How strong is plywood?
No ! 1/2″ plywood is not strong enough to hold the books without bowing. I would suggest using 3/4″ solid boards. You can find these in the pre-cut lumber section at Lowes or H-Depot – Menards. If you want extra strength for the shelves allow enough room in your height to run a 1″ x 2″ on edge under the front of the shelf. *Remember to add to the overall height of the shelf by the height of the 1″ x2″ or your books won’t fit. Plywood is not the best looking as the front edges show all the plys of the plywood. Plywood does not hold nails and screws very well going into the edge of the plys.
I’d think not. Beam strength is proportional to the cube of the thickness. For example, if you double the width of a shelf, you double the load carrying capacity. If you double the thickness, you have eight times the capacity. So a 3/4″ shelf will have over 3 times the load carrying capacity of a 1/2″ shelf. http://www.google.com/search?hl=en&rlz=1… Most 3/4″ plywood is good for bookshelves up to about 30″, so I think 24″ on 1/2″ is going to sag.
