Blocks for raised bed

[Tommygun85]

Hi, I was hoping someone could shed some light on which blocks are best to use for a raised bed.

I plan to construct a 12' x 2' raised bed. I am going to use blocks to construct it, and it will be 4 blocks high. Are 3.5N medium density blocks good enough to use, or should I use 7N blocks? I am obviously concerned about the pressure from the soil pushing the walls out.

Also, will the walls withstand the pressure from the soil if I build it as a single skin block wall? Or should I double it up? (Not sure if that is the correct terminology!)

Thanks for any help you can give.

 

[r896neo]

Just use 7's the price difference is negligible and they keep the water out better. either paint the inside with liquid dpm or line it with dpm sheet