Zone 7, 100 year old house has 2 layers of siding. The original siding has lead paint of course. The outer siding won’t hold paint. Was insulated in the 70s with formaldehyde foam injected into the wall cavities. Current plan is to use SPF as external insulation, using vertical furring strips embedded in the SPF to secure the new siding. The inner siding has a 4″ reveal while the outer is more like 12″ reveal. There are vertical furring strips between the 2 layers of siding which creates an air gap.

I’m currently planning on stripping the outer layer of siding off due to its poor condition and concern that the SPF won’t stick to it. I’m also concerned that the air gap will allow convective air currents to flow, decreasing the effectiveness of the added SPF.

1) Am I overly concerned about the air gap between the 2 layers of siding. It just makes sense to me to remove this worn out material instead of burying it behind insulation. Am I adding more work that is unnecessary?

2) Also plan to leave the lead painted siding in place if it is in good shape and SPF will bond to it.

Doing this as homeowners so the EPA lead-safe practices don’t technically have to followed but we will do what makes sense.

Thanks for the feedback.

Tim