Surface water is often thought of as temporary water, like rain and melting snow. Groundwater, is the naturally occurring water that resides below the surface of the earth. It, too, can be a source of water intrusion to create waterproofing issues. Either kind can find their way into your home or business and result in minor to major damage if proper waterproofing efforts have not been made to safeguard your structure.
Surface water is often thought of as temporary water, like rain and melting snow. Surface water is also as its name implies: Water either falling on top of the earth’s surface (like rain) or topical water bodies like rivers, lakes and streams. Ultimately, surface water may indeed seep (through gravity and excess water conditions) into the earth, essentially becoming groundwater.
As you may know, water exists under the ground. The effect of groundwater on foundations depends on several factors – where the structure sits in relation to the groundwater water level, fluctuating water tables, soil content, and so on. Changing conditions in the environment affect your property’s water levels/water tables which, in turn, can impact your home’s foundation. Groundwater, then, is the naturally occurring water that resides below the surface of the earth. It, too, can be a source of water intrusion to create waterproofing issues.
A French drain, which may also be called a curtain drain, perimeter drain, weeping tile, or agricultural drain, is a gravel-filled trench that includes a perforated or slotted pipe. These drains are used to direct surface water from a specific area, such as a home's foundation.
French drains direct surface level water toward the lowest point and allow it to seep through the surface level gravel into the drain. This gravel also blocks the passage of excess debris. The water is then collected in the perforated pipe, running at the base of the drain, and directed away from the home and toward a more suitable area for daylighting or infiltration.
French drains differ from typical surface drains because they collect water over the entire length of the drain instead of one particular spot. French drains can also prevent water from collecting and pooling in specific areas, saturating the ground below, which may lead to water problems at the surface or below. Instead, this water is directed to a more desirable location such as a dry well or an area of your choosing.
HOW DOES A FRENCH DRAIN WORK?
If you're researching French drains, you're probably already facing some drainage issues and looking to learn more about what types of problems a French drain can solve and whether one is right for your property.
Remember that liquid always seeks out the lowest point it can reach along the easiest path, readily moving into empty pockets in loose soil. That's the secret to a French drain: It provides a reliably easy path, creating a sunken channel that encourages water to percolate out of the surrounding soil and flow along a smooth course. Gravity is essential for a French drain to function properly, as it first forces water down from the surface and out of saturated soil, then pulls it along the downward-sloping pipe to the desired discharge point.
Flooding in your backyard. If heavy rains have left your yard with an unwanted water feature or the spring thaw has saturated your yard, a French drain can help. Placing a French drain in this wet region allows the drain to collect unwanted water and redirect it to a safer location, giving you back your green space.
Damage to your outdoor patio. Your patio is a great source of pride and a meeting place for family and friends, but excess water can damage the area, deteriorate the pavers, and also create a breeding ground for mosquitoes, ruining your ability to spend time outdoors. A French drain can work as a shield, collecting water before it reaches the patio and diverting it away. This will eliminate the standing water that mosquitoes need.
Damage to the foundation and low-level areas like your basement. Check the walls in your basement. If you notice a musty smell or wet floor, you need a French drain immediately. A French drain can stop this water from ever reaching your home, protecting your basement from flooding and your home's foundation from incurring additional damage
FOUNDATION (FOOTER) DRAIN TILE FOR GROUND WATER
Foundation drainage tile systems are one of the most important aspects of residential and commercial construction. Drain tile systems are also one of the most misunderstood aspects. Because these systems are usually deeply buried and cannot be easily modified or corrected, it is vitally important that they are installed correctly. Foundation drainage systems which are installed properly can serve a dual roll.
Many buildings around the nation have full or partial basements. These basements are really reverse swimming pools. In other words, most people don't want water in their basements. Foundation drain tile systems act as the means by which ground water can be transported away from your basement. If you want a dry basement, you must have an adequate foundation drainage system.
The water content in the soil surrounding your house can fluctuate seasonally. There is always a point at which you can dig and hit water. Geologists often refer to this as the water table. This water table rises and falls in response to the amount of precipitation in any given time period. The water table in many parts of the country can rise to within a few feet of the surface during wet spells. Water will take the path of least resistance. It can choose to go sideways through a crack in your foundation, or it can go down alongside your foundation into a pipe. I'm sure that you will agree that it is a better idea for the water to go down the pipe.
A foundation drain tile system has four main components. The drain tile (pipe), the filter media (gravel), the gravel cover, and the water outlet. All of these elements must be installed for the system to function properly.
The drain tile or pipe is usually 4" in diameter and is perforated or has pre-drilled holes along its length. Depending upon the type, it can be purchased in rolls up to 250' or in 10'sections. Fittings are available to allow you to go around corners or interconnect the pipe.
The filter media or gravel is used to cover the drain tile. Water can flow readily through this gravel and find its way to the pipe. Remember, water takes the path of least resistance. Some soils (heavy clays) resist water movement. If your soil is like this, the water would rather go sideways into your basement than down through the clay soil to the drain tile. The gravel that is used most often is large (1 - 1 1/2" diameter) washed rounded gravel.
The gravel cover is a barrier which keeps silt and mud from clogging the gravel or the draintile pipe. During excavation, dirt removed from the hole is "fluffed." This means that it is disturbed and broken up. It is loosened further during back filling procedures. All of these small dirt particles (silt) can be easily carried through the gravel by the rain water or snowmelt which enters this soil. Without a barrier, these silt particles immediately clog the gravel and drain tile and render it useless.
SOIL GRADING & GUTTER DOWNSPOUT DRAINAGE
The right soil grade can prevent basement leaks before they start by directing the water flow away from or around the house. The first rule to grading is: the soil should always slope away from your home. It sounds like common sense but foundations are often set too deep in the ground during construction causing marshy ground, wet basements or flooded slabs.
Many building code officials respond to this problem by requiring that the top of the foundations or slabs sit at least six inches above the highest point of the soil at any location around the house. Also the ground must fall away from the foundation at least six inches within the first 10 feet around the perimeter of the house. Remember, this is just the minimum requirement. When it comes to residential grading - the more slope the better.
If you have grade problems for an existing house, you first have to look at the lot to know how to fix it. Look at the overall lot grading and the layout. Understand surface water may enter from adjacent properties.
If you are lucky enough to have a sloped lot, your task of establishing grade can be accomplished. All it will take is a small piece of earth moving equipment like a Bobcat or skid-steer loader.
If you have a situation where ground is slopping towards your house (houses built on hillsides), the trick is to slope the ground gently by creating a swale. This swale, or ditch, allows you to do two things. It gets water away from the house and at the same time collects the water which runs downhill towards your house. You direct this swale around a corner of the house and continue until the natural slope of the ground is falling away from your structure.
If you have a flat lot you face a more serious challenge. Sometimes the ground is so flat you can’t create a swale or sloping condition. In this case, you will need to pipe roof water as far away from the house as possible. Downspouts that dump water onto the ground near the house can cause serious problems with hydrostatic pressure.
You can also consider surrounding your house with a moat, something like the old castles used to have. This moat is simply a ditch that is dug around the problem areas of your house. A two foot wide by two foot deep trench can be very effective. Once this trench is excavated, fill it with large 1-inch washed gravel up to within one inch of the top. This trench acts as a collection area for surface water. As long as your soil can absorb water (even at a slow rate) you will have improved drainage conditions around your house.
The soil types in your area can determine the effectiveness of your drainage system, or dry well. Soil scientists refer to soil types by texture or by how much sand, silt and clay is present. Many times the topsoil is porous (as would be used for planting) and absorbs the surface water. The sub-layer of clay or similar non-porous soil prevents the water from continuing in a downward movement and directs the water laterally. If non-porous soil next to the foundation slopes toward the house, water will begin to accumulate.
It is also important to understand your soil type because expansive soil can cause serious structural problems to your foundation. Your house can move if it is on unstable soil or if the moisture level in the soil changes. Soil movement can cause damage to the foundation and framing, evidenced by cracks in the slab or foundation, cracks in the exterior or interior wall covering, uneven floors and/or misaligned doors and windows. This type of movement is usually associated with slab on grade construction; however, this may also occur in structures with basements and crawlspaces. Expansive soils on slopped lots can also cause a house to creep down hill or even cause a landslide.
Possible Solutions for Unstable Soil
If you already have a home on expansive soils, you can take preventative measures by maintaining a uniform and constant level of moisture in the soil to prevent shrinking and using proper drainage systems and grading techniques to prevent swelling.
Proper grading (in conjunction with a gutter and downspout system) is one of the easiest ways to manage surface water, reduce the possibility of water penetration and structural damage from hydrostatic pressure, and control the water content in expansive soils.
RETAINING WALL DRAINAGE & EXCAVATION
A retaining wall is intended to hold back soil when there is a drastic change in elevation. Often retaining walls are used to terrace yards that originally had a steep slope. Additionally, retaining walls can help create usable outdoor space as well as control erosion. Low retaining walls are frequently used as planting beds and can add interest to an otherwise flat yard.
An improperly built retaining wall may bulge, crack or lean, creating an unsightly eyesore and a headache for you.
Base - First, a retaining wall must be built on a suitable base. Block manufacturers as well as experienced contractors and engineers stress the importance of starting with a good base. The base of a retaining wall should be set below ground level. The taller a wall is, the further below ground level it should be set. Crucial for supporting the rest of the wall, a good base is made of compacted soil and at least a six inch layer of compacted sand and gravel.
Backfill - Second, a retaining wall must have properly compacted backfill. Backfill refers to the dirt behind the wall. In order to provide proper drainage, at least 12 inches of granular backfill (gravel or a similar aggregate) should be installed directly behind the wall. Compacted native soil can be used to backfill the rest of the space behind the wall. If you intend to do landscaping behind the wall, a 6+ inch layer of native soil should also be placed over the gravel fill.
Drainage - Third, since most retaining walls are impervious, which means water cannot pass through the wall itself, efficient drainage is crucial. When drainage goes unaddressed hydrostatic pressure will build up behind the wall and cause damage such as bulging or cracking. There are a number of ways to ensure proper drainage of water from behind a retaining wall. First, is to make sure you backfill at least a foot of space behind the wall with gravel. Second, is having a perforated pipe installed along the inside, or backfilled, bottom of the wall. And third, weep holes will be needed to allow water to drain through the wall.
Height - Fourth, it's important to know that the height of a retaining wall determines the load it can bear and how much extra reinforcement will be necessary. Typically, residential retaining walls are built between 3 and 4 feet high. This height provides excellent strength without requiring anchors, cantilevers or other additional reinforcements. If your property requires a higher wall you have two options: you can have the wall specially designed by an engineer or you can use a series of 3-4 foot walls to create a terraced effect.
What's The Solution?
The best way to approach any building problem is to first do the things that are easy and low cost. Then proceed in a logical order doing the next least costly technique with the most positive likely result. With moisture problems, the best approach is almost always to remove or control the source of the moisture, not to try to stop it at the last line of defense.
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