When building a bookcase or cabinet, the greatest span or length of a shelf to prevent sagging has a variety of factors that must be considered. Here are 4 factors that you have to take into consideration – 1. How is the load distributed? 2. What is the load expected to be? 3. What is the shelf made from? 4. How is the shelf reinforced?
1. Distribution Of The Load.
There are tests that have been conducted in order to give these recommendations. First, the worst case scenario was looked at for the load distribution. 6 bricks that totaled 42 pounds were placed in the shelf’s center. In a normal situation though, the weight usually is distributed throughout the shelf as a whole.
2. The Load Expected
Another variable to take into consideration is the shelf’s length. If the shelf is longer, the more may be put on it, so the more weight it will have to bear. For every foot of the shelf, there will be about 20 pounds of books. Let’s say the shelf is 3 foot long then. It will have to be able to support 60 lbs. Of course, different books are different sizes, so we have to take that into consideration. But this is an average.
3. The Shelf’s Material.
Another factor to consider is the type of material used, and it’s weight capacity. Is it plywood, particle board, or a hardwood of some sort? Every lumber has it’s own stiffness and load bearing.
4. How Is It Reinforced?
Last of all, if you need to increase the span of the shelf, you will have to increase the reinforcement of it so it won’t sag.
Here are some guidelines: By taking these 4 factors we have developed a chart with the guidelines that you can use in order to figure the maximum span of the shelves to prevent any sagging. Of course, the practical approach would be to use plywood or 4/4 lumber for the reinforcement. It will produce shelves that have a minimum sag but still have visual appeal.
The Maximum Span For A Shelf 10″ Wide That Is Full:
3/4 Particle Board – 24 inches
3/4 Plywood – 30 inches
4/4 Solid Stock – 36 inches
6/4 Solid Stock – 60 inches
3/4 Plywood Reinforced With The Following:
1-1/4 wide face strip edging – 36 inches
1-1/4 wide face strip for the sides – 32 inches
Aluminum stripping on the underside – 36 inches
Molding strips on the underside – 36 inches
Keep these in mind and factor in any variables that you come across. These should give you a good estimate on the spanning of any shelf for a bookcase that you want to build. They will definitely make a difference in sagging shelving or not.