how much floor slope can you have without noticing it?

I meant where the table crosses the level and unlevel planes..

Depends then how you orient the table.

But that assumes surely that the walls are still truly perpendicular ? If a building with a rigid steel frame were struck by an earthquake such that one end dropped by say 20cm then its quite possible that all the interior angles of the frame, and thus the corners of the rooms remained at 90%. So just as you have might have an imperceptibly sloping floor, so you might also have imperceptibly sloping walls which can accommodate kitchen units or wardrobes without giving any visual clues at all. Although obviously if you decided to store balls or loose liquids on the shelves inside the units or wardrobe then that should possibly give the game away.

It's about 25mm in 2 metres in here, and that's noticeable. Though ICBA to get the long level and check exactly, it slopes in all sorts of directions and isn't flat either, so it may be some bits are stepper than that.

It probably wasn't flat when it was built, and that's about 300 years ago.

Andy

Man, I'm just lurking through here because I wanted to see where it was noticeable, but I just had to reply once I saw this haha

I have a 1 cm / 1 m drop in a room and that is noticeable. That is about 0.6 degrees.

Really. Often it depends on the person. One give away could be if you have an aquarium and the water is sloping. I stayed in an old hotel room on CI some years ago, and you could feel the tilt upstairs. Brian

I've a floor at work far worse than that, didn't notice until I put a desk on it and tried to level it up.

I had to move a pile of magazines may years ago when the tiles started to fall off the ceiling below!

Brian

There is a difference with living with it and noticing it. You can probably get away with not noticing a relatively steep slope until you introduce a point of reference that is truly horizontal. Kitchen units, as mentioned earlier, will show the slope as the bottom of the level cabinets are close to the floor providing a point of reference

The ceilings in my house were not level* and sloped by approx 2.5cm over a distance of around 3.5m. This was not that noticeable when the walls and ceiling were painted the same colour however when removing paper from the walls the difference in colour between the ceiling and bare plaster made the slope very noticeable.

Exactly wrong, your sense of balance can detect slopes much less than you can see visually. Try it

Do people actually detect the slope on a driveway, patio etc. to facilitate drainage?

I normally use a level to get it right. I can tell if I am on a slope, but not how steep it is.

I know that my house slab is well up above the dirt it sits on because I set it up with a theodelite when building the house on a bare block of land and used what we call a backhoe to push the dirt up to the walls once the walls were done. You can't pick it by eye or by walking on it.