My house is 17 years old, has a ridge and soffit vents along the whole length of the house. Attic has 24 inches of blown in insulation. I am considering following three options - which one would be most efficient performance and cost wise?
1. Expanding foam insulation between the rafters underside of the roof
2. Or rigid foam insulation held back with some sort of strapping
3. or just adding more blown in insulation