The answer to this question is important for two reasons.
First, if you are looking to purchase a property and it's clear previous work was done, you need to be sure the work performed was done in accordance with the building code.
Second, you, the homeowner, will have to pay to have the work brought up to code and prove the work meets the building code requirements, even if it was the previous owner who did the work.
Let's take a look at what the implications of previous structural work done to the foundation of your home would mean.
Previous Structural Work
Underpinning or bench footings often indicate a problem area that had previously existed with the property. For most older homes this is either a result of inadequate footings below the foundation wall, poor soils, or some other equally important and significant structural issue. The importance of discovering previous structural work like this, whether done by you or a previous homeowner decades ago, is the work needs to be backed up by a building permit and engineering reports too.
If it's found the structural work is non-compliant, you're looking at a significant cost to have the work brought up to the standards necessary. So if you are serious about making an offer on a property and are thinking the lack of a building permit is something you can ignore, better think again.
What Are Your Options?
If you own a property and are unsure if prior work on the home was done with a building permit, you have two options to exercise; both help you to discover if there was a building permit issued. The first method is to conduct an anonymous search to determine what permits the municipality has issued for your property in the past. The other method is to contact the municipality directly to determine what work was done and under what building permit.
If you discover your home has unpermitted work and have no intention of having the work inspected by the municipality to determine if it meets the building code requirements, you must disclose the unpermitted work to the next buyer so they are aware of the risk they are assuming when purchasing your property.
If you are looking to purchase a home and it has been disclosed there was unpermitted work done, the larger risk is you, as the buyer, may not be able to get financing for the house. That means even if you were interested and ready to buy the property because it has a great finished basement apartment perfect for your family's needs, you may not get financing.
If you want to bring the work up to code, then you will need to work with an architectural professional to help document the existing condition and open up portions of the covered work to show the municipal inspector how the structure was put together. You will be responsible for all costs associated with bringing the work up to code.
So if you hear your contractor suggest you can do the work without a permit, contact your municipality to double check. It's in your best interests to do so.