Yard Drainage: Moisture Control in Foundation Repair

Moisture Control

The basic goal of yard drainage is moisture control. Here I will examine moisture as a key component of natural processes on earth. I will discuss the important role of moisture in the soil while showing how moisture works to recycle everything back to the soil. Here I will discuss how moisture control compliments foundation repair objectives. On this page, I discuss the basic important tasks of a yard drainage project and I provide guidelines for getting the job done correctly. Here is the “what” and the “how-to” advice for anybody who has to deal with foundation repair and yard drainage.

Yard Drainage Problems

Examples of yard drainage problems include flooding, erosion, sedimentation, piping, ponding, negative drainage, faulty grade, seepage, soil saturation, soil-moisture fluctuation, excessive humidity, and wicking. These problems can create or aggravate a variety of undesirable soil conditions including soil scars, slope creep, landslide, soil consolidation, soil subsidence, soil shrinkage and soil expansion. In addition, poor yard drainage control can cause erosion, efflorescence, pop-outs, spalling, and cracking of concrete, block, brick, stonework and stucco whether in the form of building foundation walls, concrete slabs, sidewalks, patios, retaining walls, fencing, or other hardscapes.

Adverse yard drainage can also facilitate damage and destruction of metals including reinforcing steel, anchor bolts, post bases, fence poles, wrought iron, aluminum thresholds, window frames, utility enclosures, and gas pipes. Finally, poor yard drainage can provide an environment for pests including moss, mold, mildew, dry rot, mosquitoes, termites, and rodents to name just a few.

Moisture: Agent of Mobility

Moisture is the medium of life and is virtually everywhere in our environment. Moisture is nature’s agent of mobility giving the chemical elements a place and a way to become active and to be modified as they interact among themselves. Moisture also plays an active role in the breakdown and recycling of earth materials. Moisture makes it all happen!

Water is the liquid phase of Moisture. Due to the temperature range on earth, water easily becomes ice (a solid) or water vapor (a gas), assuming quite different properties in each of these three forms. As moisture travels around the “hydrosphere”, changing back and forth between the three states, it molds and modifies the earth. Humans also mold and modify the earth. When we do so, we try to create structures which are durable and stable. The ultimate success of our efforts in this regard will depend largely upon how well we apply our knowledge of certain earth processes. This leads me to a discussion of weathering.

Moisture and Weathering

Moisture plays a key roll in the weathering of rock, eventually transforming solid rock into small particles. When water vapor in the atmosphere condenses and falls on rocks in the form of precipitation, mineral particles within the rock are mechanically dislodged and then carried away by the liquid water. Moisture collecting in tiny cracks in rock will cause pressure within the cracks, breaking the rock when temperatures drop and water expands to become ice.

Our human-made infrastructure is also subject to the cracking and wearing away caused by precipitation. After a few winters, concrete walks and driveways begin to shed their surfaces, exposing and dislodging aggregate and leaving small holes on the pavement surface. These problems can be mitigated through the use of high-quality concrete, the application of protective coatings, and the proper management of yard drainage.

Chemistry Happens

Chemical weathering is an ongoing process in nature, requiring only the daily variations in temperature and humidity to proceed. As the air cools at night, humid air gives up moisture (condensation). As the air warms during the day, moisture evaporates and returns to the atmosphere. Moisture condensing on the surface of rock (or concrete) will dissolve certain chemical compounds which then travel with the liquid water in solution. These dissolved compounds will be deposited elsewhere when the moisture evaporates.

Here is an example of how poor yard drainage destroys concrete: Because of poor drainage, water ponds on the patio after it rains. After the pond evaporates, a white powder appears on the surface of the concrete. This powder is called efflorescence- mineral deposits which are the residue when the moisture evaporates. Nature is turning your concrete into dust.

Minerals in contact with moisture can become hydrated, changing their physical size and structure. When certain chemicals become dissolved, the solution becomes acidic and the weathering process accelerates. Corrosive solutions can easily penetrate concrete, leaching soluble minerals. Minerals in exposed rock or concrete will react with oxygen in the atmosphere (oxidation). When this happens to human-made metals, we call it rust.

Moisture will attack and destroy concrete with reinforcing steel or “rebar” in a process called spalling. Moisture seeping into the concrete will cause corrosion and expansion of the steel. The pressure causes pieces of the concrete to pop out- exposing the rebar and concrete to further damage and threatening the integrity of the structure. Metal pipes and posts which are embedded in concrete are similarly destroyed. These problems can be minimized by keeping all embedded rebar at least two inches from the concrete surface. All exposed metals should be protected from corrosion with proper coatings and maintenance. Equally important, is the control of yard drainage so that moisture does not accumulate around these sensitive areas.

Earth Processes Poolside

Weathering is part of an earth process called erosion involving the transportation of mineral particles from one place to another. Running water, acting with the force of gravity, is an important agent of erosion, able to transport large quantities of sediment from rocky hillsides down to broad valleys and ultimately to the ocean floor. A steep gradient and a heavy rainstorm will create a high volume of running water with high energy, abrading the slope and keeping minerals in suspension. As the gradient flattens out and stream volume is reduced, the minerals fall out of suspension and are deposited in a process called sedimentation.

Erosion and sedimentation are important considerations in the construction of yard drainage improvments. A few years ago I tackled a yard drainage project after a series of heavy rainstorms. There was an over-steep slope going up behind a residence with a swimming pool in between. What happened during the rains was a great example of how running water can transport large volumes of material from one place to another. Unfortunately for the homeowner, the water transported a large volume of sediment from the face of the hillside to the bottom of the swimming pool!

Problems of slope stability require sound construction and maintenance practices. Fill embankments should never be steeper than a 2 (horizontal) to 1 (vertical) slope ratio. Irrigation of on-slope vegetation should be kept to a minimum. Equally important, surface yard drainage from above should never be permitted to flow over the face of the slope.

Slope Protection

Proper control of yard drainage requires that we avoid erosion for obvious reasons. Any sloping ground on your site is a candidate for erosion and bare soil is the most erosion-prone. Planted slopes can also have erosion problems if plants have shallow root systems and require heavy irrigation. For this reason, sloping ground should be landscaped with deep-rooting plants which are drought-tolerant (require little or no irrigation). There are a wide variety of slope-protection systems which can be used to complement or replace vegetation. There are also a few important guidelines for grading and drainage control which should underlie any program of erosion control. Let’s talk about them:

A sound yard drainage plan will direct all surface drainage away from the top of any steep-sloping ground on the property. If runoff water must go down the slope face, it should do so within the confines of a drainage conduit such as a pipe or concrete swale. Surface runoff which is draining toward the top of a slope can be collected in a “brow ditch”. Water in the brow ditch would then be directed to flow into the concrete swale. If a down-pipe is used, water in the brow ditch would be collected in a grated sump box from which a buried down-pipe would transport the water to the base of the slope for dispersal into the storm drain system or an energy-dissipating structure such as a concrete box filled with rip-rap.

Concrete ditches are quite common around hillside developments designed by civil engineers. I have worked on repair projects for a number of these and one thing I can say without hesitation: all of these type drainage control systems require maintenance. The ditches will inevitably become cracked and the sumps will fill with debris causing eroding storm water to flow where it is not supposed to. Regular inspection and maintenance will prevent major problems in the future.

Foundation Soils

An important earth process to for our discussion of yard drainage is “soil building”. Nature starts making soil whenever earth materials come in contact with the atmosphere. The soil mineral particles, together with air and moisture in and among the particles, create an environment for microbes to grow. These bacteria, molds, spores and fungi give life to the soil. Seeds of pioneer species of plants find their way into the soil and germinate when conditions are right. The plant roots interact with the microbes and deliver carbon, which they get from the air, in exchange for nitrogen and other important nutrients. As plants reproduce and die, their remains become incorporated back into the soil (decomposition) and become food for a variety of life forms including ants and termites which have taken up residence. The soil uses everything to build new life. Soil is the foundation for all terrestrial ecosystems including the human ecosystem but nothing happens without moisture.

In our discussions of yard drainage and foundation repair, soil is a very important component. The geotechnical term for live soil as I have described it above is “top soil”- that portion of the soil which is rich in organic matter. In a typical soil profile, the material beneath the topsoil (subsoil) consists of weathered rock-clays, silts, sands and gravels. At some greater depth will be a “formational” material or “bedrock”. These would include such rock formations as conglomerate, sandstone, shale, limestone, and granite. In general, topsoil does not provide adequate support for buildings and other structures which must be founded on the subsoil or bedrock materials. In that sense, the topsoil is a nuisance which must be removed and should not be incorporated into any grading or backfill operations. Topsoil is often stockpiled during grading to be spread out again where landscaping planting has been proposed.

The soil building process is good for gardens but bad for buildings. Remember that living soil is an agent of decomposition. Building materials, especially wood, are food for soil. A wooden house is a feast for a healthy soil and moisture is the key to the front door. A principal goal of yard drainage must be to protect the structures on the property from moisture acting upon the soils which surround and support the building foundations.

Positive Drainage

Good yard drainage requires that all surface drainage be conducted away from the foundations of buildings and other structures (positive drainage). Build high and dry and avoid “negative" yard drainage. Storm water can erode and undermine hillside foundations. Water ponding near foundations can saturate foundation soils and reduce their capacity to support the structure.

During periods of heavy rain, “expansive” foundation soils can swell and actually lift the structure up. During dry periods, this process will reverse and the structure will settle as the soils dry out and shrink. It is possible to mitigate this condition by protecting those moisture-sensitive soils by creating and maintaining positive yard drainage.

Ponding at the foundation perimeter can also accelerate the weathering processes which I have discussed above. Concrete, block, brick and stucco will actually soak up water like a wick. The amount of wicking depends upon the volume of ponding water in contact and the properties of the particular material. Stucco is particularly prone to wicking.

Attack of the Living Soil

Modern building codes require that the base of a stucco exterior be held six inches above grade and terminate there with a metal “drip screed”, sometimes called FHA screed. The screed is usually attached to the wood sill plate prior to application of the wire lath. The stucco scratch and brown coats are then finished to the screed. Unfortunately, with many older homes, the stucco was brought down to or below grade with soil backfill placed against it. This practice has been the cause of many foundation repair jobs involving mold, dry rot, and severe termite damage- the attack of the living soil! Soil moisture from ponding in the back fill will wick up the stucco and create a moist environment for these and other nasty problems.

On numerous yard drainage jobs on older homes, I have recommended that the stucco be removed to expose the base of the wall framing with new drip screed to be attached. The best way to remove the stucco is to break it with a single jack (a one-hand sledge) and then use a metal claw hammer to peal it off the wire. The existing wire should be preserved for a few inches below the remaining stucco so the new lath can be tied in. Do not cut the stucco with a masonry blade. An irregular break will make it much easier to hide the splice when you put on the new stucco. This retrofit can be done by matching the existing color coat but the professional way is to put a new color coat on the entire building. This may be attractive to the customer if the existing stucco is painted or if it is old and weathered.

Crawling in the Mud

When yard drainage is ponding at the perimeter of a “pier and beam” foundation, there is the potential for that water to seep into the crawl space creating chronic moisture and related problems. This is a particular concern with the so-called “low profile” foundation. In an attempt to lower the floor level, the builder elevates the perimeter grade or excavates the crawl space area or both.

With the low profile foundation, the crawl space can become a large bog, attracting moisture (and trouble) from all directions. I have inspected a few of these and crawled out looking like the monster from the black lagoon! The best way to remove this moisture is to install a sub drain, also called a “French” drain, around the entire perimeter of the structure. I have put in my share of these systems and it can be a real chore- especially if you must remove lots of hardscape and other perimeter improvements. Sometimes, if the crawl space is too low, a sump and pump must be installed to remove the water once it is collected. I discuss the details of a French drain system on another page of this site.

What most folks living over a crawl space don’t realize is that a large percentage of air inside the house comes up from the crawl space. Bad air in the crawl space means indoor pollution and the many associated health problems. Air coming from a damp crawl space is humid air. Moisture in the air condenses on indoor surfaces and creates an environment for mold spores and mildew which are also living down below. Good yard drainage includes proper ventilation to the crawl space. Dryer outside air circulating in the crawl space will help to remove moisture. Ventilation is very important in this regard and a thorough drainage and seepage investigation will include an assessment of crawl space ventilation. If there are not foundation vents every 6 feet or so around the entire perimeter, I will recommend that new vents be added as part of the drainage improvement project. These vents can be easily added when adding a drip screed such as discussed in the previous section.

Earth-Wood Contact- A Non-Solution

Out there among well-meaning construction professionals, there are a few “non-solutions” that I need to mention here. One of these is something called a “curb wall”. Often a property owner will wish to import topsoil and plant flowers around the building. Perhaps someone is just trying to create positive yard drainage. In either case, soil is brought in and placed around the building perimeter. But now the finish grade is elevated above the top of the concrete slab or stem wall and the earth right up against the wood siding. This condition is known as earth-wood contact- something which subterranean termites love and termite inspectors will not pass.

In these situations, some termite inspectors will recommend a curb wall. The curb wall is a concrete curb which is poured on grade as a separation between the wood siding (or stucco as the case may be) and the adjacent earth. I have seen many of these in action and believe me they are a bad idea. Why? Moisture is why. Remember our discussion of wicking? The concrete curb wall is now a moisture wick along the entire building perimeter. Every time it rains or you water the flower bed, the curb wall soaks up moisture from the soil and holds it up against the wood. The result is dry rot. What is the correct yard drainage solution?

Pressure Treated Wood?

First, never put soil against wood. The exception is when the wood has been pressure treated to resist all the moisture-related damage we have been discussing. And even then I would think twice. Wood preservative chemicals can be nasty for the installer and for the environment. Also, some of the treatments out there flat don’t work. Believe me I know. I once had to replace pressure-treated poles which I myself had installed to support a big fancy deck. I poured concrete piers to replace the poles and now I don’t worry about another callback.

The correct solution to earth-wood contact is either 1. Lower the perimeter grade or if this is not feasible, then 2. Remove the wood and install new concrete. The correct solution is not always the cheap solution but in the long run it can save thousands of dollars on water damage repairs. Upon completion of the yard drainage improvements, the perimeter grade should slope away from the foundation around the entire building with no ponding water.

The Protective Apron

Recalling our discussion of the living soil, I must make my usual pitch to landscapers and gardeners who love to surround your buildings with planters filled with rich soil and lush vegetation. I can’t tell you how many yard drainage, moisture and seepage problems I have solved by convincing my customer to tear out the planters and install hardscape (concrete, brick, flagstone, etc.) walks and patios around the building perimeter.

By installing a “protective apron”, you accomplish several important yard drainage objectives. The apron creates a protective buffer between the soil and the building while moderating moisture fluctuations and armoring the soil against erosion. Irrigation is no longer being introduced into the foundation soils and the roots from plants and trees are no longer able to work under and damage footings and slabs. An added benefit is the improved access to perimeter improvements such as hose bibs, water heaters, ac condensers, gas meters, electric meters, etc. Finally, pots or box planters can now be placed on top of the new hardscape without worries about all the adverse problems of the in-ground planters. You get the best of both worlds!

Impervious Improvements

The challenge of yard drainage increases in proportion to the amount of yard area which is covered by improvements. For example, a vacant lot with 100 % soil, native vegetation and natural drainage contours is usually best left untouched. On a vacant lot, there are no improvements to protect while undisturbed soil with mature vegetation provides excellent erosion protection. Dig up plants and trees, disk or plow the field, grade in a road or a building pad and right away you have bought yourself the responsibility for higher rates of runoff and higher potential for erosion. Add buildings, driveways, walks and patios and the responsibility increases further.

Let’s say our example vacant lot is developed with 50% of the soil covered by improvements (buildings, brick, concrete, etc.) which are impervious to water. When rain falls, the water must run off the impervious surfaces until it finds its way to soil where it can begin to soak into the ground. When a storm brings 3 inches of rainfall to the property, the unimproved soil portion must now absorb the equivalent of 6 inches of rainfall. In addition, the runoff will not be uniform- due to gravity, it will become concentrated at various high-energy discharge zones and so that the demands on the soil in those zones will be greatly magnified.

Roof Gutters and Down Drains

Among the most common of high-energy discharge zones is the soil below the roof line of a building. During a rainstorm, roof runoff erodes the soil and creates a long muddy puddle. The falling water splatters mud on the siding. Often the solution is a system of roof gutters and down drains. It is now important to recognize that roof gutters do not eliminate the problem of concentrated flow. In fact, roof runoff has now been further concentrated to just a few points of high-energy discharge where erosion and ponding water will be even more intense.

Often the property owner will tolerate these zones of flooding so long as they do not interfere with access around the property and mud does not end up all over the driveway after each rainfall. If the down drain discharges into a planter behind a bush, it is “out of sight and out of mind”. I once inspected a property with a down drain which was way out of sight:

Piping in Sandy Soil

A couple wanted to buy a custom home with a nice view and a backyard deck where they could sit and enjoy the sunset. I was hired to inspect the property and pay special attention to the cracks in the breakfast nook and the odd configuration of the wood deck. After conducting a comprehensive inspection which included a floor-level survey and measurements of the deck, my attention became focused on a particular corner of the building. I crawled under the deck and made some excavations in the sandy soil near the problem corner.

What I found was a labyrinth of miniature underground caverns which extended under the building concrete spread footing away from the corner as well as down slope under the isolated concrete piers of the wood deck. The property owner did not appreciate the results of my detective work because my report killed the deal. I concluded that the corner roof down drain, which extended through a cutout in the deck, was discharging high volumes of water directly into the highly erosive sandy foundation soils supporting the building and the deck.

The underground caverns which I discovered are a phenomenon called “piping” (underground erosion) which typically occurs in certain sandy soils. I was not able to determine the location of the all the piping but it was obviously extensive and where observed, had undermined large volumes of foundation soils, thus explaining the significant settlement of the breakfast nook and wood deck which I had observed. I have seen many other instances where poor yard drainage practices were the cause of serious foundation repair problems.

Splash Block- A False Panacea

The above lesson concerning the drawbacks of downspouts is not exactly typical, but it goes to illustrate the potential damage that can occur when concentrated water is discharged into foundation soils. One common and inexpensive approach to down drain erosion is the “splash block”- a concrete pad placed directly under the bottom of the down drain. While the use of splash blocks in a yard drainage program does have the effect of dissipating the energy of the falling water, it does not address the perhaps more serious problem of yard drainage water accumulation in the foundation soils. In this regard, the “splash block” can be a false panacea.

In most yard drainage situations where moisture-related damage is an issue, I will recommend that all down drains be connected to underground pipes called “tightlines”. The term tightline is used to distinguish these pipes from “perforated pipes” which are used for underground or “French” drainage systems. Tightlines should be a minimum of 3 inches in diameter for residential yard drainage projects and may be significantly larger for commercial projects. A common specification for drain pipe on commercial yard drainage jobs is usually 4-inch or 6-inch PVC or ABS plastic, SDR35 which assures an appropriate wall thickness according to the pipe diameter. For residential yard drainage jobs, I have had good results with 3-inch or 4-inch "poly" with “belled ends”.

For temporary drainage protection or where pipe is run on the surface such as down a slope, I will use the corrugated plastic pipe, either 3-inch or 4-inch. I do not recommend the corrugated pipe for underground applications because silt will become trapped in the corrugations and this pipe is more easily damaged by roots. Drainage pipe and fittings is commonly available at irrigation specialty outlets where you will also usually get the best advice and service.

Using Area Drains

Another very common yard drainage improvement where ponding water and soil saturation is a concern would be a system of “area drains”. Only judgment and experience can tell you where to locate them and how many would be required on a particular yard drainage job. Keep in mind that fewer area drains are required on hardscape surfaces. The highest concentration of area drains will usually be around the building perimeters where I have spaced them as close as ten feet apart for lawns and planter areas.

Always use area drains which have a removable grate and a sump so that most sediment getting through the grate will settle in the sump and can be removed as part of a maintenance program. For most residential applications, plastic area drains on the order of six inches diameter will be adequate. For vehicle traffic areas, it will be necessary to get pre-cast concrete boxes with steel grates. The larger concrete drain boxes are very heavy and it is best to have them delivered and set into the hole you have prepared.

All underground drain pipes, whether connecting to area drains, or roof drainage, or French drainage systems should include cleanouts. A cleanout is a vertical pipe which extends above grade and ties into the drain pipe with a “sweep” so that in the future, if necessary, a snake or water jet can be fed into the system to remove clogs.

Rules of Proper Drainage

On a typical property with a building in the center, a proper yard drainage design should create a gradient from back to front. Backyard drainage breaks from a crown in the center and flows in gentle swales on both side of the building until it reaches the front yard where it reaches a concrete street gutter or earthen swale. Along the side-yards, the swale is usually centered between the building perimeter and the property line. Of course there are many variations on the yard drainage theme depending upon the natural topography, the shape of the property, the shape of the building, etc. However, the general idea is to keep the improvements high and dry.

Unfortunately, many properties have been developed without consideration of the rules of proper yard drainage. Even with a yard drainage plan, the reality does not always match up with what was intended by the designer. These are the type of properties with which I am most familiar and which call for creative and cost-effective solutions. It can be very expensive, if not impossible to completely re-grade a property after all the improvements have been put in place. Knowing the rules of proper yard drainage, we must seek creative solutions.

For example, I have often been able to mitigate negative yard drainage by locating area drains at low points where water is already accumulating. This is not the ideal but if you install enough area drains, you can dry up the property pretty well. Those area drains in lawn areas will require flat grates and those drains in planter areas will require atrium-type grates.

Drainage Layout

The yard drainage layout begins with a survey of the property. I make up a field drawing of the site, usually on the scale of twenty feet to the inch. I will even go to a smaller scale on larger yard drainage jobs. This is so that I can keep my drawing to a clipboard size. I use a builder’s level or site level to establish elevations around the property. I use the elevation of the building floor as my baseline or zero elevation. It is important to look for and measure the elevations and all potential points of discharge so that you know where your pipes have to go. If you find that grades are too low to achieve gravity flow, it may be necessary to modify the grading or in the worst case install a sump pump. A sump pump is always my last resort on a yard drainage job but I have put in a few over the years.

Curb Coring

Generally in urban areas, the water needs to end up in the street gutter. Many cheap operators and do-it-yourselfers are tempted to run underground pipes to daylight just in front of the sidewalk and let the outflow wash across the sidewalk onto the parkway or over the curb. Don’t do it. Chronic water on the sidewalk along with the silt and debris damages the sidewalk and breeds slippery moss which is a hazard to pedestrians. Hire a curb coring company to do it right.

Concrete curb coring is done with a diamond blade hole saw which runs in and out on a frame-and-gear assembly. Water is applied at the cutting edge to cool the blade. Once the hole is cut, a good curb coring service will install a length of pipe to extend under the sidewalk. This usually requires extending the coring barrel under the sidewalk to catch any extra concrete. The installed pipe should slope toward the street. Due to the normal pitch of the street down toward the gutter, this may be difficult to achieve. A good operator will know how to give you a pipe which is at least level so that the amount of sediment accumulating during operation will be kept to a minimum.

The number of curb holes needed depends upon the volume of the yard drainage which is being collected. On large commercial yard drainage jobs, a drainage engineer should be consulted. On most of my residential yard drainage jobs, I will install at least two and sometimes as many as four or five 3-inch curb holes. Often there is not room to core larger than 3-inch holes. If 4-inch pipe is used for the final tightline, the pipe should be split into at least two three-inch pipes for discharge through the curb.

Underground Locators

Before curb coring or any excavation can begin on a yard drainage job, the contractor should contact the free underground locating service available in the area. In California, it is USA (Underground Service Alert); in Arizona it is Bluestake. The service will notify all the underground utility companies who have facilities in or near the proposed excavation (which the contractor will delineate). The contractor should then have the option to meet with the locators at the site. Since the locator is only responsible to mark out their utilities, I like to meet with them at the site. That way I may be able to “con” them into using their equipment to locate some of the on-site underground which may not actually belong to their company.

The contractor should never trust the underground locators. Always hand “pothole” and physically locate all the important underground utilities before finalizing the trenching layout. Only after you have identified each utility for depth and orientation should you proceed.

Stakes for the Shovel Man

Before trenching for the yard drainage pipes, I lay out the trenches with offset wooden stakes. On each stake, I will use the builder’s level to shoot the top of the stake. I will then write the depth of the trench in inches as measured from the top of the stake to the bottom of the trench. During trenching, the shovel man can use his measuring tape to verify depth. Underground drain pipes should slope toward the point of discharge at no less than about one-half an inch per ten feet. With this in mind, I try to place my layout stakes on ten foot centers.

Any grass and other vegetation in the path of the proposed excavation or backfill should be carefully removed and placed in a shady spot for temporary storage during construction. The turf is cut in manageable squares and kept wet. Plant roots should be wrapped in burlap so that the soil stays in place while wetting with a hose. Significant savings on re-landscaping costs can be made by following this advice on all yard drainage jobs.

Hand or Machine Excavator?

Perhaps the most important decision on a yard drainage project is deciding how to excavate and handle the spoils. If working during the dry season, with a minimum of yard improvements and there is adequate room, a backhoe or even a mini-excavator should be considered, providing there is enough work to justify the mobilization costs. Many of my yard drainage jobs have been done in tight quarters with lots of improvements such as walks and brickwork, sprinkler systems, lush lawns and valuable landscape plants. In these circumstances, the machine excavator will create more problems than it solves.

Space for Spoils

Spoils (dirt which comes out of the trenches) may be stockpiled next to the trenches for easy backfill once the pipes are installed. Sometimes when space is at a premium, it will be necessary to install the pipe and backfill as trenching is proceeding just ahead. When working a yard drainage job during the rainy season, I always start from the point of discharge and work my way uphill. That way if we have a rainstorm, trenches filling with water will drain out as fast as possible so we can proceed when the storm abates.

Sometimes during a yard drainage project, spoils must be hauled away. If there is room to stockpile, it is usually best to do so and then wait till the end of the job to haul off the excess using a loader and dump trucks. With limited space where stockpiling is not an option, spoils must be removed as work proceeds. In these circumstances, I have had good success renting a lowboy dumpster which can be loaded either with equipment or by hand. The dumpster option is not cheap but it avoids the sometimes difficult process of finding a dump site and allows you to use a driveway or other on-site location where just piling up the dirt would not be feasible.

Underground Obstructions

One of the greatest challenges of a yard drainage repair job will be dealing with underground obstructions. These may include but are not limited to bedrock, cobbles, tree roots, ground water, construction debris, sewer pipe, drain pipe, gas lines, water mains, irrigation pipes, irrigation wire, electrical conduit, and outdoor lighting wire. The contractor will often exclude obstructions and underground utilities in the bid and this can create some unanticipated extra charges for the property owner.

The contractor must prepare the owner or property manager for such extra charges and have a well-written agreement or face the risk of a dispute. Dealing with extra charges can be an administrative headache for the contractor and where possible, I advise that allowances be put into the price to such unanticipated problems. For example, on yard drainage jobs where there are existing underground drain pipes, which may or may not become part of the new system, I will often figure to replace them. Then if I can use them it is a bonus. It is the same with irrigation systems. Sometimes it is just cheaper to simply abandon the existing system and start from scratch. This is particularly true where you are using a backhoe or trencher on the job.


Many yard drainage jobs will involve the removal, replacement and addition of hardscape improvements-driveways, walks, patios, etc. I always try to offer the customer the option to replace all hardscapes with the caveat that new work will not match the existing. If I am going to saw cut existing flatwork, I may recommend that new work be of a contrasting material to improve the aesthetics of the final result. It is also important to anticipate damage to existing hardscape due to equipment traffic, stockpiling materials, etc. A way to hide patch jobs and/or equipment damage is to include in the bid a finish top coat of high-quality epoxy paint to all the surfaces. Such a treatment will add life to the concrete and give the project the look of an upgrade.

Finishing Up

I cannot over-emphasize the importance of the final cleanup on a yard drainage project. The contractor has torn the property all to hell and the owner has been in a state of high-anxiety throughout the process. Now is the time for the contractor to give up some of that contingency money and throw in something that the owner may not have expected. For example, give the landscaping a professional pruning or add some new plants from the nursery. I like to be able to walk the project with the owner and figure out what little thing I can do before I ask for that final check. In terms of future referrals and the verification of a job well done, a truly satisfied customer is a resource of immeasurable value to the contractor.