Spray Foam Insulation Cost in Charleston, SC
Most foam quotes around here swing by hundreds of dollars because nobody explains the math. Here it is: board-foot pricing up front, real project ranges, and the factors that move your number, sourced and refreshed each publishing year.
What foam costs per board foot here.
Spray foam is quoted by the board foot: one square foot at one inch thick. Your quote multiplies that rate by target depth, so a 3-inch roof deck runs three board feet per square and a crawl wall at 2 inches runs two. Open cell, the half-pound product, lands roughly at $0.35 to $0.75 per board foot installed; closed cell, the two-pound medium-density product, runs about $1.00 to $2.00 per board foot installed.
Sources: Thumbtack 2025 rates, sprayfoamcalc.com December 2025, and r-valueassociates.com 2026 contractor benchmarks. We refresh these bands each publishing year rather than letting the page rot.
| Material | Band |
|---|---|
| Open cell, per board foot | $0.35 to $0.75 |
| Closed cell, per board foot | $1.00 to $2.00 |
What whole projects ran recently.
Bigger scopes price better per foot, and the totals climb with access and prep. Recent published bands: an attic floor job in any material runs roughly $1,100 to $6,800 per HomeGuide; foam on the roof deck (the encapsulated-attic case) typically lands from $1,500 to $9,000 and up depending on foam choice and depth; whole-home work is quoted per job because assemblies vary too much for one band. Treat any single number online as a starting point, never a quote.
| Project | Band |
|---|---|
| Attic floor (loose-fill or foam topping) | $1,100 to $6,800 |
| Roof deck / encapsulated attic | $1,500 to $9,000+ |
| Whole-home foam | Priced per job |
What moves a Charleston foam quote.
Thickness, access, prep: the three big movers. Target depth sets the board feet. Access sets the pace, because open decks go fast and tight crawls do not. Prep covers whatever comes out first, from insulation removal to mold treatment to protecting ducts and wiring. Roof-deck work in coastal wind zones can carry sealed-roof-deck specs for FORTIFIED-style upgrades, which is a premium scope we price in the open instead of bundling in silence.
Rebates that can shave the bill.
Utility programs are the money on the table. Dominion Energy SC pays insulation and air-sealing rebates to residential electric customers, with the ductwork rebate as its own program; Duke Energy SC applies discounts on attic insulation upgrades through its approved-contractor path. Confirm current amounts on the program pages at install time.
The federal 25C credit was not extended past 2025, so this page does not promise federal dollars for 2026 work. Utility rebates are the live path, and we help you file the paperwork either way.
Getting a real number.
The estimate card below carries the same bands we publish on the home page. Your exact number comes from the free on-site assessment: we walk the space together, and then you get a written quote built from what is actually up there.
| Scope | Estimated band |
|---|---|
| Crawl space encapsulationtypical range, SC average about $5,000Popular | $4,500 to $7,000 |
| Attic encapsulationopen vs closed cell swings the price | $4,000 to $9,000+ |
| Whole-home foambuilt from the on-site assessment | Priced per job |
Every home prices differently and the free on-site assessment gives your exact number. Bands sourced from CrawlSpaceCosts.com and HomeGuide; full sources on the cost guides.
Straight answers
Spray foam cost questions, answered.
What does spray foam cost per square foot in Charleston?
Per square foot depends on depth, which is why the board-foot band is the cleaner anchor: open cell roughly $0.35 to $0.75 and closed cell roughly $1.00 to $2.00 per board foot installed, with sources in the section above. In square-foot terms, attic jobs typically run about $1.50 to $4.50 depending on foam.
Is closed cell worth the premium, in dollars?
Where the foam faces moisture or grade, yes. Closed cell runs roughly double open cell per board foot and buys vapor blocking plus about double the R-value per inch, the two things our humid assemblies need most. On a dry attic floor with no moisture story, the extra dollars usually do not earn their keep.
Why do aggregator cost numbers differ from real quotes?
Because calculators price an average of averages, and houses do not ship in averages: access, prep, and assembly details swing a real quote more than the online spread suggests. Use the ranges here to bracket expectations, then let the on-site assessment produce the number you will actually pay.
Free quotes
Get your free on-site assessment.
The exact-number step is the free on-site assessment. Send the form or call (843) 439-8547 and we'll schedule it.