Dilemma of repairing old buildings 1

For commercial buildings, it's in the IEBC. There are rules for repairing structures and certain thresholds where retrofitting is required. Most jurisdictions I've dealt with follow this. I believe there are some west cost jurisdictions that are a little more strict on seismic retrofitting.

For residential, it depends a little more on where you are. Some places refer to the IEBC rules, others have their own limits. I'm used to seeing significant improvement thresholds for houses around 50% of assessed value of the improvement. So if the repair cost is worth more than half the house, the rest of the house has to be brought up to code. AHJ can give exceptions, too, of course. I did a lot of FEMA work where, in some cases, the work was more than the house was worth, but we didn't touch anything above the new foundation except the straps and anchors that held it down.

If you're repairing damage, the general rule is to put back what was there. What is installed has to be done to current code - member sizes, strength, connections, etc. But as long as you don't change the load path, you don't need to replace any non-damaged members.

@phamENG....exactly. My experience as well.

Thank you for your replies. This helps

Options provided by the IEBC code:

International Existing Building Code (IEBC)