A: You do not want to spray foam over existing insulation, encapsulating the old insulation. It will lead to moldy old insulation.
The old, settled, blown-in or batt stuff is doing NOTHING for your home’s energy efficiency, comfort, and air quality and may even be contributing to allergies and mold.
Pull up the old insulation first. Then, spray down 1 layer of closed cell Foam It Green to get the tight air seal and an R-value of 7. Then, pile on new batt or blown in on top of the foam to build up the R-value to your total desired number.
Testing has shown this one exact project can shave up to 30% off your heating bills.
By putting down 1 inch of foam before filling with batt or blown in, the project is done right, and will save you a lot of money over the life of your home. It is a good investment because it pays you back every year. Even after the cost of the project is recuperated, that extra savings keeps coming. There are no other home projects that can boast a return like that!
And, as a bonus, the increased energy efficiency increases the value of your home, too!
Whatever you do, don’t just add more blown in on top of the old stuff up there now. That is just throwing good money after bad.