Are people putting in rigid insulation correctly?

[estelle bus]

I was reading some technical specification sheets on one of the common rigid insulation board that people use. I noticed that one of them said it needs 3/4 of an inch to 3.25 in of dead air space the question is is it better to have one and a half inch of insulation with no air space or 1 inch of insulation with some airspace? And for your walls and ceiling which side should the dead air space be on?

 

[Twigg-SKO]

I was reading some technical specification sheets on one of the common rigid insulation board that people use. I noticed that one of them said it needs 3/4 of an inch to 3.25 in of dead air space the question is is it better to have one and a half inch of insulation with no air space or 1 inch of insulation with some airspace? And for your walls and ceiling which side should the dead air space be on?

You are reading specs that relate to standard construction methods, where an air-gap forms part of the overall R-Value of an installation.

In a bus there isn't room to incorporate those gaps. Don't worry about it.