Demise in this context is commercial real estate legal jargon for a lease or an area that is leased. Like lease, it appears that demise is also used as a verb and a participle adjective.
Here’s some wording from The fundamentals of commercial leasing:
The first issue to be determined in any lease is what is being
demised. The demise is the area of the building or facility
designated for the exclusive use of the tenant... Licensed areas may
also be included in the lease alongside the demised areas... While
“demising” the whole or part of a property gives the tenant exclusive possession, landlords usually reserve the right to enter the
premises for various purposes...
Source: The Free Library —
The fundamentals of commercial leasing.
The British National Corpus returns results for the demise from Drafting business leases by Kim Lewison (1985-1994). (Click to expand examples and see items 43 to 66. Also see BNC results for demised.)
Here are a few excerpts showing usage:
45: If the draftsman wishes to create a lease for a period that can
not be made certain at the time of the demise the only way is to
express it as being granted for a fixed term subject to a power to
break at the expiry of the period.
50: It is, however, established that the demise of one floor of a
building extends at least as far as the underside of the joists
supporting the floor above it... The ordinary expectation is that the
tenant will be entitled to occupy all that space between the floor of
his demise and the underside of the floor above... So the demise of a flat or a particular floor of a building will include a roof
space accessible only from that flat where there is no reservation to
the landlord... However, a demise of a “suite of rooms” on the top
floor of a building will not include the common roof...
54: Where the demise includes the whole of a building (or the top
floor) the draftsman may therefore wish to consider whether the
airspace above the building should be excluded from the demise.
61: The draftsman should therefore consider whether the landlord
should have the right to enter the demise for other purposes...
I’m not so sure your examples are being used in the way that you think they are — that is, to mean “within the boundary of” and unrelated to property leasing; I can easily imagine these to fall in line with the definitions of lease or an area that is leased:
We are seeking construction drawings for the structure within the demise of the site. —> We are seeking construction drawings for the
structure within the leased area of the site.
Those services do not belong to the demise of the building. —> Those utilities are not included in the lease [or leased area] of the building.