Shower drain - reduce 2 inch to 1 1/2 inch and venting
I have a few questions about replacing an existing bathtub with a shower as we remodel our bathroom,
The existing tub on our upper floor was plumbed with a 1.5 inch p-trap and then a horizontal run of about 9 feet before it heads vertically downwards towards the basement between all the walls. My understanding is that code calls for 2 inch drain pipe for a shower. My question is somewhere along the line (I can rip up the subfloor) I need to transition form the new 2 inch drain to the 1.5 inch line and what would be the best place to place this reducer to minimize the speed at which water can flow. It could be right at point the drain meets the the p-trap where I could reduce to 1.5 inch p-trap or I could put in a 2 inch p-trap and 2 inch line and then transition at the point the horizontal drain line connects to the 1.5 inch vertical drain line between the walls headed to the basement. I am thinking the second option would be better?
My second question I son venting- the existing tub never drained very fast. The current vent is about 52 inches form the existing p-trap. I have looked at code on the web and it varies by jurisdiction with it being with 5 feet in some and within 3.5 feet. My question is if I move the vent closer than the existing 52 inches could I increase the rate at which the water drains. If I actually left the first vent in place and added a second vent that was closer could this cause a problem?
Any advice would be appreciated