Hello, Thank You, Drain Plan and Cleanouts

[DontKnowNothin]

Hello all, this is my first post on HomeRepairForum. I just found this site yesterday but I know I will spending a lot of time here. I can hardly believe how much useful information I have found already. I've gained so much form this site in such a short time I can only hope I will be able to make some small contributions in return.

I'm in the middle of a large remodeling project and I would like to put forth a couple of plumbing related questions.

The first goes directly to LazyPup along with a comment. First the comment ... Wow, Thank You. I've been searching for plumbing related answers on the forum and have read many of your posts. I've learned a tremendous amount from reading them but one of them leads me to my first question.

1) In the thread DrainZzzzz you posted an illustration that shows the minimum trap arm length from a P trap to washer standpipe as being 4 x the trap diameter. I can't figure out why. Isn't this distance normally 2 x trap diameter? I'm sure I'm missing something just cant figure out what.

Now for my other two questions for which I would appreciate any and all feedback.

2) Is there a maximum height restriction for a Washer standpipe? I live in MD and I believe my local code is based on the NSPC and IRC. Given that, I understand the height of the standpipe above the trap is limited to 42" but can I put the trap at any height I want? We have a front loading washer that sits on a drawer base so the top of the washer is about 53" high. I'd like to put the standpipe at around 54" so it's visible behind the washer. The washer is rated to pump 8' so there is no issue there. Under UPC it seems standpipes are limited to 48" so I know I'd be out of luck if the code here were UPC.

2) Cleanouts are confusing me and I'm not exactly sure where I need them. I'm only concerned with my main drain at the moment. We are adding a new bathroom above our garage and it will be serviced by a 3" drain. The drain will travel horizontally about 9' with various fixtures draining into it before it drops vertically a few inches to get under the floor joists so it can then turn 90 degrees (We'll call this POINT A) and proceed horizontally for about 18' along an I-Beam across my garage ceiling to Point B. At Point B it will be joined by a 2" drain coming from the laundry and transition to a vertical drop for about 9' coming down inside the wall between my Garage and Family room to Point C. At Point C the vertical drop has reached the Garage floor and it will now transition into a horizontal run to travel about 10' under the floor of my Family Room to Point D where it will hit the rear wall of my basement. Here it needs to take a 90 degree turn and follow the wall for about 25' until it ties into the main drain leaving the house at Point E. I hope this makes sense, I've tried to sketch it out in the included pictures but not sure how clear it is.

Points A, B and E would be behind drywall and not accessible. Points C, D would be behind drywall but accessible. Is there anything wrong with my plan? Do I need additional cleanouts? Improvements?

Thanks again to all those who use and maintain this great site.

Eric M.

Fittings:


Overhead View:


Head-On View:

[LazyPup]

Good Evening Eric and welcome to the HomeRepairforum.

Let me begin by saying thank you for catching the typo in that illustration. You are absolutely correct that the minimum length of a fixture arm is 2x the trap diameter measured from the trap wier to the vent opening. I am working on editing that immediately.

Now for your washing machine standpipe. Both the International Residential Code (IRC) and the Uniform Plumbing code (UPC) have established 18" as the minimum height of the standpipe when measured vertically from the top flood level rim of the standpipe to the water level of the trap.

The IRC then lists a maximum height of 42" however here again the height is measured from the flood level rim of the standpipe to the water level of the trap. If it is desired to have the top of the standpipe higher than 42" above the finished floor you may install a riser and tee the P-trap into the riser then extend the input above the trap to your desired height.

Now to address your question on cleanouts. Under the IRC we are required cleanouts at:
1. A two way rodding tee or two way cleanout is required at the junction of the house sewer & House Main Drain.(House Sewer-line from the municipal sewer or septic tank to the structure & House Main Drain- The main drain inside the structure). For structures with a basement the main cleanout is usually just inside the basement wall & for structures on slab it is located approximately 3' outside the footer wall.

2.A cleanout is required at the base of all stacks.

3. Required at each 100' of straight horizontal run.

4. Required at each 40' of horizontal run when offsets are present.

5.Required at each horizontal change of direction greater than 45 deg.

6. Required at the upstream end of all horizontal runs.

7. On vertical stacks or vents the top opening of the vent is the upstream cleanout access.

Having determined where the cleanouts must be, we must then consider what constitutes a cleanout. We are all familiar with the thread adapter and threaded cleanout cap but there are other means of providing a cleanout.

The code requires a watercloset (toilet) to be on the end of a drain line or fixture arm. A WC can be lifted allowing a direct access into the drain line through the closet flange so a WC is accepted as a cleanout. With this in mind it is generally advantageous to design the drain with a Watercloset on the upstream end of a branch line. In some instances in slab construction when we cannot have a WC on the upstream end of a drain an option is to continue the run across the slab and terminate it with a cleanout extending through the footer wall on the opposite side of the structure where is can be accessed from outdoors. The precludes the need to have a cleanout cap proruding through the floor inside the structure.

I have reviewed your drawing an prepared an isometric drawing to show the placement of your cleanouts.

You will also note that I illustrated the tentative placement of the required vents for your layout.
In the upper section I illustrate the vents with dotted lines. That is because you only need one vent but you can use either option.

[DontKnowNothin]

LazyPup,

Thank You. I very much appreciate your help. I didn't intend to pick on the typo in your illustration. I thought there was some obscure reason it had to be 4", I didn't even consider it might be a typo.

Thanks too for the isometric, it is much easier to read when illustrated this way.

I was afraid I would have to put cleanouts in all the locations you identified. I'm assuming these cleanouts have to be accessible and I have no idea how I can do that. I highlighted an area in the isometric, I'm wondering why no cleanout is required there. Given the rules in the order you listed them, wouldn't #2 require the cleanout? Does #7 override #2 in this particular case?

I also changed the isometric a little more because I realized I will need to put the WC and Shower on a separate branch then the vanities and tub because there is 7" thick laminated beam separating them. I also tried to show that the tub will sit about 6' further away then the vanities in case that matters. Not sure what this does to the venting options, I'm assuming I will need both now for the bathroom. Also can the WC/Shower vent be placed downstream of the WC? I might be able to work it into a Linen closet then and I remember reading in another one of your posts that you can get a better flush if you keep the vent at least 4'-5' away.

Thanks again,
Eric

[LazyPup]

As was mentioned before, a vertical stack can be rodded (snaked) from the roof opening downward therefore the requirement to have a cleanout at the base of a stack is to permit access to rod the horizontal line to which the stack is connected. In the case of slab construction or in basements when the house main drain is in the concrete below the basement floor we put the cleanout on the vertical stack near the base. When we have a basement or crawlspace where we have direct access to the lines we install a Wye and put the horizontal cleanout on the end of the wye as illustrated so that cleanout is technically at the "Base of the stack".

I need to make a point of clarity here also. When drawing an isometric we show a Wye & 1/8 bend or combo as a 45 deg line entering the horizontal then changing to 90deg from the horizontal, thus in the illustration it appears that there is a length of pipe at a 45deg angle at the base of the stack but that angle is just representing the side input of a Wye.

Now for the new branch line for the lavatories and tub. Because a WC generates large amounts of solids in the waste line the code minimum for a line serving a WC is 3". A 3" line was more than adequate to handle the total DFU (Drainage Fixture Unit) load of all the fixtures on that line so we did not need to make any additional line sizing computations.

Adding the additional branch line to serve the tub and lavatories is fine but we must now compute the proper size of that line. Under the IRC a tub or tub /shower is rated at 2DFU's and a Lavatory is rated at 1DFU. We have one tub (2DFU) plus two lavatories @1 DFU each for a combined load of 4DFU's.

The code minimum drain and trap size for the lavatories is 1-1/4" but the code will permit us to increase the size of a drain line by one nominal trade size. Generally we always opt to use the exception and make the lavatory drain an 1-1/2" line simply to preclude the necessity of maintaining a separate inventory of 1-1/4" pipe and fittings for this limited use. An 1-1/4" line is rated for a maximum of 1DFU so even if we used 1-1/4" we could only use it for the last lavatory.

The code standard for a tub or tub/shower drain is 1-1/2". You could then run an 1-1/2" fixture arm from the tub trap to the horizontal branch. At the junction of the last lavatory drain line and the tub drain line we have a combined load of 1DFU for the Lavatory and 2DFU for the tub = 3DFU's. An 1-1/2" line is rated for a maximum of 3DFU's so we can combine the tub and lavatory lines and run 1-1/2" downstream on the branch until we come the the second lavatory. The second lavatory is adding 1DFU for a combined load of 4DFU so the proper size of the line downstream from that junction is 2" which is rated at a maximum of 6DFU's.

We must now consider the venting on all the fixtures on this branch. An auxillary vent may be reduced to 1/2 the diameter of the line it serves but not less than 1-1/4". In this case our auxillary vents will be 1-1/2" so they will not only vent this branch but it is also adequate to vent the 3" downstream.

In the present configuration the lavatory risers are dropping down below the floor then turning horizontal and coming forward a short distance to meet the branch line. This is also fine but we have a problem with the tub drain. Under the IRC the maximum horizontal length of an unvented fixture arm is computed by dividing the line diameter by the required pitch. All lines 3" or under are required a 1/4" per foot pitch and the line diameter is 1-1/2" so the maximum allowable length from the tub trap weir to the horizontal branch is 1.5" / .25" = 6'. You stated that this line may exceed the 6' limit so we must explore the options here. The first option would be to move the horizontal branch a bit further towards the tub so that it is now directly under the lavatory risers. This would shorten the tub fixture arm and also improve the venting for the lavatories. The second option would be to use the code exception that allows us to increase the line diameter by one nominal trade size. We could then make the line from the tub trap to the horizontal branch a 2" line which would give us 2" / .25" = 8'. The only consideration here is that the Wye at the junction of the tub and last lavatory lines would need to be a 2" wye and the line downstream from there would need to also be 2". If we still cannot get the required length from the branch to the tub trap we would need to install an additional vent on the tub fixture arm within the required distances of the trap.