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floor drain

Posted by ionized (My Page) on
Fri, Feb 18, 11 at 19:28

I have a floor drain that sits in a tiled area that runs 12-15 feet the entire width of the utility room. There is a lip to hold potential leaks from mishaps with the washer and water heater that sit in the containment area. The house is raised as are many in the metro area.

The first time I crawled under the house, I discovered that the drain just goes into the crawl space. I's day it is 2" PVC. It is not a real problem from a water standpoint. The trouble is that it is a rather large air leak and I am trying to seal the house up. It is really low-hanging fruit for air sealing. I would like, however, to keep the drain functional.

There is a surface drain catch basin/grate nearby on the outside that currently accepts water from a downspout and condensate from AC units. It is oversized. Is there any problem with my installing a p-trap and running a line to the grate?

I'd have to remember to fill the trap periodically, but that should not be too hard, especially if I float some mineral oil in it. I might have to install some make-up air for the dryer after I get the place sealed as the drain is probably what is providing it now.


Follow-Up Postings:

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RE: floor drain

Floor drains are required by most plumbing codes to be connected to the building drainage system and building sewer.

They are required to be trapped and vented.

Minimum size is 2".

Vents must be installed within 8 feet of the trap.

Consult your local plumbing code office for details.
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Consult your local mechanical/plumbing code office and installation instructions for your dryer for combustion air requirements.


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RE: floor drain

That's sad. I don't think I can afford to work a vent and connect with the city's drainage system, only to the nearby surface drain that connects to the municipality's storm drainage system. I will just have to plug it up to make it legal if that is necessary.

I don't have any combustion appliances in the house right now. The dryer is electric,but I just might want to have make-up air nearby as I tighten the house up. The point was that the straight, open floor drain is or would become that unless I do something with it.


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RE: floor drain

I'm no expert, but I think I've seen drains with rubber butterfly flappers in them for this purpose.

And since this is an emergency above-ground drain (like what I have on my water heater), I don't see where it has to be connected to the municipal drain system (or septic).

BTW: cold air does not rise.


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RE: floor drain

Thanks, I will be calling the local building officials about that and a natural gas service question.


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RE: floor drain

I talked with the local building office yesterday. The conversation meandered a little bit. He said that only surface water can go in to surface drainage so that would not be appropriate. Emergency drainage is allowed to go anywhere that won't be dangerous. They don't care if there is a trap or not. I should have asked him if surface drainage is acceptable in the case that the drain is there in case of a roof leak. Since he is a jovial guy, that probably would have been worth a giggle or two.

I will just put a trap on it and run it a little closer to the side of the house. I will flush it with bleach water now and then and keep the inboard surface covered with a little mineral oil.

I appreciate the rubber flapper suggestion might be best for most homeowners who won't remember to keep the trap full. In my hands, it will be more expensive and less reliable.


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RE: floor drain

Cold air doesn't rise unless the ambient air pressure inside the house is less than the exterior. Warm air inside the house will rise and escape via intended openings (bath vent, stove vent, fireplace, etc) or unintended openings (poorly sealed windows, gaps around electrical outlets and light fixtures, exterior surfaces that don't have house wrap) to the exterior.

The escaping warm air has to be replaced and is through the path of least resistance, say, maybe a floor drain that is open to the crawlspace below.

This is one of the reasons batt/fiber insulation without airflow management doesn't provide the desired (or advertised) R factor. The insulation is only fully functional if the air in the insulated area (wall cavity, etc) is static. If warm air is rising in the insulated wall cavity it's being replaced by cooler air from lower or below the cavity (an electrical outlet, wire or pipe run through the bottom plate, etc) and your interior re-heats that cavity and the cycle repeats.

Various sources list 25% to 50% of total house heating is lost just due to air infiltration (regardless of insulation).

Obviously, i'm using the term insulation pretty generically. Spray foam insulation or any closed cell insulation is an air barrier and will mitigate air infiltration.

Sorry, I'll put my soap box back in the truck.


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RE: floor drain

Thanks for your input, Oilyrover.. Everyone should have a soap box and use it frequently! In my case, it is humid air infiltration that is the enemy, not cold. I have plans to spray-foam my roof and seal the attic. The floors will be spray-foamed eventually too, but there is too much stuff that needs to be done over the crawl space right now, sub floor repairs, floor drain, other plumbing,....

I have way too much infiltration. The floor drain is a pretty big hole that should be easy to fix, then I will move on to other holes. In addition to humid air and moisture entry, I want to close that off the keep out 6-legged "friends".


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RE: floor drain

You can always just trap the existing line and still let it empty into the crawl space.

Put water in the trap and then float mineral oil on both sides to prevent the water from evaporating.


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RE: floor drain

Thanks, I was arriving at that conclusion. Running the pipe to the storm drain, even though it is close, is way too much trouble for what it is worth. The drain is really close to the side of the house so I can keep oil over both sides if I don't extend the pipe laterally. If I did extend it, there would be difficulty in doing that.


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RE: floor drain

"If I did extend it, there would be difficulty in doing that."

Just put a short vertical section immediately on the discharge side and use a screw in plug to block it off.


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RE: floor drain

Oops, I took a closer look at it and found that the pipe is magnetic metal of some sort. I also remembered the when we bought the house, it was covered over by the fiberglass bats insulating the floor.

What will be the easiest way to put a trap on this? Keep in mind that it need not be elegant. I only want to stop the source of drafts into the house keeping the emergency drain functional.


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RE: floor drain

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