# Crawl Space Vapor Barrier Installation in Wilmington, NC > Reinforced 12–20 mil liner meeting ASTM E1745, seams taped and terminated at the wall — not the 6 mil. What it costs, and when it is the wrong answer. URL: https://910crawlspacepros.com/services/vapor-barrier-installation/ Home / Services / # Crawl Space Vapor Barrier Installation Crawl Space Vapor Barrier Installation 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 vapor barrier installation across Wilmington and the Cape Fear region. Vapor barrier installation is the placement of a sheet material across the crawl space floor — and, in a sealed crawl space, up the piers and perimeter walls — to stop moisture moving from the soil into the space as vapour. The specification of that sheet is where most quotes differ. ## What we do on the first visit Measure the footprint and perimeter, check clearance for working, assess whether existing liner can be removed cleanly, and confirm the space is dry enough to line at all. ## What ASTM E1745 actually requires ASTM E1745 is the standard specification for plastic water vapor retarders used in contact with soil under concrete slabs and in crawl spaces. It sets minimum requirements across three properties: water vapor permeance, tensile strength, and puncture resistance. A product either meets it or it does not. A Class I vapor retarder is one with a permeance of 0.1 perms or less. That number is the entire point of the material — it is what stops soil moisture entering the space as vapour. ## Why 6 mil builder sheet is not a crawl space liner The 6 mil polyethylene sold as a general-purpose construction sheet is unreinforced. It meets neither the puncture resistance nor the tensile strength that a working crawl space needs, and it tears the first time someone crawls across it to service a duct or run a cable. A torn vapor retarder is not a vapor retarder. Reinforced liner — a scrim layer sandwiched between plies — is what allows the material to survive being walked on for a decade rather than a season. That is the difference the mil rating alone does not tell you: reinforced 12 mil outperforms unreinforced 20 mil in service. ## Termination and seams are where liners fail The floor is the easy part. The failures we are called to look at are almost always at the edges: liner that stops short of the wall, liner taped to a dusty block surface that released within a year, or piers left unwrapped so moisture tracks up them. Proper termination means the surface is cleaned first, the liner is mechanically fastened as well as sealed, and it runs high enough up the wall to sit above the level water has historically reached. Seams are overlapped generously and taped with a tape rated for the liner, not general-purpose duct tape. ## What's included Removal and disposal of failed existing liner Debris clearance so nothing sharp sits under the new material Reinforced 12–20 mil liner meeting ASTM E1745 Generous seam overlap, taped with a seam tape rated for the material Piers individually wrapped and sealed Perimeter termination mechanically fastened to a cleaned surface Liner run above the historic high-water line where one is present Photographs of seams and terminations before the space is closed ## Related reading Vapor Barrier for a Crawl Space: Spec and Standards How to Choose the Best Vapor Barrier for a Crawl Space What Thickness Vapor Barrier Does a Crawl Space Need? Price my vapor barrier 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 Insulation Crawl Space Waterproofing 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 vapor barrier 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 vapor barrier installation 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 Vapor Barrier Installation questions What thickness vapor barrier do I need? Reinforced 12–20 mil meeting ASTM E1745 for a crawl space that will be entered. Thickness alone is not the specification — reinforcement matters more. Reinforced 12 mil will outlast unreinforced 20 mil in a space anyone crawls through. How much does vapor barrier installation cost? Typically $1,500–$4,000 for the liner component, driven by square footage, perimeter length and how much old material has to come out. That is the liner alone; vent sealing and dehumidification are separate line items. Does a vapor barrier alone fix crawl space humidity? Partly. It stops moisture rising from the soil, which is usually the largest single source. It does nothing about humid outside air entering through open vents, which on this coast is the other half of the problem. That is the gap full encapsulation closes. Should the vapor barrier go up the walls? In a sealed crawl space, yes — floor, piers and perimeter walls, terminated near the top. In a vented crawl space the walls are outside the thermal boundary and floor-only is normal practice. Is a vapor barrier the same as a termite barrier? No. A termite barrier is pest-control work — a chemical soil treatment or physical shield installed by a licensed pest company — and we do not do it. A vapor barrier is a moisture liner. The two coexist under coastal homes: if you have a termite bond, tell both contractors, because the inspection strip your pest company needs at the top of the foundation wall affects where the liner terminates. 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 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.