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When installing insulated glass panels in a wood sash how much clearance should there be from the edge of the glass to the wood? I will be using 1/8" setting Blocks on the bottom.
Ive always just left enough clearance so we dont introduce any shear on the IGU. 1/16-3/16 all the way around depending on the application.
Insulated glass manufacturers will tell you 1/8" minimum on each of four sides.
We no longer use setting blocks. We use an RTV sealant that effectively glues the glass to the wood, so there is no movement. We make divided light sash, so no large panes expanding and contracting.
We will order insulated glass 1/8" less than the opening. The key is to not 'squeeze' it in the opening as MarkB stated. If the two panes are not aligned correctly, then you are faced with a unit that is too large to fit. Then you either chisel, route, or hatchet the opening a bit larger.
We allow 1/8” all around, when measuring I use a 8mm block in the the corner to measure from as IG grows in size due to glass misalignment and sealant.
Blocking on single light openings is important to support both panes of glass. Swinging sash should be blocked at bottom hinge corner and top handle corner to to eliminate sagging of the sash. Double hung only needs blocking at the bottom.
Wet glaze with a caulking notch built into the tooling is the best method to seal the glass but requires some planning at the tooling stage and a skilled hand at the glazing install.
Another question if I may.
Yep. This has both technical and aesthetic reasoning.
Technically, the glass unit is sealed off from the environment. This will help add life to the seals and slow down the chance of fogging.
Aesthetically, the sealant gives a uniform color between the glass and stop, and prevent fines from dripping or wicking between wood and glass. This, of course, is noticeable as one looks thru the glass unit towards the other side.