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<body><div>The glass requires 1/2" bearing on the support framing + 1/4 "edge clearance to allow for expansion.</div><div><br></div><div>Allowing 1" width for the clamping bar fastening arrangement the total width for two glass panels is 2.5".</div><div><br></div><div>For a porch roof, normal, nominal 2x framing lumber is fine for the rafters. (ie 2x6, 2x8 etc depending upon specific span and load conditions.</div><div><br></div><div>One simply needs to attach a 1x3 (ie 3/4" x 2.5") to the top edge of the rafter to create a "T" cross-section member.</div><div><br></div><div>The 1x3 provides the necessary 2.5" width for the bearing , as well as lateral stiffening for the 1.5" dimension of the rafter. while at the same time minimising the shadow cast by the framing member.</div><div><br></div><div>Standard steel stud framing channel runner will serve as a water-proof cap for the support framing member and standard "J" trim can be inserted under the edges of the upside down channel to function as condensation gutters.</div><div><br></div><div>I have lots of EPDM roof membrane around that it's easy to slice off strips from to place on top of the metal cap on which the glass can rest and be free to move. Some double-faced tape can be used to adhere it.</div><div><br></div><div>Standard aluminum clapping bars are typically a minimum of $# per lineal foot . I find it more economical to simply use beveled-edge wood battens as clamping bars and bend a sheet metal cap to snap over it, milling a dado into the batten to accept 6mm neoprene screen spline which functions as a pressure gasket.</div><div><br></div><div>This provides a basic outline of the process (effectiveness proven by decades-worth of trouble-free service) but I've obviously left out many details. Not rocket science to figure out on one's own.</div><div><br></div><div><br></div><div>On Fri, 19 Sep 2014 15:27:27 -0400, Reuben Deumling <9watts@gmail.com> wrote:<br></div><br><blockquote style="margin: 0 0 0.80ex; border-left: #0000FF 2px solid; padding-left: 1ex"><div dir="ltr"><div>Laren, <br>this method sounds great. I'm going to give it a try. </div></div></blockquote><div><br></div><blockquote style="margin: 0 0 0.80ex; border-left: #0000FF 2px solid; padding-left: 1ex"><div dir="ltr"><div> That is to lay<br>
the glass on top of the rafters (ideally beams, so they<br> have adequate width for lap and movement)</div></div></blockquote><div id="M2Signature"><div>-- </div><div>=== * ===<br>Rob Tom . . . T60BOM<br>Kanata, Ontario, Canada<br><br>A r c h i L o g i c at Y a h o o dot C A<br>(manually winnow the chaff from my edress if you hit "reply")</div></div></body></html>