New construction is faster and cheaper (no demolition). Retrofit costs more (drilling, patching, removal) but often delivers higher utility savings because most retrofitted homes were poorly insulated to begin with.
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New construction foam economics. The walls are open before drywall, so foam application is fast and inexpensive (no demolition, no patching, no removal of existing insulation). Total project cost as a percentage of new-build budget is typically 1-3%, often offset by HVAC equipment downsizing because the tighter envelope needs less heating and cooling capacity. Builder-driven decisions: many Cincinnati custom-home builders now spec closed-cell foam in rim joists and unconditioned-to-conditioned walls as standard, with full-house foam upgrades available as an option. Retrofit foam economics. The work is more involved (drill-and-fill in walls, removal of existing insulation in attics, scaffolding for cathedral ceilings) so per-sqft cost runs 30-60% higher than new-construction foam. But starting from a typical pre-1980 Cincinnati home with R-7 walls and R-19 attic, the savings delta versus the foamed final state is much larger than for a code-built new home; payback periods are similar (4-8 years). Cincinnati builder-coordination context: many Greater Cincinnati custom-home builders now offer foam as a base spec or upgrade option, with closed-cell at rim joists and unconditioned-to-conditioned walls common in custom-build packages. For homeowners building new, asking the builder up front about the foam package and HVAC sizing implications produces a meaningfully better baseline envelope at marginal incremental cost.