I searched around but couldn't seem to find an answer to this question. I'm about to start insulating my garage, starting with the ceiling/attic and then garage doors. For the doors, I'm planning to use foam board with the reflective foil and having the foil face the door. My door panels are about 2 inches deep so my question is - is it better to use 1 inch board to leave a 1 inch gap between the door and foil, or to use 2 inch board and have no gap. Using 1 inch board will have a lesser R value but the radiant barrier should work properly with an air gap. The 2 inch board obviously has a higher R value but leaving no gap eliminates any radiant barrier benefit I think. I'm in Texas so I'm trying to do whatever will keep the most heat out of my garage in the 100+ degree summer. Thanks in advance for any help.
Garage door insulation
- Thread starter dfwTX
- Start date
Kaizen
Well-known member
I wonder if that gap would constantly heat up and with no escape warp the panel?
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ducatithunder
Well-known member
Use 2" Polyiso with a foil face facing away from the space. The friction fit will help to hold the panel in place. If you need more holding power you can silicone the panel backside to the door or tap the edge.
I did my door years ago with XPS in my Maryland garage. I used 1.5" with bubble face insulation as my door was not quite 2". Its been 5 years no issues.
I did my door years ago with XPS in my Maryland garage. I used 1.5" with bubble face insulation as my door was not quite 2". Its been 5 years no issues.
Hobby_Man22
Well-known member
I asked the same question about roll up doors and sealing the air gap on the sides and top. For like $80 they make brushes that you screw into the trim work around the door and the brush presses against the door sealing air leaks.
So my question isn't about sealing around the sides and top of door, I'm talking about leaving a space between the foam board and the garage door panels. Pretty much what ducatithunder did, but with a thinner board. With the reflective foil/radiant barrier on the board facing the door, this space allows the radiant barrier to do its job.
I'm wondering whether what I said above is more effective than using a thicker foam board that would not leave a space, thereby probably negating any benefit from the radiant barrier.
For example, if the 1 inch foam board had a R3 value but also a proper radiant barrier and the 2 inch board had a R6 value but ineffective radiant barrier, which actually is most beneficial? I know some would see a higher R value and jump at that, but the radiant barrier has to have a significant effect in the direct sun in the summer.
I'm wondering whether what I said above is more effective than using a thicker foam board that would not leave a space, thereby probably negating any benefit from the radiant barrier.
For example, if the 1 inch foam board had a R3 value but also a proper radiant barrier and the 2 inch board had a R6 value but ineffective radiant barrier, which actually is most beneficial? I know some would see a higher R value and jump at that, but the radiant barrier has to have a significant effect in the direct sun in the summer.
duneslider
Well-known member
More insulation will always trump less insulation. I can't see any advantage to leaving a gap that will just turn into hot air that will have to go someplace.
I'm not certain what the point of the foil will be, I haven't seen any valid studies that show a benefit that is worth it. For example the R-value of the foil bubble wrap is like 1.* but cost more than 1" of foam that has a value of 3-5 but the foil stuff costs more than the foam.
If you put the foil on the outside of your door so it reflected the sunlight it would help more but that probably isn't going to help the curb appeal. A light colored door would do the same, as apposed to a dark colored door.
I vote for just foam board as thick as fits.
I'm not certain what the point of the foil will be, I haven't seen any valid studies that show a benefit that is worth it. For example the R-value of the foil bubble wrap is like 1.* but cost more than 1" of foam that has a value of 3-5 but the foil stuff costs more than the foam.
If you put the foil on the outside of your door so it reflected the sunlight it would help more but that probably isn't going to help the curb appeal. A light colored door would do the same, as apposed to a dark colored door.
I vote for just foam board as thick as fits.
I used 3/4 foam siding insulation with a reflective/radiant barrier on a single side. I glued it directly to the door panel, with no air gap, ising PL 30. It insulates well from the suns radiant heat and when it is really cold outside the temperature I can feel around the gaps is of inside the room. I have not tried FLIR testing or anything but I went one summer and winter without insulation on the door and attic and said screw that afterwards. I have some things in my garage I definitely do not want freezing or getting too hot, so other than the foam board I used rolled out batting in the attic over the garage for the rest of the insulation and it works great. During the summer I can keep it at right around 72 so long as I don't leave the door open too long. If I am going back and forth I just kind of give up at that point. I think my window unit is 8000 BTU and if I try to get it any cooler it would just run non-stop and never get below 72. I would go bigger and keep it cooler but that is the largest I can fit in the window in my garage. I will probably do a mini-split running up to spring and be done with it. I was able to keep it in the 50's during this last winter blast with a very small honeywell unit. I'm in the Waco area so are weather is about the same. It wasn't enough for me to be super comfortable but honestly that's the coldest it has been since I last moved in and normally it keeps in the 60's without driving my electric bill sky high, and for me that is kind of the perfect work temp in the winter months. I think at the point where it was the worst during this winter storm we had it was down to about -5 F outside and low 50's in the garage so it was enough to keep all my chemicals and other things from freezing. I have another 240 Volt heater unit coming for future event's, just a lack of planning on my behalf kept it from getting to me in time to survive the snowmageddon, lol. I can't recall the R value of my door insulation but it was enough to where if I had proper sized AC in my garage I could easily keep it cooled or heated to my hearts content.
ducatithunder
Well-known member
I would not leave a air gap. The foil will block the heat as it should. If you use a smaller board thickness you will have to find a way to keep it secured as stated. I assume your door is a contractor grade door. You will be surprised how much the foam will stiffen up the door, which is another bonus of friction fitting the board.
It did stiffen up my door and does protect a little from wind noise and stuff when I am working on the garage with the doors closed as well.
