# Crawl Space Insulation in Wilmington, NC > Wall insulation for a sealed crawl space, or subfloor batts for a vented one. Which is correct depends on. What it costs, and when it is the wrong answer. URL: https://910crawlspacepros.com/services/crawl-space-insulation/ Home / Services / # Crawl Space Insulation Crawl Space Insulation What the work involves in Wilmington and the Cape Fear region, what it costs, and the situations where it is the wrong thing to buy. Last updated: 2 August 2026 ASTM E1745 reinforced liner • IRC R408.3 closed crawl space • Class I vapor retarder (<0.1 perm) • ICC-ES certified flood vents • Written scope before work starts 910 Crawl Space Pros provides crawl space insulation across Wilmington and the Cape Fear region. Crawl space insulation is the practice of adding thermal resistance either to the underside of the floor above a vented crawl space, or to the perimeter walls of a sealed one. Which of those two is correct is decided entirely by whether the crawl space is open to outside air, and installing the wrong one traps moisture against wood. This is the most commonly botched item in a crawl space, because the two approaches look interchangeable and are not. ## What we do on the first visit We establish first whether the space is vented or closed, because that decides everything else. Then relative humidity, moisture content in the joists and subfloor, and the condition of any existing insulation — fallen batts and rodent-damaged fiberglass are usual. ## Subfloor batts vs wall insulation: which one your crawl space needs In a vented crawl space, the thermal boundary is the floor above. Insulation belongs between the floor joists, and the crawl space itself stays at outdoor temperature. In a sealed crawl space, the thermal boundary moves to the perimeter walls, the space becomes semi-conditioned, and subfloor insulation becomes unnecessary — and sometimes harmful. The harm comes from vapor. Fiberglass batts with a kraft facing installed face-down in a humid vented crawl space put a vapor retarder on the cold side of the assembly in summer, which is exactly where condensation forms on the Cape Fear coast. Wet fiberglass loses most of its R-value and holds moisture against the subfloor. Vented crawl space → insulate the subfloor, unfaced, supported so it cannot sag Sealed crawl space → insulate the perimeter walls, leave the subfloor open Never both at once — that sandwiches the framing between two vapor barriers ## Why fallen batts are so common here Fiberglass batts held up by friction alone will eventually come down in a humid crawl space, because the moisture adds weight and the fibers relax. Once a batt drops it sits on the ground, wicks moisture and becomes a rodent nest. Roughly speaking, if the insulation in your crawl space is hanging in loops, it stopped doing anything years ago. Properly supported batts use wire rods or straps at regular spacing, not staples through the facing. In a sealed crawl space we generally move the insulation to the walls with rigid foam board, which cannot sag and does not absorb water. ## Insulation and the fire code Rigid foam board used on crawl space walls has to be covered or be of a type rated for exposed use, because unprotected foam is a flame-spread issue. This is the detail cheap installs skip. Where foam is left exposed, it must be an approved product with a tested thermal barrier or ignition barrier for that application. ## What's included Assessment of whether the space is vented or sealed before any material is chosen Removal and disposal of fallen, wet or rodent-contaminated existing insulation Unfaced batts with mechanical support in vented spaces — never friction-fit alone Rigid board to the perimeter walls in sealed spaces, with the rim joist detailed Rim and band joist insulated and air-sealed, the biggest single leak in most homes Code-compliant covering or an approved exposed-use product for any foam No vapor-facing installed on the cold side of the assembly Photographs of the completed install ## Related reading Crawl Space Insulation Cost in Wilmington, NC Crawl Space Insulation vs Encapsulation Price my insulation Free quotes within 24 hours. Free on-site assessment first. Website What do you need? Select a service… Crawl Space Encapsulation Crawl Space Insulation Crawl Space Waterproofing Crawl Space Mold Removal Crawl Space Vapor Barrier Installation Crawl Space Dehumidifier Installation Crawl Space Drainage Crawl Space Sump Pump Installation Crawl Space French Drain Crawl Space Cleanup Crawl Space Structural Repair Sagging Floor Repair Crawl Space Door Replacement Flood Vent Installation Not sure — I need someone to look ZIP code Continue Your name Phone What are you seeing? (optional) Back Request my inspection Got it — your request is in. We'll be in touch with a quote. Standards we work to ASTM E1745 — vapor retarder specification Class I vapor retarder, below 0.1 perms IRC R408.3 — unvented crawl space conditioning NC Residential Code crawl space requirements Other services Crawl Space Encapsulation Crawl Space Waterproofing Crawl Space Mold Removal All services → ## DIY, cheap quote, or done properly Most of the price difference between quotes is not labour — it is which of these steps the quote silently leaves out. DIY Cheapest quote Done properly Liner 6 mil builder sheet, laid loose 6–8 mil, taped seams, not fastened to walls Reinforced 12–20 mil to ASTM E1745, sealed to piers and walls Groundwater Not addressed Sealed over — water ends up under the plastic Drainage and sump first, liner second Humidity control None, or a household dehumidifier on an extension cord Undersized unit, condensate draining to the soil Unit sized to cubic footage, pumped to a proper discharge Vents Left open, or foam blocks pushed in Covered, not sealed Sealed and detailed so the space is genuinely closed Wood already affected Bleach from a spray bottle Surface treated, moisture source left in place Growth removed, framing treated, dried, then sealed What it costs $300 – $900 in materials $1,500 – $3,000 $4,200 – $14,000 How long it holds A season or two Often fails within a few years Liner life measured in decades when water is handled first ## How insulation work runs 01 Assess and measure Humidity, moisture content in the framing, standing water, clearance and access — photographed throughout. 02 Written scope Line by line, in the order the work has to happen, with a price against each component. 03 The work Water handled first where present, then the fix itself, then verification. 04 Verify and hand over Post-work readings recorded and left with you, along with the photographs. , not a heading: this is a CTA, not a section of the document outline. --> Get crawl space insulation priced for your home Free on-site assessment across Wilmington and New Hanover, Brunswick and Pender counties. Call (910) 886-2018 Get a free quote ## Crawl Space Insulation questions Should I insulate the crawl space floor or the walls? Walls if the crawl space is sealed, floor if it is vented. The insulation belongs at the thermal boundary, and sealing the space moves that boundary from the subfloor out to the perimeter walls. Doing both traps the framing between two vapor retarders. How much does crawl space insulation cost? Typically $1,500–$4,000 depending on square footage and whether existing material has to be removed first. Wall insulation in a sealed crawl space usually costs less than subfloor batts across the same footprint, because there is less area to cover. Can I insulate a crawl space that has moisture problems? Not usefully. Insulation added over a moisture problem hides it and gets wet, and wet insulation has almost no R-value. Fix the water and the humidity first — otherwise you are paying to install something that will be removed again. Does crawl space insulation qualify for a tax credit? Insulation and air-sealing improvements can fall under the federal 25C energy efficiency credit, unlike encapsulation on its own. Keep the invoice itemised so the insulation portion is separable, and confirm eligibility with a tax professional. Related services Crawl Space Encapsulation A sealed liner across the floor, piers and walls, taped and mechanically fastened, with the vents closed and the space dried. It is the full system, not a sheet of plastic laid on dirt. Crawl Space Waterproofing Stopping water getting in, before anything gets sealed. Grading, downspout extensions, perimeter drainage and a sump where the water table demands it. Crawl Space Mold Removal Remove the growth, treat the framing, and fix the moisture that fed it. Cleaning without correcting the humidity means it returns within a season here.