We are building a log home and considering electric radiant heat under hardwood flooring, my problem is the reflective barrier, it would be hard in areas to staple a foil insulation to the underside of the subfloor because of the spacing of the engineered floor joist in areas. Can put foil insulation on top of the subfloor and install your electric radiant heating system over the foil?

http://www.flickr.com/photos/29703438@N03

reflective barriers are totally useless without an airspace.

you would need to insulate another way.