We've had a reserve study done and updated every 5 years. So far some of our biggest unexpected maintenance costs have been water related (Washington has lots of water that seems to seep in everywhere, and then rots the wood) and underground utility type things (when you have to dig a hole to find what's wrong, and that always costs money).

Our initial construction was not done to as high a standard as I would have liked (simple stuff like not installing the flashing around windows correctly, and using the lowest quality outlets they could possibly buy, not burying utilities as deep as they should have and us doing gardening and finding underground utilities unexpectedly), and we have paid for it over the years. We added a line item to the reserve study to deal with some of the siding/water intrusion issues because given our architecture all the other buildings will likely also have problems in the future.

Other than that our reserve study has been a good guide for maintenance scheduling things like painting. We just contracted to have our reserve study redone (it was last updated about 5 years ago), and the Province of Ontario law now requires a 30 year projection (I think before it was for 20 years), so I'm looking forward to seeing how that is different. They did the site visit a few weeks ago. He did say that the costs for some of the things like re-roofing have gone up faster than inflation, so I think we may be behind in some of our set asides. Our community has 13 buildings. 10 duplexes, a 4-plex, a 6-plex, and the common house, on 5 acres.

We do the maintenance on all the buildings, individuals are responsible for the insides. (our by-laws do say that individuals are responsible for windows in their units, but it doesn't mention doors one way or the other). One thing I'd suggest for new communities is to lay out from the beginning exactly what is maintained by the community vs. what is maintained by individuals. (for example, who replaces toilets, (we say fixtures are the responsibility of individuals), but then if an individual doesn't recall their bathtub regularly, and that leaks into the walls, who pays to fix etc).