Any career preservationist (and many amateurs) can relate to the frustration of realizing even one photograph of an altered structure could prove invaluable to a modern-day restoration or research project.

For those of us who love historic buildings and might be working on a rehabilitation, for example, it’s important to document what you see before the structure begins to change. Once you alter physical aspects of a structure, you can never return it to what it was.

In the end, maintaining a record of your property means that no matter what happens in the future, you and others will be able to know precisely what was once there. Below are six simple ways to create that invaluable record and ensure the legacy of the historic structure that matters to you.

1. Prepare yourself with questions about all the possible details to document.

Think to yourself, “What could be lost? What are the materials that make up this structure? Where are the visible signs of craftsmanship? What elements are important to remember?”

Or, to look at it from a different angle, consider the original craftsman who built the structure in question—what would they want us to remember if their work disappeared?

If you train your mind to consider what details you need to document on paper, computer, or through photography, it will be easier for you to know the right direction to take and not feel overwhelmed.

2. Imagine what you would want in the worst-case scenario.

A seasoned preservationist once asked me, “If the structure and all evidence of it burned in a fire tonight, would someone be able to reconstruct it based on your documentation?”

If you feel confident a structure will stand for eternity, or that someone else could save the day if disaster struck, a lot of important historic features and architectural elements could be gone for good. Adopting a worst-case mindset will encourage you to leave no details undocumented in case all is indeed lost.

3. Learn how to create architectural photos.

Photography is one of the first skills a preservationist should learn. Don’t worry if your photo skills don’t typically reach beyond the pressing of your smartphone’s touch screen. Instead, focus instead on what you can—and should—document.

First, you want to start with the big picture. If you’re photographing a staircase that has become too unstable and cannot be saved, you would begin creating images of as much of the staircase as you can fit in the frame. Make sure it’s clear where the staircase is in relation to the rest of the property. Next, create detail photographs of the balusters, risers, and any ornamentation. Try to document details straight on; images created from an angle can warp perspective and lead to a false interpretation.

5. Measure the architectural features.

When documenting architectural features that are at risk, don’t underestimate the usefulness of simple math. Grab a rigid ruler (soft ones stretch out over time, so measurements won’t be accurate), measure what might not be rehabilitated or reconstructed, and then write those measurements down. Consider sketching what you are measuring, too. You can use the sketches to identify exactly what elements your measurements refer to for people who may use your notes in the future.

If, for example, you’re turning your carriage house or stable into a garage, measure the length and width of the carriage house interior. If divisions or stall partitions no longer exist, see if you can find holes in the ground or markings on the wall that could indicate where they used to be. Measure the length and width of those, too, as well as the height for any markings on the walls. You can be a real go-getter and record using Historic American Buildings Survey (HABS) standards, but it’s okay to measure however you feel comfortable.

6. When it comes to documenting details, trust your gut.

Things you may believe to be insignificant usually won’t be. If they are, no harm done! If you think that maybe, possibly, you should photograph that odd nick on the brick wall of your historic kitchen, don’t think twice—document it for posterity.

Through it all, keep this in mind: If a building is set to be demolished, or is beyond repair already, documenting what you can preserves a unique record of that structure that could prove very useful to someone many years down the road.

An earlier version of this story was published on December 6, 2016.