Learn English – Comma before “as well as”

In this context, "as well as" is a coordinate conjunction, combining two clauses into one sentence. A good rule of thumb here is to substitute another coordinate conjunction you're more familiar with, such as "and"; if you were to use "and" in place of this phrase (for instance, "We have carried out works for private individuals and property developers and carried out our own projects") it would not take a comma.

That said, Mustafa is also right; the second clause of the sentence can't stand alone without a verb. Throwing a verb in there as suggested should make everything okay.