Gutters and Drainage for Landscapers and Concrete Crews
Why this matters
A gutter system is a roof drain. On a moderate rain, a few hundred square feet of roof feeding one downspout delivers a steady stream at its outlet, and the whole job of the gutter installer was to put that water somewhere other than against the foundation. Landscapers and concrete crews undo that work more often than anyone else, without touching a gutter: a bed raised against the wall, a pop-up drain mulched over, a downspout extension pulled off to fit a patio form, a slab poured flat against the siding. The basement leaks or the slab settles a season later, and by then the bed or the slab is the last thing anyone suspects.
Safety first
- Digging near a downspout line is digging near other private lines too: irrigation, landscape lighting, gas to a grill, power to a shed. None are marked by 811. Hand dig within 2 feet of anything you have traced, and if you strike something that is not drain pipe, stop and keep people back; for gas, everyone moves away and calls 911 and the gas utility from a distance. See related: How to Find the Private Lines a Utility Locate Will Not Mark.
- Ladders and gutters: never lean a ladder on the gutter itself; it crushes and pulls loose. Use a standoff or set the ladder against the wall below.
- Concrete: wet concrete is alkaline enough to burn skin; wear waterproof gloves and boots and wash off contact promptly.
What the drainage system is
Gutters and downspouts collect the roof's water and drop it at a few points around the house. Each outlet concentrates the runoff from a whole section of roof into one spot, which is why one misdirected downspout does more damage than a season of rain falling evenly.
Where it goes next is one of four places:
- A splash block or extension at the surface, carrying water a few feet out.
- A buried downspout line, usually 3 or 4 inch corrugated or smooth pipe, running underground to a pop-up emitter in the lawn, a daylight outlet at a slope or a curb, or a dry well.
- A storm sewer connection, where the municipality allows it. Many prohibit tying roof drains into the sanitary sewer.
- The foundation drain, which it should never go to. The perforated pipe along the footing (drain tile) is meant to take groundwater away from the foundation, not to receive a roof's worth of water right beside it. A downspout tied into it floods the very thing it is protecting.
Grade is the slope of the ground around the house. The residential code wants the ground to fall at least 6 inches within the first 10 feet from the foundation (IRC R401.3 in the 2021 edition, as adopted by your jurisdiction). Where lot lines, walls or slopes make that impossible, it calls for swales or drains to carry water away instead, and it wants impervious surfaces within 10 feet of the foundation, such as a patio or walk, sloped at least 2 percent away.
On sites with expansive or collapsible soils, the same code wants roof water discharged at least 5 feet from the foundation or into an approved drainage system (IRC R801.3 in the 2021 edition, as adopted). That condition is what triggers the 5 feet; outside those soils it is good practice rather than a code line, and a local amendment may say more.
See related: Drainage + Grading Around Foundation Reference.
How other trades send water back to the wall
Burying the outlet. A pop-up emitter under 3 inches of fresh mulch or sod cannot pop. A daylight outlet buried by a regraded slope backs up the whole line. The water then fills the pipe and comes out at its weakest point, usually the joint at the downspout boot, right at the foundation.
Regrading toward the wall. A bed built up against the foundation with a soil edge that holds it level, or a lawn graded flat to the house, sends surface water to the wall. A raised bed also brings soil up toward the siding, the sill plate and any weep holes in brick veneer.
Pouring a slab against siding. Concrete poured tight to the house with no slope away, or sloped toward the wall, makes a shelf that collects water at the base of the siding. It also puts the siding's bottom edge into contact with the concrete. The code wants wood siding, sheathing and framing kept at least 6 inches above earth and at least 2 inches above concrete steps, porches, patios and similar surfaces, unless the wood is treated or naturally durable (IRC R317.1 in the 2021 edition, as adopted). Fiber cement and other siding manufacturers set their own clearances, commonly in the same range; read the product's installation instructions.
Crushing or cutting the buried line. An excavator's tracks, a compactor or a heavy pour over corrugated pipe flattens it. An edging trench or a post hole cuts it. Either way the line still accepts water at the downspout and goes nowhere with it.
Pulling an extension and not replacing it. Downspout extensions are removed for every mowing, edging and forming job. One left off for the season dumps the roof at the corner of the foundation.
How to find a buried downspout line
- Start at the downspout. If the downspout goes into the ground through a boot or an adapter, there is a line.
- Look for the outlet. A round grate or cap in the lawn (a pop-up), a pipe end at a slope, a ditch or a curb. Outlets are usually downhill and in the direction the yard falls.
- Run water down it. A garden hose in the downspout for a few minutes shows where the water comes out and how fast. No water at any outlet means it is going into a dry well, a buried break, or a connection you have not found.
- Trace it. A drain contractor can push a camera with a transmitter down the line and mark its path and depth from the surface. Over a short run with a known outlet, a straight line between the two is a guess, not a locate; lines jog around trees and corners.
- Ask. Gutter installers and previous landscapers sometimes leave a sketch with the homeowner.
Worked example: a patio slab against the back wall
A concrete crew is pouring a 10 by 20 foot patio along the back of a house, 10 feet out from the wall and 20 feet along it. The house has fiber cement lap siding. A downspout at one corner of the patio area runs into a buried line that the crew traces with a hose and a drain contractor's locator: it runs under the planned slab, at about 10 inches deep, to a pop-up 25 feet out in the lawn.
The slope the slab needs. A patio is an impervious surface within 10 feet of the foundation, so it slopes at least 2 percent away from the house. Over the 10 foot depth that is 10 x 0.02 = 0.2 feet, or 0.2 x 12 = 2.4 inches of fall from the wall edge to the outer edge.
The height at the wall. The bottom edge of the siding sits 8 inches above existing grade. The siding's instructions, for this example, ask for 2 inches of clearance above a paved surface. So the slab's top at the wall can be no higher than 8 - 2 = 6 inches above existing grade. The crew sets it at 5 inches, leaving 3 inches under the siding, and checks the door threshold: it sits 7 inches above existing grade, 2 inches above the slab, so water on the slab cannot reach it.
The height at the outer edge. 5 inches at the wall minus 2.4 inches of fall leaves the outer edge 5 - 2.4 = 2.6 inches above existing grade. The lawn beyond is then reshaped to keep falling away from the slab's edge rather than forming a lip that holds water against it.
SECTION THROUGH THE PATIO, HOUSE AT LEFT
siding bottom edge ...... 8 in above old grade
| 3 in clear
|------------------------ door threshold 7 in
| slab top at wall 5 in
|=====================.
| 2 percent fall =====. outer edge 2.6 in
| 2.4 in in 10 ft ====.
| base under slab \ lawn keeps
| drain line, solid pipe \ falling
| ~10 in down, cleanout at boot ---\-> to pop-up
+------------- 10 ft ---------------+ 25 ft out
foundation
The drain line under the slab. Corrugated pipe under a slab is the wrong pipe: it crushes under the pour and the compaction, and nobody can dig it up afterward. The crew replaces the run under the slab with solid smooth-wall drain pipe on a compacted bed, keeps the line falling toward the pop-up (at a common 1/8 inch per foot, the 25 foot run drops 25 x 1/8 = 3.1 inches), and adds a cleanout at the downspout boot so the line can be cleared without breaking concrete. The pop-up stays at grade, clear of mulch.
The check before the pour. The crew runs the hose down the downspout again after setting the new pipe: water appears at the pop-up within a minute and none ponds at the boot. Then they pour.
What this would have looked like without the checks. A slab poured level at 6 inches against the wall, with the old corrugated line crushed under it. Every rain, the downspout backs up at the boot, overflows onto a flat slab, and runs to the wall, with 2 inches of clearance at the siding and no slope to carry it off.
What changes the answer
Brick veneer. Weep holes along the bottom course let water that gets behind the brick drain out. A bed or slab that covers them traps that water in the wall. Keep finished grade and paving below the weeps.
Stucco. A weep screed at the bottom of the wall does the same job and has its own clearance from grade and paving in the stucco system's instructions. Do not pour or pile soil over it.
Walkout and below-grade walls. A slab against a foundation that has soil on the inside face (a basement wall) puts water directly on the waterproofing. The slope matters more, not less.
References
- International Residential Code, 2021 edition, Sections R317.1, R401.3 and R801.3, as adopted by your jurisdiction.
- The siding manufacturer's installation instructions for clearance to grade and to paved surfaces.
- See related: Drainage + Grading Around Foundation Reference
- See related: How to Find the Private Lines a Utility Locate Will Not Mark