Quick answer
Hardscape drainage is the planned route rain and meltwater take across, under and off a patio, walkway, deck or other hard surface, so the water leaves without pooling, softening the base or reaching the house.
It has three parts: the slope of the surface, the water that gets into the base and joints, and the place the water finally goes. Sources print patio slopes from about 1 to 2 percent and disagree on the exact figure, so the plan and your local code decide.
Quick facts
The key facts about Hardscape Drainage, with sources:
- Illinois Extension patio slope
- Minimum 0.5 percent, desirable 1 percent, maximum 2 percent 1
- Colorado State patio slope
- 1 percent to 2 percent for a patio-terrace 2
- ICPI paver slope
- A minimum of 1.5 percent, in its layout instructions 3
- IRC R401.3 as reproduced by Maricopa County
- Hard surfaces within 10 feet of the foundation slope at least 2 percent away from the building 4
- Ground next to the foundation
- Fall of at least 6 inches within the first 10 feet, which is 5 percent 4
- Soil grade at foundation walls
- Minimum 4 percent away from the house, per Illinois Extension 1
- Oregon State paver guide
- Slope down one inch for every 4 feet, away from the house 7
- Before any digging
- Call 811 at least two working days ahead 8
Key takeaways
- A hard surface sheds water, so it needs a built-in slope away from the house. Published patio targets run from about 1 to 2 percent.
- Slope figures belong to different things. One is for the paved surface, one is for the soil beside the foundation, and one is for the ground in the first 10 feet.
- Water also moves through joints and the base. Heavy clay and wet soils can need extra base or a perimeter drain pipe, according to ICPI.
- Where a deck meets a wall, the ledger and its flashing decide whether water runs off or gets in.
- Never aim patio water at a neighbor or into the sanitary sewer, and call 811 before any digging.
Why a flat patio is a drainage problem
Patios, porches, walks and driveways are usually nonporous, so rain runs across them instead of into them. PNNL’s building science guide says that when these surfaces are not graded properly, water collects around the foundation and can cause water intrusion and structural problems 5.
That is the heart of hardscape drainage. A flat slab or paver field does not hold water in a crack or a joint. It sends it somewhere. The only choice is where.
A slope toward the lawn or a drain sends it away. A slope toward the house, or no slope at all, sends it to the wall or leaves it as a puddle.
Oregon State’s paver guide makes the same point for installers. It says the area needs a gradient so that water can run off the pavers and avoid pooling or ponding that can damage the pavement over the long term 7.
This page owns the question of slope and drainage on patios, paths and decks. It does not cover the whole yard. For ground-level yard water, see our drainage and grading service guide. For roof water, see downspout drainage.
How water leaves a hard surface: slope, joints, base and outlet
Surface slope. The first line of defense is a slight fall. Illinois Extension lists patios with a minimum slope of 0.5 percent, a desirable slope of 1 percent and a maximum of 2 percent 1.
Colorado State Extension lists a patio-terrace at 1 percent to 2 percent 2. ICPI’s construction guide for interlocking pavers says slopes should be a minimum of 1.5 percent 3.
Joints and the base. Not all water runs off. With pavers, some soaks through the joints into a compacted aggregate base.
ICPI says the thickness of that base depends on traffic, soil type, subgrade drainage and moisture, and climate, and that continually wet or weak soils in colder climates need bases 2 to 4 inches thicker 3. Our hardscape base specification guide covers the layers in detail.
A drain for the base. ICPI describes a perforated drainage pipe, 4 inches in diameter, surrounded by at least 3 inches of open-graded stone and wrapped in geotextile, placed along the pavement perimeter to remove excess water in the subgrade soil and base.
It says the pipe should be sloped and directed to outlets at the sides or ends, and recommends drain pipes in clay or other slow-draining soils subject to vehicular traffic 3.
An outlet. Every slope and every pipe ends somewhere. A lawn that slopes away, a swale, a channel drain or a pipe that daylights downhill all count.
If the end of the line is a neighbor’s yard, a public sidewalk or the sanitary sewer, the plan is not finished. For channel drains, see channel drain vs. French drain.
- Rain lands on the surfaceA nonporous surface sheds it 5
- Surface slope carries it awayPublished patio targets run 0.5 to 2 percent 12
- Some enters joints and the baseBase thickness depends on soil and climate 3
- A perimeter pipe or open base moves itPipe sloped to outlets at the sides or ends 3
- An outlet takes it somewhere safeLawn, swale or storm point, never a neighbor or sanitary sewer
Order of travel for water on a paver or concrete patio. The step 5 wording is a safety rule, not a measurement. Source: [5] [1] [2] [3]
Slope figures by source: what each number applies to
| Source | Number | What it applies to | Note |
|---|---|---|---|
| Illinois Extension | 0.5 / 1 / 2 percent (minimum, desirable, maximum) | Patios 1 | A table row for patios only |
| Colorado State Extension | 1 to 2 percent | Patio-terrace 2 | Also lists entrance walks at 1 to 4 percent and driveways at 1 to 15 percent |
| ICPI Tech Spec 2 (revised February 2020) | Minimum of 1.5 percent | Paver slopes in layout 3 | A minimum, for interlocking concrete pavers |
| IRC R401.3 as reproduced by Maricopa County | Minimum 2 percent | Impervious surfaces within 10 feet of the foundation 4 | Edition not printed in that document; adoption varies |
| PNNL, citing the IRC and ENERGY STAR | 2 percent, or at least 0.25 inch per foot | Slabs, walks and driveways, for 10 feet or the edge of the surface, whichever is less 5 | A building science guide, not a code |
| Oregon State Extension paver guide | Down one inch every 4 feet | A paver slab sloping away from the house 7 | About 0.25 inch per foot, or roughly 2 percent, by our arithmetic |
| Illinois Extension | Minimum 4 percent | Final soil grade around foundation walls 1 | Soil, not the patio surface |
| IRC R401.3 as reproduced by Maricopa County | At least 6 inches in the first 10 feet | Ground around the foundation 4 | 5 percent, by our arithmetic |
Three different slopes, easy to mix up
The patio surface, the soil beside the foundation and the first 10 feet of ground each have their own figure. Using the 5 percent ground figure on a paver patio, or the 1 percent patio figure beside a foundation wall, mixes them up.
Example: what a percentage means in inches across a patio
The patio depths below are invented. The percentages are the ones printed by the sources above. Fall in inches equals the depth in feet, times 12, times the percentage. This is arithmetic, not a recommendation for your patio.
| Patio depth away from the wall (example) | At 1 percent | At 1.5 percent | At 2 percent |
|---|---|---|---|
| 8 ft | 0.96 in. | 1.44 in. | 1.92 in. |
| 10 ft | 1.2 in. | 1.8 in. | 2.4 in. |
| 14 ft | 1.68 in. | 2.52 in. | 3.36 in. |
Check the fall with a string line
ICPI says stakes should be marked to establish grades, or string lines tied to them, and that grade stakes should be checked periodically during the job 3. A homeowner can ask a contractor to show the string line and the fall in inches before base goes in.
For comparison, Oregon State’s one inch every 4 feet puts the fall at 2.5 inches across 10 feet 7.
A 6-inch fall in 10 feet, the IRC figure for the ground, is 5 percent and is much steeper than any patio row here 4. Notice how little height the patio figures need.
A patio that falls 2 inches in 10 feet looks flat to the eye but still sheds water.
A 14-foot patio at 2 percent drops almost 3.4 inches, which affects where the finished edge meets the lawn, a step or a door threshold.
Where hardscape drainage shows up: plans, bids and inspections
On a patio plan. Look for a spot elevation or an arrow that shows the direction of fall, and a note about where the water exits. Use our patio size planner to think about size before you ask for a design.
In a bid. Look for the base depth, the geotextile, any perimeter pipe and the outlet. Our patios and walkways guide explains how those lines usually appear.
In a permit or inspection. Some jurisdictions check grading and drainage near the foundation. Whether yours does depends on local adoption of the code.
At the house wall. A patio or deck beside a wall is where drainage mistakes cost the most. The section on decks below picks that up.
Outdoor drainage around patios and decks
A deck is different from a patio because water falls through it. The boards are spaced, so rain lands on the ground below as well as running off. The drainage questions are what happens at the wall, under the deck and at the footings. Building Science Corporation’s Info-304 sheet is about the first of these.
At the wall. Info-304 says a deck ledger pressed against the wall’s water-resistive barrier acts as a horizontal dam that blocks drainage.
The ledger’s structural fasteners breach the barrier, so the ledger can channel water to the fastener holes and into the wall.
The sheet recommends flashing over the ledger so water drains away from the connection, tying the membrane flashing into the wall’s drainage plane with sheathing tape, and treating joist ends with sealant to reduce water absorption 6.
It was published in 2009, so check the details against your local code and your deck builder.
Under the deck. The ground below still has to shed water away from the foundation.
The ground rules in the table above apply: the IRC figure of 6 inches in 10 feet, and Illinois Extension’s 4 percent for soil beside foundation walls 41.
We did not find a university source that gives a separate slope for ground under decks, so we do not state one.
Next to a patio. PNNL advises holding the patio slope for 10 feet or to the edge of the surface, whichever is less, and adding drains or swales where lot lines, walls or slopes block a 6-inch drop 5.
A deck skirt, a stair landing or a planter beside the patio can trap the water that slope was meant to move, so look at the edges too.
Downspouts. A downspout that empties onto a patio or deck puts roof water onto the surface you are trying to keep dry. Route it as the downspout page describes. If you are choosing between the two surfaces, our deck vs. patio comparison covers the differences.
Deck work at the house wall needs a pro
Ledger attachment is structural. Do not cut into the wall, move flashing or add fasteners without a qualified deck builder or your local building department. Call 811 before digging any footing or drain trench 8.
What good drainage does, and what it cannot fix
What good drainage does
- Keeps water from collecting around the foundation, which PNNL links to water intrusion, mold and indoor air quality problems 5.
- Prevents pooling and ponding that Oregon State says can damage pavement over the long term 7.
- Lets a base dry out. ICPI says wet or weak soils need thicker bases in colder climates, so drier soil asks less of the base 3.
- Gives a bid line you can compare, such as slope, outlet and pipe.
What it cannot fix
- It cannot fix a roof that dumps water onto the surface. That needs a downspout plan.
- It cannot beat a high water table or a neighbor’s runoff. Illinois Extension notes that runoff from adjacent properties can complicate drainage and advises consulting an engineer or landscape architect first 1.
- It does not make a heavy clay soil drain. ICPI recommends drain pipes in clay or other slow-draining soils for vehicular pavement 3.
- A correct slope cannot make up for a base that was not compacted or an edge that was not restrained.
Limits and open points
The slope figures come from sources written for different readers. Illinois Extension and Colorado State Extension write for homeowners.
ICPI writes for pavement installers, and the copy we read is a member distributor’s mirror because ICPI has merged into another association. PNNL writes for building professionals.
Maricopa County’s page reproduces a code section for its permit applicants and does not print the edition 43.
We did not load the International Residential Code from the International Code Council directly. The ICC page refused our request.
The R401.3 wording above is as Maricopa County reproduces it, and PNNL cites the 2009, 2012 and 2015 editions for the 2 percent figure 5. Check the edition your city adopted and any local amendments.
The Oregon State figure of one inch every 4 feet is a plain instruction from a 2011 installation guide. It converts to roughly 2 percent only by our arithmetic.
We did not find a university source that sets a slope for every type of surface. Gravel paths, permeable pavers and stamped concrete all differ. For pavers meant to absorb water, read about the permeable system.
What drives the cost of getting the drainage right
We do not print prices on a glossary page. These are the things that change a bid for the drainage part of a hardscape job.
The site. A site that is already sloped away from the house needs less work than one that slopes toward it. Regrading, a retaining edge or a drain adds scope.
The base. ICPI ties base thickness to traffic, soil, drainage and climate 3. A thicker base means more excavation, more stone and more haul-off.
The drain. A perimeter pipe, geotextile, cleanouts and an outlet are separate lines. So is the trench to get to the outlet.
Soil and water. Clay, a high water table and runoff from uphill all raise the odds that a drain is needed 31.
Lifespan. We found no sourced lifespan for a patio drain, and it varies with soil, climate and maintenance. Ask any company what it warrants and in writing. Use our landscaping estimates guide, the cost hub and the paver calculator to compare quotes.
How a drainage check goes on a new or existing patio
The check below is a way to plan a conversation, not a how-to for building a patio. Layout and base work need a trained installer.
- Note which way the water goes now. After a rain, look for pooling and for staining or damp at the wall.
- Ask which standard or code figure the plan follows, and for what surface, using the table above.
- Ask for the fall in inches across the patio and where the water exits.
- Ask whether roof water, a spigot or a neighbor’s runoff reaches the patio.
- Have the contractor mark utilities. Call 811 at least two working days before digging begins 8.
- Photograph the grade and string line before the pavers go down, and confirm the same fall after the job.
Our guide to choosing a landscaping company lists what to ask any bidder. Check your state licensing rules first.
Keeping the water moving after the job
Drainage fails slowly. Soil settles, joints fill with debris, plants grow into outlets, and downspout extensions get kicked off.
Oregon State says regular cleaning and sweeping of pavers is recommended, especially in shaded or damp areas where they are prone to efflorescence, which is a chalky deposit 7.
It also says re-sealing may be needed regularly to protect against stains, algae and loss of joint sand 7. Our page on paver joint sand covers the joints.
After a heavy rain, walk the edge of the patio. Look for water standing in the same spot, soil washing out from under an edge, and a gap that has opened between the patio and the wall. Fix the first two early. The third one is a pro call.
If a perimeter pipe was installed, ask where its outlet is and how to check it. ICPI says outlets should be covered with screens to prevent animal ingress, so they need an occasional look 3.
Warning signs and when to call a professional
Warning signs. Pooling more than a short time after rain, a slab or pavers that have tilted, a damp line on the wall above the patio, staining at the base of a ledger board, and soil washed out along an edge.
Call a pro for these. Any ledger or flashing repair, any regrading that changes how water leaves your lot, any wall or slope beside the patio, and any water entering the house.
Illinois Extension advises consulting an engineer or landscape architect before changing a yard’s drainage so you do not do more harm than good 1.
Never direct runoff onto a neighbor. Illinois Extension notes that stormwater runoff can become a liability, sometimes pitting neighbor against neighbor in court 1. Do not connect patio drains to a sanitary sewer either. If you are not sure where your public storm connection is, ask the city or utility.
Drainage must not end at a neighbor or in the sanitary sewer
Where the water exits is part of the design. A pipe outlet or a slope that points at an adjacent lot can create a legal and a physical problem. Call 811 before any digging 8, and check local rules before adding a drain that discharges off your property.
Standards, codes and who sets them
| Authority | What it is | What it says here | Status |
|---|---|---|---|
| IRC R401.3 (International Code Council) | A model building code. A city or state must adopt it, and many amend it | Ground falls 6 inches in the first 10 feet; hard surfaces within 10 feet slope at least 2 percent away 4 | Law only where adopted; edition and amendments vary |
| ICPI Tech Spec 2 | An industry technical specification | Slopes should be a minimum of 1.5 percent; base and drain guidance 3 | Voluntary, unless a contract or city adopts it |
| University Extension guides | Educational publications | Patio slope ranges and foundation soil grade 12 | Guidance |
| Local grading and stormwater rules | City or county ordinance | Where water may discharge, and what needs a permit | Law; check locally |
Hardscape drainage next to related ideas
| Idea | What it is about | Where to read more |
|---|---|---|
| Hardscape drainage (this page) | Slope and water on patios, paths and decks | You are here |
| Permeable paver systems | A paver system built to let water soak through | Linked in the limits section above |
| Channel drain vs. French drain | Two pipe and grate drains for surface or subsurface water | Covered in the channel drain comparison linked above |
| Downspout drainage | Moving roof water away from the house | Covered in the downspout page linked above |
| Yard drainage service | Regrading and drains for the whole lot | Covered in the drainage guide linked above |
Myths about patio drainage
- Myth A level patio is fine if it does not pond.
- Reality Illinois Extension’s table has a minimum slope of 0.5 percent for patios, and ICPI says slopes should be a minimum of 1.5 percent for its pavers 13. Zero fall is outside every source we read.
- Myth One slope figure covers everything near the house.
- Reality The soil beside the foundation, the first 10 feet of ground and the patio surface each have a different published figure 142.
- Myth Pavers drain through the joints, so slope does not matter.
- Reality Oregon State says the area needs a gradient so water can run off and avoid pooling 7.
- Myth A drain pipe fixes any wet patio.
- Reality ICPI describes pipe as a way to remove excess water from the subgrade and base, in clay or slow-draining soils 3. It does not fix a surface that slopes the wrong way.
- Myth A deck needs no drainage plan because water falls through it.
- Reality Building Science Corporation says the ledger can act as a horizontal dam and send water into the wall 6.
Where climate and soil change the plan
Two regional variables matter for patios. The first is freeze and thaw. ICPI says greater base thicknesses are often used in regions with numerous freeze-thaw cycles, expansive soils or very cold climates 3.
The second is the soil itself: clay and other slow-draining soils are where ICPI recommends drain pipes 3. Expansive soils are a separate regional problem that moves slabs.
See our expansive soils research for the regions it covers. Code adoption also varies by city and state, so the figure in your permit may differ from the ones above.
When this matters, and your next step
Drainage matters most when you are planning a new patio or deck, when water stands after rain, or when a wall near a patio shows damp or staining.
Your next step is to find out which way the surface falls today. Put a level on a straight board, or measure with a string line, and compare the fall with the table above. If the patio is new, ask the installer what fall they built and where the water exits.
If water reaches the house, stop guessing and ask a pro. Use our drainage guide to see what the work involves, then find a landscaping company that quotes the slope and the outlet in writing.
- If Water pools on the patio but the wall is dry
- Then Check the fall with a string line against the figures above; ask a contractor about regrading or a surface drain
- If The wall is damp or stained above the patio
- Then Treat it as a water-entry problem; call a pro before any repair
- If Water stands at the deck ledger or under the deck
- Then Ask a deck builder to check flashing and the ground grade 6
- If Roof water lands on the patio
- Then Fix the downspout first. See downspout drainage
Questions about Hardscape Drainage
How much slope should a patio have?
Sources print different figures. Illinois Extension lists patios at 0.5 percent minimum, 1 percent desirable and 2 percent maximum. Colorado State lists 1 to 2 percent.
ICPI says paver slopes should be at least 1.5 percent. The IRC, as Maricopa County reproduces it, sets at least 2 percent within 10 feet of the foundation. Your local code decides.
Which direction should a patio slope?
Away from the house. Oregon State’s paver guide says the slab should slope downwards away from the house to allow water drainage. PNNL says the same for patios, porches, walks and driveways, because water collecting around a foundation can cause water intrusion and structural problems.
What is the slope of a patio in inches per foot?
Two percent is about a quarter inch per foot, and 1 percent is about an eighth. PNNL cites ENERGY STAR’s recommendation of at least 0.25 inch per foot. The inch figures are our arithmetic from the percentages, so use the figure in your plan or code.
Does the IRC require a patio to slope?
As reproduced by Maricopa County, IRC R401.3 says impervious surfaces within 10 feet of the foundation shall slope a minimum of 2 percent away from the building. Whether that applies depends on the edition and amendments your city adopted. Check with your building department.
How do you fix a patio that drains toward the house?
Ask a qualified contractor. The fix depends on the patio type and may involve regrading, resetting pavers, adding a surface drain or replacing the slab. Do not guess if water reaches the wall. Illinois Extension advises consulting an engineer or landscape architect before changing a yard’s drainage.
Do pavers need a drain pipe?
Not always. ICPI describes a perforated pipe around the pavement perimeter to remove excess water from the subgrade and base, and recommends drain pipes in clay or other slow-draining soils subject to vehicular traffic. Many patios on well-drained soils have none. Ask what your soil and climate need.
How do you drain water from under a deck?
Slope the ground away from the foundation and keep roof water off the area. IRC R401.3, as reproduced by Maricopa County, calls for a fall of at least 6 inches in the first 10 feet. We found no university figure specific to ground under decks, so ask a qualified builder.
Why does water get into the wall at a deck?
A ledger board attached to the wall can act as a horizontal dam. Building Science Corporation says it blocks drainage and can channel water to the fastener holes and into the wall. Flashing over the ledger, tied into the wall’s drainage plane, directs the water away. Deck work at the wall needs a pro.
Can patio drainage go to my neighbor’s yard?
It should not. Illinois Extension notes that stormwater runoff can become a liability and sometimes ends up in court. Plan an outlet on your own lot or at a public storm connection that the city permits, and ask your local stormwater office what is allowed.
Do I need to call 811 before adding patio drainage?
Yes, before any digging. USA North 811 says to call at least two working days before you begin and to wait until each utility operator has responded. The service is free. A drain trench, footing or base excavation all count as digging.
Sources
- University of Illinois Extension, Good Growing blog: Landscape Drainage for Homeowners (Christopher Enroth, February 12, 2020), retrieved .
- Colorado State University Extension, Water-Wise Landscape Design: Steps (GardenNote 411, published October 2014, reviewed July 2025), retrieved .
- Interlocking Concrete Pavement Institute, ICPI Tech Spec 2: Construction of Interlocking Concrete Pavements (revised February 2020), PDF as republished by a member distributor, read as text with pdftotext, retrieved .
- Maricopa County Planning and Development, Building Elevation Requirements (reproduces IRC R401.3 Drainage and R404.1.6; edition not stated), PDF read as text with pdftotext, retrieved .
- Pacific Northwest National Laboratory, Building America Solution Center: Patio slabs, porch slabs, walkways and driveways slope away from house, retrieved .
- Building Science Corporation, Info-304: Integrating Deck Ledger Board with Drainage Plane (effective May 20, 2009), retrieved .
- Oregon State University Extension, 10-Step Guide to Installing Pavers (Jim King, 2011), PDF read as text with pdftotext, retrieved .
- USA North 811, DIYers (call 811 before you dig), retrieved .
Expert review
Written by the HyreYard Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Patio slope ranges come from Illinois Extension and Colorado State Extension. Paver slope, base, drain pipe and outlet guidance come from ICPI Tech Spec 2 (member-distributor PDF, read as text).
The IRC R401.3 wording comes from Maricopa County’s reproduction, because the ICC page refused our request, and its edition is not printed. PNNL supplies the foundation-water rationale and the ENERGY STAR figure.
Deck ledger water entry comes from a 2009 Building Science Corporation sheet. Percent-to-inch conversions are our arithmetic and are labeled. The patio depths are invented examples. No prices are given.
Suggest a correction. We fix errors and say what changed.