How to Determine the Age of a Building

by Nick Gromicko, CMI®
Building technologies and fashions have followed well-known trends that allow inspectors, clients and anyone else interested to roughly determine Crude, square nails may be hundreds of years oldwhen particular buildings were constructed. Here are some methods based on a building's materials, components and styles. 
Estimates of Building Age Based on Building Materials


  • 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.


  • 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 ReceptaclesModern electrical receptacles are polarized and grounded

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.  


  • In the late 19th century (1890), linoleum became common for use in hallways and passages, but it became better known for its use in kitchen floors in the 20th century, up through 1960. Originally valued for its water-resistance and affordability, it was surpassed by other floor coverings by the mid-20th 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.Old linoleum floor
  • 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 receDutch-style Colonial housently, 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 18th century foundation, for instance, especially if there was a fire that destroyed the rest of the structure. 

Estimates of Building Age Based on Architectural Style 
  • 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, Mcmansions are hastily-built and often too large for their plot of landelaborate homes owned by a class of suddenly-rich businessmen who enjoyed grandiose displays of their new wealth.
  • Early 20th 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.
In summary, there are many ways that inspectors and their clients may estimate the age of a building.