HVAC prior to spray foam?
I was under the assumption that one would FIRST spray foam the underside of the roof and then install the HVAC duct work, not the other way around. Ran into a scenario where they will install the HVAC duct work first and then spray foam the underside of the roof.
Even though the duct work will sit below the roof deck area. It will get in the way when the spray foam the roof area. At least that was my assumption.
Has anyone seen it done that way? Duct work first and then spray foaming?
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This question has to be addressed to your spray foam contractor.
Of course it is more awkward to work in an area with ductwork than it is to work in an area without ductwork. But anything is possible, as long as the contractor agrees to the conditions.
This is a jobsite coordination issue that should be handled between the GC, the mechanical contractor, and the insulator. In general, the insulator comes in after the framing, mechanical, electrical, and plumbing are all done and signed off by the inspector, so what you are describing is what I would normally expect.
If the ductwork is going to significantly inhibit the insulator from getting himself and his materials in the right places, then he may need to do part or all of his installation first.
Foam installers retrofit roof decks in attics full of mechanical equipment every day. Some of these guys can reliably & accurately hit their target from 8 feet away when there isn't room to get up-close & personal with it. Only in the most cramped of areas would it be impossible to foam a roof deck with the ducts & air handler in place (but I'm sure those conditions might exist in very low pitch trussed roofs.)