Spray foam insulation, when properly installed is both an air barrier and when closed cell foam is used at the proper depth a vapor barrier! Before hiring any contractor you should establish the brand of foam being used and verify that with the named manufacture. Please ask for ESR reports and MSDS sheets on any foam being installed in your home. A couple areas where you might consider spray foam insulation include:
In general, cantilevered steel beams are a nightmare. If part of the steel beam is in contact with exterior temperatures, then it's best if the interior portion of the steel beam is covered on all sides with insulation. This is generally impossible (because the interior portion of the cantilevered beam generally supports a load, meaning that you can't wrap the steel beam in insulation on all sides).
Spray Foam Attic Insulation
I am an Architect in Toronto. I am designing a new roof addition to a row house building. Because of existing conditions and the shape of the new roof. It may be easiest to use closed cell spray foam within the areas of the joists. My question is when spray foam is used in this situation do I need to worry about how the joist members may be thermal bridges? It is not common to provide a little bit of rigid insulation to protect the joist members? The additional layer of outboard insulation will require an extra layer of plywood above the insulation which will add to cost.