How to Construct an Exterior Retaining Wall

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I will discuss the nuances of constructing landscape retaining walls from various materials. In many areas, retaining walls require a building permit, so confirm with your local building department before beginning construction. Only walls over 48″ in height in my township necessitate a ticket, but it is best to double-check.

There are numerous varieties of retaining wall materials currently available. Fieldstone, railroad ties, pressure-treated ties, brick, interlocking masonry blocks resembling fieldstone and brick, etc. The types require slightly different installation procedures but share similar fundamental concepts. You must begin with a strong foundation. Do not build on topsoil, damp loam, or other soft and malleable ground materials. Your wall will shift with the earth and eventually decompose. Suppose you are dealing with topsoil or soft ground. In that case, you will need to excavate and remove this soil to a depth of one to two feet below ground level, followed by the placement of a solid sub-base gravel or item material, compaction, and then the construction of your wall. A reliable sub-base will provide you with years of attractive retaining walls that require minimal maintenance. A wall less than 4 feet tall is considered a landscape element in my region. Over four feet in height, the building department requires a permit and construction drawings. CONSULT with them before constructing a wall. Multiple-tiered retaining walls can be used to build beautiful garden spaces. Additionally, seating areas and flower gardens can be created using this method.

TOOLS NEEDED:

Wheelbarrow, sledgehammer, tape measure, pencils, string line, level, 60-cent spikes, 3/4″ electric drill, wood bits, extension cords, 7 1/4″ electric saw, inexpensive carbide blades, pointed and square shovels. Additionally, you will need suitable stray material to fill your wall back as you construct it. 3/4-inch gravel works best. Several 2′ lengths of #4 or #5 rebar were reduced to 24″ in size. The use of pin bars, picks, and electric display hammers can greatly facilitate work.

WALLS CONSTRUCTED FROM WOODEN TIERS

Whether using 6 x 6 pressure-treated ties, railroad ties, or other dimensional lumber, at least one link must be placed below the finished grade. Establishing one connection below the rate will aid in anchoring the bottom of the wall and preventing it from falling out once the backfill is placed behind it. The most crucial tie is the first or foundation tie. It must be level, aligned with the other bricks along the length of the wall, and securely fastened. Drill a hole at least every 4 feet along the size of the ties, beginning at one end and always ending with a hole at both ends, using a 3/4-inch drill with the appropriate-sized wood bit for the rebar you have; once the bottom or base tie has been installed. Drive a piece of the 2′ rebar into the ground with your sledgehammer until it is flush with the top of the bond. This will hold the first tie-in position securely. Now, position the second level of relations on top of the first. Ensure the joints are offset so no two end joints line up vertically. This is crucial for the wall’s resilience. I also want you to set the second tie 1/4 to 3/8 inches behind the front of the bottom link. This is known as

“battering.” As each subsequent connection is added, it will set back by the same amount, causing the face of the wall to slope slightly backward. The wall is being pushed back into the earth behind it. Once the second row is in position, drill pilot holes large enough to accommodate the installation of your 60-cent spikes using your drill. DO NOT attempt to drive these barbs through a tie that has been pressure treated. You will only deform or break the end or tie. When these barbs are partially driven into the wood, it is nearly impossible to remove them. They are also relatively costly, so you should avoid wasting them. Beginning at one end, space the barbs 3 to 4 feet apart, placing one on each end of every tie. As the backfill is again deposited behind the wall, the pressure will once more attempt to push the wall forward. This integral “lean” will maintain your wall sturdy. After installing the second tie, backfill behind the first two ties and in front of the bottom link. Take some time to remove any remaining rocks or other residue from the ground. This will create a safer working environment as you construct your wall upward.

Depending on the completed height of your wall, you may be required to install “dead-men” every few feet along the length of the wall, every few courses. As an additional anchor behind the wall, a portion of the tie is turned at a 90-degree angle and nailed to the anchor with a cross piece. What is required is a 3′ long T-shaped piece with a 2′ cross-end piece situated behind the wall with the end of the extended leg nailed to the border between ties. This becomes a wall anchoring device once it is backfilled. In addition to attempting to drive your battered relationship forward, the pressure must pull the anchor out of the solid ground. If done correctly, this is unlikely to occur. The exterior face of the wall will appear to have a six-inch wood piece every few feet, but this is the anchor piece’s butt end.

As you proceed upward with each course of ties, you will backfill each class, delicately tamping the stone to prevent excessive settlement and eliminate any air pockets in the soil behind the wall caused by the excavation. DO NOT be tempted to throw large rocks behind the wall to expedite the task of backfilling. Frost action will exert pressure on the large stones, which may cause your fence to collapse. 3/4-inch gravel drains rapidly, keeping water that can freeze and thaw away from the rear of your wall, and smaller gravel provides a smaller surface area for frost to push against. If you work in a typically wet room, you may wish to install a perforated PVC drain conduit behind the first tie, with the end(s) leading to the sun. If you must use a drainage conduit, cover it with a filter fabric to prevent silt from entering and clogging the pipe. Place a small quantity of stone over the line, followed by the material, and continue with your ties and backfill gravel as described above.

If you want grass or plants along the wall, you must determine when to cease backfilling with stone. It is acceptable to plant flowers behind the wall but avoid the temptation to use plants or shrubbery with deep roots. The roots will exert pressure against the wall from behind. If you intend to place topsoil behind the wall for plantings, install a filter fabric at least two ties below the wall’s apex to prevent the soil from eroding into the gravel below.

PREFABRICATED MASONRY RETENTION WALLS

Additional equipment needed:

In addition to the tools listed above, a gas-powered 12-inch miter saw with masonry blades is required. Get multiple blades because they degrade rapidly. Also needed are a chipping chisel, a brick set, and a 5-pound lump mallet.

Numerous precast concrete masonry structures are designed for retaining walls on the market today. Visit multiple retailers to compare the per-unit prices and local availability. Similar preparation is required for a wood binding wall. As an anchor, the first course of the block should be placed below the final grade. A substantial sub-base of stone, stone dust, or concrete must be compacted before construction to prevent the wall from settling. This base must be as level as possible, as an unlevel beginning will be visible as the wall rises and can lead to wall failure. Ensure that the row is perfectly linear or that the curve is gradual.

Most of these precast units have a lip-and-groove configuration that allows you to stack one piece on top of the following while simultaneously assaulting the wall. No guessing. Some are also equipped with pins pushed into the block below to secure individual parts further. All of these walls require a stone backfill. Many also have large openings in the league that must be filled with stone to further aid water drainage behind the wall. A dead man assembly is typically unnecessary if these walls are maintained under 4′ in height. Ask your salesperson if they carry prefabricated corpses. It will save a great deal of effort.

ANCHORING YOUR WALL:

A mesh netting dubbed “Geo-Grid” must be installed on top of the first course of precast blocks and typically every two to three methods after that. This netting is available on coils and can be cut using a utility knife. Generally, the mesh extends into the terrain the same distance as the wall’s height. Four-foot-tall walls and four-foot-wide netting are standard, but many walls require engineering and may necessitate additional netting. The net is placed atop the first course within 1″ of its front margin. The second row of blocks is then placed. After the second course is constructed and connector pins are inserted between the blocks, the netting is stretched rearward into the hillside to remove wrinkles. On top of the net, a layer of good soil/stone is deposited and compacted to the top of the second course. The sheer weight of the soil placed behind the netting will hold the wall in position. This procedure is repeated up to the wall’s height.

All the manufacturers I’ve encountered can provide a completed wall cap. This gives your constructed walls a neat and clean appearance. If the wall is low enough, it can also be used as a seat to observe the garden behind. Installing the top covers requires an adhesive and caulking gun. Generally, the bond cannot be applied below 40 degrees. Check the adhesive tube for application instructions.

All blocks consist of linear sections. You can remove a portion of the block’s back to create an inside curve or separate the backs to create an outside angle. In every circumstance, the fronts are held firmly together. (NOTE: The geogrid should NOT overlap on an inner curve. This can cause the blocks to slide across the double layer, collapsing the wall. Remove the overlapped portion of one of the layers.

There are numerous brands and varieties of masonry wall units, and their installation procedures vary marginally. Be careful to read the instructions before beginning. Some manufacturers anchor each course to the one below with plastic pins, while others use steel dowels. Most require that the units be filled with clear gravel. Take your leisure. The wall must be eternal.

Stone drainage pipe inserted behind the wall.

Installing drainage piping at the base of your wall to transport away surface and groundwater is advisable and may be required by your local building department. Freezing water can topple or severely damage a structure. It is possible to use perforated plastic pipe, and flexible plastic pipe is now available in rolls, making it very simple to construct curved walls with few or no connections.

Also available is piping enclosed in fabric. If you do not use the pipe with cloth already attached, you must install filter fabric over the plain pipe after it is installed and covered with stone to prevent silt from clogging the lines’ openings over time. Ensure that the ends of the tube are exposed to allow for the free movement of any groundwater. As your wall progresses, the first 1-foot space behind the wall must be filled with clean stone to allow water to flow down behind the wall and into the drainage conduit. The soil behind this section may be existing soil, so long as it is correctly compacted. The stone is brought approximately 1 foot below the finished grade, and then the final foot of topsoil is applied. This prevents the entry of ambient water behind the wall. Using plastic tee fittings, you may need to drill additional holes through your partition for other drainage exits if your wall is long. Carefully notch the wall block and insert the tee into your created cavity. The subsequent course of blocks will secure the garment fitting.

HANDRAILS

In my location, walls higher than 30 inches must have a handrail to prevent anyone from climbing over the fence from above. You must install a bar if your wall has a footpath on top. Consult your local building department to determine if a permit is required. There are specific requirements for installing a handrail behind the walls. Consult your supplier.

Before beginning your endeavor, perform a quick Internet search using “images” in your search engine to discover the countless styles of wall design ideas, etc., available. Perhaps it will inspire your endeavor.

Pete

Your Accommodating Building Inspector

 

http://www.Wagsys.com

Software for the Building Inspection and Code Enforcement System

Pete Ackerson is a building inspector with over 30 years of experience in the public and private construction sectors. In the Eastern United States, he has worked in building design and field construction on projects ranging from schools to treatment plants, private residences, and condominiums to sizeable residential landscaping endeavors. Together with two other building inspectors, he founded Wagsys LLC in 2006, which developed software for municipal building departments, planning boards, and Zoning Boards of Appeals.

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