Drainage grading and slope field guide for site crews

Grading for drainage, and the one rule under all of it

Site grading is shaping the ground so water moves where you want it: away from the building, across the surfaces, and off the lot to a legal outlet. Every other rule in this guide is a way of serving that one. Water has to leave. It leaves by sheeting off graded surfaces that all tip the same direction, or it stays, finds the low spot, and goes where you did not want it, which on most sites is the foundation.

Here is the thing about water on a site. It does exactly one thing, every time, with no exceptions: it runs downhill and it stops at the lowest point it can reach. There is no judgment in it. If the lowest reachable point is the corner of the basement, that is where it goes, and it will get there through a hairline crack you cannot see. So grading is not decoration and it is not the lawn looking nice. It is deciding, with dirt, where the lowest point is and making sure that point is somewhere safe.

The order of the work follows the water. You shed it off the building first with positive grade, you carry it across the yard with slope and swales, you collect it where it has to concentrate, and you discharge it to an outlet that is legal to discharge to. Skip the outlet and you have just moved the problem to the property line. The grade that has nowhere to go is not drainage. It is a delay.

How much should the ground slope away from a house?

The ground should fall away from the foundation, and the common code rule is a drop of at least 6 in within the first 10 ft, which works out to about 5 percent. That figure lives in the IRC at the foundation drainage section, commonly R401.3, and it is the single most important grade on any residential site. The first 10 ft is where roof water, surface water, and snowmelt either get pushed out or get delivered to the wall.

The code carries two practical exceptions you will meet on real lots. Where a lot line, a wall, a slope, or another barrier makes 6 in of fall in 10 ft impossible, the rule allows swales or drains to carry the water away instead, and where impervious surfaces like patios and walks sit within 10 ft of the building, the slope can be less, commonly held at a minimum of 2 percent away. Confirm the figures against the adopted code edition and any local amendment before you build to them.

The number rookies miss is what happens after they leave. Fill settles. The 6 in of fall you graded against fresh backfill becomes 2 in of fall, then flat, then negative as the trench around the foundation consolidates over the first year or two. So you over-build the fall against settlement, you compact the backfill in lifts rather than dumping it, and you tell the owner that the day the grade tips back toward the wall is the day they call you, not the day water is in the basement.

What is the minimum slope for drainage?

For lawn and planted ground, the working minimum is about 2 percent, which is 1/4 in of fall per foot, roughly 2 ft of drop over 100 ft. Below that, turf and soft ground do not sheet water reliably. The surface is never as flat as the survey says, so a 1 percent design grade has low spots that read as zero or negative once the sod is down and the soil settles, and zero slope ponds.

Hard paving can run flatter because it is true and smooth. Concrete and asphalt commonly hold a minimum around 1 percent, with 2 percent the comfortable target, and a finished slab can move water at 1 percent where a lawn at the same grade would pond. The other end of the range matters too. The steepest grade you can mow safely with a walk-behind or rider is commonly 3:1, a 33 percent slope, with anything steeper handed off to ground cover, terracing, or a wall, because a 2:1 bank is a non-mowable, erosion-prone face.

So the band you grade lawns into is narrow on both ends. Flatter than 2 percent and it ponds. Steeper than 3:1 and it cannot be mowed and it erodes. Most of the yard wants to land between those, with the steeper grades reserved for swales and transitions where you accept the maintenance to get the fall you need. These are common practice targets, not a single code number, so the civil drawings and the local grading standard govern the actual values on a permitted job.

Reading grades: elevations, contours, and the benchmark

A grading plan talks in elevations, and the whole sheet hangs off one fixed point: the benchmark. The benchmark is a known elevation, an iron pin, a manhole rim, a marked spot the survey ties to, and every other number on the plan is measured up or down from it. Lose the benchmark or shoot from a different one halfway through and your finish grades are off by whatever the two points differ, which is how a site gets graded perfectly to the wrong datum.

Spot elevations are the called-out numbers at specific points, the corners, the drains, the high and low points. Contours are the lines connecting equal elevations, and reading them is reading the shape of the water: lines close together mean steep, lines far apart mean flat, and a contour that points uphill is a swale, while one that points downhill is a ridge. Finish grade is the surface when the job is done. Rough grade is where you leave it before topsoil and finish, usually set a few inches low to leave room for the topsoil that carries the finish slope.

Cut and fill is the bookkeeping of dirt. Cut is where you take soil away to drop the grade, fill is where you add it to raise the grade, and a balanced site moves the cut into the fill so you neither haul off nor truck in. You shoot the grades with a laser level and a rod for most site work, a rotating laser and a receiver on a grade rod reading the cut or fill at each point, or a builder's level or transit for shorter work, or GPS and machine control on larger sites. Whatever the tool, the discipline is the same: one benchmark, checked, and every grade referenced back to it.

Swales: the graded channel that carries the water

A swale is a shallow, graded channel, usually vegetated, that collects sheet flow and carries it along a controlled path to where you want it to go. It is the workhorse of site drainage. When you cannot fall straight away from the building all the way to the outlet, you fall to a swale and the swale carries the water the rest of the way, around the structure, along a property line, or to a drain or a daylight point.

A swale has two slopes, and people only think about one. The cross slope is the side walls tipping water into the bottom, broad and gentle so it is mowable and stable, often around 4:1 or flatter on the banks. The longitudinal slope is the fall along the flow line, the bottom of the channel running downhill so the water actually moves. That flow line commonly wants about 1 to 2 percent. Too flat, under roughly 1 to 1.5 percent, and the swale ponds and grows cattails instead of carrying water, which is why some standards call for an underdrain below a flat swale. Too steep and the flow speeds up enough to scour the channel.

Keep the swale broad and shallow rather than narrow and deep. A wide, gently dished swale spreads the flow, stays as sheet flow longer, mows like the rest of the lawn, and disappears into the yard. A narrow, steep-sided ditch concentrates the water, erodes, and reads as a scar. The dry swale is the same idea with a gravel-and-underdrain section below the grass for sites where the surface alone cannot move or infiltrate the water fast enough. Either way the swale is graded, checked with a level along the flow line, and given a real outlet at the low end, because a swale that carries water to a dead flat spot just relocates the pond.

Sheet flow versus concentrated flow

Water moves two ways across a site, and the whole game is keeping it in the gentle one as long as you can. Sheet flow is a thin, broad film of water moving evenly across a surface, slow and shallow, the way rain runs off a properly graded lawn. Concentrated flow is water gathered into a stream, a channel, a pipe, or the rut it cut itself, moving fast and deep. Sheet flow is harmless. Concentrated flow is where erosion lives.

The reason is velocity and volume in one place. Spread a storm across a whole slope as a film and no single spot sees much water or much speed. Funnel that same storm into a 2 ft wide channel and the velocity climbs, the water picks up energy, and energy moving over soil is erosion. Every point where flow concentrates, the inlet, the head of a swale, the spot where two slopes meet, the end of a downspout, is a point you have to protect, because that is where the soil leaves.

So grade to keep it sheet, and where it has to concentrate, plan for it. Spread the discharge back out where you can with a level spreader or a wide apron. Armor the points where you cannot, with turf reinforcement, rip-rap, or a hard inlet. The mistake is letting flow concentrate by accident, in a low spot nobody graded out or at a downspout dumping on bare soil, and then chasing the gully it cuts. You do not fight the gully. You go back and find where the water concentrated and either spread it or armor it.

What is a French drain?

A French drain is a gravel-filled trench with a perforated pipe in the bottom, wrapped in filter fabric, that collects subsurface and surface water and carries it underground to an outlet. It is how you drain water you cannot grade away on the surface: a chronically wet area, water seeping out of a slope, the soggy yard that will not dry between rains. The water enters through the gravel and the pipe perforations, runs down the pipe, and leaves at the low end.

The slope is what makes it work, and it is the most common thing done wrong. The pipe needs fall along its length, commonly a minimum of about 1 percent, which is 1/8 in per foot, with 2 percent better where you have the depth for it. A French drain laid flat is a buried gravel trench that holds water, not a drain. It has to fall continuously from the high end to the outlet, checked with a level as you lay the pipe, not eyeballed in the trench.

The fabric and the outlet are the other two halves. Wrap the gravel envelope in non-woven geotextile so soil fines cannot migrate in and silt up the voids, which is the slow failure that kills a French drain in a few years, and use clean angular stone, commonly 3/4 in washed, not pea gravel that packs tight. The pipe is perforated, often a rigid PVC with holes or a sock-wrapped flexible pipe, and it must daylight at a lower elevation or tie into a drain that does. Add a cleanout at the high end or at a bend so you can flush it. A French drain with no fall and no outlet is the most expensive way there is to bury a problem in your own yard.

The footing drain and the foundation

The footing drain, the foundation drain, is a perforated pipe run in gravel around the outside of the footing to catch groundwater before it builds against the wall. It is the subsurface partner to the surface grade. The grade keeps surface water off the foundation, and the footing drain handles the water already in the soil, relieving the hydrostatic pressure that pushes water through the wall and cracks it.

It is the same construction as a French drain, sized and placed for the foundation. Perforated pipe at or just below the footing, surrounded by clean stone, wrapped or covered in filter fabric, sloped to fall around the building to a daylight outlet, a sump, or a storm connection. On a basement or a wet site it is not optional, and it is buried for the life of the building, so it gets done right the one time the trench is open or it does not get done at all.

The detail that fails is the connection between the surface and the subsurface water. Crews tie the downspouts into the footing drain to save a trench, and now every roof storm is pumped straight to the wall the footing drain exists to protect, overwhelming it and surcharging the gravel against the foundation. Keep roof water on its own line to its own outlet. The footing drain is for groundwater, not for the roof.

Catch basins, area drains, and inlets

When water has to be collected from a low point and carried off in pipe, you set an inlet. A catch basin is a box set into the grade with a grate on top and a sump below the pipe outlet, sized to catch surface water at a low point and drop it into a solid pipe that carries it to the outlet. The sump is the working part: it sits below the outlet pipe so sediment and debris settle in the bottom instead of washing down the line and clogging it. You clean the sump, not the buried pipe.

An area drain is the smaller version, a grate over a catch box in a planting bed, a courtyard, a patio low point, draining a defined area into pipe. Both are the answer where you cannot grade water away on the surface, a fenced low corner, a sunken patio, a courtyard between buildings, and both live or die on the pipe having fall to a real outlet. The grate goes at the true low point, set slightly below the surrounding grade so water runs to it, not past it. A grate set high is a grate the water sheets around.

The pipe network is solid, not perforated, because its job is to carry collected water, not to gather more along the way. It needs continuous fall to the outlet, commonly around 1 percent or more, and it benefits from a cleanout at the upstream end and at bends. The downspout often ties in here, into a catch basin or directly to the pipe, and at the discharge end a pop-up emitter lets the water out at grade and closes when flow stops so it does not become a chipmunk door. The whole system is only as good as where it ends, which is the outlet, again.

Downspouts and roof water

Roof water is the biggest single load of water on most sites, and the downspout that dumps it at the foundation is the number-one cause of a wet basement. A roof gathers the rain off a large area and concentrates it at a few downspouts, and a downspout discharging at the base of the wall is pouring that whole concentrated load into the exact soil the foundation grade is trying to keep dry. Fix the downspouts and you fix most residential water problems before you grade anything else.

Get the water away from the wall. The simple version is a downspout extension carrying the discharge out past the foundation backfill, commonly a minimum of 4 to 6 ft and ideally closer to 10 ft, onto grade that falls away. The buried version is a solid pipe from the downspout run underground to a pop-up emitter or a drain at the low end of the yard, which is cleaner and gets the water farther but has to have fall and an outlet like any other pipe. Either way, the discharge lands on positive grade, never on a flat or back-sloped spot where it just soaks in next to the house.

The buried roof line is solid pipe to its own outlet, kept separate from the footing drain. The trap to avoid is the popular shortcut of running the downspouts into the perforated footing drain or a gravel pit at the wall, which delivers the roof storm to the foundation through the very drain meant to protect it. Roof water gets its own dedicated, sloped, solid line to daylight. That separation is the difference between a downspout system that protects the foundation and one that floods it.

Retaining walls and the grade change

A retaining wall holds a grade change, and the load that fails it is usually not the soil, it is the water in the soil. Water collecting behind a wall builds hydrostatic pressure that can double or triple the lateral load the wall has to resist, and it freezes and expands on top of that. A wall that bows, leans, or blows out almost always drained badly, not built weak. So drainage behind the wall is not a finishing detail. It is the structural design.

The drainage behind a wall is a system. Clean, free-draining gravel backfill against the wall instead of the native soil, so water moves down through it fast rather than saturating and pushing. A perforated drain pipe at the base of that gravel, the weeping tile, sloped to carry the collected water to an outlet at the end of the wall. Filter fabric between the gravel and the retained soil so fines do not migrate in and clog it. And weep holes through the face on segmental and masonry walls, commonly spaced a few feet apart, to let any water that reaches the face escape rather than build. The pipe needs fall and an outlet, same as every other drain on the site.

The terrace is the alternative to one tall wall. Two shorter walls stepped up a slope, with a planted bench between them, break the height into pieces no single wall has to hold, and the bench can carry its own swale to manage the water across the face instead of behind one wall. Tall walls cross into engineered territory, where the height, the surcharge, and the soil drive a designed wall with designed drainage, so the geotech and the wall design govern above the heights the manufacturer's general detail covers.

Soil and infiltration: why clay and sand grade differently

How fast a soil takes water in decides how much you can drain into the ground and how much you have to move across the surface. Sandy soils have large pores and a fast intake rate, so they drink water and a yard on sand can often shed and infiltrate without much pipe. Clay soils are dense and fine, with a slow intake rate, so water sits on top of clay and runs off, and a yard on clay ponds where the same grade on sand would drain.

That difference changes how you grade. On clay, you cannot rely on the ground to soak up water, so you need more positive surface grade, more swales, and more pipe to physically carry the water off, because infiltration will not bail you out. On sand, gentler grades and infiltration features like dry wells and rain gardens can do real work. Grading a clay site like a sand site is a classic way to build a yard that ponds: the grade looks fine on paper, but the soil never accepts the water the plan assumed it would.

Compaction is the hidden version of the same problem. Construction traffic, stockpiles, and heavy equipment compact the subgrade and even decent soil until its intake rate collapses, so a site that drained fine as a field ponds after it is built because the soil under the new lawn is packed to the density of a parking lot. The fix is to break up and amend the compacted topsoil zone before the finish grade and sod go down, and to keep equipment off the areas meant to infiltrate. A percolation test tells you what you actually have, rather than what the soil map says you should have.

Erosion control and stabilizing a slope

Bare soil on a slope erodes, and the steeper and longer the slope, the faster it goes, because erosion is velocity over loose soil and slope makes velocity. The defense is cover. Get something living or holding on the soil before the rain does the cutting: seed and mulch on a gentle grade, sod for instant cover, and an erosion-control blanket or turf reinforcement mat on a steeper slope where seed alone would wash off before it roots. The blanket holds the seed and the soil while the roots take, which is the only thing that stabilizes a slope long term.

Match the protection to the velocity. Gentle, short slopes hold with seed and mulch. Steeper slopes and swale bottoms that carry flow need a blanket or a mat rated for the velocity they will see. Where concentrated flow leaves a pipe or a swale and hits soil, you armor the spot with rip-rap, a bed of graded stone that breaks the energy of the water and spreads it before it touches dirt. The rip-rap apron at an outlet is not optional on anything with real flow. It is the difference between a drain that discharges and a drain that digs a crater.

During construction, the erosion control is a regulated set of best management practices. The silt fence, a fabric barrier staked along the down-slope edge, holds sediment on the site so it does not wash into the street, the storm system, or the neighbor's lot. Inlet protection, stabilized construction entrances, and check dams in swales do the same job at other points. These are required on permitted sites under the local stormwater and erosion rules, tied to the EPA construction stormwater program, and they are inspected. The principle outlasts the permit: keep the soil covered and keep the sediment on your own ground.

Stormwater and the legal outlet

Every drainage system ends somewhere, and that somewhere has to be legal to drain to. You cannot collect a site's water and discharge it onto the neighbor's lot, into a wetland, or in a way that floods downstream, and doing it is how a grading job turns into a lawsuit. The legal outlet is a point you are allowed to discharge to: a public storm system you are permitted to connect to, a drainage easement, a natural watercourse, a swale that carries it to one of those, or infiltration back into your own ground.

The rules vary by jurisdiction, so they govern the job. Many places limit how much you can change the rate and volume of water leaving a site, which is why detention and retention exist. A detention basin holds the storm and releases it slowly, so the peak leaving your site is no worse than before you built. A retention basin or an infiltration system holds it and lets it soak in, releasing little or nothing. Which one a site needs, and how big, comes from the local stormwater code and the civil design, not from a rule of thumb.

On anything beyond a simple residential regrade, this is permitted, engineered work. The civil drawings and the grading and drainage permit set the outlet, the detention, and the discharge rate, and the local stormwater authority and the AHJ enforce them. The field job is to build to those drawings and confirm the outlet exists and works before you grade everything to drain to it. A beautifully graded site that drains to a point you have no right to use is not finished. It is a problem with a deadline.

How do you fix a yard that ponds?

You fix a ponding yard by finding why the low spot is low and giving the water a path out, which almost always means re-grading to a positive slope or adding a drain with a real outlet. First, find the actual low point and the actual high point with a level, not by eye, because standing water hides the true grade and the spot that looks lowest often is not. Then decide whether the water can be graded out to a lower point on the lot or whether it has to be collected and piped.

Most ponding traces to one of a short list. The grade is flat or negative where it should fall, often from settled fill or a patio or addition that interrupted the original drainage. The downspouts dump at the low spot. The soil is compacted clay that will not infiltrate. Or an old drain has silted up and lost its fall. The fix follows the cause: re-grade to 2 percent away on a lawn low spot, extend the downspouts, break up and amend compacted soil, or set a catch basin at the low point and pipe it to an outlet. A French drain helps where the water is subsurface, but a French drain with no fall and no outlet just moves the pond underground.

The callback case is the patio that ponds or back-pitches toward the house. A paver or slab surface graded flat, or settled until it tips the wrong way, holds water against the door or the wall, and on pavers it works down into the joints and bedding on top of it. The real fix is to lift and re-lay or re-grade the surface to fall away at the proper slope, because a sealer or a strip of caulk does not move water, slope does. The same minimum applies as anywhere else: about 1 to 2 percent on the hard surface, away from the structure, to an outlet.

The accessible route grade where a walk is involved

Where a walkway is part of an accessible route, the grading has to satisfy the accessibility limits at the same time it sheds water, and the two pull against each other. An accessible route commonly caps the running slope, the grade in the direction of travel, at 5 percent, which is 1:20, and the cross slope, perpendicular to travel, at 2 percent, which is 1:48. Run a walk steeper than 5 percent in the direction of travel and it becomes a ramp, with its own handrail, landing, and length rules.

The conflict is the cross slope. You want a walk to shed water across itself, but the accessible cross slope is held to about 2 percent, so you have exactly that 2 percent to drain the surface and not a bit more. Grade it flatter and it ponds and ices. Grade it steeper to drain better and it fails the cross-slope limit and becomes a hazard for a wheelchair or a cane. So the accessible walk is graded right at the 2 percent cross slope, drained to the side, with the surrounding grade picking the water up off the edge.

These figures come from the ADA Standards for Accessible Design and the related public right-of-way guidance, and they are enforceable where the route is required to be accessible, with state and local amendments on top. Confirm the limits and the conditions against the standard that governs the project rather than building to memory, because the tolerances are tight and an accessible route that misses the slope by a percent is a route that fails inspection.

Field example: grading a wet backyard to drain

A backyard ponds along the back of the house after every rain. The walkout grade behind the house reads dead flat by the level, and the natural low point of the lot is a back corner 80 ft away that sits about 14 in lower than the house grade. The downspouts dump at the wall. That is the whole problem in three measurements.

Work the numbers. To fall away from the house at the lawn minimum of 2 percent, the first 10 ft off the wall needs about 2 1/2 in of drop, and you want more than that against settlement, so you grade the first 10 ft at closer to 5 percent, about 6 in of fall, then carry the lawn out at 2 percent toward a swale. The swale runs the 70 ft from there to the low corner. At a 1.5 percent flow line that is about 12 1/2 in of fall over 70 ft, which the 14 in of available drop covers with room for the outlet. The downspouts get buried lines run to pop-up emitters out in the yard, discharging onto the swale path, not at the wall.

The outlet is the corner, which on this lot drains to a roadside ditch the property already drains to legally, so no new permit issue. The clay subgrade gets the compacted topsoil broken up and amended before sod so it accepts what the swale does not carry off. Every number came off the level and the available fall, not a guess, and the record of those grades is what proves the yard was built to drain when someone asks a year from now.

What to document

A grading job is buried the day it is finished, so the record is the only thing that proves it was built to drain when the question comes a year later with water in the basement. Write down the grades and the drainage while you can still see them.

Capture the finish grade slope and direction for each area, the benchmark and datum the grades were shot from, the swales with their flow-line slope and where they run, every drain with its type and the outlet it discharges to, the French drain or footing drain slope, the downspout treatment, and the legal outlet the whole site drains to. If you upsized a drain, added a swale, or amended compacted soil, note why. The next person standing in a wet yard needs to know where the water was supposed to go and who decided the path.

Common mistakes

• Leaving the grade flat or pitched back toward the foundation, or grading fresh fill that settles to negative within a year.
• Discharging downspouts at the foundation, or tying them into the perforated footing drain that protects the wall.
• Grading a swale too flat, under about 1 percent, so it ponds and grows cattails instead of carrying water.
• Laying a French drain with no fall, no fabric, or no outlet, so it becomes a buried gravel trench that holds water.
• Grading a clay site like a sand site, trusting infiltration that the soil will never deliver.
• Building a drain or swale that carries water to a dead flat spot or the property line instead of a legal outlet.
• Running concentrated flow onto bare soil with no rip-rap apron or spreader, then chasing the gully it cuts.
• Shooting grades off two different benchmarks, or losing the datum partway through the job.

Field checklist

Standards and references

The foundation grade rule comes from the building code. The IRC at the foundation drainage section, commonly R401.3, calls for the grade to fall away from the building, with the widely cited figure of 6 in within the first 10 ft, an exception allowing swales or drains where that fall is impossible, and a reduced slope, commonly 2 percent, for impervious surfaces near the building. The IBC carries the parallel requirement for commercial work. Confirm the exact section, figures, and exceptions against the adopted code edition and any local amendment, because the numbers and wording shift between cycles.

Above the building code sit the civil drawings and the local grading and stormwater code, and on a permitted site they govern the actual grades, the detention, and the outlet. The geotechnical report governs the soil questions, the infiltration the design can count on, the retaining wall heights that need engineering, and the compaction. The minimum lawn and paving slopes, the swale flow line, the French drain slope, and the maximum mowable grade in this guide are common practice targets that good drainage design uses, not single code mandates, so let the civil design and the local standard override them whenever they are stricter.

Erosion and sediment control on construction sites is regulated under the local stormwater program tied to the EPA construction stormwater rules, with the silt fence, inlet protection, and stabilized entrances as the standard best management practices that are required and inspected. Accessible routes follow the ADA Standards for Accessible Design and the public right-of-way guidance for the 5 percent running and 2 percent cross-slope limits. Cite the document that controls the point, confirm the edition the jurisdiction has adopted, and let the permit and the engineered drawings win over any rule of thumb.

Units, terms, and conversions

Drainage slope reads three ways across a survey, a spec, and a contractor's tape, and they all mean the same fall. A grade can be a percent, a ratio, or a fall per foot, so the same slope shows up as 2 percent, as 1:50, or as 1/4 in per foot depending on who wrote it down.

Percent slope is the vertical fall divided by the horizontal run, times 100, so 2 ft of drop over 100 ft is 2 percent. As fall per foot, 1 percent is about 1/8 in per foot and 2 percent is about 1/4 in per foot. As a ratio, slope is written run to rise, so 3:1 is 3 ft of run for 1 ft of fall, which is about 33 percent, and the bigger the first number the gentler the slope. Elevations and grades are in feet and decimal feet on a survey but in feet and inches on a tape, which is its own conversion to keep straight on site.

Positive drainage

Grade that falls away from a structure and toward an outlet, so water sheds instead of ponding or running back

Slope (percent)

Vertical fall over horizontal run times 100; 2 percent is 1/4 in per foot, or 2 ft of drop in 100 ft

Swale

A shallow, usually vegetated graded channel that collects sheet flow and carries it to an outlet at a 1 to 2 percent flow line

French drain

A fabric-wrapped, gravel-filled trench with a perforated pipe, sloped at least about 1 percent to a daylight outlet

Sheet flow

A thin, broad film of water moving evenly across a surface, the gentle flow grading tries to keep, versus concentrated flow that erodes

Finish grade

The surface elevation when the job is done, carrying the drainage slope; rough grade is left low for topsoil

Benchmark / datum

The fixed known elevation every grade on the site is measured up or down from

Legal outlet

A point the site is allowed to discharge to, a storm system, easement, watercourse, or its own ground, not the neighbor's lot

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