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I want to build a raised garden bed with a stone wall. Height would be 1 foot. Since this will be in the front of the house I'm looking at "nice" stone, so not just concrete blocks. I will probably do something like 20ft by 4ft.

I'm thinking of using stone that has that "lip" on the back to make it easy to get the back setting correct. Two main questions:

  1. Now I've done some googling around and I can't seem to get a straight answer to whether I need a foundation poured or not. I'm in Montreal so we have pretty cold winters but depending on what site you look at even some manufacturers just talk about a gravel foundation being needed, so now I'm confused about when I would really need to pour concrete and when 2ft of gravel would be enough.

  2. The bed would sit on a slope in two directions. It runs parallel to the driveway, which slopes down towards the street (I.e. the 20ft down. I measured about 5 or 6 inches down over the 20ft). But also the beds would run into the "hill" (that actually contains the septic drain field so its a hill of sand and the ground here is very very sandy to begin with). So the wall on the driveway side would just have to hold the dirt in the actual raised bed, which I assume should be no problem at 1 foot height. But on the hill side it feels more like a retaining wall. I hope this sketch shows what I mean. Slope runs down the arrows.

enter image description here

So how deep do I have to build the wall on that side? Does that side actually need a foundation and wall at all or can I just put a row or two of stones for looks so that it actually looks like a garden bed and not just a retaining wall, given that the hillside is holding itself right now as well?

  1. I don't need a drain pipe behind the 1 foot high wall in the front that runs along the driveway do I? From what I read so far it seems that I might just add a bit of gravel in the front behind the wall before filling in dirt especially since we have sandy soil (we have lots of commercial sand pits here actually).
  • You really don't have to pour a footing for the wall but it will help support it and keep it from moving or settling. For a long lasting good even wall I would put in at least a small footing to prevent or reduce any movement. – Ed Beal Aug 23 '16 at 13:49
  • For what it's worth, we used a product that has the back lip and a center tongue/groove. (RomanStack). Height is about 16 inches. We dry fit them including the top course, and they're holding up great. I did bed them in sand/gravel just for levelling purpose. The dry fit drains well. I can even generally walk on the wall, though it's not super stable in a few spots - an adhesive for the top would lock things in. I do like the dry fit as it was easy to reconfigure a few years later. – Matthew Wetmore Jun 21 '17 at 6:19
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For a footing, make a t-footing out of pressure-treated lumber. For the 20' run, buy two 12' and two 8' length of 2x10. Get those lengths as will be explained later. Make sure the are very straight, no cup, no twist, no hook. Pick through the pile for straight ones. They need to be straight.

Dig a rough level trench 10-12" wide and 11-12" deeper than bottom of your stone.

In the middle of the trench, stand an 8' length on edge (like a joist) and fill/compact both sides with 1/4-minus, sand or gravel. Butt the 12' length to the 8' length and do the same so that they run in the middle of the 20' trench from end to end. The top edges should be level.

Complete the fill/compaction to be level with the top of the 2x10s.

Lay the second 8' 2x10 on top of the 12' one that you just buried. Screw or lag them together. Lay the 12' over the remaining exposed length of the buried 12' and on top of the buried 8' length. Screw/lag together.

That is it. Lay your stone on top center on the T.

That is the basic idea. For the corner detail, use lap joints.

Good luck.

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    I would not use wood under stone even pressure treated rots when in the ground. A gravel or concrete footing would be the best method and is suggested by all the mfg's that I have installed. – Ed Beal Nov 22 '17 at 16:59

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