30+ yrs as a carpenter and don’t know of any real rule of thumb. Call-out varies with severity of notching, joist size and span. I’d recommend qualified contractor or SE and let it go at that.
-Kent
I believe that code reads (or at least used to) that if you “cut” or “alter” the structrure a building permit and inspections is required. It used to be in our county that extending the sistered joist a minimum of 4’-0 past the affected area with bolts was acceptable. Now the only acceptable sister must run from bearing point to bearing point.
This building permit thing is practically never followed, but it is a violation, which if complied to would make our lives a lot simpler.
and material type.
By and large altering does not include reinforcing or beefing up. I doubt any building permit would be required if, as a home owner you decided to sister the joists in your home to add stability to a floor. I can see a permit required if you were going to “alter” the structure. Reinforcement is not altering, it is just that, reinforcement. If I were to decide to cut a new door way in and existing home I would definately go and get a permit and submit drawings to illustrate what was going to occur. This is a requirement here in Ontario. I have submitted drawings to a building I was renovating that I had done up myself and had them accepted by the inspector. His decision was that it was structuraly sound and well within code limits and let me proceed.
Larry
The IRC requires all joists to have bearing supports at the ends (R502.6). So using that as a guide, joists must run full length from support to support, or they must be engineered.
The design of joist splices/connections would vary depending on where it is along the span, what the calculated forces are, and how much of the original joist was cut out.
I agree that the splices in the picture (if you can call them that) to repair the notches do look inadequate as the ends barely extend past the cut area. Not enough length to transfer load to the uncut section.
JMO and 2-nickels … 
P.S. Joist “sistering” is generally accepted to mean a full length similar member (a sister) is added from bearing to bearing, where a joist “Splice” or “Reinforcement” (sometimes referred to as a “scabbed” section) is generally accepted to mean a partial length section is added.
I was a carpenter in CA and CO for 30 yrs and never heard a rule of thumb.
Sistering requirements depend on the joist size, span and the severity of the notching.
“Recommend evaluation by a qualified Structural Engineer or contractor.”
-Kent
Oops. I keep thinking posts haven’t posted and then find them after reposting. Anyway, yes. Materials too.
As a contractor, if I found a joist to be defective due to overboring, notching and could verify the the bore/notch was out of place or size based on dimension per IRC or other code applicable.
I would consider the entire joist defective and replace end to end if possible. We did this not long ago, had to pop the block out and run a 22’ 2 x 12 from exterior thru siding. If the middle third begins to fail, I very much doubt that I or any framer would want a 4’ piece of lumber supporting a fair amount of weight with … nails??? Maybe there is a partition resting on that joist, maybe part of the roof has settled on the partition… hmmmm.
In my locality, (So. Cal) I simply can’t imagine a City Official calling out a defective joist during a remodel, and nailing on a Daughter 2’ on either side of the overbore or over notch. And thinking I did a job properly.
Maybe… A letter from a SE and some type of pattern on the Joist ends with SDS screws or something if totally unfeasable to slide thru from exterior.
Cheap = Dead people sometimes. Remember the Skywalk failure a couple years ago. Those were bolts and steel members.
Cheers.
Add proper lag bolt hardware and your good to go! Looks like the handy work of WDO Contractors.