If you are about to add a room, a garage, or even a large patio to your Chattanooga home, drainage is probably not the first thing on your mind. It should be near the top of the list. Every square foot of roof, slab or hardscape you add changes where water goes on your lot, and the building department is going to want to see a reasonable plan for that water before your permit moves forward. Homeowners who deal with it up front save themselves a redesign later. Homeowners who do not often end up with a finished addition and a new drainage problem they did not have before.
A new roofline means new runoff that has to land somewhere, usually through new gutters and downspouts that did not exist before. A new slab or patio is impervious surface, which means rain that used to soak into the ground now sheets off toward whatever is downhill, often the foundation of the addition itself or a neighbor's yard. And if the addition changes the grade around your house even slightly, a slope that used to carry water away from the foundation can end up carrying it toward a wall instead. None of this shows up until the first hard rain after the project is done, which is the worst possible time to discover it.
Where the new roof water will go. New downspouts need a real discharge plan, piped away from the foundation or to daylight, not just a splash block at the base of the wall. See our downspout drainage page for what a correct setup looks like.
The grade around the new footprint. We check which way water will flow once the addition and any new hardscape are in place, and whether the slope still carries it away from both the new structure and the existing house next to it.
Whether the lot already has a problem. If your yard already shows the signs of failed drainage, adding more roof and slab on top of an existing problem almost always makes it worse. It is far cheaper to fix that before the addition than to retrofit a French drain around a finished patio.
Chattanooga's building department reviews how a new structure handles stormwater as part of the permit process, particularly on additions that add roof area or impervious surface. Exactly what documentation is required depends on the size and location of the project, and your contractor or designer can tell you what your specific permit will call for. What we can tell you is that showing up with a clear plan for where the water goes, rather than figuring it out after an inspector asks, keeps your project moving instead of sitting in review.
The right sequence is drainage plan first, then permit application, then construction. If your lot needs a French drain along the side that will see more water once the addition is built, or a curtain drain above a sloped section, that work is far easier to do while the yard is still open than after landscaping and a new patio have gone in around it. Our French drain cost guide gives you a number to plan around while your addition budget is still flexible.
It is not too late to fix. We assess plenty of yards after an addition has already changed how water moves, and the same exterior fixes still apply. Read more on our why is my yard always wet page.
Call (423) 497-3591 for a free on-site assessment. Tell us what is being built and we will walk the lot with you before you finalize the plans.
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