Whirlpool tub alternative P-Trap placement

[Chris rondestvedt]

I am installing a whirlpool tub on the 2nd floor of a residential home. Joists are 2x10. Adding 1 and 1/8 inches of subflooring yields a total height from 1st floor ceiling of 10 and 5/8 inches to work with for drainage.

There are joists under the overflow valve perpendicular to the drain path that change direction just before the drain shoe to then follow parallel to the drain path.

To minimize notching of the joists I'd like to know if the p-trap can be moved from directly under the overflow drain (normal configuration) to directly under the tub drain shoe..

The home is located in Virginia Beach, VA.

Looking forward to hearing from the forum.

Chris

 

[FullySprinklered]

It's been done.

 

[Sponsor]

 

[hj]

It is known as a "toe outlet" waste and overflow.

 

[FullySprinklered]

It's been so long ago I don't even remember what I did. Early nineties, I think. Ran the overflow pipe down into a 45 to skirt a joist, then another 45 to run it into a tee straight down under the tub drain. There's a thread issue there, but I can't advise on that anymore.

 

[Chris rondestvedt]

Hi,

Many thanks for your comments!

The more I got into this master bath remodeling project the more I realized I needed to do more research in order to ask the right questions. I also realized that the project had to be considered as a whole and not individual pieces.

Following are my questions and what I think are the applicable portions of the Virginia state plumbing code. It was interesting to me to see how the plumbing codes varied from IPC to individual states.

Any perspective you may provide will be much appreciated!

Chris

1. Q: As shown the bathroom remodel plumbing concept picture (file code 1) is this a horizontal “wet vent” configuration with tub and shower sharing a drain and vented by the toilet stack/vent as shown?

a.Q: In this case is the tub trap arm 18 inches to the horizontal wet vent?

Table 709.1 Drainage fixture units tub load factor 2 shower 2; minimum trap each 1.5 inch

Table 709.2 Fixture unit value for 1.5 inch trap tub 2 shower 2; for 2 inch trap tub 3 shower 3

Table 710.1 (1) Maximum drainage fixture units for 2 inch pipe at ¼ inch per foot 21

Table 710.1(2) Horizontal fixture branches for 2 inch pipe

-Max number drainage fixture units for horizontal branch 6 units

- Max number drainage fixture units: Total discharge units into one branch interval 6

909 Wet Venting

909.1 Horizontal wet venting permitted. Any combination of fixtures within two bathroom groups located on the same level is permitted to be vented by a horizontal wet vent

2. Q: If not a wet vent, is the configuration showing an approximately 7.5 foot ft tub trap arm (8 ft trap arm allowed by Virginia Plumbing Code table 906.1) to the vent with shower joining the trap arm acceptable?

908 common vent

908.1 Individual vent as common vent. An individual vent is permitted to vent two traps or trapped fixtures…located on the same floor level

908.2 Connection at same level. Where the fixture drains being common vented connect at the same level the vent connection shall be at the interconnection of the fixture drains or downstream of the connection

3. Q: If not acceptable would a separate vent of the shower p trap to the existing 2 inch vent shown in file code 3 make the configuration acceptable?

4. Q: Would changing the piping and fittings from the toilet stack/vent up to and including the combo wye from 2 inch to 3 inch alter the tub trap arm calculation?

From 906.2 my understanding is that trap arm length is determined by pipe slope and pipe diameter as expressed in table 906.1 for 2 inch pipe at ¼ in per foot maximum trap arm is 8 feet though for 3 inch pipe at 1/8 inch per foot trap arm is limited to 12 feet.

5. Q: Is a 2 inch p trap for the tub required if the trap arm is 2 inch pipe or can the p trap be 1.5 inch to match the tub drain piping? Virginia plumbing code Ch 7 table 709.1 shows minimum trap size for bathtub and shower to be 1.5 inches and note follows “d. Trap size will be consistent with fixture outlet size.”

6. Q: Would a tub with 1.5 inch drain pipe and 1.5 inch p trap have better scouring action during draining than a 2 inch p trap?

7. From the Virginia code Chapter 9 paragraph 906.3 “a vent shall not be installed within two pipe diameters of the trap weir”
Q: Does this also mean that the minimum distance from tub 1.5 inch drain to overflow sanitary 1.5 inch T connection is 3 inches (ie 1.5 x 2)? See standard configuration Option #1 in file code 2

8. In Chapter 10 sec 1002.1 “…the horizontal distance [from the fixture outlet to the trap weir] shall not exceed 30 inches measured from the centerline of the fixture outlet to the centerline of the inlet of the trap

Q1: As shown in the file code 2 picture option # 2 can the tub p-trap be moved downstream 30 inches from the sanitary T?

Q2: If so will this change the beginning of the tub trap arm in terms of allowed distance from trap to vent?

Q3. Can a ¼ bend be used at the bottom of the sanitary T to change the direction of flow toward the downstream p-trap?

9. Q: Is a p trap directly below a drain as shown in file code 2 option #3 allowed as long as there is a 3 inches horizontal connection to the overflow drain/vent? Trying to avoid joists