# Dado for Window Glass



## valerio (Apr 4, 2009)

I would like to make some windows to put on the roof of my greenhouse project and will be using 2x4 lumber. Does any one have any experience with this type of project? My glass is tempered 5ft long x 21 in wide x 3/16 in thick. If dados are the best way to do this, what is the suggested depth and width. Also since I have eleven to make does anyone have suggestions on how to build a jig to speed the proecess? Any comments would be appreciated.


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## derek willis (Jan 21, 2009)

I would have thought that a bearing guided rebate (dado) cutter would be the simplest thing to do, they usually cut to 12mm depth, but you can lower the cutter and run through again if this is not enough, depth would depend on the fixing method for the glass, if you are fixing with beads then you will need an extra deep rebate, if you are just fixing with putty or mastic then a shallower rebate will do. Most suppliers sell cutters with various bearings to cut wide and narrow rebates.


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## Ralph Barker (Dec 15, 2008)

I'd think your approach would depend on the design of the frames and the roof support, but I'd concur on using a rabbet cutter with a bearing and perhaps an edge guide on the router. Having at least 1/2" of the glass supported at the edge sounds about right, but you might also want to have one or two struts supporting the middle of the panes. And, don't forget to allow for expansion/contraction.

I'd also suggest checking your local building codes for design restrictions on ceiling applications for glass, and/or recommendations from window industry groups. Safety would be the primary concern with overhead glass.


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## Ghidrah (Oct 21, 2008)

Agree with rabbits on the frame. Depending on whether you are creating a removable independent sub frame or the frame will also be doing double duty as rafters and glass frame. 

Be aware a green house moves considerably due to air pressure and temp variations. Be prepared for some, (possibly severe) condensation issues.

Consider allowing the glass to sit high on the frame maybe 1/16". Use Ice/Water barrier as a weather seal and an elastomeric, (rubber roofing) strips as a cushion in the rabbit for the glass. I'd suggest sub frames, (easier to remove if issues arise and don't hard fix the sub frame to the rafters. Make a ledge to set the frame on and take the weight.

If you can afford tin use it over wood for the exterior trim cover you won't have to paint it every couple yrs to control rot.


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## bobj3 (Jan 17, 2006)

Hi valerio

I disagree with the rabbit way,, you don't want a place for the water to sit to be trapped ,, you can buy some channel from the glass outlet,,made just for that type of job..the norm is Alum.stock with a rubber channel seal..that can be screwed to the 2 x 4 stock...some call it sky light window channel.

The last one I made was a A-Frame green house and the Alum.worked out just great...makes the job clean and easy..

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valerio said:


> I would like to make some windows to put on the roof of my greenhouse project and will be using 2x4 lumber. Does any one have any experience with this type of project? My glass is tempered 5ft long x 21 in wide x 3/16 in thick. If dados are the best way to do this, what is the suggested depth and width. Also since I have eleven to make does anyone have suggestions on how to build a jig to speed the proecess? Any comments would be appreciated.


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## valerio (Apr 4, 2009)

Thank you all for the information. I purchased some neoprene rubber blocks to sit around the window glass. Now another question.....Say that I cut rabbits on the 2x4 deep enough to accomodate these blocks which are about 1/4 in Wide x 2 in. Long x 3/16 in thick, which should take care of any movement of the glass plus the 1/2 inch for the glass itself. Do I than fill the air spaces between the blocks with caulking or do I just leave the air spaces and caulk around both sides of the glass? 

I will also do some checking on the aluminum channel w/rubber.


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