In my case it's an 8' x 12' engineered wood shed in Phoenix but the question could apply to other unconditioned structures. I should note that the shed has two lower wall vents and a roof peak vent. I'd like to lower peak temperatures during the summer inside the shed. I'm considering fiberglass rolls or radiant barrier sheeting, but not both due to costs and the fact that radiant barrier will perform better with an air gap. I've not found an intelligent article online about this. Most articles are copied over from info on conditioned home insulation or are biased due to a radiant barrier product they want to sell. Any thoughts on which will work better? Is it possible that traditional fiberglass insulation will do absolutely nothing considering the shed is ventilated? My goals I think are realistic. I'm trying to keep the interior peak temperatures as close as possible to ambient exterior temperatures (realizing that the interior temperatures will be higher no matter what I do without using power).

I think this article may answer your questions: http://www.radiantbarrier.com/radiant-barrier-versus-fiberglass-batt-insulation/ My thought: If you have to choose between a radiant barrier and fiberglass, go with the radiant barrier, especially if the building is located in a hot zone and is unconditioned. Let us know the results for any action you do take to lower the temperature within the building.

Can you do anything to cast shade upon it?