How long for a building to decay?

[Norseman]

Basically I need to know how long it would take for a fairly well constructed stone building (and a stone tower) built using Roman tech to decay. I am assuming temperate, but rough, temperatures with lots of rain.

[Mayabird]

Those things can last for a while, considering the ruins are still around all over the place. At least a couple thousand years, then. Are you also counting them if they get buried under sediment/worm poop/whatever?

[Norseman]

Those things can last for a while, considering the ruins are still around all over the place. At least a couple thousand years, then. Are you also counting them if they get buried under sediment/worm poop/whatever?

Perhaps decay is the wrong word, collapse is more appropriate. I mean the towers fall down after a while, walls crumble etc. I need to figure out how much damage would be done after, say, forty years.

[frigidmagi]

Part of it also depends on the people. Many Roman buildings were literally torn apart by people for the building stone, it was a case of literal don't build them like they used to.

Another part is the environment. In a desert, buildings of stone last a very long time, in a forest where trees, grass and other plant life will be constantly attacking it, they last not as long. If the winters are cold the stone will crack relativity quickly, the first ones happening in a decade as water seeps into the stone freezes (widening the crack) and thaws again and again. Within these cracks plants grow, tearing the place apart. In decades the place is a ruin without human repair.