Why be frantic? What sort of boards are we talking about? Pine? Oak? How much weight?

Rather than look for an authoritative reference, you could just lay one of the boards across two garbage cans or sawhorses or the seats of chairs, and press down or load stuff on it to get a sense of its rigidity.

Usually a 1" thick shelf will hold. This is pretty standard. I've built lots of shelves using a 3/4" shelf of plywood with a strip attached on the vertical edges to stiffen the shelf. This could be any thing from 1 to 11/2 inches. You can use 2 pieces of 1/2" plywood glued together, add the strips and increase the strength and so on. This gives you the effect of a solid wood shelf but takes advantage of the strength of the plywood. This works well and saves $$. Obviously, the wider the shelf, the thicker/stiffer it needs to be. I try to stay in the 36" range for books for the width of the shelf. This is variable for a few inches. If you have a space say, 41inches wide that you want to put shelves in, you wouldn't want to divide it and have 2 narrow little spaces. So you thicken/stiffen your shelves to accomodate the width. So this is a common sense kind of thing. Some types of wood are naturally stronger that others and that is to be considered as well. But to answer your question, 1" thick shelves..36" width.

Frantic because I thought I had this information on hand and can't find it AND because I promised husband and dad if they helped me I'd find this information for them.

My bookshelves will be LONG. I can't remember the exact footage. Maybe 80 inches? This is a newer house so the studs should be roughly what? Every 14 inches. We can certainly put a bracket thingy at every stud. However, I was hoping that we wouldn't do that because you loose storage space with the supports that hang down.

Additionally I don't expect to books on every shelf straight across the whole thing. However, having said that- it is probably best to plan on that because in this house we don't get rid of many books.

Our furniture is knotty pine. I am going to make the front facia pieces be knotty pine. That would be for decoration. But the board itself could be something else- suggestions?

Ginger

There is not much that will help prevent sagging on a shelf 80" long. Except a 2x6 under the center----which will look very tacky as well as take up storage room.

Plywood is the best material for your job. What Wayne suggested is really good advice---except for the word 'vertical' in the third sentence----I think he meant 'horizontal'.

Build the shelves with ply and add the knotty pine as trim on the front. By making the shelves 40" wide---a double vertical piece in the middle and using 1/4" dadoes for mounting the shelves---you get the 80" length with maximum support and room.

HandyMac is right -- short of using miniature steel trusses, you're not spanning 80" with shelves supported only at the ends. Halving that distance, combined with the edge stiffeners, will get you there nicely.

Thank you. I appreciate your help.
As you can tell I'm very new to this whole process.
And I'm probably not being very clear either.

We will most likely put supports in the form of those brackets (they look like maybe big L's) all along the 80 inches It is my preference to have one long span but failing that we will devide the space in half and have two spans (as suggested above).

again, Thank you everyone.

Ginger

We had these in our house growing up. We put the vertical supports and brackets generally every other stud (except on the bottom shelves where we lined hardback books wall to wall, we did use a support at each stud (16 inches) here for extra support and safety).

Our shelves were 1x8 stained pine. No problems with sagging. These must have been in my parents house for 15 years...and when I first moved out they moved as well and we cut the boards shorter and they "lived" in my first 2 appartments.

Good luck!

If I'm getting the picture right after these other posts, these are to be shelves laid on metal brackets with no sides. Just shelves on the wall. If this is the case, for 80", you would use 3 "runs" of brackets. The first one would be at 16" from the end of the shelf, the second at 48" the third at 64". This will allow you to have spans LESS than the 36" we originally suggested. Every other stud will place each "run" 32" apart, leaving a 16" overhang at each end of the shelves. The only negative to this would be the "centering" of the shelves on the space, as you would have to place the "runs" where the studs exist. For this, a 1" shelf will be fine, whether solid stock or plywood stripped on the edges. A ready made shelf,1" thick, can be made from COMMON STEPTREAD that can be bought at almost any lumber supply. This is 1" thick with one nice rounded edge. This is typically 12" wide so may have to be ripped to a narrower width. Commonly comes in pine but is available in other types also. I would reccomend this highly. Hope this makes sense and helps.....

Sorry, I've left out 1 "run" of brackets. For 80" shelves and to evenly place the "runs" on existing studs, the method I described would need 4 "runs" of brackets..The first one 16" then 32" then 48" then 64". By extending the shelf length to 96"or some figure above 80" to allow for overhang on the ends, you could evenly place the "runs" every other stud and proceed as I described in my last post. 16"-48"-80". Sorry about the mistake and confusion.

I am getting the idea you are intending to build one shelf---correct? When you made mention of book shelves, most of us immediately envisioned book case style shelves.

In the event you mean one shelf on a wall that is 80" long----supported by L brackets----one bracket on alternating studs will be plenty of support. That means the L bracket spacing will be about 32" apart.

Ginger, I gave you some info on the Organizing the Home Forum. I just want to say, don't put those "wall standards w/ slots for brackets" at EVERY stud.

The bracket itself gets in the way. Every-other will be strong enough.

(I have one shelf--why only 1, I don't know--that's sagging; i've contemplated emptying it and flipping it over so it can sag the other way. But I know I won't get around to it. And I'd have to cut new notches in the back so the shelf can "wrap around" the standard on the wall so it doesn't have a gap back there.)