Why must reflective insulation be installed adjacent to an air space?
An air space allows heat to be converted into radiant energy. Installing reflective insulation adjacent to an air space allows this radiant energy to be reflected away from the building envelope. This is one of the primary reason for the bubbles in reflective foil insulation, especially in underslab an radiant heat applications. Always try and achieve the maximum airspace possible within your applications constraints. Using firring strips is generally the easiest and most efficient way if no adequate airspace is present.
