Insulation in a New House

Amber Carl asks,

We are building a new house in Delaware and our builder wants to use a new type of insulation. The insulation is a combination of 1/2″close cell spray and a BIBS insulation. Our attic will have an R 45 and the walls will have a R 19 with the two types of insulation. The house will be constructed with 2×4 walls and a house wrap. Do you think we will have a mold problem because of built up condensation between the two types of insulation? Our builder said this would be a good way to get the R value we want for a good price. Thank you, Amber Carl

Our Answer

Amber, I'm a little confused by this approach. Both BIBS (Blow in Blanket) and foam systems (like Icynene) are solid insulation technologies and I don't see how combining the systems would make sense, or result in a cost savings. I'd probably pick one, be sure it is installed in accordance with the manufacturers specifications and stick with it.