4 Ways to Determine the Age of a House

Age of a house

Knowing the age of a house lets you help the customer understand more about what he’s buying.


The general age of a house might be obvious to you. Then again, it might not. Where you can reasonably assume that a house in a new development was built within the last few years, it’s not as easy with older properties.

The reason why it’s important to know the age of a house, or at least have a good idea about it, is because particular hazards exist in older properties that you won’t find in a new house. But with a few age clues, you’ll have a better idea about what to watch out for.

Age of house

Square nails are usually iron, and may be rusty.

#1: Square Nails Imply Age

While it’s certainly possible that the builder of a newer home might have commissioned the fabrication of square nails, it’s highly improbable. Square nails were the norm in the 1800s and on back.

Very early square nails (prior to the 1800s) have a rough look from end to end, including the nail head. Examples from the late 1700s through the mid 1800s were also square, says InterNACHI, but had a more uniform appearance. Conversely, from the late 1800s through today, nails are usually rounded and uniform.

#2: Aluminum Wiring is Old, but Knob and Tube is Older

Aluminum wiring is an older wiring style, which was in use from the late 1960s through the late 1970s, when, as InterNACHI explains, copper was expensive. It had a short run because it became known as a fire hazard.

Even where it’s not in use anymore, the existence of knob and tube (K&T) wiring reveals that the house was likely built no later than the 1940s but might have been installed as early as 1880. The house could be older, of course. Knob and tube wiring is characterized by porcelain tubes with cloth-covered wires running through them. You’ll usually see K&T wiring mounted on joists and inside walls.

#3: Old Electrical Outlets Aren’t Grounded

One of the most obvious signs that a house is older is the presence of electrical outlets with only two slots instead of three. Non-polarized outlets have two slots that are the same size, and these are the oldest. Polarized outlets came next, with one slot wider than the other.

New electrical outlets have two different size slots, plus one round hole below the slots. The hole indicates that it allows grounding, although a ground wire may or may not be present. Although outlets might be used and reused over and again, non-polarized are the oldest, and polarized with a ground are the newest.

Age of house

Some original fixtures might have a date stamp.

#4: Other Age Clues that Help

InterNACHI also explains that there are other ways to help date a house. The electric or water meter might have a date stamp, and toilets might have the date inside the lid.

When all else fails, if you really need to learn the age of the house you can check with the county tax assessor’s office. It’s a bit out of the way, but all you need is the house address. For a fee, they will provide you with the date the house was built.

Home inspection is an interesting field with a lot of mysteries that need to be solved. One of them is the age of the house, but you can find plenty of clues that will help. If you’re ready to start a new career that’s as rewarding as it is challenging, click here to enroll now in ICA School’s home inspection course.

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