Constructing raised bed with integrated bench - how to stablize

electrofelix · 29-04-2021 8:22pm #1

I have 3 lengths of marcocarpa wood 2x12" by 3m and I'm looking to construct a raised bed with an integrated bench (image below).

The main problem is probably going to be cutting and supporting the bench part. As the width of the pieces of wood is 12", which seems too low, and 24" seems a little on the high side, I'm aiming for 18" from the ground to be comfortable.

I have a bench mitre saw so some cutting will be straight forward, but I don't think it can manage that type of elongated U shaped cut to be able to have the bench seat at 18". Will this need a separate circular saw or is a drill + jigsaw going to be sufficient for the task? Or are there better approaches here that won't result in a lobsided uneven cut.

Looking at https://www.railwaysleepers.com/projects/benches-chairs-from-railway-sleepers/les-mables-raised-beds-with-bench-seats-from-new-railway-sleepers do I need to build up some underneath support, or if I put some running horizontally from the front piece to the concrete wall will they be sufficient to support. I am a little hesitant about having some of the wood fully surrounded by soil based on some recommendations to use DPC to keep the soil away. So I'm trying to consider that with the construction. Plan to use danish oil to treat the wood first.

Screws: is 6.7 x 100mm suitable here, over doing it, or not strong enough?
https://www.screwfix.ie/p/timbascrew-wafer-timber-screws-gold-6-7-x-100mm-50-pack/1792j

I'm expecting to cut some 2x2 posts from the wood to use to help attach screws from the rear side so they remain hidden, open to alternative approaches.

Looking to do something a bit like the following image:

Some photos so you can see the space I'm working with
ND6mV3C.jpg?1

bamayang · 02-05-2021 8:03pm

Dunno is it any help to you, but I built that exact thing last year. Couple of pics of it here:
https://imgur.com/gallery/4BeRhmp

kadman · 02-05-2021 10:21pm

Any raised bed put against a house wall needs to be at least 150mm below your existing dpc so as to
avoid bridging the damp course and creating possible problems.

electrofelix · 03-05-2021 2:27pm

bamayang wrote: »

Dunno is it any help to you, but I built that exact thing last year. Couple of pics of it here:
https://imgur.com/gallery/4BeRhmp

Thanks, it looks like you didn't worry about adding additional support from what I can see? How thick were your pieces of wood?

kadman wrote: »

Any raised bed put against a house wall needs to be at least 150mm below your existing dpc so as to
avoid bridging the damp course and creating possible problems.

I'm guessing it's an outside shed that didn't have any insulation anyway hence it wasn't worried about. I'm against a boundary wall, so also not an issue but I might stick some DPC on the wall to limit the amount of damp that will end up on the other side to avoid mold forming there and having the neighbour cause a bit of a fuss.

bamayang · 03-05-2021 3:40pm

electrofelix wrote: »

Thanks, it looks like you didn't worry about adding additional support from what I can see? How thick were your pieces of wood?

I'm guessing it's an outside shed that didn't have any insulation anyway hence it wasn't worried about. I'm against a boundary wall, so also not an issue but I might stick some DPC on the wall to limit the amount of damp that will end up on the other side to avoid mold forming there and having the neighbour cause a bit of a fuss.

I used 8”x4” sleepers, built on the narrower edge up against a garden shed.
I used random offcuts or cement blocks under they seat to support it. It is hidden by the soil so wasn’t overly worried about appearances.

kadman · 03-05-2021 6:16pm

Sorry guys, posted in the wrong thread.:o
K

py · 08-05-2021 12:00pm

I've done something similar to the example picture in your original post. Slightly different scenario in that my sleeper bench is integrated in to a retaining wall so it's makeup is a bit different. I'll take a picture when the rain subsides here.

Some stuff to consider:
How will the overall structure be secured? Vertical posts on the corners and near the walls with concrete/post mix? Or are you installing it on top of the the tiles and securing it to the wall with posts/nails?

With regards to the height of the seat, you could integrate planters to the front of the raised bed on either side of the bench and have a small step made out of the wood to shorten the height of the seat. That probably sounds as clear as mud so may need to photoshop/paint something on to your example image to explain further.

For my own under seat support, I used four struts made out of off cuts from the sleepers. They connected the underneath of the seat part to the wall of the bench part. Like this. Unfortunately I don't have pictures of the underneath but it was rigid and no moving it even with 2 adults standing on it.

py · 11-05-2021 12:55pm

Sorry for delayed response. Here's my own sleeper bench. I've yet to sand and paint it. Might be a few more weeks until I get to that. As I needed the vertical posts for the retaining wall, I opted to have the seat part extend over them. As I mentioned earlier, I am using struts for strength underneath. I also used Timco 250IN 10inch decking screws. Covered them up with some oak dowels and will ensure they're flush with the seat when I sand it. It's not moving anywhere. When I get it all finished I'll post a follow up image on the forum somewhere.

electrofelix · 12-05-2021 11:57am

Thanks, I was thinking of letting it overhang over the front as well, so that the seat could be slightly deeper without all the weight being placed on the rear overhang so as to reduce the strain on the rear supports.

Constructing raised bed with integrated bench - how to stablize

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