A condominium, or condo, is the form of housing tenure and other real property where a specified part of a piece of real estate (usually of an apartment house) is individually owned while use of and access to *common facilities* in the piece such as hallways, heating system, elevators, exterior areas is executed under legal rights associated with the individual ownership and controlled by the association of owners that jointly represent ownership of the whole piece.

...

Technically, a condominium is a collection of individual home units and *common areas* along with the land upon which they sit. Individual home ownership within a condominium is construed as ownership of only the air space confining the boundaries of the home (Anglo-Saxon law systems; different elsewhere).

---

common area n. in condominium and some cooperative housing projects, the areas not owned by an individual owner of the condominium or cooperative residence, but shared by all owners, either by percentage interest or owned by the management organization. Common areas may include recreation facilities, outdoor space, parking, landscaping, fences, laundry rooms and all other jointly used space. Management is by a homeowners' association or cooperative board, which collects assessments from the owners and pays for upkeep, some insurance, maintenance and reserves for replacement of improvements in the common area. This can also refer to the area in a shopping center or mall outside of the individual stores, for which each business pays a share of maintenance based on percentage of total store space occupied.

--------------------------------------------------
Note added at 1 hr (2011-09-20 19:11:19 GMT)
--------------------------------------------------

ops, è saltato il secondo link:
http://legal-dictionary.thefreedictionary.com/common area

--------------------------------------------------
Note added at 1 hr (2011-09-20 19:13:54 GMT)
--------------------------------------------------

that's how I've always understood the meaning of distacco condominiale in italian, but this is definitely not my field

--------------------------------------------------
Note added at 2 hrs (2011-09-20 20:14:15 GMT)
--------------------------------------------------

I mean, I might have mis-understood it

I've also found this: http://www.proz.com/kudoz/italian_to_english/architecture/43...

--------------------------------------------------
Note added at 15 hrs (2011-09-21 09:50:11 GMT)
--------------------------------------------------

still trying to figure this one out...

"su distacco" is a technical term of the "real estate jargon".
muri perimetrali su distacco = it means that the perimetral walls of the apartment faces a void (it could be a green area, an empty plot, an internal courtyard, a skylight well et al...) which belongs to a different property from that one the apartment is part of.
http://forum.wordreference.com/showthread.php?t=2106690