How out-of-level or out-of-plane does a floor need to be before it is noticeable?
Many of the houses I've lived in have floors that are out-of-level, visible to the naked eye. At what point does that happen?
(I realize that rigid flooring materials like tile need a floor that is in-plane, but that's not my concern here.)
Beauty is in the eye of the beholder. The larger the room, it easier it is to visually pick up on a level problem. I tend to be a bit of a fuss budget, but I can usually pick up on a 10 foot span that is much more than 1/4 to 3/8 inch off level. This is a pretty objective observation that would be more pronounced to a trained eye than a casual observer.
Thank you for this question and thank you Shirlock Homes for your answer. It is hard to get an answer on level standards. After looking at dozens of sites I have seen only two relevant answers. The other said 1:50 which is about an inch in 4'or 1/4" per foot. That's twice what water flows at in drain lines. That's pretty steep and apparently exceeds ADA requirements per another site. To your question, based on my testing with a 6'level, you have to be greater than 3/4" per 10 feet for the bubble to hit one of the lines. Until laser levels came along that was the standard used. It must have been to code. The person who built my house either didn't build the foundation and wall level or it settled. From the center beam to the wall it drops 0.9" in 10'. That said my 6 foot level shows the bubble between the lines on most of the floors. I am repairing flood damage at one corner that caused the footer to break. I know how to deal with that. I can easily raise that corner up to level with the rest of the wall with the new footer. My question is do I raise the whole side of the house up 1.375" to be level with the center beam. My conclusion is a pro might know, using a laser level shows it, but no one else will notice. It is not worth damaging the house to correct it.