof r . four composite boards 215 mount on walls 205 and support an appliance ( not shown ). roof curb 200 is similar to roof curb 100 , except as described below . as shown in fig5 and 6 , unique to roof curb 200 are a diverter plate 235 and a diverter angle 245 . diverter plate 235 covers a portion of roof r removed so that ribs f in roof r do not prevent flush mounting of diverter angle 245 on roof r against roof curb 200 . like top support channel 135 , diverter plate 235 has strengthening ribs 236 for supporting wall 205 and diverter angle 245 . diverter angle 245 has upstanding flanges 247 that define an impervious dihedral angle 249 . angle 249 is such that flanges 247 provide a flow path for water to pass around roof curb 200 , rather than collect against the upwardly disposed wall 205 , which , over time , might cause local corrosion or sealant failures . diverter angle 245 is sealingly connected to diverter plate 235 . in operation , water flowing down roof r toward roof curb 200 would encounter then flow along flanges 247 , then onto the portion of roof r lateral to roof curb 200 , thereby bypassing roof curb 200 and continuing to flow down roof r . referring to fig7 , an embodiment of a method of making 300 roof curb 100 configured according to the invention includes : a step 305 of determining curb size ; a step 310 of cutting extrusions ; a step 315 of cutting bottom extrusion ; a step 320 of cutting steel channels ; a step 325 of drilling corner connections ; a step 330 of applying corner block mastic ; a step 335 of assembling extrusion corners ; a step 340 of determining composite board dimensions ; and a step 345 of cutting composite boards . referring also to fig8 , step 305 involves determining a curb size to ascertain a curb length for walls 105 a , as shown in fig1 , and a curb width for walls 105 b , top support channel 135 and bottom support channel 140 , as shown in fig2 . step 310 involves cutting the side extrusions or walls 105 a according to the curb length of step 305 . preferably , a roof curb assembler uses a 12 - inch compound - sliding miter - saw with a carbide tooth blade for cutting aluminum . mitering the interfaces among walls 105 promotes relative flushness as well as flushness with respect to roof r . step 315 involves cutting the top and bottom extrusions or walls 105 b according to the curb width of step 305 . step 315 differs from step 310 in that a roof curb assembler must cut walls 105 b so as to accommodate seams or corrugations in roof r . step 320 involves cutting top support channel 135 and bottom support channel 140 according to the curb width of step 305 . preferably , a roof curb assembler uses an angle grinder with cutoff blade . top support channel 135 and bottom support channel 140 also may require notching to accommodate roof support structures . step 325 involves aligning a template relative to and drilling pilot holes through walls 105 so as to register with throughbores 112 in connection blocks 110 . a roof curb assembler temporarily maintains relative positioning of the template and walls 105 with a locking c - clamp . the roof curb assembler drills two 5 / 16 - inch diameter holes at each end of each of walls 105 . step 330 involves applying a 5 / 16 - inch diameter bead of gun grade sealant , preferably panlastic , to the top , bottom and corner of each of corner blocks 110 with a caulking gun . this provides roof curbs 100 and 200 with an integral water - tight seal that is superior to post - installation sealant treatments common to other roof curbs . step 335 involves driving ¼ - inch × ½ - inch phillips head bolts through the holes in walls 105 and corner connection blocks 110 . tightening the bolts urges walls 105 and corner connection blocks 110 to come together , and urges the mastic applied to corner connection blocks 110 at step 330 to flow into any gaps , thereby sealing the joint . step 340 involves determining the slope or pitch of roof r , and an appropriate measurement for the “ x ” dimension shown in fig8 , corresponding to the pitch so that composite boards 115 provide a generally level mounting area for an appliance ( not shown ). the “ y ” dimension is fixed , preferably at 5 - ½ inches . preferably , stock trex ® boards 115 for cutting are 5 / 4 - inch × 6 - inches . step 345 involves using a circular , table or radial - arm saw equipped with a wood - cutting carbide blade to cut stock trex ® boards 115 as required to fit tightly in channels 125 . referring to fig9 , an embodiment of a method of making 500 roof curb 200 configured according to the invention includes : a step 505 of determining curb size ; a step 510 of cutting extrusions ; a step 515 of cutting bottom extrusion ; a step 520 of cutting steel channels ; a step 523 of cutting diverter plate ; a step 525 of drilling corner connections ; a step 530 of applying corner block mastic ; a step 535 of assembling extrusion corners ; a step 540 of determining composite board dimensions ; and a step 545 of cutting composite boards . referring also to fig1 , method of making 500 is substantially identical to method of making 300 except for an additional step 523 . step 523 involves cutting diverter plate 235 according to the curb width determined at step 505 , which is similar to step 305 . a roof curb assembler must cut diverter plate 235 so as to accommodate seams , corrugations or ribs f in roof r . specifically , holes in diverter plate 235 must align with ribs f . referring to fig1 , an embodiment of a method of installing 400 roof curb 100 configured according to the invention includes : a step 405 of marking roof for cutout ; a step 410 of placing walkboards for support ; a step 415 of cutting panel ; a step 420 of installing side support channels ; a step 425 of installing rear support channel ; a step 430 of applying mastic for curb ; a step 435 of installing curb base ; a step 440 of cleaning area ; a step 445 of applying sealant ; a step 450 of applying mastic ; a step 455 of installing composite boards ; a step 460 of applying foam tape and sealant at board joints ; a step 465 of cutting out insulation ; and a step 470 of installing retainers . referring also to fig1 , step 405 involves placing roof curb 100 , as assembled above , onto the portion of roof r where an appliance is desired . bottom wall 105 b should vertically register with supporting structural purlin . a minimum 6 - inch distance should exist between top wall 105 b and the upper supporting structural purlin . a roof curb installer then traces along the interior of flanges 120 of roof curb 100 with a standard lead or grease pencil . step 410 involves disposing boards or paneling , having sufficient strength to maintain a roof curb installer &# 39 ; s weight on roof r , just outside of the tracing generated in step 405 , proximate to where the roof curb installer will cut roof r . step 415 involves drilling ½ - inch starter holes in roof r at each corner of the tracing of step 405 , then using a double - cut shear , which minimizes shavings and chips , to cut roof r along the tracing . a roof curb installer will need a reciprocating saw to cut through corrugations in roof r . step 420 involves sizing and temporarily clamping in place side support channels on top of any insulation and between the upper supporting structural purlin and lower supporting structural purlin , just outside of the lateral edges of the hole in roof r generated at step 415 . step 425 involves sizing and temporarily clamping in place a bottom support channel between the side support channels installed in step 420 , just outside of the bottom edge of the hole in roof r generated at step 415 . step 430 involves inserting lockseam plugs on the bottom corrugations occurring along the bottom edge of the hole in roof r generated at step 415 . once installed , the lockseam plugs may be filled with mastic . a roof curb installer applies ⅛ - inch × ½ - inch panlastic tape over the lockseam plugs around and aligned with the edges defining the hole in roof r . the tape should be butted , not lapped , at corners . finally , the roof curb installer applies a continuous bead of sealant on top of the tape . step 435 involves positioning roof curb 100 over the prepared hole in roof r and securing flanges 120 of roof curb 100 to the support channels with self - drilling ¼ - inch × ⅞ - inch metal screws at six - inch intervals . step 440 involves sweeping or vacuuming away all metal chips and shavings . step 445 involves applying a continuous bead of sealant around the intersection of roof r and roof curb 100 . step 450 involves applying gun grade mastic in the outer corner of channels 125 of walls 105 and to the butt ends of composite boards 115 . step 455 involves attaching composite boards 115 to walls 105 with self - drilling ¼ - inch × ⅞ - inch metal screws , and to adjoining composite boards 115 with self - drilling # 6 × 2 - inch screws . step 460 involves applying sealant along the joint between walls 105 and composite boards 115 . the roof curb installer then applies foam tape on the top surfaces of the composite boards 115 . step 465 involves trimming a four - inch wide roll of insulation from building scrap . the roof curb installer places the insulation in pocket 128 in walls 105 defined by channel 125 , vertical wall 127 and flange 120 , as shown in fig4 . temporary adhesive may aid in retaining the insulation in pocket 128 . the roof curb installer then slits the building insulation from each roof curb corner inwardly , then removes the insulation from the facing . the roof curb installer folds the facing up each inner side of roof curb 100 and secures the folds thereto with retainers and self - drilling screws . the roof curb installer then tapes each corner to seal vapor retarder completely . referring to fig1 , an embodiment of a method of installing 600 roof curb 200 configured according to the invention includes : a step 605 of marking roof for cutout ; a step 607 of marking roof for diverter plate ; a step 615 of cutting panel ; a step 620 of installing side support channels ; a step 625 of installing rear support channel ; a step 627 of preparing diverter plate ; a step 628 of installing diverter plate ; a step 630 of applying mastic for curb ; a step 635 of installing curb base ; a step 637 of preparing diverter angle ; a step 638 of installing diverter angle ; a step 640 of cleaning area ; a step 645 of applying sealant ; a step 650 of applying mastic ; a step 655 of installing composite boards ; a step 660 of applying foam tape and sealant at composite board joints ; a step 665 of cutting out insulation ; and a step 670 of installing retainers . referring also to fig1 a and 14b , method of installing 600 is substantially identical to method of installing 400 except for steps 607 , 627 , 628 , 637 and 638 . step 607 involves placing diverter plate 235 adjacent to the top edge of the tracing generated in step 605 , which is similar to step 405 , and tracing around diverter plate 235 . step 627 involves attaching corrugation plugs to diverter plate 235 over the holes aligned with ribs f in roof r . the roof curb installer applies tape panlastic over the side and outer edges of diverter plate 235 , being careful to butt and not lap the ends , so that a minimum of ¼ inch is exposed around the panel cut out . the roof curb installer applies gun grade mastic over the tape panlastic . step 628 involves placing diverter plate 235 in the cutout in roof r so that corrugation plugs snugly fit in the corrugations in roof r . self - drilling threaded fasteners secure diverter plate to roof r . mastic must be applied around holes on the bottom side of the panel strips . step 637 involves applying a 5 / 16 - inch bead of mastic to the back and ⅛ - inch × 1½ - inch tape panlastic to bottom of diverter angle 245 , then positioning diverter angle 245 against roof curb 200 on roof r . step 638 involves securing diverter angle 245 to roof curb 200 and roof r with self - drilling threaded fasteners . the invention is not limited to the particular embodiments described herein , rather only to the following claims .