The Charleston Lowcountry and York County on the South Carolina side of the Charlotte metro, across Charleston, Dorchester and York counties. Each town below has its own permit authority and its own housing stock, and both change what the work involves.
In this climate insulation is mostly a humidity problem wearing an energy-efficiency costume. The crawl space is where most Lowcountry houses lose the argument.
The traditional vented crawl space was designed for a drier climate. Here, humid outside air enters a cool crawl space, condenses on the framing and ductwork, and produces exactly the damp, musty conditions that lead to wood rot and mould — while the air conditioning upstairs works harder because it is dehumidifying a house sitting on a permanently wet cushion.
Encapsulation reverses it: a sealed vapour barrier across the ground and up the piers, sealed vents, insulation at the perimeter rather than between the joists, and usually a dehumidifier. The comfort difference is often more noticeable than the energy saving, because the house stops feeling clammy.
Attics are the other half. In a climate with this much sun, an under-insulated attic drives afternoon cooling load hard, and ductwork running through that attic loses a meaningful share of what the system produces before it reaches a room.
In Charleston and Summerville the dominant problem is summer, and it is a moisture problem before it is an energy one. A vented crawl space draws humid air under the house, condenses it on framing and ductwork, and leaves the air conditioning fighting moisture from below all season. The productive move there is usually to bring the crawl space perimeter inside the insulated envelope rather than to stuff more insulation between the floor joists, where it sits in humid air, gets wet and eventually falls down.
In Rock Hill the summer load is still real but the heating season carries more weight, which shifts the balance between sealing, depth and where the boundary is drawn. What holds in all three towns is that air sealing generally returns more per dollar than added depth: uncontrolled air carries moisture as well as heat, and adding insulation over an unsealed ceiling plane leaves the mechanism intact.
Insulation on its own is not usually permitted work in Charleston, Summerville or Rock Hill.
In the Lowcountry, permits come from the City of Charleston for Charleston and the Town of Summerville for Summerville.
In York and Lancaster counties, from the City of Rock Hill for Rock Hill.
It matters most if an attic is being converted to an unvented assembly, because that is a conversation with a specific building official rather than a product choice.
One exception is worth raising early: converting a vented attic into an unvented, insulated assembly changes how the building envelope works, and the residential code sets conditions for that. It is a question for the building official before it is a product decision.
The method is; the priorities are not. On the coast the crawl space usually comes first, inland the attic and the heating season carry more weight.
Not before the ceiling plane is sealed. Depth over an unsealed ceiling improves the number on the quote and leaves the air moving.
Sealing top plates, penetrations, chases and the hatch is labour rather than material, and it is usually the better money.
Only if the smell is coming from moisture the insulation work actually addresses, which in a raised house usually means the crawl space rather than the attic.
Air moves upward through a house, so what is under the floor ends up in the rooms above it.