Types of Walls

Timber Walls
Upside: Only moderately challenging to build by yourself up to 4 feet high. If an engineer has designed the wall, located the deadmen, and specified the backfill and drainage, you can install an even taller wall yourself.
Downside: Not as long-lived as masonry. Making square cuts is challenging. Also, components are heavy and hard to manage alone. Plan on about three days to build a wall 4 feet tall by 15 feet long.
Cost: $10 to $15 per square face foot installed, depending on your region—higher if extensive excavation, soil prep, and backfilling are needed.
Remember:
Use 8-foot-long, 6x6-inch pressure-treated wood designated "For Ground Contact," and have all materials delivered. Follow all rules for landscape fabric, drainage and backfill. All timber walls require deadmen every 4 feet at midwall height or higher. Pin the first tier of timbers to the ground with #4 rebar.

Interlocking Concrete Block
Upside: Also called segmented retaining walls, interlocking-block systems from Keystone, Risi, Rockwood, Tensar, Versa-Lok, and others are mortar-free and easy to assemble. Units are small and modular, so walls can taper, turn, wrap, and curve. Available in many textures, shapes, and colors, these engineered systems, which can be used for walls up to 20 feet high, rely on several techniques including:
•Keyed, battered design (block shapes key into one another and are stacked so they lean into the hillside)
•Backfill trap (block shapes allow backfill to be shoveled into the block webbing, trapping each block individually)
•Geo-grid webs (block maker supplies geo-grid plastic-net tiebacks that attach to the block and are buried 5 feet in the hillside at specific heights).
Downside: You can't mix and match manufacturer's systems. Block systems that use metal pins to tie blocks together can be a challenge to line up exactly.
Cost: About $12 to $20 per square face foot installed, depending on block configuration and site. More expensive systems tend to be stronger and stack higher.
Remember:
Arrange before delivery from the masonry yard where materials will be stockpiled in your yard and if the forklift used to off-load the truck will fit through backyard gate, etc. Follow all rules for landscape fabric, drainage, and backfill. Use manufacturer's calculators to determine how many blocks, pins and tiebacks you'll need. When stacking blocks, sweep off each layer; small pebbles can disrupt the pattern. Cap walls with flat units or stone held down with silicone caulk.

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