© 2008 by Raymond Alexander Kukkee
Photo Credit © 2009 WLK Photography
Do You Need a New Retaining Wall?
Perhaps parts of your yard have become unsafe, rough, and too steep to cut safely with the lawnmower. Perhaps the soil has already eroded away leaving deep, ugly channels because a poorly-built, ancient log retaining wall collapsed during a big rainstorm. Maybe you’re just tired of looking at the mess.
It really doesn’t matter why your lawn looks like a moonscape, it just does. Clearly it is time to do something to remedy the eyesore. Offhand comments from your neighbors helpfully suggesting you’ll need a well-designed retaining wall built by their contractor cousin Vinny have ratcheted up the pressure to do something, and soon.
If you’re like most homeowners, cost is a genuine concern. The new colored stacking concrete blocks your neighbour used to construct his wall look fine, but they are too expensive. You may have already decided not to use inexpensive railway ties because of reasonable concerns about the creosote chemical on them.
The question is, how can you build a new, attractive retaining wall on a limited budget? The answer may be the use of landscaping timber.
Landscaping timbers are pressure-treated timbers that come in various dimensions . Several profiles are available and the timbers are offered in common lengths. One advantage in using structural timbers over railway ties is weight, being somewhat lighter than old railway ties. Alternative “timber” materials including extruded plastic timbers are available, but can be a lot more expensive than natural wood.
Important, basic considerations that must be made in building any retaining walls include the following:
Planning: Do draw a plan of the proposed wall in advance, including the height, grade levels, and any necessary abutments or jogs. A plan can and will help avoid making costly mistakes.
Height: a retaining wall should not be more than 6′ high for safety considerations. Ideally for lighter timbers of smaller dimensions, a retaining wall should never be more than 2- 3′ in height. An excessively high retaining wall may also require fencing or guard rails included. Consider reducing the height by stepping the wall back, or installing two lower retaining walls instead of one, and take advantage of the potential decorative appeal a landscaped flat between them offers. Check with your local jurisdiction for any restrictions and restrictive design criteria, and also obtain a building permit if necessary
Drainage: Excessive water movement through the soil, or on the surface can and will seriously damage a retaining wall that is not provided with drainage. If excessive surface water runs down the landscape, do consider installing a French drain. (See: How to build a French drain) For structural stability, include arrangements for drainage in the form of coarse gravel backfill and a perforated weeping tile on the uphill side of the base.
Structural Stability: If the proposed wall is both long and high, the design must include abutments, vertical support posts, deadmen timbers or the equivalent. Right-angled offsets may be incorporated into the basic plan to provide extra strength. A right-angled offset may also be used to advantage in the design —to incorporate an access stairwell. These measures prevent the wall from “pushing out” typically with subsequent distortion and eventual structural failure of the wall.
Material Supplies Required
You will need to calculate how many timbers are required. Measure the length and height of the proposed retaining wall. You will also require:
Crushed stone or crushed coarse gravel for the wall footing.
Sections of reinforcing steel bar, or galvanized pipe
An appropriate length of 4″ perforated weeping tile
Fill and topsoil
Reinforcing steel bar, or galvanized steel pipe
Long lag bolts or spikes.
Deadmen galvanized cable (optional) and suitable T’ anchor plates, galvanized, sized for the timbers chosen
Wooden stakes or pickets
Carpenter’s 4′ level, a line level, laser or transit level if available
Drill and appropriate drill bits
Sledgehammer, 5 or 10 lb.weight
Shovels, pick axe, and rake
Hand saw or Chain saw
Grinder, steel cut-off saw, or hack saw
Vibrating (whacker-packer) plate packer if available
Let us proceed with the construction!
1. Remove old structural components and trash.
2. Establish the precise location of the wall, driving pickets into the ground.
3. Excavate the trench, removing grass and all soft soil. Only as a last resort, add fill if necessary, but DO compact it using water and a tamper or packer.
4. Ensure the base is level. If leveling is not possible because of bedrock or other intrusions, consider dividing the retaining wall, placing the two sections on different levels.
5. Install 6″ to 8″ of crushed rock. Compact it to level.
6. Install a carpenter’s line to lay the first row of timbers.
7. Lay the first course of timbers. Drill holes in them, and drive 24″ lengths of steel bar, or galvanized pipe through them securely into the ground. You may choose to leave the steel sticking up and pre-drill the next course to sit on the protruding stubs, or hammer them flush to the top of the timber. Check the level of the timber course and adjust it as necessary, and establish pickets to mark the elevation of the final, top course.
8. Install the drainage weeping tile on the UPHILL side of the first course, level with the bottom of the timbers, placed with the holes facing DOWN. Ensure the ends of the tile direct any potential water flow away from the wall at the end. Cover the weeping tile with 6″ of crushed rock or very coarse gravel. Disguise the ends of the pipe as required with stones or grill.
9. Proceed with the second course of timbers. Ensure the timbers are plumb, or back-set about 1/4″ for extra stability. Start with a 4 ft. length of timber if you are using 8 ft lengths. ALWAYS offset the joints for strength and stability.
10. If the wall is to be high, install deadmen timbers or cables at right angles and bury the anchor timbers in solid, undisturbed soil. Install galvanized “T” plates, spiking them securely to the timbers.
11. Back fill each course as you go. Install coarse gravel behind each timber to ensure drainage percolates harmlessly down to the weeping tile. It is important to backfill, water, and compact the grade as you proceed with each layer of timbers to minimize future settling of the soil.
12. Complete the subsequent courses to achieve the final height desired. Fasten the final course with lag bolts or suitably long spikes.
13. Complete the filling process; bring to grade, rake and roll smoothly, and landscape as desired. Place topsoil and seed or sod as needed, and stain or paint the timbers if desired. Plant some beautiful bushes in front of the wall if so desired.
Now that you know how to build a retaining wall with landscaping timbers,you can apply the same technique to building a raised patio.
Is that Incoming I hear?