We live in the central plains area and have been experiencing many days this summer where the temperature is 100 degrees and greater. Our attic gets so hot that it sets off the fire alarm (the alarm folks fixed the problem by installing a higher temperature alarm). We have known for some time that the venting in the attic is inadequate. There are no gables where a gable vent would be appropriate, so we will probably have to put in a ridge vent. Insulation is blown and not very thick. After researching the problem, I have determined that to solve the hot attic problem and improve our cooling bills, we can (1) add insulation in the form of blankets perpendicular to the floor beams, (2) staple a radiant barrier to the bottom of the roof rafters, or (3) put in a ridge vent along two of the main ridges.
Eventually I think that we will have to do all three, but right now I only have the time and money to do one of the three alternatives. My question is this: given the choice, which alternative is the most cost effective in terms of lowering attic temperature and electric bills?