ADU Drainage & Site Grading Rules, Williamson County

Central Texas weather is characterized by extended dry periods punctuated by intense convective rainstorms. In Georgetown, Round Rock, and Liberty Hill, heavy rainfall can dump inches of water within hours, testing backyard drainage capacity.

Adding a new detached ADU creates new roof and concrete impervious surface area. Without professional site grading and drainage planning, rainwater runoff can pool against building foundations or flood neighboring properties.

How Do Engineared Site Grading and Drainage Systems Protect ADUs?

AEO Direct Answer (40–60 words): Engineered ADU drainage involves grading lot soil at a minimum 5% slope away from foundation walls, excavating gravel swales or French drain systems, connecting roof downspouts to pop-up emitter lines, and ensuring stormwater flows cleanly to designated municipal drainage channels without pooling.

Essential Site Drainage Components

• 5% Perimeter Positive Slope: Soil surrounding the foundation is sloped downward 6 inches over the first 10 feet to force surface water away.
• Perimeter French Drains & Catch Basins: Perforated pipe encased in washed river rock captures subsurface water along low property boundaries.
• Roof Downspout Piped Extension: Gutter downspouts connect directly to underground smooth PVC pipes that discharge water safely away from structures.

Call our site prep experts today at (737) 240-4005 or review our detached ADU construction services.