You could hire a plumber (electrician, etc) to inspect and identify what is out of code (many things likely) and what HAS to be done to the existing system as part of the new addition to meet code (likely very few things) - but that would be $100-200 per utility type.
If you are using an architect on the addition (very likely to be able to get a building permit) he/she should identify ALL items needed to be upgraded as part of the project and put the changes on the plans.
Or, you can, when you select a bidder, BEFORE signing a contract, require that he revise his bid (subject to your acceptance of new cost) and state in his bid that his bid includes all work on existing systems needed to meet code, and that his bid (revised) reflects those costs. That would provide substantial protection against overruns. This "to meet code" has become a catch-all in recent years for some contractors to get jobs by bidding low, then say that everything that should have been included but was not is now needed to "meet code". I have encountered cases where an addition was priced as if everything coming to it was suitable as-is, and zero upgrades to electrical, plumbing, HVAC capacity, or relocation of existing utilities under the addition site was assumed - not a very realistic or fair representation, but some do it to get the low bid and get the job, then immediately turn into change-order artists to cover what they should have included in the first place.
Likely code compliance items - though some communities can get pretty sticky:
1) install backflow preventer if there is not one - couple hundred $
2) install pressure relief tank on water heater if there is not one - maybe $100+ a bit additional
3) upsize septic system if adding a bedroom or bathroom (most areas size based on number of bedrooms, a few factor in number of bathrooms) - so if adding those might need to upsize septic tank and/or leach field in your area, if on septic
4) GFCI or AFCI breakers on all circuits connecting to new addition
5) upgrade incoming water line, outgoing sewer line size for more capacity - usually not an issue with newer homes, but '64 is likely in the midrange - could have 3/4" water line or 3" sewer line for instance, instead of 1 or 1-1/4" and 4" respectively.
6) possible electrical system upgrade for more capacity
7) HVAC system replacement for more capacity, including new ducting from furnace to the addition quite possibly
8) in some nasty areas, if addition is more than a certain percentage of square footage of existing house (50% typically) or more than so many $ (around $30-50,000 commonly) they require that before you can add plumbing, HVAC, electric etc to an addition the WHOLE house system has to be upgraded to current code - this can get quite pricey and commonly add in the $10,000 range to a normal size house remodel.
9) additional parking spaces - some areas figure need based on number of bedrooms, especially if built as an in-law or rental-capable apartment
10) basement egress changes if addition will block or remove a door or egress window, or if current egress is not legal
11) make all handrails, railings, steps, etc on entrances and stairs (at least those used to access the addition) to current code
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Here is a prior response to a question about sewer line relocation with some ballpark cost info FYI -
https://answers.angieslist.com/what-I...
