I did a Google search and got this

In general, heat treated or tempered glass is four times stronger than annealed glass. Tempered glass cannot be drilled or cut without shattering. All fabrication needs to be done while the glass is in the softer, annealed condition. Annealed glass can be cut, drilled, notched and edge finished.

It's incredibly difficult to accurately cut a double-glazed unit, and nearly all installers will recommend simply replacing that panel with a single glazed piece, or having a new factory-cut piece made (more $$$).

Paul1977: Can a double glazed door with standard clear glass on the outside and laminated annealed glass on the inside be cut to put a cat door in, or does the glazing unit need to be replaced?

Thanks

For a few years the building code has required safety glass in doors (I think it used to be optional if there was a vision rail). What that means is the non laminated glass pane would be toughened, and toughened glass is difficult to cut without disintegrating. 

Toughened glass should have an S safety logo mark so look for that in a corner. 

Cutting laminated standard glass should be possible but making a shape cutout in situ without making a mess? You'd have to ask a professional. Maybe one of those non transparent cat doors would hide any cosmetic defects. 

Perhaps they could smash out the outer pane. Even if they can retain the outer pane it will lose airtightness and suffer internal condensation unless they have very specific processes applied to supersede that problem. In the UK repairing IGUs is a thing but not so much in New Zealand.

Low e glass is usually on or inside the outter pane so it may look inconsistent if you've got low e elsewhere.

Replacing the IGU with a factory cat door, if possible, is more ideal.  

This is why I'd say pre-emtively install a cat door in double glazing even if you don't have a cat.

bfginger:

Paul1977: Can a double glazed door with standard clear glass on the outside and laminated annealed glass on the inside be cut to put a cat door in, or does the glazing unit need to be replaced?

Thanks

For a few years the building code has required safety glass in doors (I think it used to be optional if there was a vision rail). What that means is the non laminated glass pane would be toughened, and toughened glass is difficult to cut without disintegrating. 

Toughened glass should have an S safety logo mark so look for that in a corner. 

Cutting laminated standard glass should be possible but making a shape cutout in situ without making a mess? You'd have to ask a professional. Maybe one of those non transparent cat doors would hide any cosmetic defects. 

Perhaps they could smash out the outer pane. Even if they can retain the outer pane it will lose airtightness and suffer internal condensation unless they have very specific processes applied to supersede that problem. In the UK repairing IGUs is a thing but not so much in New Zealand.

Low e glass is usually on or inside the outter pane so it may look inconsistent if you've got low e elsewhere.

Replacing the IGU with a factory cat door, if possible, is more ideal.  

This is why I'd say pre-emtively install a cat door in double glazing even if you don't have a cat.

You could get one of those infrared chimes so there's a "ding dong" whenever the cat approaches the outside of the door.