Grit Blogs > Of Mice and Mountain Men

Garden Project 2016 — Part 4

By Allan Douglas


Tags: raised bed garden, landscape timbers, retaining wall, gardening, building a wall, Doug Bittinger, Tennessee,

Of Mice and Mountain MenPreviously we have covered layout, squaring, trenching, and ground pins in this garden project of mine. Now, let's look more at the arrangement of the timbers themselves and the joinery.

Staggering Joints

Staggered Joints

Joints, where the end of one timber butts up against the end of another, are weak points. You want to stagger these so that the joints in one row do not fall too close to joints in the row just above or below it.

Longer is Better

Make use of long pieces of timber — they're stronger than many short pieces. In the beginning, as I stair-step up the slopes, short pieces cannot be avoided. But I will want to transition to longer pieces as soon as possible. Cut-offs can be used by placing them between longer pieces.

Lock the Corners

Locked corners

Be sure you alternate the overlap at corners to lock the timbers securely together (as pictured above).

Mark Your Fasteners

Marking screws

When you drive a screw or spike into a timber, use a construction pencil (with a wide, flat, sturdy point, as opposed to the delicate conical point of a standard pencil) to make an obvious mark on the outside of the timber where the fastener is. This will make it easy to avoid driving one fastener in on top of another. At the corners, mark both the side and the end to give yourself a clearer vision of where it is. Pencil is good because it washes off with the rain, so you don’t deface your pretty wall.

Pay particular attention to fastener placement at corners, or they will hit the fastener in the timber below it.

Buttresses

If you will have long, high walls, you will want to consider adding buttresses to help keep the dirt on the inside from pushing (bowing) the wall out at the top. There are several ways to do this, but the easiest is to use a post hole digger to drill a hole 18 inches deep beside the wall. Then, concrete a 4x4 into the hole so that it supports the upper part of the wall. This works well for 3- to 4-foot-high walls. Anything higher than 4 feet that will be holding back dirt will need a more aggressive approach, like anchored tie-backs or external cantilevered buttresses.

Cantilevered Buttress concrete

Stepping and Filling

I started at the low corner and worked in two directions — along the barn and along the back wall. When I got to the outside-back corner, I had to start filling in and building up in order to go around the corner and work up the outside-end wall.

Back Wall - End Wall

I used a large number of my initial 40 timbers just building height to accommodate this corner.

High corner_Ground timbers in

The final side to be dug in was the front, from the corner of the barn to the highest corner. Now that these are all in, there will be no more trenching or rebar pinning, so I can put those tools away.

Where From Here?

My goal for the initial 40 timbers I bought was to get all the ground timbers in and all corners locked together with at least one additional run. I have accomplished that with one timber to spare.

The next step will be to figure out where the permanent steps will be in the wall.

I do not think it practical to simply build up all walls until they are level along the tops of the walls. If I do that, the high corner will be 6 inches high, the front corner at the barn will be 39 inches high (the corner diagonally opposite will be similar), and the lowest corner (behind the barn) will be between 5 and 6 feet high! That would take a lot of timbers, and a lot of dirt to fill it up level.

A better solution might be to step it down to retain a slope, but a much less drastic slope.

A long wall might look like this:

DrawingTH

This is a simplified version, but the idea is to make three or four major steps rather than seventeen little steps. The little steps would be fine, except that I want to attach fence panels atop the timbers to keep rabbits and dogs out of my vegetable patch. A few steps of three layers would make that possible.

That’s enough for this round. See you next time when I begin filling in these stair steps!