How to insulate a garage door for hot climates – DIY on da cheap!

If you live in a hot climate like Arizona, a metal garage door turns that space into a solar oven, especially if it’s facing South and/or West. There’s a number of products on the market as well as some creative DIY solutions for those on a limited budget. I did a ton of research and have done several doors so I’ll share that with you here.


1. Cardboard. It’s free, paintable and better than no insulation, but still lets some heat radiate in. Double cardboard works better, but on a double door the weight starts to add up and you might need to adjust your door springs to compensate. I tried a few panels and decided it wasn’t worth the effort to hunt down unmolested sections large enough to do the whole door. I also had some reservations about it being a fire hazard, especially as the heat dried it out and if it got hit with sparks from a metal working project. If any water got through the cracks in the door, it could get soggy and even heavier. So I went with option #2 on my most recent home.

2. Refectix radiant barrier insulation. This is two mylar reflective sheets over a bubble core. It’s a lot more durable than shipping bubble wrap, you can step on this stuff and it doesn’t pop. I did the entire double door for about $60 worth of materials, available at local hardware and home improvement stores. It’s lightweight and easy to cut with a utility knife & straight edge. Just measure the inside of each panel and trim for a snug fit. It’s pretty forgiving to work with and looks alright too. It’s April and we’ve already hit 100 in the afternoon, but standing inside the door I don’t feel like I’m facing a space heater.  It provides a minimal amount of sound deadening and if you damage a section you can fix it with aluminium foil tape or buy a small roll to repair what you need. It’s also reasonably fire resistant and unphased by water. If your goal is to mitigate heat and want to keep the costs down without looking ratty, this is a good way to go.


Finished Project


Here’s the thing about radiant barrier insulation: There must be an air gap between the insulation and the surface you’re trying to insulate against heat. I confirmed this by placing one section directly against the garage door panel and sure enough, it heated right up. See also the manufacturer’s product specification sheet. So I added a few double-thick cardboard strips behind the insulation to create a 1/2″ space and sure enough, it now keeps the heat at bay. One could also accomplish proper air gap spacing using strips double-sided tape or the insulation itself.


Air gap for radiant barrier



Spacers for air gap


If you trim your panels for a snug accurate fit, and your door is like mine, they’ll hold in place on their own on the top, bottom and right side. Along the left side, they’ll start to come out when the door is open. You can secure those with double-sided tape, foil tape or some strips of moulding cut for a snug fit. All are viable, choose what ya like! Also note that all garage door panels are not the same size even on the same door, so measure twice, buy & cut once. You can join sections of this material neatly by using foil tape.


Moulding retainers



3. Ridgid styrofoam. I’ve used this before and it does work quite well for heat and cold. It’s not too expensive when purchased in large sheets but it can be a bit messy to cut and work with and can break while bending it to fit within the panel. I wasn’t crazy about the appearance of the lettering either. They do make garage door insulation kits where one side has a thin plastic veneer and the other side has grooves to facilitate bending without breaking. This system looks very nice but will cost ~$150-200 and you can’t buy just one if a panel gets damaged. If you need to work against heat and cold and want a super clean factory look, those veneered panels are the way to go.

4. Fiberglass batting. Owens Corning makes a kit with a white plastic sheeting on one side. They come with plastic fasteners that look good in concept but in practice break easily. One could secure this in place with some wire or moulding. Cost for a double-door is almost $200, but if your goal is to stop heat and cold and need extra sound insulation in the garage, this option can’t be beat.

5. Spray in insulation. This is the one option I haven’t personally tried. Spray foam insulation is used in better modern homes and renovations. It’s well regarded for complete insulation and blocking all gaps. To the best of my knowledge it needs to be applied with proper equipment and if you don’t like it you can’t easily remove it. That’s why I haven’t tried it.

So there it is, for less than $100 you can greatly extend the hours and season you can work in your garage, plus all that extra heat isn’t radiating into your house nor degrading any items you store in the garage.

– Kenn Ranous


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