Attic insulation vs crawl space encapsulation

Attic insulation vs crawl space encapsulation: two envelope upgrades that cut energy bills. Compare which to tackle first, costs, and what each protects against.

Attic insulation addresses heat loss and gain through the roof — in most climates, the attic is the single largest source of energy waste. Blown-in fiberglass or cellulose to R-49 (the DOE-recommended level for most US zones) costs $1,500–$3,000 for a 1,000 sq ft attic; spray foam (R-6.5/inch closed-cell) runs $3,000–$7,000 but also air-seals in one step. ROI is typically 2–4 years through lower heating/cooling bills, and it's the upgrade most energy audits flag first. Crawl space encapsulation seals the underside of the building envelope with a heavy-duty vapor barrier (12–20 mil polyethylene), interior perimeter drainage, a sump pump, and a dehumidifier. It targets moisture — the root cause of mold, wood rot, pest attraction, and musty indoor air — rather than thermal loss directly, though sealing the crawl space also reduces drafts and can improve HVAC efficiency by 10–15%. Full encapsulation costs $5,000–$15,000 depending on square footage, existing moisture damage, and whether a sump system is needed. The two projects complement rather than compete: attic insulation is almost always the higher-ROI first move, but if your crawl space has standing water, mold, or sagging insulation, encapsulation becomes urgent. Many contractors offer both, and bundling can save 10–15% on the combined project.