Are you building a patio and don’t want water to pool on it or back up against your house? Worried it will seep down against the foundation and into the house? The correct patio slope will help keep water from sitting on it or backing against your house.
Patios within 10 feet of a foundation must have a 1/4” per foot or 2% fall away from the building. The 2% fall or slope is required for hardscape surfaces such as pavers, wood, concrete, gravel, or other materials. The slope will move water off the surface and away from the foundation.
In this article, we’ll take a look at how sloping a patio helps with drainage, how much the fall should be, and code requirements. We’ll explain how to calculate the slope, and how to fix the grade of an existing patio. By the end of the article, you’ll have a better understanding of how much slope is needed, and how to fix an existing surface.
- Should Patio Slope Away From the House?
- How Much Slope Should A Patio Have?
- What Is the Minimum Slope for Drainage?
- What Is the Proper Slope for a Patio?
- What Slope Is Too Steep (Maximum Slope)?
- How to Calculate Patio Slope
- How to Slope a Patio for Drainage
- Fixing A Patio With An Improper Slope
Should Patio Slope Away From the House?
Water pooling or backing up against a building can damage outdoor furniture and foundations. Sitting or backing water can also seep into basements and wreak havoc there too. Angling or grading the ground or a patio away from a building is one way to prevent water damage. Patio slope may be referred to as grade, slope, pitch, angle, or fall and is commonly expressed as a ratio, percentage, or fraction.
Patios commonly are made of concrete, pavers, flagstone, brick, cut stone, tile, loose material like pea gravel, or a mix of materials. When constructed to the correct slope, patios will ensure proper drainage and protect your home, outdoor furniture, and investment. Water sitting on or under the patio surface can cause furniture to swell or rust, deck material to shift, and the growth of mold, mildew, and moss.
How Much Slope Should A Patio Have?
The lay of the land is a key consideration when placing and building a patio, and ensuring it falls so it sheds water quickly. Surfaces stretching out from a building should move water away from the structure. It may be necessary to angle the grade towards one end or even a corner depending on its relationship to foundation walls and the flow of the ground.
The slope, setbacks, and materials also may be governed by local ordinances and codes that differ from other areas. It is best to check locally for any requirements or restrictions.
Code Requirements for Patios
The main concern for most codes is people and building safety. So, ensuring patios are constructed to meet safe usage requirements, don’t interfere with egress, and won’t cause damage to the structure which could lead to injury are important.
The 2018 IRC (International Residential Building Code) is used by many States and jurisdictions to guide their codes. Some States use older versions of the IRC, and others use completely different regulations.
Section R401.3 addresses drainage and requires the grade or slope to fall 6” or more in the first 10-feet. An exception is impervious or hardscape surfaces like patios within 10’ of a building, they must have a 2% or greater slope away from the structure.
A 2% grade is 1:48 or 1-inch every 4-feet or 1/4″ per foot. In addition to the building code, many home associations and communities may have other unique requirements.
How Patio Fall Is Expressed?
The fall, slope, grade, pitch, or angle of a patio is often expressed as a ratio, percentage, or fraction. Under Section R401.3 of the IRC, the fall of an impervious or hardscape patio must be 1:48, or 2%, or 1/48. That translates to 1 unit of fall for every 48 units of run or 1/4″ per foot.
How to Measure Slope for a Patio?
Unlike stairs which are measured from their lowest point to highest, the slope of patios is measured from the highest point, commonly nearest a building, to its lowest. So, instead of using the rise over the run, we use the fall over the run. The size of the patio determines which is the easiest way to measure the slope.
Measure the distance out from the building to where the patio ends. Convert that distance from feet to inches and divide by 48. For example, a 16’ run is 192-inches which has a 4” fall (16’ x 12 = 192 ÷ 48 = 4”). The resulting value is the overall required fall of the surface from one side to the other to achieve a fall to run ratio of 4:198 which reduces to 1:48, or a 2% slope (4 ÷ 192 = 0.02 x 100 = 2%).
Using a 4-foot builder’s level and tape measure to identify the slope is helpful and accurate in short distances. A short 6” level or a 2-foot level is often used when laying pavers and bricks which fall 1/4″ per foot, and a long, flat board with a 4 or 8-foot level is useful for checking larger concrete surfaces. However, patios may need to slope in more than one direction, which means a string line and string-level is helpful.
What Is the Minimum Slope for Drainage?
The minimum slope for drainage under Section R401.3 of the IRC is a fall of 6” or more in the first 10-feet out from a building or a 5% grade. Proper drainage is important to protect structures from moisture damage and erosion.
Drainage pipes fall under plumbing codes and need a minimum slope of 1/4″ every foot. They may slope to a maximum of 3” per foot, or run vertically. The minimum slope for hardscape or patios within ten feet of a building is 1/4″ per foot or a 2% grade away from the dwelling.
What Is the Proper Slope for a Patio?
Hardscape surfaces within 10 feet of a building are subject to the IRC and must have a minimum slope of 2% or 1/4″ per foot away from the structure. Hardscape refers to permeable and impermeable walkways, patios, and decks that are permanently placed as part of a building’s exterior.
Patios made of hardwearing materials like pavers, flagstone, brick, cut stone, tile, concrete, loose material like pea gravel, or even wood, composite, or plastic materials are classed as hardscape. That means the proper slope for patios, regardless of construction material, must have a 1:48, 1/4” per foot, or 2% grade.
Many professionals acknowledge that while the overall average fall across a patio’s run is 2%, individual pavers, bricks, or tiles may range from 1/8” to 3/8” per foot. Packing and screeding sand to a perfect 2% grade while placing heavy or irregularly textured stones or pavers is the reason for the individual deviations.
What Slope Is Too Steep (Maximum Slope)?
The minimum required drainage grade within 10 feet of a building, according to the IRC, is 5%. Most disability associations identify a maximum 1:12 (8%) slope for unassisted wheelchair movement.
Sidewalks must have a longitudinal slope of 1:20 (5%) or less, or they are classed as a ramp. The lateral slope of a sidewalk cannot exceed 5%, and for comparison, the maximum recommended slope for a golf green is 3%.
Many restaurants set up patios on existing sidewalks with a slope of 2% to a maximum of 5%, which supports the practice that the maximum slope of a patio is 5% or 5/8” per foot. Furniture sitting with the grade may not experience much from a 2% (1/4” per foot) patio grade at all. You may, however, feel a tilt if diagonal or perpendicular to the grade if it is 5%.
Some individuals argue that a 2% slope is too much and worry that their glass will spill. A 1/4″ per foot translates into 1/16” in 3” – the base diameter of a wine bottle – and most glasses have a smaller base, so experience less of a deviation. A 2% grade won’t negatively affect your outdoor enjoyment.
How to Calculate Patio Slope
There are different ways to calculate the slope for a new patio. The easiest way is to measure the distance from (or closest to) the building to where the outside edge will be and multiply it by 1/4 or 0.25 for a 2% or 1/4″ per foot drop.
- For example, a 20-foot patio run multiplied by 0.25 calculates the patio fall to be 5” from one edge to the other.
To calculate the slope of an existing patio, use a 2 or 4-foot builder’s level. Place the level on the surface, lift the end furthest from the structure, and measure the distance lifted to make it level. Divide the distance by 4 with a 4-foot level, and 2 with a 2-foot length to determine the fall per foot.
- For example, using a 4-foot level results in a 1” lift, 1 ÷ 4 = 0.25 or 1/4″ or 2% fall per foot. If the lift is 1/2″ when using a 2-foot level, 1/2 ÷ 2 = 1/4 or 0.25 or a 2% slope.
How to Slope a Patio for Drainage
A laser level or contractor’s level can be helpful to determine and set slope, but a string line and line level are still the go-to. Remember to contact local utilities to ensure there are no lines where you plan to place the patio.
To set a string line, hammer a stake into the ground at each corner of the patio site and mark the desired elevation on the stake closest to the structure. Mark a point 6” up from the desired elevation on that stake and run a string around all 4 (or more) of the stakes to form the perimeter.
Pull and tie the string taught to each stake and use a line-level to adjust each side by moving the string up or down at the stake so it is level with the 6” mark on the starting stake.
The distance from the building to the outer string, multiplied by 0.25 determines the 2% slope in that direction. The outer edge of the patio will drop that distance, plus the 6” below the string line.
- For example, a 15’ distance would be 15 x 0.25 = 3.75” or 3-3/4”. Add that to the 6” the string line is above the starting level, and the outer patio edge will be 9-3/4” below the string line. The thickness of the drainage base will be added to that for excavation and ground preparation.
Section R506.1 of the IRC addresses ground preparation and requirements for concrete used on-grade, including concrete patios. The site for a concrete deck should be cleared of vegetation and topsoil (R506.2) to a depth that allows for the drainage layer and concrete. Any clean fill added should be leveled and compacted (R506.2.1).
Set the 2-by forms in place based on the size and shape of the patio and drive stakes to support the forms. Determine the required fall, commonly 2% or 1/4” per foot, and secure the boards to the stakes to maintain the required slope.
Place, spread, and compact a 4” thick gravel drainage base or layer (R506.2.2) compacting it in 2” layers. Grade the surface of the gravel, so it is parallel to the slope of the forms. That will mean the concrete is a uniform thickness and saves money. A vapor barrier is not necessary unless the patio will be enclosed and heated (R506.2.3).
Reinforce the forms and check their slope is correct before the pour. The forms are used to screed and level the concrete, so you want them set and secure. Slabs need to be a minimum of 3-1/2” thick (R506.1) with reinforcement in the upper third (R506.2.4).
Pour or place the concrete, screed, and level it, let it set some, and then smooth or broom finish the surface, and edge the perimeter. Protect it from precipitation for 24 hours and enjoy. It will take the concrete about a month to fully cure.
Ground preparation, fill, and drainage base requirements for paver patios are similar to what is required for a concrete patio, with the addition of landscape fabric and a sand layer. Outline the patio shape for excavation using a string, chalk line, or spray paint, and determine the required fall.
Remove vegetation, topsoil, and soil to the required depth – add the thickness of the pavers, 4” gravel base, and 1 to 2” of bedding sand. Level or slope the ground with the desired fall, and compact any loose or added soil.
Add, spread, and compact 4” of gravel in 2” layers so the surface is sloped to the fall line. Around the perimeter, install edge restraint to hold the sand and pavers in place.
Roll landscape fabric over the gravel to prevent weed growth, and spread the layer of builder’s sand on top. Place, pack, and smooth the sand to the required slope. Use a rake, trowel, or screed board to help remove waves and bumps, and lay the pavers. The slope of individual pavers will depend on their dimensions.
Fixing A Patio With An Improper Slope
A patio that collects water or allows water to flow back and sit against the foundation needs to be re-sloped. Fixing a patio with an improper slope doesn’t necessarily require the removal of the patio, re-sloping of the base, and rebuilding of the patio, although it might. The size of the patio and how much the fall needs to be adjusted impact repair options.
A concrete patio with few to no cracks may be re-sloped using a leveling compound, thinset, slurry, or another layer of concrete depending on how much the slope needs to be improved.
Another method is to dig a hole under the edge of the slab, place a hydraulic jack under it, and raise it to the new level. Use sand, mud, or another material to hold the concrete at the new level.
There are other ways to lift and re-slope a concrete patio, but they are more costly. There are professionals that do mud-jacking or use a polyurethane slurry type liquid injected under the pad to lift it. The mud or slurry flows under the slab, lifting it, and solidifies, holding it up to maintain the new slope.
The size of the patio, pavers, and how much requires re-sloping will determine how best to proceed. A small fix often requires lifting out some pavers. Adding, tamping, and smoothing sand, and replacing the removed pieces. Larger paver patio slope repairs are best done by removing all the stones and installing a proper base or replacing an existing one.
Building a patio or repairing one so water doesn’t pool or sit against the foundation is important. A 5% grade away from structures is required by the IRC to move water away from a foundation. However, the code allows for hardscape such as patios to have a minimum 2% fall or slope since water will flow more quickly off it than off grass covered fill.
I hope you have a better understanding of how much slope a patio requires, and how to build or repair a patio for the proper slope.