I live in a condo in Florida, and I have noticed that when it rains outside, I could hear gurgling in the floor drain that is used for overflow from the T&P valve on my water heater. The pan's drain pipe sits over the floor drain with a gap, and the T&P valve is attached to a pipe that just points straight down at the pan, so there are air gaps in this system, which is how it is supposed to be configured to prevent contamination from drain to supply, although the drain is the questionable part here...

Aside from this, however, I believe the AC drain connects directly to the same drain pipe inside the wall. I'm not sure if code allows this.

Both the floor drain and the AC seem to be tied into the roof drain, hence the gurgling noise from that area when it rains. I've poured vinegar down both the floor and AC drains on different days, and have seen and smelled the liquid coming out of the roof drain downstairs. And having both of these tied together to the roof drain (every apartment in the stack is connected this way), I am even less sure if code allows...

The worst part though, is that a major rain storm hit us today and in 3 units, water was occasionally gushing out of the floor drain in some cases like a geyser. I have never seen this much rain nor water coming out in copious amounts from these drains in the 20 years I've lived here. In my unit, I also found the AC float switch was tripped, and upon opening the AC unit I discovered similar debris as what was on the floor in the mess of water that backed up into my apartment.

So my question here is whether any of this is allowed by code- to have either of these (floor drain used by T&P valve, or even the AC drain) connected to the roof's storm drain? And who should I contact to get this corrected?

Apart from any code violations, it just seems illogical to connect anything else to a roof drain system. If it gets clogged near the bottom end of the pipe, then water would start coming out of the floor drain from the lowest apartment in the stackup- especially in strong rain.

1 Answer 1


In most areas in the US (I suspect it may be different in other countries) with public sewer systems, there are two separate systems:

  • Sanitary Sewer

This collects the water used by homes and businesses. In fact, except for filling swimming pools and watering lawns, the sewer usage is presumed to be the same as the water supply usage and so the sewer amount is billed based on the metered water supply. This includes usage in toilets, tubs and showers, sinks, clothes washers, dishwashers and other typical household usage. This sewer system is limited in capacity - designed for Superbowl half-time flushing, not for thunderstorms. All the sewage is treated, which costs a significant amount and is a major part of your water bill.

  • Storm Sewer

This collects runoff rain water from streets, roofs, parking lots, etc. It can be very high volume during major storms. Depending on the system, it either gets minimal treatment or none at all.

Typically any drain inside your house will be connected to the sanitary sewer. I would certainly expect that to be the case for T&P relief valves. Condensate gets interesting - apparently in some places it is routinely sent outside, either onto the ground or into the storm sewer, and in other places it is deliberately sent into the sanitary sewer.

Based on all of that, and on my (limited compared to some other people here) experience, my hunch is that:

  • Roof drainage should go to the storm sewer.
  • Inside drains should go to the sanitary sewer.
  • Condensate could go to either sewer, depending on local practices, but if drained inside, as would be the case generally with an apartment building, should probably go to the sanitary sewer.
  • Under no normal circumstances should storm surge come back up through the internal building drain system.

This last one is the key. It could be a once in many years overflow where due to interconnections between sewer systems it is expected that there may be storm overflow into the sanitary system then it will likely come out of every first floor drain in the area, but not with an ordinary storm. On the other hand, if this happens with every storm then it the drains in the building may have been connected improperly.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.