Building technologies and fashions have followed well-known trends that  allow those interested to roughly determine when  particular buildings were constructed.  Here are some methods based on a  building’s materials, components and styles.

Nails

• Prior to the 1800s, nails were hand-made by blacksmiths and nail makers  and appear crude compared with modern nails. They are often squared rather than  rounded, and have a beaten look on the top of the head.
• Type A- and Type B- cut nails were used from 1790 to 1830. They were  made from wrought iron and are squared.
• Wire nails, used from 1890 through today, are modern, machine-made  nails that are rounded and more practical to use than the earlier designs.

Wiring

• Aluminum wiring was used extensively from 1967 till 1975, a  period during which copper was prohibitively expensive. Aluminum use  was generally discontinued when its potential as a fire hazard become  publicized.
• K&T or knob-and-tube wiring was an early method of electrical  wiring installed in buildings from 1880 to the 1940s. The system is considered  obsolete and can be a fire hazard, although much of the fear associated with it  is exaggerated.

Electrical Receptacles

Electrical receptacles evolved from earliest to most recent in the following  order:

• non-polarized:  These early receptacles are made up of two slots  of equal size, with no ground slot.
• polarized:  These receptacles are two-slotted, one of which is wider  than the other to allow for proper polarity.
• grounded, polarized:  Modern receptacles were changed to permit  grounding of an appliance or device. They can be identified by the round hole  beneath the center of the polarized slots.

Flooring

• In the late 19^th century (1890), linoleum became common for  use in hallways and passages, but it became better known for its use in kitchen  floors in the 20^th century, up through 1960. Originally valued for  its water-resistance and affordability, it was surpassed by other floor  coverings by the mid-20^th century.
• Asphalt tile was used for floor tiles starting around 1920 through  the 1960s. The earliest tiles are darker because they contained more asphalt,  unlike later tiles that had higher levels of synthetic binders.
• Vinyl asbestos tiles became popular in response to consumers who wanted  lighter-colored tiles of varying color patterns.

Structural Panels

• Plywood’s use began around 1905.  It is made from thin sheets of veneer  (layers of wood that are peeled from a spinning log) that are cross-laminated  and glued together with a hot press. Since it is made from whole layers of logs  rather than small strands, plywood has a more consistent and less rough  appearance than oriented strand board (OSB).
• Waferboard or particle board was developed in the 1970s and, like plywood,  is still used today. This material appears similar to OSB, except the wooden  strands from which it is composed are not aligned.
• OSB was developed the 1980s and is manufactured from heat-cured  adhesives, and then rectangularly shaped wood strands that are arranged in  cross-oriented layers. Produced in large, continuous mats, OSB is a solid-panel  product of consistent quality with few voids and gaps. While OSB was  developed fairly recently,  it became more popular than plywood in North America by 2000.

Keep in  mind that houses, especially older ones, have evolved over many years. It can be  very difficult to reliably date a building based on the presence of a single  material or component. The majority of a house might be newer than its  18^th century foundation, for instance, especially if there was a fire  that destroyed the rest of the structure.

• American Colonial (1600 to 1800):  North America was colonized by  Europeans who brought with them building styles from their homelands. This broad  category includes the following regional styles and their characteristics:
  • New England style (1600 to 1740):  These homes feature steep roofs  and narrows eaves used in simple timber-frame houses, usually located in  the northeastern United States, primarily in Massachusetts, Vermont,  Connecticut, New Hampshire and New York.
  • German (1600 to 1850):  Most often found in New York,  Pennsylvania, Ohio and Maryland, these buildings generally feature thick,  sandstone walls.
  • Spanish (1600 to 1900):  Located in the American South, Southwest,  and California, these houses are simple and low, built from rocks, stucco,  coquina and adobe brick, with small windows and thick walls.
  • Other home styles from the American Colonial period include Georgian,  Dutch, French and Cape Cod.

• Classical style houses (1780 to 1860):  Many houses built during  the founding of the United States are a throwback to ancient Greece, emphasizing  order and symmetry. Among the styles common to this era are Greek Revival,  Tidewater and Antebellum.
• Victorian (1840 to 1900): With the technological innovation  of mass production came the ability to produce large homes affordably.  Queen Anne, Gothic Revival, Folk and Octagon are some of the architectural  styles common to this era.
• Gilded Age (1880 to 1929): The “Gilded Age” is a term popularized by Mark  Twain to describe extravagant wealth. This era saw the construction of large,  elaborate homes owned  by a class of suddenly-rich businessmen who enjoyed grandiose displays of their  new wealth.
• Early 20^th Century homes:  Homes built during this period  were compact and economical, somewhat smaller and less pretentious than earlier  Gilded Age homes.
• Post-War homes (1945 to 1980):  Very simple and affordable, some  critics believe they have no style at all. Soldiers returning from the World War  II spurred the construction of these homes, which emphasized utilitarianism  over style more than preceding periods.
• “Neo” houses (1965 to present):  Theses houses borrow styles from  previous architectural eras, such as Victorian, Colonial and Mediterranean.  “McMansion” is a word used to describe large, quickly-constructed, flamboyant  and poorly-designed neo-eclectic homes.

Other Ways to Determine a Building’s Age:

• Check the meter reader. Sometimes, the meter reader will bear a date stamp.
• Check the inside of the toilet. Toilet manufacturers often stamp the inside  of tanks or lids with the year the toilet was made. Toilets are usually  installed right after construction, so you can often determine a newer home’s  age by inspecting a toilet.
• In log homes, it may be possible to tell the building’s age by analyzing the  tree rings in a piece of timber removed from the building. The science on which  this is based, dendrochronology, does not arrive at an age based on the number  of tree rings, but rather focuses on patterns of tree rings and compares these  with known pattern ages for a specific region. This method is destructive and it  requires a specialist.
• Local town, county, or state tax records usually indicate the date or  year a building was constructed.
• Historical real estate listings may include indications of building age.
• Census records can prove that a house was present at the time the census was  taken.
• Papers found inside the building will often indicate when the building was  present. A house will probably be at least as old as, for instance, newspapers  from the 1920s found in a crawlspace.
• Employ an architectural investigator to date the house by studying its wood,  plaster, mortar and paint.
• The aluminum spacers within thermal-paned windows often bear the year of  production, which can at least provide an approximate date of  installation.
• Sewer grates are sometimes stamped with the year they were manufactured,  which may provide an age for the neighborhood.

by Nick Gromicko