Basement bathroom.

Quick question about a basement bathroom that was roughed in with a 2" trap below the concrete and a 2" stub sticking above the concrete. I cannot see how the trap is vented but the nearest vent is from the rough in for the sink which is 2" with a clean out. Then has a reducing sani tee down to 1 1/2" vent where the sink drain ties in. I have created a dap out but got to thinking about the venting and whether it was proper. Any help is appreciated.

Here is a simple pic of the layout.

venting

I'm not certain that I understand your diagram; is there a stack at the 2" location of the sink? (Middle of diagram). If not, is the only stack the 4" one that is 7.5 feet away? If this is the case, then the arrangement does not appear to be vented properly, and flushing the toilet is likely to cause continuing problems.

Yes, at the sink there is a 2" to 1 1/2" sani tee which is vented back to the main stack. Is that sufficient for a bath tub or shower. I'm not certain how they are supposed to be vented.

I would guess that the shower and toilet are wet vented thru the lav. The lav shouldn't reduce, it needs to stay 2". Our code makes us keep the vent within 4 or 5 foot.

pipe sizes everywhere

needs more information, on your diagram. You are close to the limit. Seven feet is one foot too long, unless your pipe size is bigger than i think it may be...

Besides, it is always good to plan a little more venting than the absolute minimum when you have three fixtures.

i am not an expert.

david

venting

HOW the sink, shower, and toilet pipes come together is the most important thing. The next item would be that the vent normally has to be 2", unless you use the code that allows 1 1/2". Your toilet is not 7 1/2' from the vent, if everything is done correctly, but rather is only about a foot or so from the vent.