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Insulated my garage door w/ a radiant barrier, I may have made my issue worse

Insulated my garage door w/ a radiant barrier, I may have made my issue worse

Old 07-17-20, 09:24 PM
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Insulated my garage door w/ a radiant barrier, I may have made my issue worse

I recently bought a house in sunny Arizona. My garage faces west. Anyone who knows AZ or most places not in cold climates is we have no basements. I needed a workshop so I am using roughly 40% of my 3 car garage as a workshop. I did a few web searches and watched a few YouTube University videos and decided to go with a Reflectix radiant barrier. It wasn't until I was at the big box stores that I thought the R value of 3 could be better if I put 1/2" styrofoam with a Reflective barrier facing the door. Then the Reflectix on the very far inside of the door giving the required air barrier between it and the door/styrofoam. In the morning until about 2 it's bearable in the garage after that and into the night it holds so much heat in the garage it's litterally a sauna in there. It also doesn't help I added 10 4' of these lights. And surprisingly they actually get very warm bso any heat in the garage I feel gets trapped because the Reflectix is now keeping that heat in since it's the same in both sides. Other than spraying foam in my rafters above my garage and running some sort of AC/swamp cooler do you think the Reflectix is causing the heat to stay in the garage, should I remove it?

The mobile browser won't let me upload pics but here they are hosted.


1/2" foam with reflective

Last edited by PJmax; 07-18-20 at 10:49 AM. Reason: added pics from links
Old 07-17-20, 09:54 PM
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Insulation in general will keep the heat in longer. Nothing to do with the radiant barrier. They are usually snake oil, IMO.

R value is resistance to heat loss. So by adding R value to the door, once it does heat up inside... you keep the heat in longer. That's how insulation works.
Old 07-18-20, 03:58 AM
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My garage is insulated (walls, ceiling & door) and it can be a sauna as well. You pull 4'000 pounds of hot car inside an insulated box and it's going to get hot. It's a nice benefit in winter but it can be uncomfortable in summer.

The important thing to remember is that insulation does not heat or cool. It only slows the movement of heat as XSleeper mentioned. With Arizona temperatures and sun it's only a matter of time before the heat outside soaks through the insulation and into the garage. Without insulation the garage may hit 120f at Noon but with a few R of insulation it may delay it until 2 or 4 in the afternoon but it's still going to get hot.

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