Interesting comments above, none of which I would disagree with. I have not read the requirements but from my college days training as a mechanical engineer I would say that to minimise loss of strength in the joist any holes should be on the centreline (that is mid-way between the top and the bottom as opposed to half way between the ends) as the top and the bottom have all the tensile/compressive stresses. Similarly if there are any notches made  they should be at the ends of the joist rather than the middle as the greatest compressive stresses will be experienced at the mid-point, diminishing to zero at the ends. Also in order to minimise any loss of strength there must not be notches and holes at the same point along the joist.

In order to regularise this it is easy to put rules in place to say "notches are allowed along this section of the joist" and "holes are allowed along this section of the joist" and to make sure nobody puts a hole and a notch at the same point make sure they don't overlap. Regardless of the rules, holes are better than notches for minimising loss of strength, but are not always the practical solution so it has to be accepted that some notches will be cut. If you make a hole in the section where they are supposedly not allowed, the joist will retain more strength than if you put a notch, but can you be sure that a plumber will not come along at a later date and put notches in the same place?

Alasdair

Interesting comments above, none of which I would disagree with. I have not read the requirements but from my college days training as a mechanical engineer I would say that to minimise loss of strength in the joist any holes should be on the centreline (that is mid-way between the top and the bottom as opposed to half way between the ends) as the top and the bottom have all the tensile/compressive stresses. Similarly if there are any notches made  they should be at the ends of the joist rather than the middle as the greatest compressive stresses will be experienced at the mid-point, diminishing to zero at the ends. Also in order to minimise any loss of strength there must not be notches and holes at the same point along the joist.

In order to regularise this it is easy to put rules in place to say "notches are allowed along this section of the joist" and "holes are allowed along this section of the joist" and to make sure nobody puts a hole and a notch at the same point make sure they don't overlap. Regardless of the rules, holes are better than notches for minimising loss of strength, but are not always the practical solution so it has to be accepted that some notches will be cut. If you make a hole in the section where they are supposedly not allowed, the joist will retain more strength than if you put a notch, but can you be sure that a plumber will not come along at a later date and put notches in the same place?

Alasdair