I have three floor joists that have approximately 1/2 inch hole in them less than 2 inches from the bottom. Is there a recommended fix or approved method to correct this to meet code? These joists are in excellent condition otherwise. Someone drilled through them years ago to run cable through. There are other holes above 2 inches on other joists.
Replacing them? Getting an engineer? For a 1/2 hole in at least 8in joist? Seriously? I mean I'm sure the joist has lost some percentage of its strength. Like pretty small percentage. I would speculate that the lost strength is within tolerance limits for wood, which is not uniformly perfect. Unless you plan on having sumo wrestlers fight on top of those joists, I would just let them be....
As Vitaliy points out, replacing the joists is completely unnecessary, however, I did look into it and came across this article: http://ifbholz.ethz.ch/natureofwood/pc/st/st5.html
Knots and holes do affect the strength of a joist but the three most important factors are: the dimensions of the lumber, the location of the hole, and the size of the hole. Best-case scenario is that you have a hole just big enough for the purpose needed, directly in the center of the joist. Worst-case scenario is that you have a hole that is too large and is located at the bottom of the beam (the tension face). As the article points out, a 1/2 inch hole in the tension face of a 2x10 joist can reduce the bending strength of the joist by as much as 9 percent!
This will give you some good insight on how to fix this - basically, depending on how close the hole is to the bottom or top, you can install steel strapping to address the tension or compression loading. Two important points: you want to avoid using too many screws and effectively "perforating" the tension/compression lines, and also make sure the strapping extends far enough past the hole to take up the distributed loading:
Whilst not a direct answer this thread will give you all the detail you require: http://www.homeownershub.com/uk-diy/filling-holes-in-joists-280701-.htm
I'd advise leaving them alone if no sagging has occurred.