Typically you get one year from approval to begin construction. Sometimes one year to complete construction.

you should ask the city to get the correct answer but as dsc_arch said you usually only get a maximum of 1 year or maybe even 18 months to begin construction. but i will guar-own-TEE that approved plans will not be viable for a building permit 5 years down the road.

What constitutes "starting" a house addition? What if one were to dig for a foundation within the year of approval, then put the whole thing on hold for economic reasons, until 5 years from now?

i would venture to say that you are setting yourself up for disaster expecting to build something 5 years out even after digging yourself a hole. the manicupality will see your intentions when you walk back to their table expecting to continue the construction process. dsc_arch and FRaC have mentioned a fairly standard timeline, but it never hurts to present your scenario to the city or ask what their timeline really is.

Plus I would think my building permit would run out and I'd have to reapply right?

What city/county are you in?

Your best bet may be to try to get a full building permit now and then file for extensions.

You can always try to get a variance. You can explain your situation etc. and they will listen and sometimes understand. It is always worth a try.

Typically you just have to submit before the change, not get everything approved. I know of projects (in Los Angeles) that had permits kept active for years and years. The city will charge you a lot of renewal fees to keep filing for extensions, but it could be worth it. A variance typically costs thousands of dollars..

yes, what city/county are you in? they are seemingly trying to decrease density, this seems wrong all around. I've never heard of this.

Planning and zoning are intensely local matters.

Unless one of your fellow archinecters here happens to live in your zip code, their general advice is good, but insufficient to tell you all you need to know.

Go onto your city's website, find the planning department's page, and start digging. Or, God forbid, pick up the phone and call them. You won't be tipping them off about your intentions unless you identify your property.

municode.com

knock - decreasing density isn't always 'wrong'.

as citizen said, zoning is a local matter. for example i live in a 50's housing tract where second stories were recently banned. the main reasons were to protect the original design and to protect the privacy of the homeowner (there is floor to ceiling glass in living spaces and bedrooms, exterior courtyards, and a 6 foot high privacy fence at the property line).

usually i am against a lessening of property rights but in this case i supported it and there was about 95% neighborhood support.

Technically, downzoning is bad. It devalues your property and limits the potential return on investment. No one is going to buy out your property unless your house is that "teardown across the street."

My parents recently had their zoning changed because of a neighbor across the street (she opened a salon in her garage) and because of the number of potential customers she could have, they rezoned the entire corner block high-density mixed-use.

My parents and their neighbors sit on one of like 4 places in the entire county where you could put a 10-story building.

I think my parents lot now is worth more than their house.

so says citizen. ditto.

In the 5 years of not being allowed to build an extra story you could lobby to have the zoning changed.

An attractive desing I saw once was the basement was just high enough above grade to still be a basement and then terraced plantings on all sides dropped down to basement level allowing full height sliding glass doors in basement.

It seems like a fairly simple matter to me. Go for the Zoning Aproval asap. If your approved you should be grandfathered as long as the zoning regulations allow. Typically it is longer than one year,
more like for or five years. This is usually regulated by State Statutes and not local Zoning Regulations. If you apply for a building permit...usually they will limit the building permit to one year by the local building code. If you have any questions go in and see the local planner....they don't bite. They should be able to tell you what you need to do inorder to secure a zoning permit to allow you to add one floor. If they are a pain....bring along a lawyer or a friend who looks and acts like a lawyer (Monkey Suit Required). Planning officials are very careful when speaking with a lawyer cause they know if they go to court it is there word against and attorney....not no skid row bum. I would not expect them to give you an extension. So figure out how to build out at least the shell. A building permit will allow this in most cases durning the one year period inwhich they allow to you build a project. Then again you can always go back to them if need be and request and extention for building out the project. What they going to say....NO! I don't personally think so.