How to Fix Sagging Bookshelves

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Are your bookshelves sagging? Fix 'em good, fix 'em cheap, right here.

Cheap can be good. But we all know there are some things you just don’t buy generic, right? Bookshelves or bookcases can be very expensive or very cheap. Until now, if you had a lot of books to put on a shelf, you needed to buy the expensive, real hardwood shelves—otherwise they would sag in the middle like an aging pensioner from Iowa on a steady diet of bacon and corn. Okay. So how do we stiffen up these cheap-o particle board bookcases?

This solution will work, that’s the first thing you need to know. I used it on my own $25 bookshelf from Wal Mart, and I crammed literally hundreds of pounds of books into this thing, with no sagging. Second, it’s a quick fix. Third, it’s cheap! How fitting.

First, if you don’t have cheap particle board bookshelves, go get some. Wal-Mart has a great selection of the build-it-yourself variety. In my opinion, the “espresso” or black finish looks best, and in this case it will be easier to work with. If you have those “oak” or “cherry” look bookshelves, you’ll need to do a little more work, but hey, a functional non-sagging shelf for under thirty bucks is a killer deal, even if there’s a little work involved.

Next, hit the big box hardware store and grab some 1 x 2 poplar. If they don’t have that, spring for the Hemlock. This stuff is cheap, and actual dimensions are ¾” by about 1 ½”, and you’ll need it in lengths that correspond to the width of the shelves in your unit. If you have a six foot tall unit like I do, you’ll need three lengths at about three feet (my actual dimensions were 28 ¼” long for each brace). The Home Depot usually has a cut-it-yourself miter hand saw station, complete with tape measure. If you know your dimensions beforehand and you don’t have a saw at home, it will be very convenient to cut your material at the time of purchase.

Before you leave the store, pick up a small box (you’ll only need fifteen) of 2” screws. These can be the bugle head drywall type or the self-tapping wood screw type. If you don’t have a 1/8” drill bit for your drill, pick one of these up too. If you have black or “espresso” finished shelves at home, pick up a rattle can of black spray paint for a buck. Otherwise grab a small can of stain that matches the finish of your shelves. If you have a circular saw at home (for the talented) or a table saw (for the inept), you’ll need it—otherwise arrange to borrow a friend who has one.

When you get home, if you have a new bookcase, go ahead and follow the instructions and build it. For existing shelves, just pop out the adjustable shelves that sit on those little pegs. These will need to be braced with the poplar 1 x 2 we just bought. The shelves that are screwed to the sides will typically not sag because they have sufficient support vis-à-vis having been firmly attached to the case.

What you’ll be doing is screwing each poplar board into the back side of each shelf. This is so that the bracing we’re doing will be hidden from view, and will provide support where it’s most needed—directly below your books. In addition, the shelves retain their adjustability. If you’re looking at the shelf from the back, the poplar board will attach, skinny side up, flush with the top surface of the shelf; and the screws will run through it into the shelf, from the back, horizontally. Clear as mud? And pretty as a homemade mud fence too.

Now, in order to make our bracing on the shelves without wrecking the strikingly gorgeous design of our bookcase, we’ll need to make room for the brace. This is accomplished by cutting ¾” off the back of each of our adjustable shelves. This will give us the extra room we need to fit that ¾” of poplar in behind them. Would it be possible to simply screw the poplar braces to the bottom side of the shelf? Yes, but it’s a weak design: as pressure from your books pushes down, it will pop the screws right out of the particle board, making the shelf pretty useless. We want to build something durable. Screws are designed to be strongest in shear load; that is, perpendicular to their long shape.

So now we’ve cut ¾” off each shelf, on the back side. A table saw is great for this; otherwise try to make a straight cut with a circular saw. Pre drill five holes in the poplar brace along the top side, about ¼” from the top edge. Evenly space them out, with one in the center, two an inch from the ends, and two halfway between those and the center. Pre-drilling the poplar brace will prevent it from splitting; this is critical.

Now start screwing your braces to the back sides of your shelves, being sure to hold the top edge flush with the top surface of the shelf, and extra careful to send them in straight. Do not over tighten the screws. If you feel the need to use wood glue, knock yourself out, but you don’t really need it.

Once the braces are installed, if you have the espresso finish, carefully spray the black paint onto the exposed surfaces of the brace—the very back top edge, and the underside and facing side of the brace under the shelf. If there’s overspray, no big deal, it will dry and it will match pretty daggone good. And I’m not sure if that’s okay to say or not, but I’ll say it anyway. If you have any other finish, like “cherry” or “oak”, you’ll need a brush and your can of stain in order to get the brace to match in color. A little extra work.

When everything is dry, reinstall the shelves in the bookcase, reinstall the books on the shelves, and prepare for a blissful sag-free existence. Now when you grab your leatherbound copy of The Complete Works of William Shakespeare you will not wax woeful at the sorry sagging state of the shelf upon which it sits. Enjoy! And pass it along. It’s a great way to save some hard-earned cash.


Bella Delanna
Posted on Apr 28, 2011
Dr. Johnson C Philip
Posted on Mar 26, 2010