--- title: "Drainage Planning for Home Additions in NC | AGCS" url: https://agcshomesolutionsllc.com/blog/exterior-drainage-around-home-additions description: "Protect your home addition from water damage in North Carolina clay. Learn how to relocate downspouts, re-route drainage swales, and grade foundation perimeters." lang: en --- Skip to content Additions & Remodeling (https://agcshomesolutionsllc.com/blog/remodeling) # Exterior Drainage Around an Addition: Relocating Downspouts and Preserving Swales Adding a new master wing, family room, or sunroom increases your home's roof surface area and dramatically changes how rainwater flows across your lot. Too often, homeowners focus entirely on interior floor plans while ignoring site drainage. When a new addition blocks a natural drainage corridor or dumps thousands of gallons of roof runoff near the new foundation, the result is standing yard water, saturated crawlspaces, and foundation settling in native Piedmont red clay. ## The Increased Roof Runoff Calculation A modest 600-square-foot addition (e.g., 20x30 feet) collects roughly 375 gallons of water during a 1-inch rainstorm. During a typical Carolina summer thunderstorm delivering 2 to 3 inches of rain in an hour, over 1,000 gallons of concentrated stormwater pours off that new roof section. If downspouts simply discharge next to the new foundation stem wall, water saturates the freshly backfilled trench, exerting hydrostatic pressure and seeping into the crawlspace. ## Preserving Existing Surface Drainage Pathways and Swales When a home was originally built, the lot was graded with positive slopes and swales to channel water away from the foundation and toward property boundaries. Building an addition often extends into these natural drainage corridors, effectively creating an unintended earthen dam. Sump water from uphill properties becomes trapped against the new structure. Before excavation, AGCS surveys the lot's overland flow and re-engineers shallow interceptor swales around the perimeter of the proposed addition to route uphill runoff safely around the new footprint. ## Hard-Piping Downspouts to Daylight Splash blocks placed under downspouts are entirely inadequate for managing addition stormwater in clay soils. AGCS installs buried, solid, smooth-wall 4-inch PVC or SDR-35 drain pipe connected directly to downspouts via inline cleanout adaptors. Thin, perforated, corrugated black pipe easily crushes under lawnmowers and clogs with tree roots. The solid drainage lines are pitched at a minimum 1% slope (1/8 inch per foot) to carry roof runoff at least 15 to 25 feet away from the foundation, discharging to daylight or into a gravel-lined dry creek bed. ## NCRC Foundation Grading Mandate Under North Carolina Residential Code Section R401.3, final surface grade around the new addition must fall at least 6 inches within the first 10 feet away from the foundation wall. AGCS ensures the backfilled soil around the addition is thoroughly compacted to prevent settlement troughs that hold ponding water against foundation masonry. Related service: Home Additions & Major Remodeling (https://agcshomesolutionsllc.com/home-remodeling-contractor-lincolnton-nc) ยท More in Additions & Remodeling (https://agcshomesolutionsllc.com/blog/remodeling) ## Get a Free Estimate Call (980) 888-3107 (+19808883107) or send us the details of your project. Same-day response during business hours. Get Free Estimate (https://agcshomesolutionsllc.com/) Call Now: +19808883107 Free Estimate: https://agcshomesolutionsllc.com/ ## Structured data ```json [ { "@context": "https://schema.org", "@type": [ "GeneralContractor", "RoofingContractor" ], "@id": "https://agcshomesolutionsllc.com/#business", "name": "AGCS Home Solutions LLC", "alternateName": "AGCS Home Solutions", "url": "https://agcshomesolutionsllc.com/", "telephone": "(980) 888-3107", "email": "Agcshomesolutions@outlook.com", "logo": "https://agcshomesolutionsllc.com/favicon.svg", "address": { "@type": "PostalAddress", "addressLocality": "Crouse", "addressRegion": "NC", "addressCountry": "US" }, "areaServed": [ { "@type": "City", "name": "Lincolnton, NC" }, { "@type": "City", "name": "Denver, NC" }, { "@type": "City", "name": "Gastonia, NC" }, { "@type": "City", "name": "Mount Holly, NC" }, { "@type": "City", "name": "Cherryville, NC" }, { "@type": "City", "name": "Shelby, NC" }, { "@type": "City", "name": "Kings Mountain, NC" }, { "@type": "City", "name": "Hickory, NC" }, { "@type": "City", "name": "Newton, NC" }, { "@type": "City", "name": "Conover, NC" }, { "@type": "City", "name": "Maiden, NC" }, { "@type": "City", "name": "Crouse, NC" }, { "@type": "City", "name": "Dallas, NC" }, { "@type": "City", "name": "Belmont, NC" }, { "@type": "AdministrativeArea", "name": "Lincoln County, NC" }, { "@type": "AdministrativeArea", "name": "Gaston County, NC" }, { "@type": "AdministrativeArea", "name": "Cleveland County, NC" }, { "@type": "AdministrativeArea", "name": "Catawba County, NC" } ], "openingHoursSpecification": [ { "@type": "OpeningHoursSpecification", "dayOfWeek": [ "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" ], "opens": "08:00", "closes": "21:00" }, { "@type": "OpeningHoursSpecification", "dayOfWeek": [ "Sunday" ], "opens": "09:00", "closes": "21:00" } ], "paymentAccepted": "Debit cards, Credit cards, Deposits, Contract-based progress payments", "hasCredential": { "@type": "EducationalOccupationalCredential", "credentialCategory": "license", "name": "North Carolina General Contractor License #106996", "description": "Building classification, Limited limitation. 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