Radiant barrier vs Radiant Barrier with insulation

[DieselSJ]

Getting ready to start the insulation and siding phase of my build. Garage is a 30x30 Versatube. There is a 1"+ air gap between the frame and the outer skin. I'm not so concerned with keeping heat or cool in as I am with keeping the Arizona heat out of the garage. So I want something with a radiant barrier between the frame and the skin.

Looking at something like the radiant barrier only from warehousefoil.com (or any of the equivalent products that are radiant barrier only) and comparing to a radiant barrier with a layer of FG insulation, such as SolarGuard. I am not interested in any of the "bubble" type products, so let's keep those out of the discussion.

I can get the radiant only delivered to me for less than $400. That is the commercial quality, "tear proof" with white on the inside. If I go with the radiant + insulation, I'm looking at almost $1100 delivered. That is for the SolarGuard which is radiant + 3/4" FG + white poly.

Is the extra cost worth it? Would the $700 be better spent on some type of insulation blanket vs having the insulation as part of the radiant barrier?

 

[Radix2]

I'd think the way to go is to paint the outside with a radiant/light color and insulate conventionally on the inside. Getting a radiant barrier to work with small clearances, ect. is very difficult, and the radiant barrier is most effective on the outside.

If you already have a aluminum/galvanized roof, I don't think there is much more to be had in this direction.

 

[DieselSJ]

I'm not really interested in having a silver garage. Siding is a very light tan color. Doesn't matter the color of anything here - during the spring/summer/fall, everything gets too hot to touch no matter what color it is. Radiant barriers between the siding and the frame work extremely well here. With a full 1" air gap between them with full air flow being able to get in from the bottom of the siding and out through the roof vent it is very effective at keeping the heat out of the building.

I really have no plans to do finished walls inside so conventional insulation is not really an option.

 

[DC73]

I really have no plans to do finished walls inside so conventional insulation is not really an option.

Then, you are really just wasting your money on radiant barriers. Heat gain into a building is transferred by 3 methods: Radiation, Convection, & Conduction. Radiation is the warmth you feel from the sun. Convection is from the movement of air. Conduction is direct heat transfer through the walls (as the outdoor temperature climbs and heats up the outer surface of the wall, the heat moves into the wall and eventually reaches the interior of the building).

By far the greatest heat gain into a building is via convection and conduction. Once you air seal a building and properly insulate, there is not much heat gain from radiation. At that point, radiant barriers are not usually cost effective unless you can do it at very low or no cost. They might help somewhat with comfort but I don't think they are worth much additional expense.

120 degree outdoor air is going to heat your building through convection and conduction and a radiant barrier will do nothing to stop it.

DC