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I recently built this set of shelves for my basement. Because of the insulated walls I do not plan to anchor them.

The shelves are not as solid as I hoped. After doing some research, I think one main contributor is the design I chose where a joist “tail” rests on blocking vs just having the end of the shelf rest on the blocking so the legs are not really tied to each other.

Thoughts on making this better?

Should I redo the legs and move them over?

Add bracing on short side of shelf from leg to leg?

Add diagonal bracing along the back?

Add a shelf at the floor level?

Thanks in advance for your advice.

enter image description here

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    The problem is that you have no lateral support. When you have long vertical members, each connection is effectively a single fastener. You need something to tie the vertical members together at different elevations, at least on the rear of the shelves. Either diagonal bracing, or a shear panel.
    – Huesmann
    Commented Aug 30, 2023 at 12:56
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    Two excellent answers, so just a comment: Re: Add a shelf at the floor level? Do not do that! It would not make a significant difference in the problem, it would be a huge mess if you ever had a flood, and it would prevent sliding things easily underneath, which you are already doing. Commented Aug 30, 2023 at 14:05

2 Answers 2

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Take a lesson from the flat-pack furniture designers and cover the entire back and sides from the top shelf to the bottom shelf (attached to the shelves not the posts) with thin, cheap sheet goods.

You could use tempered Masonite, pegboard, El Cheap-o paneling or anything else that you can find that's thin and stiff. If you have a pneumatic brad nailer, you'll be done in no time. If not, you can use brads, carpet tacks or any other fastener with a head (not finishing nails). Screws would be overkill.

Nail perhaps every 3-4 inches along the long sides, every 2-3 inches along the short sides. Nail into all three shelves.

This will prevent racking in any/all directions. Warning: make sure the whole deal is plumb and level before you attach the back and sides, because you will never be able to adjust it after the back and sides are installed.

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    Essentially, this is another way to achieve diagonal bracing; it just uses the sheet goods to spread the bracing over a larger area. I've done both, for different purposes; my bookcases use a plywood back, the tool shelves use pegboard, the water-barrel platform uses diagonal braces (mortised in for greater strength, since 80G of water weighs over 660 pounds).
    – keshlam
    Commented Aug 30, 2023 at 14:03
  • Glue is also useful, unless you will be taking this apart to move it. I think of sheet goods in this application as "an infinite number of overlapping X braces." If there's any chance of dampness or flooding, 4 bricks or 4 concrete blocks to elevate the legs from the floor is useful.
    – Ecnerwal
    Commented Aug 30, 2023 at 15:26
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    White Masonite hardboard is available at a bit higher price than plain brown, and would help improve visibility of stuff on the shelf if darkness and shadows are a concern. Current (2023) cost under US$20 per 4 x 8 foot sheet at both the orange and blue box stores.
    – MTA
    Commented Aug 30, 2023 at 15:59
  • I agree that this is one method. A simple 1x2 nailed (2 nails at every shelf/leg that it crosses) diagonally would do the exact same thing. It would work even better with another 1x2 nailed on the opposite diagonal. The number of nails recommended is severe overkill, though.
    – FreeMan
    Commented Aug 30, 2023 at 18:57
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The answer depends on how are they unstable.

if they are racking (deforming in a parallelogram shape) side to side, then you need to add a corner on the back wall from the upright to the shelf to make a triangle that will stabilize the corner

enter image description here

if instead they are racking front to back then you need a diagonal on the side to stabilize.

enter image description here

if it's because it is only standing on 3 legs then you need to either spend a lot of time fine tuning the lengths of the legs or use a wedge to support the floating leg.

Another option I can glean from the picture is bringing down a 2x4 from the rafters in the ceiling to tie the rack to the ceiling and provide anti-tipping protection that way.

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