How to Install a Retaining Wall

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How to Install a Retaining Wall

Preliminary Decisions

• Your first decision is the type of retaining wall you like to install. Keep in mind that county regulations or other issues may factor into this decision.
• Materials for building a retaining wall include (in price order) 6 x 6 treated lumber, segmental wall, block-parged and block-stone or brick veneer.
• These decisions may be predicated by factors such as proximity to trees, driveways and other obstacles. Each wall has its own parameters to work in and one size does not fit all.
• Attached is a Fairfax County typical retaining wall detail for more specific instructions. They have changed the rules a bit since the release of the county typical detail as follows:
  -No permit is required if a wall is under 2′ in height, although you may want to build it to retaining wall standards to keep the retaining wall performing properly.
  -At 30″ or greater you must have a safety railing in most cases and the retaining wall must be designed and stamped by a structural engineer.
  -At 8′ tall the wall is considered critical and your contractor must have a Class A Builders license.

How to Install a Block Retaining Wall (most common)

• If a wall is 24″ in or greater you must pull a permit and install the retaining wall according to the plan approved by the county.
• A footer detail is required and must be adhered to. Typical footers are a minimum of 2′ deep to meet the frost line which keeps the wall from “heaving” from below.
• The footers will have a minimum of 2 – # 4 (1/2″) re-bars running horizontally.
• There should be 1 – # 4 re-bar in an L shape running from the footer and up the block at least every 16″ on center or one per block.
• Those cells that have the re-bar in them should be grouted or filled with concrete for extra support.
• The wall is to be parged on the back side for waterproofing.
• Behind the wall there should be approximately 6″ of gravel (57 stone) with a 4″ corrugated, perforated drain pipe with a sock over it to sift out any debris that may get into the pipe.
• Install 2″ weep holes, 8′ on center, from the drain pipe to the outside of the wall to transfer water from hydrostatic pressure to the outside of the wall.
• Backfill the wall with gravel to 8″ – 12″ from the top grade.
• Fill the remaining area with soil for plants to grow.
• Install the required railing system.
• If the wall is to be finished block, parge the wall with mortar.
• You may also veneer the wall in brick or stone.

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Typical Retaining Wall Detail