Everything about insulation is easier and cheaper before the drywall goes up. Once it is closed in, correcting a missed rim joist or an under-insulated cathedral section means demolition. This is the sequence we work to on new construction, and the decisions that matter at each point.
Decide the thermal boundary before framing is finished
The single most consequential decision is where the thermal boundary sits — at the attic floor, or at the roofline. If mechanical equipment and ductwork are going into the attic, the roofline is almost always the right answer, because it brings that equipment inside conditioned space. Deciding this after the ducts are run is a much more expensive conversation.
Schedule after rough-in, before drywall
Insulation goes in after electrical, plumbing and HVAC rough-in are complete and inspected, and before drywall. That window is often tighter than the GC expects, and it is the most common source of schedule friction on a build. We coordinate directly with the GC on sequencing so we are not the trade holding up the board.
Match the product to the assembly
- Basement and foundation walls — closed cell, for moisture and vapor control
- Rim and band joists — closed cell, sealing the full perimeter
- Roofline and cathedral sections — foam that follows the geometry
- Interior partitions and floors between levels — open cell for sound
- Regular exterior wall framing — fiberglass is often the right value choice
- Garage ceilings under living space — foam, sealed at the cantilever
Do not skip the details that inspectors check
Attic hatches, recessed light housings, the top plate line, duct chases, and the transition where the garage meets living space are all points where new construction routinely underperforms. They are small items individually and they add up to a significant share of total leakage. On a new build there is no reason to leave any of them.
Plan the fire barrier into the scope
Spray foam requires a thermal barrier in living space and an ignition barrier in attics and crawl spaces. In finished areas drywall usually handles it. In unfinished attics and crawl spaces we apply DC 315 intumescent coating and document it for the inspector. Building this into the scope from the start avoids a failed inspection and a return trip.
Sound is worth budgeting for now
Filling interior partitions and the floor cavity between levels with open cell foam is inexpensive while the framing is open and effectively impossible to retrofit later. Bedrooms, bathrooms, home offices and media rooms are the ones owners consistently wish they had done. It is the cheapest quality-of-life upgrade available at this stage of a build.
Work from the drawings
On new construction we work from the plans and specifications, confirm the R-value targets required by the local code official, and coordinate with the GC on staging and access. If the spec calls for something we think will underperform in a given assembly, we will raise it before we install it rather than after.