Roll them up and put them in a poster/document tube then store them someplace dry.

Yep best way and also the cheapest. When you go to sell leave it on the conter with a note.

We found our plans (not on blueprint, though) and it tears easily. I’ve also found the plans to my parents’ and grandparents’ houses on blueprint. They were just stored rolled or folded in boxes and are not too bad, but getting fragile. I want to copy Grandma’s for myself because I love the house so, and give the original to the current owner.

How old are they? If less then twenty years just roll them and stick in a tube as was already mentioned. If they are truly blueprints they are probably getting fragile so I would get copies made ASAP so when the originals fad you still have a useful copy. For a couple bucks they can probably make a pdf of them for you too.

They need museum type acid free archival preservation. Flat storage preferred. Rolled eventually disintegrates. Having them archivally framed would be best. https://www.archivalmethods.com/

We used these in school and always worked.

https://www.amazon.com/s?k=telescoping+drafting+tube

Are they really blueprints? Actual blueprints were superceded by "black line" or sepia prints by the 1960s or so.

In either case, all these prints fade if left exposed to direct light over time. They best, and only way, to actually preserve them is to keep them in a light free location, ie, drawer, tube or whatever. Framed prints will fade as will simple prints. The only way to really ensure them over time is to xerox copy them. I'm not sure how long xerox prints last.

Our house was built in 1932 and has had five owners. We have the blueprints and put them in our safe deposit box.

If you roll them up, roll with the print on the outside. That way when you unroll they are more manageable. Do not roll tighter than say 2" diameter. Ditto the comment about getting pdf scans made at your local print shop.

"Blueprints" have white lines with a blue background, "Blue Line" prints have blue lines wIth white background; both of these are made with an ammonia process. If the prints have black lines with a white background, it may have been made with a ammonia or Xerographic process. Either way the originals should be protected from light. If you wish to display them, have them copied on archival paper.

(Chocolate chip cookies should always be made with walnuts)