Mounting / Support requirements for an oversized book case

Question

I am building a large bookcase, 12 feet wide by 5 feet high. Not a problem if it sits on the floor but the twist is that I must raise it up 18" due to a wall to wall hot water baseboard heater and electrical outlets along that wall.

I plan to use use 9 heavy-duty angle supports (rated 125 lb load) every 16 inches on the wall and wood support legs (1 inch decorative spindles every 3 feet on the front edge of the 12" depth unit. I estimate the load to be close to 800 lbs of books and items plus the lumber.

I have a few questions:

1. I believe I have sufficient load support. The brackets alone support 1,125 (9*125) lbs. With the additional front leg support, does this provide ample support?

2. What kind of screws should I use to hold the brackets? The sheetrock is 5/8 thick and the support bracket is 1/8". I don't want the screws supporting the brackets to snap under the load. Would 3" steel nails be better?

3. The leg supports are 1" spindles. Would it be advisable to use a 4X4 baluster - the kind used at the end of a staircase. Obviously a 4*4 would provide a ton more support - but its bulkier and less attractive -- but is it overkill? I guess I can space them every 4 feet?

Thanks for any assistance!

PS - The unit would be secured at the top. It will reside in a space that has a soffit for ductwork and will be secured to the crossbeam for stability, so no danger in tipping forward.

Answer 1

1. The angle brackets alone should be adequate if two things are true: Your case is well-built, and it's fastened securely to the wall. The spindles will do little to support the unit should they be accidentally knocked out by children, pets, or you. They shouldn't be considered a critical support component, in my opinion.

2. No, don't use nails. They don't have the pullout strength of screws and aren't removable (practically speaking). Use large wood screws (#14 or so), or lag screws (1/4" to 5/16" or so if the bracket holes allow). The key is penetration into the framing lumber. I'd want 2" of depth into the lumber itself. Pilot properly for maximum strength (slightly smaller than the screw shank). Also a factor is the number of screws per bracket. I'd want at least two. Also a factor is mounting of the cabinet to the wall. If you have a stout back panel, or a set of rails through which you can fasten, decorative or hidden screws into the framing will take much of the load off the brackets.

3. I addressed this earlier. Any support legs must have adequate diagonal bracing to prevent knockout. This means that the effort and expense may make them impractical. In any case, 1" is probably too small. Look to heavier oak stair balusters in the 1-1/2" or 2" size, with the milled dimensions being slightly smaller.