replacing plumbling

[hellegpt]

I have a laundry room that was added on to the garage. The water lines are connected to the plumbing going to the kitchen sink. I have a sink in the laundry room used as the vent. This has given us real bad odors in kichen and laundry sinks. I want to take out the sink in laundry and repipe the vent through the roof. I want to take the pipes going to the kitchen plumbling and go outside, using the laundry room outside wall. I will have to drill a hole out for pipes.
How can I do this myself and do I need to tie into the outside sewer line. I know I will need a professinal for this due to going into the city sewer lines.
I need to know the best way to handle this and the cheapest way to do this myself.
Any suggestions would be helpful.
Helle

[LazyPup]

On the surface this seems like a small project, but once you begin examining the details it is quite complex and will require considerably more information before we can form and actual game plan.

In most jurisdictions, especially in colder climates which are subject to freezing they will no longer permit any DWV(Drain, Waste & Vent) piping on the outside of the structure with the singular exception of the vent roof terminations, on the other hand your profile says you are located in Plano Texas, which is in the Dallas, Fort Worth metroplex where you only occassionally get a winter freeze, so your codes may be more laxed on this point.

You stated that you are on a municipal sewer system so I would suspect the sewer is in an easement parallel to the street on the front side of the house.

You stated that the laundry room was added onto the garage and I am guessing that it is on the backside of the structure. This means your new sewer line would need to run parallel to the backside of the house to a corner, parallel to the side where it would make another corner and parallel to the front of the house where it would tie into the existing house sewer line.

You would first need to know the location and depth of the existing house sewer line, then compute the length of the run from the house sewer around the house and to the point where you intend to exit the new drain line from the house. Once you know the lenght of the run you could compute the required pitch elevation for the new line by multiplying the length of the run by 1/4" per foot slope. (Some codes will allow 1/8" per foot with the expressed approval of your local inspecting authority).

NOTE: Most jurisdictions will not permit a structure to have a second connection to the municipal main, and even if they did it would probably prove cost prohibitive. The homeowner is responsible for running the line from the structure to within 3' of the municipal main, then the municipal sanitation dept makes the final connection. That final connection is typically about $1500 to $2000 and in some jurisdictions it would double your monthly sewer tax bill.

We are not permitted to run a parallel trench within a 45deg downslope angle from the building footer wall, so when running parallel to the structure wall, for each required foot of depth you must remain one foot outside the footer wall. Example, if we must trench 24" deep we must position the trench at least 24" away from the footer wall.

FOR AN EXAMPLE, let us assume for the moment that you must run 30' from the point where you exit the structure to the rear/end wall corner, the run 36' along the end wall to the front of the structure and another 25' to the existing house sewer.

The total run is 30'+ 36'+ 25' = 91'
91' x 1/4" per foot = 91 x .25 = 22.75"

Most codes require a minimum 12" burial therefore we must have a 12" burial at the point where the new line exits the building and the new line would require an additional 22.75" of pitch so the existing house sewer would need to be a minimum of 22.75 + 12" = 34.75" lower than the point of exit. Keep in mind that these figures are only offered as an example of how to compute the required elevation and you would need to make accurate measurements of your location to compute the actual pitch you require.

If you cannot achieve the required pitch the alternative is to install a "sewage ejector pump" which could then pump the effluent from the point of exit to the existing house sewer, however, keep in mind that even a small code approved sewage ejector will typically add about $700 to $800 material cost to the project. This does not include the cost of labor to install the pump or the necessary electrical supply to the pump).

Now let us consider the pipe sizing for the kitchen and laundry drains.

The code minimum for both the kitchen sink and the laundry sink is 1-1/2" while code minimum for a washing machine standpipe is 2". (A washing machine is permitted to discharge into a laundry tub with an 1-1/2" drain).

Under the International Residential Code (IRC) the maximum horizontal distance of an unvented waste arm from the fixture trap to the vent is computed by dividing the diameter of the line by the required pitch of the pipe. By example, all lines less than 3" diameter are required a 1/4" per foot pitch and the kitchen sink requires a 1-1/2 line, therefore the maximum combined horizontal distance from the kitchen sink trap to the vent may not exceed 1-1/2" divided by 1/4" = 6ft. (The Uniform Plumbing Code-(UPC) derates the length by approx 40% therefore the maximum length of a 1-1/2" line under the UPC is 3' 6"). When it is necessary to run horizontal lines greater than these distances we must add additional auxillary vents within the prescribed distance.

For load calculation the kitchen sink, laundry sink and washing machine standpipe are all three rated at 2DFU's (Drainage fixture units) each.

An 1-1/2" line in a horizontal run is rated for a maximum load of 3DFU's. therefore you could run 1-1/2" from both the sink and laundry sink, but at the point where they join the combined load is now 4DFU's and it would require a 2" pipe which under the IRC is rated up to 6DFU's (Under the UPC 8 DFU's max).

The IRC will permit a 2" line to run 8' horizontal from the trap weir to the vent, while the UPC only allows 5'.

If you can post a rough illustration of your house with the location of your kitchen and laundry as well as the approximate point were you anticipate exiting the building and an approximate location of the existing sewer line I will try to compute the pitch and layout for you.