The height of the visible retaining wall is 52", just over 5ft. The old beds are 10 feet away from the wall. The existing beds and barrels near the wall would be replaced by the new beds. The new beds would be 20" tall and 12' wide and we were hoping to have them 3 feet away from the retaining wall for access around all sides. Can we do that without causing harm to the retaining wall?
by beeda
7 Comments
I don’t see why not. At 3ft you should be far enough away from the footings. Just make sure to call to check for underground utilities. You wouldn’t want to plant anything above wires or pipes.
As long as you are not digging out soil/dirt from near the wall base, I don’t see any concern building *raised* beds anywhere in there.
Separate, raised beds will cause no problems unless you build them directly into the wall and/or damage the base of the wall. If they’re sitting on the surface, put them anywhere.
Structural engineer here. The footing for the retaining wall probably extends anywhere from 0-3′ from the face of the wall. Best to avoid disturbing or removing soil for about 5′ or so off the face, and never dig under the bottom of the footing.
That said, if you aren’t digging below the current soil level, and it is a true raised bed, then it can go right up against or 3′ away from the retaining wall without any issues.
Do you own the wall? The only caveat I can think of is that you might need to tear down the beds later on if your survey includes an easement for the retaining wall, and they need to do work on the wall.
You are perfectly safe on the structural front. Since you are placing these beds on the low side (the toe) of the wall, you aren’t adding “surcharge” pressure that would push the wall over. The danger zone for weight is always uphill behind the wall. Actually, adding weight in front of a retaining wall generally adds passive resistance, which is fine. The only thing you need to watch is drainage. That CMU wall likely has a gravel footing or weep holes to let water escape. Make sure your new beds don’t create a dam that traps water against the wall’s base. Keep that 3 foot alley graded so water flows away from the blocks, not into them.
Functionally, 3 feet is the industry standard minimum for a wheelbarrow and kneeling space, so don’t cheat and go smaller than that or you will regret it every time you need to weed. Before you buy the lumber, I’d suggest running a quick visualization in GardenDream to check the massing. Those 20 inch beds are tall, and seeing them next to a 52 inch wall might feel a bit like a canyon if you aren’t careful. It’s a good way to verify that the spacing feels comfortable rather than claustrophobic before you commit to the layout. Visually though, bringing them closer is the right move to stop that gravel area from feeling like a parking lot.
52” is less than 5ft, btw.