Gray water darin line size

[hookerp]

I have a bath room on the second floor of my garage. I am going to tie it in the the main 3 inch drain line. The lines that come from the sink and the shower, should there 3 inches also or can thay be 2 inches?

Thanks

[LazyPup]

The sink line should be 1 1/4 inches.
If the shower is a combination tub & shower it is an 1 1/2 line.
If the shower is a shower stall it requires a 2inch line.

You must also take into consideration the distance of the trap from the vent. You may need to increase the line size one trade size, or you may need to create a vent.

[hookerp]

The original plan was for just one bathroom downstairs. That is why I have a 3 inch line. Wher the drain line becomes a vent stack should in open it up to for inches? I will have atotle of 2 sinks at 1 1/2 inches an2 showers at inches with one toilet at 3 inches and 1 at 4 inches.

[LazyPup]

For the purpose computing line size the code uses a standard index called a DFU (Drainage fixture unit.) In order to determine a value for a DFU they selected the bathroom lavatory as the standard since it has the smallest diameter drain. Through trial and error it was determined that a 1 1/4 drain under gravity flow would pass 7.5 gal/min which was then established as 1 DFU. From that, the other drains were measured to create a table of values for each type of drain.

I.E. Lavatory 1 DFU
Bath/shower 2 DFU
shower stall 2 DFU
water closet(toilet with greater than 1.6 gal flush 4 DFU
Water Closet(water saver, 1.6 gal or less) 3 DFU
Kitchen sink 2DFU
Dishwasher 2 DFU
Laundry Tub 2 DFU
Laundry group (washing machine and tub) 3 DFU

Etc etc....

Each fixture is also assigned a minimum trap size....
Lavatory bowl 1 1/4"
Tub/shower 1 1/2"
Shower stall 2"
Toilet 3"
Kitchen sink 1 1/2"
Laundry sink 1 1/2"
Washing machine 2"

In all cases the waste arm serving a fixture must be equal to or greater than the minimum trap size, but may not be greater than one nominal pipe size larger.

Once you have determined the total DFU's on any given section of the line, you must then consult the line sizing table to determine the maximum DFU permitted for each line size.

1 1/4" Horizontal run 1 DFU Vertical run 1 DFU
1 1/2" ................... 3 ................... 4
2" ........................6 ...................10
2 1/2" ....................12.................. 20
3" .......................20................. 48
4" ......................160 ................. 240

The minimum diameter of a line run under a slab is 3"

The main vent must be equal to the diameter of the main drain line and must continue undiminished in size up and out through the roof.

If it is necessary to run an auxillary vent, the diameter of the vent line may be reduced to 1/2 of the diameter of the line it serves once it is 6 inches above the highest flood level rim of the fixture, but in no case may it be less than 1 1/2 inches. The line must then be increased to 3 inches at least one foot inside the attic space before it penetrates the roof to prevent frost closure in the winter.

As you can see from these tables, you must examine each drain or group of drains individually to determine the proper line sizes. As you can see, if you were to connect two lavatories to a common drain, you could run a 1 1/4 inch line to the junction of the second lavatory, then the line would have to increase to 1 1/2.

You must also consider the length of the waste arm.

Maximum trap arm distance ( Trap weir to vented stack or line)

Uniform plumbing code
1 1/4" ......... 5ft
1 1/2" ..........6ft
2" ............. 8 ft
3" .............12ft
4" or larger ...16ft

International residential code
1 1/4" line.....2ft 6 in.
1 1/2"..........3ft 6 in.
2"............. 5ft
3"..............6ft
4"..............10ft

[hookerp]

3 inch line l 1 1/4 inch line 2 inch line
l ____________l______________l_______
l
l
Pup,
This gal is a little confused!!! From reading your reply, I think the line can be a 2 inch.
The horizontal run of the line in question is about 10 feet before it hits the 3 inch line
and the vertical length of the 3 inch is about 10 feet before it hits the 4 inch line.
Does this drain line that ties into the 3 inch need to be a 3 inch or can it be a 2 inch?

[LazyPup]

Go b ack and read my previous post,,

distance from trap to vent, there is an illustration in that post.

The lavatory traps are normally only 1 1/4 inch traps, therefore you can only increase the waste arm diameter to 1 1/2 inches, however, there is a 1 1/4-1 1/2inch trap available. It is an 1 1/2 trap with a 1 1/4 reducing ferul in the slip joint. If you were to use those traps, you could then increase the line size to 2 inch to get the 8 ft of run from the furtest sink to the 3 inch vertical.

[mrcaptainbob]

I had NO idea there was that much to consider! You've just upped the respect for plumbers yet ANOTHER notch! Thanks for that education!!

[LazyPup]

MrCaptainBob..
Extreme care must be taken when determining the size of drain lines.
If a line is sized correctly the water flow should fill the pipe 1/2 full, allowing the top half as an air space for venting purposes.

IF a line is too small the velocity of flow in the pipe is deminished by lack of vent air and increased pipe wall friction. The end result is a line that will continually clog. By contrast, if a line were sized too big, the level of water in the pipe will now be well below the proper 1/2 fill. While the water will flow freely, there is not enough depth in the water to suspend the solid particulates in the line. The solids then lay in the pipe and the water passes around them. Once the water passes the solids are then left exposed to the vent air and they dry in place, again causing a clogged line.

In fact, an oversized line will often clog faster than an undersized line.

[Troy]

Once again I am impressed, LazyPup!

Try

[LazyPup]

Troy
To date we have discussed how to compute the slab elevation, DWV layout, Supply piping and to some degree, the final trim out components of the plumbing system.

There are a few other topics that are equally important although seldom discussed......

HOTS ON THE LEFT...COLDS ON THE RIGHT...*&$* DONT RUN UP-HILL...AND DONT BITE YOUR FINGERNAILS........

So much for Plumbing 101....next semester we will discuss the proper display of male cleavage while working under the sink..........lol.