Spray closed cell foam insulation about 2 inches thick in walls and 3 inches thick in rooftops. To tell if a contractor is spraying this much insulation, you must inspect multiple areas to ensure the foam is thick enough. If it is too thin, extra heat can escape, and sight-checking isn't always reliable enough. Open cell foam is sprayed to fill inner walls completely, making it easier to examine walls.
Wicking is the process that draws water up into materials through a combination of pressure differences and the bonds that water makes with the surfaces it comes in contact with, which allows water to seep up through boards and concrete floors. If the basement or foundation area is very wet, foam insulation may only make it easier for water to seep up into the structure itself, channeled into the boards and posts where the foam cannot reach.
Foam insulation may seal gaps that pests use for entry, but it is not sure protection against pests itself. Often ants and termites will burrow straight into the foam itself. Termites cannot eat the foam, but they will still tunnel through it, ruining its properties. Use foam insulation with an insect barrier.
Contractors must spray foam very thoroughly throughout the crawl space. If any gaps are left, the air will flow naturally through these gaps, and the insulation will do little good. It is difficult to tell if there are gaps in foam insulation since the insulation is not cut and laid down in smooth panels. Even a small gap can mean extra energy costs.
Some types of foam, most notably closed cell foam, may pull away from the studs after it has hardened. This is not usually the fault of the contractor spraying the foam. It may mean that sudden temperature changes have occurred or that the foam compounds have not been mixed properly. Either way, it leave gaps in the insulation where heat can enter or escape.