Garage Door Foam Board Method
If your garage is catching direct sunlight, then you definitely stand to gain from adding a radiant barrier inside the garage on the door and/or any other walls that are catching direct sunlight from the exterior.
Keep in mind that a garage is typically not conditioned (being heated or cooled) so the results are more about tempering the heat gain in the summer. To really maximize results in the garage, you want to address any and all surfaces catching direct sunlight. If your garage door does not catch direct sunlight, then adding the radiant barrier to the door is not going to make a difference in cooling the garage. Radiant barrier is effective when there is radiant heat, so address any and all walls/surfaces that get sunlight.
A radiant barrier in a garage application is primarily used to keep the garage cool. If you want to keep the garage warm, you should use traditional insulation on the garage door to add R-value and then seal up the garage air tight.
The Easiest Method to Cool the Garage
The simplest and fastest way to cool the garage is to add radiant barrier to a garage door using foam board with foil attached to one side. This allows for the air gap to be between the foil and the garage door. It’s an easy, no-mess alternative to other options: no glue, tape etc. You can make a foil-faced foam board, or purchase pre-made ones at the home improvement store, to make this application super easy.
This application works best when you cut the foiled foam board into rectangular pieces slightly larger then the opening in the garage panels, this allows you to pop them in under the metal frames. Be sure there is an air space between foil and garage door.
Speaking of ventilation in the garage, in addition to adding a radiant barrier, you should consider adjusting the proximity switch on the garage opener to allow a 1-2 inch gap at the bottom of the garage door. Then create an opening at the top of the garage to create a ventilation channel. If you have attic stairs in the garage area, then we suggest propping them open a couple inches to allow the hot air to come in from outside, flow up toward the attic stairs and go out the attic. This ventilation path will allow the air temp in the garage to stabilize and become close to ambient (outside) air temperature.
If you do not have attic stairs or an opening in the garage that vents to the attic, then you can create one yourself. Simply cut a hole in the ceiling of the garage to vent. To make it look nicer, you can attach a return air grill (like the ones you see in your home for your A/C to cover the hole in the garage, but still allow for air flow.
Can’t Find Foil-faced Foam Board? Make Your Own!
Most big box retailers sell a foil-faced foam board (we show Perma-R but it’s also sold under different names/brands); even if a retailer sells a different brand, that’s ok! You’re basically looking for a foam board that has aluminum adhered to one side.
If you’re still not able to locate any in your area, don’t worry – you can make your own! All you need to do it purchase some sheets of foam and then attach AtticFoil® on to one side using a spray on adhesive or even thumbtack-like fasteners. The single-sided AtticFoil® works really well for this type of project, but if you only need a small amount of foil, you can purchase the mini roll (250 sq ft) of the 48″ wide double-sided instead.
Once the foil is attached, you’re ready to continue with the installation as shown above.
Installing Radiant Barrier on Garage Walls
If your garage walls also catch direct sunlight, then you should add a radiant barrier inside the garage on the walls that are catching direct sunlight from the exterior.
In the photos you see here, the customer was mostly concerned about keeping the heat inside the garage, which is why the foil is closest to the inside of the garage space.
This customer did not use sheetrock over the foil, just insulation and AtticFoil®. If he wanted to cover with sheetrock he would have needed to create airspace between the foil and sheetrock with furring strips.
*Note: if keeping heat out of the garage is your goal, you’d ideally want the foil closest to the outside (i.e. in between the walls studs).
To see more garage door and garage wall installations, check out our DIY Project Gallery.