While insulating my garage door, I'm considering replacing the existing plain glass with something better. I'm considering replacing each pane, or simply attaching a second layer on the inside of the door, to create a double pane effect.

What kind of glass should I use for insulating a garage door window?

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    Hello, and welcome to Home Improvement. You're looking for double-pane glass, but I don't think it's available as a garage door retrofit. In any case, "shopping" questions are off-topic here. – Daniel Griscom Dec 16 '18 at 18:12
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    I wouldn't consider it unless the garage door is insulated . My doors are insulated and much more cold comes in around the top and sides than the windows. – blacksmith37 Dec 16 '18 at 22:10
  • Part of the project has included weather stripping along the interior and exterior of the door ( I agree that's made a substantial improvement). The framing around the windows has a nice inset that looks like a great spot to attach a second pane of glass. Sounds like my best bet is to just use off the shelf glass. – Dan O'Boyle Dec 16 '18 at 22:28

That would be double pane or triple pane, gas filled windows, but you would likely have to have them custom made.

  • And don’t forget it needs to be tempered or laminated glass if it’s in a door, within 18” of a window or door, or if it’s within 18” of the floor. – Lee Sam Dec 16 '18 at 22:01

You shouldn't alter a garage door at all. If you change the weight of the door, you will mess up the counterweight.

Many people do not realize this because they've never lifted a garage door (the opener does all the work)... but a garage door is balanced. You should be able to open one, certainly a residential one, with one hand, and if you move it to a height, it should stay there.

That is where spring rate comes into play. The door must be "balanced" (weight of the part of the door that is on the vertical equals spring tension) through the entire range of motion. You have some limited range of adjustment on the spring. But go too far and you get a tilted spring rate: the door wants to spring upwards when near top, and drop when near bottom. Or the reverse. That is when you need a different rate spring.

Garage door insulation kits exist, but they are designed to be of trivial weight.

Garage door safety is serious business, and the counterweight stores a lot of energy. It's most dangerous to people trying to service the counterweight mechanism. It's less about the spring grenading, and more about the door making unexpected movements, in particular, unexpectedly dropping.

I recall one building where some epsilon-minus designed the opener to act on the spring shaft instead of the door. Terrible design. Left free to move, the cables, drums and spring shaft are fast enough to keep up with any door movement. Not in this case. When the door is all the way up (stored horizontal), it is lazy about coming back down. Turning the counterweight shaft didn't move the door, it only slacked the cables, which is a cardinal sin because then, the cables pop off the drums. When gravity finally took the door, it dropped like a guillotine. Doors kill.

If you want a better insulated window door, figure out who made your door and consult with them about available options. They may sell door panels that do what you want cheaper and with less of your time than you could build one. More importantly, they could consult with you about any spring changes that would be needed. Springs are deadly and are not to be trifled with.

  • This seems a bit alarmist and would be counter to an entire industry of garage door insulation kits. Since this is a thing people do regularly, maybe you could provide more information on best practice instead of a generalization about the danger? For example - While I wouldn't want my springs to snap, ensuring a safety wire is installed means any damage would be much more controlled. – Dan O'Boyle Dec 17 '18 at 13:24
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    @DanO'Boyle Those kits are of trivial weight, not multipane windows. You say alarmist, I say experienced. I've expanded the answer. – Harper - Reinstate Monica Dec 17 '18 at 19:44

Don't use glass if possible, use clear plastic (acrylic, poly-carbonate, etc...) instead. For reducing thermal loss, glass is a really poor thermal insulator compared to plastics.

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