On a non-conditioned building, there really is nothing better than a radiant barrier to control the heat gain. Structures like sheds, carports and barns can all benefit greatly by adding a layer of radiant barrier near the roof line and any sun-catching walls to keep the heat out.

Say No to Traditional Insulation

On a non-conditioned building, traditional insulation is not necessary. The goal is not to make the structure airtight in order to keep cold (or hot) air inside of it; the building is vented, so it can't be airtight. Therefore, the most realistic expectations you can have for a building that you are not heating or cooling, is to get it at (or close to), outside air temperature (also known as ambient air temperature). Getting the air temperature lowered is largely relative to the amount of ventilation you have going through the structure. However, keeping the inside of a metal structure at or near ambient temperature is practically impossible if you do not have a radiant barrier. The radiant barrier will work to reduce the surface temperatures, and the ventilation to help bring the air temperatures down. 

Why A Radiant Barrier is your Best Investment on a Barn or Shed

The main problem with heat gain in a metal edifice is that it will absorb so much radiant heat that the inside temperatures will far exceed the outside temperatures. The simple solution to this is a radiant barrier; it will essentially act like shade. Most of the heat that would normally come off the building into the space below the roof line will instead be reflected back out because of the foil barrier. Keeping 97% of that radiant heat out of the structure is the key to a comfortable space, even without conditioning it. Tons of people have used radiant barrier on garages, barns, carports, airplane hangars, work sheds, warehouses etc. with great results in comfort.

Perforated or Solid?

Metal is a vapor barrier; a vapor barrier stops vapor (moisture) from passing through. In a vented barn, shop, airplane hangar, storage facility, etc., the construction is not airtight (remember, this is because they are not being conditioned). For this reason, a perforated product is the best choice to allow any areas of condensation to dry out. Using a solid product would essentially trap moisture behind the foil layer, and trapping moisture is not something you ever want to do intentionally.

What About Moisture Problems?

Interior moisture (condensation) is created when warm-moist air hits a cold surface (usually the metal of the building). A vapor barrier only stops moisture from passing through/drying out; it does not stop the actual source of moisture. The best way to protect yourself against moisture accrual is to make sure you have proper/good ventilation in order to prevent moisture from accumulating in the first place. Your second defense against moisture is to use a perforated radiant barrier product so that if moisture does exist, it has a chance to pass through the foil layer and evaporate.

Attaching Radiant Barrier to Metal Frames

Attaching a radiant barrier to the metal support beams can be tricky, but you have several options to make it work. The easiest route is if you have wooden framework for the structure because then you can staple the radiant barrier directly to that framework. Otherwise you can try some of these other ideas:

• Use a high-temperature rated adhesive (like Liquid Nails) to glue the foil to the metal supports. This can be messy, and time consuming.

• Attach some wooden beams (furring strips) to the metal supports so that you can staple the foil to the wooden battens; again, this is time consuming and can be messy.

• Use magnets to hold the foil to the metal framing.

The foil is not heavy so the goal is just to get it in place securely.

Installing Radiant Barrier in the Walls of your Barn/Shed

If you install the foil on walls catching direct sunlight, it is best to have the foil closest to the outside layer as possible, while still maintaining an air space on one side of the foil. This way it will block the heat at the entry point, rather than letting it travel though all the siding materials.

Remember, as long as you can achieve the air gap on at least one side of the foil, it WILL work. If you cannot attach it in that space with an air gap, then the next best option would be to install it between the purlins.

What if my shed, barn, etc. is conditioned?

Without having the foil on the outside of the thermal envelope (the area being conditioned), a radiant barrier is not going to offer you a real benefit. It really belongs outside the thermal envelope. So if your construction will be heated and cooled, then you want to get the layer of radiant barrier closest to the outside, and then you can proceed with installing traditional insulation and then drywall/sheet rock to finish it out. Simply put, you layers will be like this:

• Roof deck

• Air gap (created by foam strips)

• Radiant Barrier Foil

• Batt Insulation

• Sheetrock/Drywall

If you do not have access to the wall cavities, or if the building was already finished out before you had a chance to add radiant barrier, then you're probably best off with spray foaming the area and going the route of air sealing up the entire attic space.

Whichever your situation may be, a conditioned or non-conditioned metal structure, the bottom line is this: adding a radiant barrier is the biggest improvement you can make, for the smallest initial investment. A single layer, installed closest to the outside, is going to result in a more comfortable structure and a more efficient building.