# Crawl Space Encapsulation: What It Includes & Costs > What crawl space encapsulation includes: liner spec, vent sealing, drainage sequence and dehumidification — plus costs and when it is the wrong answer. URL: https://910crawlspacepros.com/services/crawl-space-encapsulation/ Home / Services / # Crawl Space Encapsulation Crawl Space Encapsulation 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 encapsulation across Wilmington and the Cape Fear region. Crawl space encapsulation is the practice of sealing a crawl space from both the soil below and the outside air — a reinforced liner across the floor and up the walls, the foundation vents closed, and the space conditioned so relative humidity stays under control through the year. Done properly it removes the moisture source that drives fungal growth, cupped flooring and softened framing. The word covers a lot of ground, though, and two quotes using it can describe genuinely different work. What follows is the specification we work to and what each part of it is for. ## What we do on the first visit Nothing is quoted from a photograph. The assessment takes about an hour: a relative humidity reading in the crawl space, moisture content readings in joists and subfloor at several points, a check for standing water and for the high-water mark that shows where it has been, and a look at clearance, access and the condition of any existing liner. You get the photographs and the readings whether or not you go ahead. ## Liner specification, and why 6 mil is not enough The liner is the component most quotes differ on, and it is largely invisible once installed. We use a reinforced liner of 12–20 mil meeting ASTM E1745, the standard covering water vapor retarders used under concrete slabs and in crawl spaces. A Class I vapor retarder is one with a permeance below 0.1 perms — that number is the point of the material. A 6 mil unreinforced builder sheet meets neither the thickness nor the puncture resistance that a working crawl space needs. It tears the first time anyone crawls across it to service a duct, and a torn vapor retarder is not a vapor retarder. The reinforcement — a scrim layer between plies — is what lets a liner survive being walked on. ## Why drainage has to come first This is the sequence error that produces most of the failed encapsulations we are called to look at. Where groundwater rises into the crawl space, a liner laid over it does not remove the water; it covers it. The water is then under an impermeable membrane, where it cannot evaporate and cannot be seen, and the first sign of it is usually odour or a failed liner seam months later. On the Cape Fear coast this matters more than it does inland. The regional water table is high, the soil drains quickly at the surface and slowly below it, and roughly 57 inches of rain falls a year. Where the assessment finds water, perimeter drainage and a sump go in first, and the liner follows. ## Sealing the vents, and what the code says Foundation vents exist on the assumption that outside air is drier than crawl space air. For most of the year here it is not, and venting pulls humid air across framing that sits below the dew point. The moisture condenses on the wood. Closing the vents is therefore part of the system rather than an optional extra — but a closed crawl space has to be conditioned. IRC R408.3 treats an unvented crawl space as requiring either a supply of conditioned air or mechanical dehumidification. Sealing without either is the version of encapsulation that earns the technique its bad reputation. ## Conditioning: sizing the dehumidifier properly A dehumidifier is sized to the cubic footage of the space and the moisture load, not chosen from a shelf. An undersized unit runs continuously, never reaches target, and fails early. The condensate has to go somewhere real — a pump to a discharge point away from the foundation, not a bucket and not the soil under the liner. We re-measure relative humidity before leaving and record it. Below roughly 60% is the number that matters, because that is where fungal growth stops being supported. ## What's included Reinforced 12–20 mil liner meeting ASTM E1745, not 6 mil builder sheet Liner run up piers and perimeter walls, mechanically fastened and sealed All seams overlapped and taped with a seam tape rated for the liner Foundation vents closed and sealed, not simply covered Insulated, gasketed access door where the existing one leaks Dehumidifier sized to actual cubic footage, with condensate pump Condensate and any sump discharge routed away from the foundation Post-install relative humidity reading, recorded and left with you ## Related reading Crawl Space Encapsulation vs. Vapor Barrier Is Crawl Space Encapsulation Worth It? Crawl Space Encapsulation Cost Per Square Foot in Wilmington, NC DIY Crawl Space Encapsulation The Real Negatives to Crawl Space Encapsulation Should Crawl Space Vents Be Open or Closed? Crawl Space Encapsulation and the Federal Tax Credit Common Encapsulated Crawl Space Problems How Long Does Crawl Space Encapsulation Last? Does Crawl Space Encapsulation Add Value to Your Home? Price my encapsulation 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 Insulation 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 encapsulation work runs 01 Assess and measure Relative humidity in the space, moisture content in the framing, standing water, clearance and access. Photographed throughout. 02 Dry it out and clean it up Drainage where groundwater is present, debris and failed insulation removed, affected framing treated and dried. 03 Line and seal Reinforced 12–20 mil liner across floor, piers and walls, seams taped, terminated and sealed at the perimeter. Vents closed and sealed. 04 Condition and verify Dehumidifier sized to the cubic footage, condensate pumped to a real discharge. We re-measure RH before leaving. , not a heading: this is a CTA, not a section of the document outline. --> Get crawl space encapsulation 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 Encapsulation questions What is crawl space encapsulation? Crawl space encapsulation is sealing the crawl space from the ground and the outside air: a reinforced liner across the floor and up the walls, foundation vents closed, and the space conditioned with a dehumidifier so relative humidity stays controlled year-round. It is a system, not a sheet of plastic. How much does crawl space encapsulation cost? In the Wilmington area, $4,200–$14,000, with a typical project near $5,500. Liner and vent sealing are the fixed part; drainage, mold treatment and structural repair are what create the spread. When is encapsulation the wrong answer? When the crawl space still takes on groundwater and the budget will not cover drainage. Sealing over active water traps it under the liner where it cannot evaporate. In that case the honest sequence is drainage now, encapsulation later — not a cheaper encapsulation. Does an encapsulated crawl space still need a dehumidifier? Nearly always in this climate. Sealing stops moisture entering from soil and outside air, but the space still exchanges some air with the house and holds residual moisture. Without conditioning, relative humidity in a sealed crawl space commonly settles above 60%, which is enough to support fungal growth. Will encapsulation cause moisture problems by trapping air? That concern comes from sealing without conditioning. A closed crawl space with no dehumidification can hold moisture, which is why IRC R408.3 treats an unvented crawl space as requiring either conditioned air supply or mechanical dehumidification. Sealed plus conditioned is the tested assembly. Related services Crawl Space Insulation Wall insulation for a sealed crawl space, or subfloor batts for a vented one. Which is correct depends on whether the space is closed — installing the wrong one traps moisture against wood. 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.