Woodworking Tips via Email #1:
Shelving Spans

If you're designing a cabinet or a bookcase, what's the greatest length (span) a shelf can be without an objectionable sag? There are four factors to consider: 1) how the load is distributed, 2) the expected load, 3) the shelf material, 4) the method of reinforcement.

LOAD DISTRIBUTION. For the tests we conducted to create our recommendations (see below), we wanted to determine the worst possible situation for the distribution of load. So we use six bricks (42 pounds) and placed them right in the center of the shelf. However, in a normal situation, the weight would probably be distributed over the entire shelf.

EXPECTED LOAD. Another factor used to determine maximum span is the total expected load -- the longer the shelf, the more books (and weight) it has to hold. A running foot of average sized books weighs about 20 pounds. So a three-foot shelf filled with average sized books would have to support 60 pounds. Records albums (does anyone use these anymore) and encyclopedias would weight more, paperback books less.

SHELF MATERIAL. The third factor used to determine maximum span is the type of material used -- particle board, plywood, solid wood. Each has a different stiffness.

REINFORCEMENT. Finally, if you want to increase spans, you can add reinforcement to reduce the amount of sag.

GUIDELINES. Taking the four factors into consideration, the chart shows some general guidelines for the maximum span for shelves to avoid objectionable sag. Note: The most practical approach is to use 4/4 stock or plywood with reinforcement. This will produce shelves with minimum sag and the best visual appearance.

MAXIMUM SPAN FOR 10" WIDE SHELF FULL OF BOOKS

Jacobean (1600-1690)
An English style of furniture, which is medieval in appearance with straight lines, rigid designs, sturdy construction, ornate carvings and a dark finish. Much of the early American furniture was patterned after this style.

Early American (1640-1700)
Rudimentary utilitarian furniture made from local woods. It was brought from or modeled after European furniture styles, particularly from England , France , the Netherlands , Scandinavia and Spain .

William and Mary (1690-1725)
Named after William and Mary of England (1689-1694). It has Dutch and Chinese influences and is characterized by trumpet turned legs terminating in a ball or Spanish foot, padded or caned chair seats, and Oriental lacquer-work.

Queen Anne (1700-1755)
Named after Queen Anne of England who reigned from 1702-1714. The Queen Anne style is a refinement of the William and Mary style with a moderately proportioned, graceful appearance. It is characterized by cabriole legs terminating in a pad or drake foot, fiddle-back chair back, and bat wing shaped drawer pulls.

Colonial (1700-1780)
Combined the furniture style characteristics of William and Mary, Queen Anne, and Chippendale. Colonial furniture tended to be more conservative and less ornate than English and European furniture of the same style period.

Georgian (1714-1760)
Named after George I and George II who reigned England from 1714-1760. Georgian furniture is a more ornate version of Queen Anne. It is characterized by heavier proportions, elaborately carved cabriole legs terminating in a pad or ball-and-claw foot, ornate carvings, pierced back splats, and the use of gilding.

Pennsylvania Dutch (1720-1830)
A simple, utilitarian American country style of furniture with Germanic influences. It is characterized by colorful folk painting on case pieces.

Chippendale (1750-1790)
Named after British designer and cabinet maker Thomas Chippendale, who published his furniture designs in "The Gentleman and Cabinet Maker's Director" in 1754. The Chippendale style can be classified into three types: French influence, Chinese influence, and Gothic influence. In the United States , the Chippendale style was a more elaborate development of the Queen Anne style with cabriole legs, ball-and-claw foot, and broken pediment scroll top on tall case pieces.

Robert Adam (1760-1795)
Named for architect Robert Adam who studied ancient architecture in Italy . While in England , he designed furniture with classical details that would fit the character of his classically designed homes. The Adam style was limitedly reproduced by cabinetmakers in the United States . Adam interior millwork and woodwork was reproduced in South Carolina .

Hepplewhite (1765-1800)
Named after English designer and cabinetmaker George Hepplewhite whose designs in "The Cabinet Maker and Upholsterers Guide" were published posthumously in 1788. The Hepplewhite style is neoclassic and was reproduced in the United States particularly in the Carolinas, Maryland , New England , New York and Virginia . It is characterized by a delicate appearance, tapered legs and the use of contrasting veneers and inlay.

Federal (1780-1820)
Combined the neoclassic furniture style characteristics of Hepplewhite and Sheraton. It is characterized by graceful straight lines, light construction, tapered legs, and the use of inlay, and contrasting veneers.

Sheraton (1780-1820)
Named for English designer Thomas Sheraton who published his designs in "The Cabinet Makers and Upholsterers Drawing Book" in 1791. It is a neoclassical style characterized by delicate straight lines, light construction, contrasting veneers and neoclassical motifs and ornamentation. The Sheraton style was the most reproduced style in the United States during the Federal period.

Duncan Phyfe (1795-1848)
Named after American cabinetmaker Duncan Phyfe. The Duncan Phyfe style is considered by some art historians as more of an adaptation and refinement of Adam, Sheraton, Hepplewhite, and Empire than a style in itself. It is characterized by carved or reeded legs and neoclassic motifs.

American Empire (1800-1840)
Patterned after French Empire with classical influences. It is moderate in proportion with classical ornamentation, coarse carving, and a dark finish.

Shaker (1820-1860)
A simple and utilitarian style produced by the religious group, the United Society of Believers, in self-contained communities within the United States . It is characterized by straight tapered legs, woven square chair seats and mushroom shaped wooden knobs.

Victorian (1840-1910)
Named for Queen Victoria of England who reigned from 1837-1901. The Victorian style draws its influence from gothic forms with heavy proportions, dark finish, elaborate carving, and ornamentation. The Victorian period was the first furniture style of mass production.

Arts and Craft (1880-1910)
The Arts and Craft is characterized by simple utilitarian design and construction. Arts and Craft style furniture is also referred to as Mission .

Art Nouveau (1890-1910)
A naturalistic style characterized by intricately detailed patterns and curving lines.

Scandinavian Contemporary (1930-1950)
A simple utilitarian design style in natural wood popularized by Danish and Swedish designers.