Shelf materials explained

It is difficult to recommend a type of shelf material and be specific about the thickness and the spacing between supports as they depends so much on the weight being placed upon them and the grade of the material used.

You will get efficient and thoughtful service from Maxrac.

The comments below are for comparison purposes only and advice should, where possible, be obtained from the manufacturer or supplier of the shelf material.

This page only deals with the shelf material, see our other page for methods of supporting shelves.

For the comparison below:

• A light load is considered to be small plants, vases, trinkets etc.
• A medium load is considered to be paperback books.
• A heavy load is considers to be large hardcover books, large plants etc.

The actual classification of an intended load must be 'common-sense', if in doubt, build stronger.

Always remember what a shelf was originally designed for before suddenly putting a heavy item on a shelf intended for only light objects.

The overhangs at each end beyond the brackets should always be kept to a minimum, generally no greater than 20% of the distance between the support brackets.

timber - pine board - chipboard - MDF - blockboard - plywood -glass
shelf stiffener - timber edging

Solid timber

Solid wood is strong and available in a variety of planed widths to suit most shelving needs - where the required width cannot be obtained, tongued and grooved board can be used to avoid the separate planks from warping open - alternatively the separate planks could be joined using dowels or other means.

Timber is easy to work and can be finished using polishes, varnish or paint.

The thickness required to avoid sagging will depend upon the weight being placed on the shelf and also the distance between the supports. Use 18mm thick timber as a minimum and support the shelf at no greater than 700mm centres or 25mm timber with supports no greater than 900mm.

Slatted timber - an alternative for wide shelves is to make a slatted shelf using a number of strips of timber fixed to battens underneath - the under battens then being secured to the support brackets.

Edge laminated softwood board

Edge laminated softwood board (pine board etc) - made up of strips of softwood (typically 25 to 100mm wide) glued edge to edge to achieve finished boards upto 600mm wide.

This is typically as strong as solid timber and often looks as good except at very close up - some boards may be found to incorporate a lot of filler to build the surface up to a smooth finish, this can have a detrimental affect on clear finishes.

Use the support spacings as above for solid timber.

Chipboard

Plain chipboard - unlaminated chipboard is the cheapest and weakest material. It is generally unsuitable for shelving as the finish is poor.

Laminated chipboard - laminated chipboard is cheaper than solid timber and comes in a number of different types of veneer. It is not so strong as solid timber and will tend to sag except under a very light load. Use 12mm chipboard as a minimum and support the shelf at no greater than 300mm centres for all but the lightest of loads. Or 18mm chipboard with supports no greater than 700mm apart.

MDF

MDF (Medium Density Fibreboard) is stronger than chipboard. Care needs to be taken when when working with MDF as it is manufactured using urea-formaldehyde resin which can be harmful. Adequate ventilation and wearing a face mask to avoid breathing in the dust when machining it are essential.

Formaldehyde can also be released over time in low concentrations; not everyone is affected but some people can be adversely affected by just having a piece of MDF in a room.

MDF can be finished using paint to suit the decor or just sealed with a varnish. Use 18mm MDF as a minimum and support the shelf at no greater than 500mm centres for all but the lightest of loads. Or 25mm MDF with supports no greater than 700mm apart.

Blockboard

Blockboard (with the core running lengthways) is stronger than chipboard and is less likely to sag. It is easy to work with and can be finished using paint, the edges will probably need to be covered with a trim to hide the different strips. Use 18mm thickness as a minimum and support the shelf at no greater than 700mm centres for all but the lightest of loads.

Plywood

Plywood is stronger than laminated chipboard and is less likely to sag. It is easy to work with and can be finished using paint, the edges will probably need to be covered with a trim to hide the different layers. Use 18mm thickness as a minimum and support the shelf at no greater than 700mm centres for all but the lightest of loads.

Glass

Glass can be an attractive shelving for light loading and many DIY stores stock pre-cut glass shelving either on its own or as part of a complete shelving kit - special brackets are available for glass shelving, they have clips and lips to hold the glass in place. The glass is specially toughened so cannot be cut to size, if 'non-standard' sizes are required, go to a glazing merchant where it can be cut to size and then toughened. Never use ordinary window glass.

Shelf stiffener

Any shelf material can be stiffened to increase the load it will carry and the distance required between supports. Screw and glue the batten to the underside. A batten fixed to the wall and supporting the rear of the shelf can be used instead or as well.

Timber edging

When chipboard, plywood or blockboard has been cut, the exposed edges may be unattractive. A hardwood edging trim, cut with corner mitres, can easily be glued and pined to the edges to hide the cut edges.

Designing sag-proof shelves.

Have you ever heard a shelf groan? Well, maybe not, but some shelves look like they would if they could. So much stuff gets piled on them that they end up sagging like a limp noodle. It&#;s not a pretty sight. A span that holds up weight should look strong and sturdy. Even a slight sag sends an unappealing visual message.

A shelf sags in two stages. There&#;s a small sag when you first put weight on the shelf. This sag, or deflection, increases as more stuff is loaded on the shelf over the years. The shelf keeps on sagging, a little more each year, because wood slowly but surely changes shape under a load. This characteristic of wood is called &#;creep.&#; Arm yourself for the fight against creep with common sense engineering knowledge about how each dimension of a shelf affects its strength, or rigidity (Fig. A).

The most important dimensional factor is a shelf&#;s thickness. The effect of the other two dimensions, width and length, is straightforward; add 10 percent to the width of a shelf, and it&#;s 10-percent more rigid; add 10 percent to the length, and it&#;s 10-percent less rigid. However, add 10 percent to the thickness of a shelf and it&#;s 21-percent stronger! Strength increases at an exponential rate as you add thickness. That&#;s why wooden joists and steel beams stand on edge. A shelf that&#;s 7/8-in. thick is about 36-percent stronger than a 3/4-in. thick shelf. If you&#;re careful, you should be able to get 7/8-in. thick boards from 4/4 lumber. With such a substantial increase in rigidity, it&#;s definitely worth the effort.

Contact us to discuss your requirements of longspan shelving supplier. Our experienced sales team can help you identify the options that best suit your needs.

Shelving Standards

Let&#;s put our common sense engineering to the test. How wide or long does a cherry shelf have to be to hold up, say, a set of encyclopedias? We can use standard dimensions that have proven themselves reliable over the years to answer this question.

Encyclopedias are large books, so we need a shelf that&#;s at least 12-in. deep. (Books look best when they sit 1-in. or so back from the front edge of a shelf.) How heavy are they? It wouldn&#;t be a bad idea to place them on a bathroom scale and find out. Books and magazines can be surprisingly heavy. These standards suggest they&#;ll weigh up to 50 lbs. per running foot.

How long should a 3/4-in. cherry shelf be to hold up these books? The standards tell us that a wide hardwood shelf that carries a heavy load should be no more than 36-in. long. But this doesn&#;t tell us the whole story, and that&#;s why we have to look at one more variable before we can build this shelf with confidence.

How Strong Is the Wood?

Some species of wood are much more rigid than others. In terms of deflection under a load, hickory is about twice as strong as butternut. If we make similar shelves out of hickory and butternut, and apply the same load, the butternut shelf will sag twice as much. If we cut the butternut shelf in half, it will sag the same amount as the hickory shelf.

The shelving standards are based on averages. Is our cherry encyclopedia shelf average? No, cherry is more than 10 percent weaker than an average wood like walnut or soft maple (Fig. C). Thus, the shelf has to be shorter or thicker.

Plywood and Composite Woods

Manufactured wood products are not as strong as solid wood. Plywood is only about half as rigid as the average hardwood because it&#;s made of alternating layers of thick veneer. Wood is not as rigid across the grain as along the grain. In a shelf, the grain of some of the veneer layers runs the long way, but almost half runs the short way.

Particleboard and MDF (medium density fiberboard), collectively called composite woods, do not have the grain structure of solid wood or of plywood veneers. These products have a hard time holding up their own weight. They have about onequarter of the strength of an average wood. Nevertheless, composite wood is widely used for shelving. Comprehensive information on sizing composite wood shelves is available from an industry trade association.

The rigidity of plywood and composite wood can be improved by gluing on solid wood edges or plastic laminate faces (Fig. D.)

How to Strengthen a Shelf

After weighing the encyclopedias, you may find that they exceed the limits of the standards. In that case, we need to make a more rigid shelf. We could widen the shelf from 12-in. to 16-in., an increase of 25 percent. That would make the shelf 25-percent stronger. It&#;s an option, but for the sake of argument let&#;s say that a 16-in. shelf is too deep for our design. What else could we do?

We could shorten the shelf. Like width, it&#;s a straight percentage reduction. A shelf that is 25 percent shorter will also hold up 25 percent more weight.

A shorter shelf for our encyclopedias isn&#;t going to work, however. With all the supplements added to it, there&#;s more than three feet of books! How about making the shelf thicker? If we&#;ve already purchased 3/4-in. stock, this option is out.

It&#;s time to be creative about building a shelf that will be stronger than just one solid board. The simplest solution is to add a lip or two to the shelf. Rip some of the 3/4-in. stock into 1-1/2-in. wide strips, turn them on edge, and glue them onto the front and back edges of the shelf (Fig. E). If you need considerably more strength, make the rear strip several inches deep.

Another way to add thickness to a shelf without using expensive thick lumber is to make a hollow shelf 1- to 1-1/2-in. thick from thin plywood and strips of solid wood (Fig. F). This type of shelf is based on the engineering principles of a torsion box. It&#;s light in weight but very strong. Use it to carry very heavy loads.

Housing a shelf into the sides of a case will enable the shelf to carry more weight. A fixed shelf is more rigid than a loose shelf because its ends are joined to the sides at a stiff right angle (Fig. G). Some joints are stronger than others, so choosing one kind over another can also effect the strength of a shelf. A plain dado works fine, but a sliding dovetail is stronger because it has more mechanical strength and a larger glue surface area.

Supporting a shelf in the middle strengthens a shelf more than you might think (Fig. H). Weight on one side of a middle support helps hold up weight on the other side, like kids on a see-saw. The net effect is that one long shelf with a center support can hold up more weight than two shorter shelves.

Product Recommendations

Here are some supplies and tools we find essential in our everyday work around the shop. We may receive a commission from sales referred by our links; however, we have carefully selected these products for their usefulness and quality.

• Kreg Top Trak Kit

• Dado Blade Set

• Jig & Fixture Bar

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