Jules

The realistic repair options, roughly in increasing order of intervention:

Sistering. Fixing a new full-length member alongside the damaged one, bearing on the same supports at both ends. This is the standard repair and it works because the new member takes the load rather than reinforcing the old one. The critical detail is that it must reach the supports — a sister that stops short of the bearing points is decoration.

Flitch plates. Steel or engineered plate sandwiched to the joist, bolted through. Useful where a full-depth sister will not fit past the pipes, since the plate can be shaped around them.

Adding a support underneath. A beam and posts halving the span. Often the cheapest and most effective option if the space below allows it, because halving the span dramatically reduces the load on the damaged section.

Rerouting the plumbing. Frequently the right answer and the one people resist. Running a pipe below the joists in a dropped ceiling, or in a different direction, may cost less than structural work.

Plywood sisters glued and screwed on one side are sometimes proposed. They add stiffness and they are not equivalent to a full-depth member on both sides.

The first thing to establish is where the holes are, because position matters more than size.

A joist in bending has tension along the bottom edge and compression along the top, with a neutral zone in the middle. That means:

• A hole in the middle third of the depth, near the middle of the span, removes material that was doing relatively little.
• A notch or hole near the top or bottom edge is far more serious, because it cuts the parts carrying the most stress. A notch in the bottom edge is the worst case of all, and it is what most improvised plumbing produces.
• Holes close to the supports are affected differently again — shear dominates there rather than bending.

So before anything else, note for each joist: how far along the span, how far from the top and bottom edges, and how big relative to the joist depth. That set of numbers is what any answer depends on, and it is what an engineer will ask for first.

Worth noting the same reasoning applies to power strips, and people are even more relaxed about those.

A strip adds two more connections and is often the cheapest available. Manufacturers of heaters, air conditioners and similar high continuous loads all say the same thing about them for the same reason.

If a strip already runs to where you want the heater, that is a sign the room is short of outlets rather than a solution to it.

For next time — and this is worth saying because it is entirely preventable — a cable and pipe detector costs very little and finds this before it happens.

Also worth knowing that cables commonly run vertically above and below outlets and switches, and horizontally near ceiling level, because that is where installers put them. Treating those zones as no-go for fixings avoids most strikes even without a detector.

One thing worth saying about rules of this type generally: trying to reverse-engineer the single reason behind a code provision is a losing game.

Provisions usually accumulate several justifications over decades, and finding one reason that does not apply to your situation is not permission. If a particular run genuinely cannot be done the normal way, that is a conversation with an inspector before the work rather than a decision made on site.

For future use, since everyone does this eventually: keep a small bottle of acetone with the glue, not in the bathroom.

The moment you need it is the moment you have one hand available, and having the solvent in the same box as the adhesive turns a twenty minute problem into a two minute one.