How to raise the height of my garden bed without support posts?

[TimGeo]

I would like to raise my garden bed by 1 sleeper (200mm) and I would like to know what would be the strongest method that does not require me to install extra post supports.

As you can see in this old image, the posts end at the height of the existing garden bed, I plan to raise the height so it's more in line with the back fence so I can fill more soil and I would like to clad it with merbau so any fixings will be hidden away anyway.

I had considered these options and I was wondering if there is a safe and strong solution in any of these options.

my first idea is to drill through the top of the new sleeper and into the existing one, cut a little window in the face of the lower sleeper where the bolt ends and install a nut and bolt system, essentially clamping the two together, using how ever many I would need along the length of the sleeper.

my second idea would be to cut a 400mm piece of sleeper and screw in a bunch of bugle screws from the back so it's secured and hidden, maybe 2 to 4 of these along the back along the length of each sleeper.

any other suggestions would be great

below is the desired result I would like to achieve.

Thanks!

[MitchellMc]

Hi @TimGeo,

I like your idea of adding 400mm lengths of sleepers at the rear to join the new sleeper sections with bugle screws. If you weren't going to fill the soil all the way to the top of the new sleepers, then I think you could get away with using landscape screws countersunk into the top sleepers and then reinforcing them with a few brackets from behind. I've created the below rendering to illustrate.

Please let me know if you have any questions.

Mitchell

[TimGeo]

Looking at the above drawing, I feel like the plates dont have enough surface area to keep it rigid, especially if I want to fill up to 20mm below the top, perhaps it's perfectly fine this way, but I would prefer the sleepers as they would have more surface area to clamp on with bugle screws.

If that is perfectly fine for a few decades of stability, would you be satisfied with say 3 or 4 spread over the span, and clamp it down with 6 countersunk lanscape screws?

[MitchellMc · Accepted solution]

That would be fine @TimGeo. The sleeper idea sounds good in my books.

Mitchell