Rough Plumbing a Bathroom: What do you wish you knew before you started?

pgray007 · Sep 30, 2015

I'm going to embark on my first major plumbing project, which is roughing and (eventually) finishing a bathroom above my detached garage before I close up the walls in the garage.

Walls are all open, and the detached has a water supply from the main house and drain w/ holding tank/pump installed an operable. PEX is the standard in my area so no copper sweating or any of that.

I installed an irrigation system so familiar with the basics of working with PVC, and I've read some books on rough plumbing and think I "get it," but for those of you that have done this, what are the few "newbie" or "darn I wish I new..." kind of tips?

I've thought about hiring a plumber to check my work/plans but everything seems relatively straightforward, but I'm worried I don't know what I don't know.

Big Bad Dad · Sep 30, 2015

Spacing of the toilet flange from the walls is very important. The toilet manufacturer's manual can give the dimensions. Remember to allow for the thickness of the drywall or whatever you are using....

creativecars · Sep 30, 2015

My Grandpa always told me:

Cold on the Right
Hot on the Left
Leaks cause rot and
**** don't flow up hill

homebuilt burner · Sep 30, 2015

The height of the sink. Don't forget about the thickness of drywall/tile and where the switches are going to be in relation to pipes and mirrors. If it is a small bathroom make sure you have enough room for the door to swing in regards to the sink and toilet and a place to stand while opening the door.

gungatim · Sep 30, 2015

use 3/4" line to the tubs for more volume, don't forget to put plywood backers into the studs for towelbars, don't skimp on shutoff valves, use copper and stay away from pvc/cpvc, buy quality fixtures...basic stuff.

engineer2 · Sep 30, 2015

Correct venting is very important.

tcianci · Sep 30, 2015

The phone number of a real plumber!

sberry · Sep 30, 2015

Make sure the room is legal size for a bathroom if possible and place stool at recommended space which I believe is 12. While it may seem like a good idea to leave a little extra it isn't.

pgray007 · Sep 30, 2015

sberry said:
Make sure the room is legal size for a bathroom if possible and place stool at recommended space which I believe is 12. While it may seem like a good idea to leave a little extra it isn't.

Why do you mean by this? I get the legal size but not the stool placement.

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404 · Sep 30, 2015

When measuring, marking, and cutting pvc drain pipe, mark which end is the wanted, correct length part and which is the waste cut off. Sometimes the two are close to each other and putting (priming, glueing) in the wrong one is annoying.

The distance from the center of the toilet flange to the finished wall is not one standard value. There are several choices, so pick the toilet in advance.

pmiranda · Sep 30, 2015

Measure twice, cut once, and measure again before you start gluing it up. I'd fit it all together before gluing to make sure your slopes are correct. Make sure your cut edges are clean and deburred so they don't catch hair and food.
Better to rent the right tool than waste time using a POS for cutting and especially crimping. Pressure test before closing up the walls even if you technically don't need an inspection.

HiWind · Sep 30, 2015

just done one - all good advice above!
Waterproof everything beneath tiles or paint with Bitumen or PVA sealer
Get your falls right - test with wet paper and hose
Mock up layout with everything in place to see what conflicts
Try get your tile lines to tie into:
Centre of sink, top edge of shower glass etc
Good tiler is with it!

HiWind · Sep 30, 2015

engineer2 said:
Correct venting is very important.

This!

zhaddock · Sep 30, 2015

creativecars said:
My Grandpa always told me:

Cold on the Right
Hot on the Left
Leaks cause rot and
**** don't flow up hill

Ha! My GP said similarly "All you need to know to be a plumber is that **** doesn't flow up hill and payday is on Friday."

JohnX14 · Sep 30, 2015

I'd hire a plumber based on the questions being asked. I've done my share of plumbing and layout. But it's not easy if you've never done it. Sure cutting, gluing, soldering etc are not difficult. It's seeing the whole picture, and venting, draining, cleanouts, etc. Along with the legality of whether you are allowed to install your own plumbing, getting permit, inspection.

theoldwizard1 · Sep 30, 2015

Big Bad Dad said:
Spacing of the toilet flange from the walls is very important. The toilet manufacturer's manual can give the dimensions. Remember to allow for the thickness of the drywall or whatever you are using....

There is also a minimum distance from the sink drain centerline to the wall. You can cheat this, if it is offset or it you use a "bottle trap".

More finish plumbing related. There are 2 different gauges of chrome plated traps available. The super thin ones they sell in most big box stores (22 gauge) that you feel like you can crush in you hand and the heavier ones you can find on line (17 gauge; Lasco) Remember 1-1/2" for kitchen and laundry sinks, 1-1/4" for bathroom sinks.

Keel · Sep 30, 2015

I like to make panels so I can get to the pipes if need be, so much easier than having to cut drywall, mud, sand,etc after a repair..

Daniel Dudley · Sep 30, 2015

If you are putting together a complicated drain line, dry fit everything, anbd put index marks on all the pipes and elbows, so you can reassemble it and glue up the sections the same way you had it the first time.

gregtwojeeps · Sep 30, 2015

pgray007 said:
Why do you mean by this? I get the legal size but not the stool placement.

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I think he means the toilet drain rough in from the finish wall surface like this : Pardon my drafting skills

gahrajmahal · Sep 30, 2015

The book from Home Depot Plumbing 123 is excellent. Go to a real plumbing supply for your supplies. You will get better fittings and end up making fewer trips.

There is such a thing as a rear exit toilet if you don't have room for the drain under the toilet. It does not cost much more.

nadogail · Sep 30, 2015

Sewer connections, in my city, need to be permitted and inspected.
Plan on paying a professional plumber for his assistance and expertise. You might find a plumber who will do your work "on the side", mine prepared the isometric drawing and broke the slab, ran and connected the soil pipe but allowed me to pull the permit as an owner/builder.
He also had, and gifted to me, a good toilet he had removed from a customer who had a bathroom remodel done.
My city inspection was quick and easy.

bighead51 · Oct 1, 2015

You forgot "Don't chew your finger nails"

Todd.Brock · Oct 2, 2015

I read that you have to run drain line upstairs then tie in to an existing stack? What about vent line ? Does that need to done too ? I would consult with a plumber if that isn't in place. It's one thing to tie in and finish.

But if all that's in place, I believe six feet to a vent is rule of thumb I was taught, account for backer board mortar and tile height when setting toilet flange , be consistent with your stub out heights. Don't plumb hot water to the *******. ...don't ask me how that happened...try to tap into a hot and cold line that will support a ****, shower and shave all at the same time. When drilling through joists , be aware of rules for large holes- middle third- no more that X percentage or total height. Will have to google it but you get the idea. But a good hole saw.

MushCreek · Oct 2, 2015

I just finished building my own house, and did all of the work myself, from basic shell to plumbing to electric to HVAC. Many of these things I had never done before. Plumbing was by far the hardest trade to get good answers on. Part of this is because there are different codes in different areas, and even regional variations on the same code. I have three different plumbing books, and each one has different 'rules'! I could not get a plumber to act as a consultant or do part of the job. All of them insisted on doing the whole house, or nothing, something I simply could not afford. On-line help was hard to get, too, with most people saying, "Hire a pro!". I did hire a plumber to do the under-slab work, and once I learned how drains and vents work, I found he had done it wrong. It works, but it's not code. If you can figure out the rather vague codes, and follow what your local jurisdiction requires, it's not hard.

By comparison, electric is easy. One clearly defined national code with no vague gray areas.

As for toilet set-backs, there is a standard- it's 12" from the centerline of the flange to the finished wall. Almost all toilets are made to this. You can get 10" or 14" set-back toilets, but they are rare and likely would have to be ordered. Go with what you can get at a home store on a Sunday afternoon.

Watch the alignment if you have pipes coming out of a slab, My 'professional' plumber put in two 4" PVC pipes, and managed to get them 2" out of line with each other. I had to use an 8" wall, since they were too far out of whack for a standard 6" wet wall.

Big Bad Dad · Oct 2, 2015

In addition to the dimension of the toilet flange from the rear wall, keep in mind that the minimum allowable dimension from a side wall or vanity, etc. is 15" from the wall surface to the centerline of the toilet. (That's for us big guys so we dont get stuck.....) :bounce:

PhantomEB · Oct 2, 2015

Subscribed as a second bathroom is in the plans.... 60x60 corner tub, separate shower with vanity and toilet. Gotta figure out what to do with the window. Girls never gonna leave it.

It's a moderate sized house that lends itself to huge rooms in the basement.... Spare room down there that's just my work out room now is bigger than the master above it.

Buddies say throw a wet bar down there I am like why? I drink beer. I only need a decent bar fridge down there!

pgray007 · Oct 10, 2015

Big Bad Dad said:
In addition to the dimension of the toilet flange from the rear wall, keep in mind that the minimum allowable dimension from a side wall or vanity, etc. is 15" from the wall surface to the centerline of the toilet. (That's for us big guys so we dont get stuck.....)

And as part of the vagaries in codes described above, SC apparently allows a 12" clearance. I guess we demand that our constipated residents be of narrower frame!

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pcmeiners · Oct 10, 2015

As to second floor bathrooms, a drain/trap preferably hidden in case of sink or bath overflow, inconspicuous if possible, like behind toilet. Pitch floor toward drain, slight elevation on door saddle.

If possible use 2x4s which are thoroughly seasoned or used (straight/square) around tub/shower to eliminated shrinkage.

2" drain pipe rough in pvc, if pipe id hidden bring 2" to sink/tub outlet if you can get this past code inspection, just about eliminates clogs forever.

If renovating older bathrooms and they have no-hub spun cast, just remove it, especially if it has pipe manufactured after 80s, it does not last.

Water hammer arresters on all fixtures.

Raw water filter, small filters which catch **** in the supply pipes; better then replacing faucet valve bodies, cleaning faucet screens, valve bodies in general.

With old bathrooms check if the room is square, as tile floors make it very noticeable if not.

Walls, full coat oil base primer, latex is OK for top coat, oil base or your seams/screws will show after a while

Insulate tub with fiberglass batting, especially if against outside wall .

3/4" supply pipe throughout.

If you have tub, the cheaper one do not have a good depth to them, get deeper tub. Better off with real cast iron, ***** to go up stairs, last longer.

speed bump · Oct 10, 2015

The only thing I really regret on my last bathroom remodel is I didn't think about how changing things like tub width and vanity cabinet drawer setups affect where my plumbing needs to come out.

JC23 · Oct 10, 2015

Just finished an upstairs bath and all of the above are great tips.

I would add test all water lines before drywalling in and do the same with your electric.

zmaxmotorsports · Oct 10, 2015

Big Bad Dad said:
Spacing of the toilet flange from the walls is very important. The toilet manufacturer's manual can give the dimensions. Remember to allow for the thickness of the drywall or whatever you are using....

12" to the center off the studs works for most rough ins.

zmaxmotorsports · Oct 10, 2015

homebuilt burner said:
The height of the sink. Don't forget about the thickness of drywall/tile and where the switches are going to be in relation to pipes and mirrors. If it is a small bathroom make sure you have enough room for the door to swing in regards to the sink and toilet and a place to stand while opening the door.

zmaxmotorsports · Oct 10, 2015

engineer2 said:
Correct venting is very important.

zmaxmotorsports · Oct 10, 2015

tcianci said:
The phone number of a real plumber!

zmaxmotorsports · Oct 10, 2015

theoldwizard1 said:
There is also a minimum distance from the sink drain centerline to the wall. You can cheat this, if it is offset or it you use a "bottle trap".

More finish plumbing related. There are 2 different gauges of chrome plated traps available. The super thin ones they sell in most big box stores (22 gauge) that you feel like you can crush in you hand and the heavier ones you can find on line (17 gauge; Lasco) Remember 1-1/2" for kitchen and laundry sinks, 1-1/4" for bathroom sinks.

I use 1 1/2" for both,people dump too much stupid stuff into bathroom sinks clogging 1 1/4" drains too easily.
Pvc traps and fittings are fine for most residential stuff,In omaha we only have to use 17g for commercial work.

zmaxmotorsports · Oct 10, 2015

Daniel Dudley said:
If you are putting together a complicated drain line, dry fit everything, anbd put index marks on all the pipes and elbows, so you can reassemble it and glue up the sections the same way you had it the first time.

Fittings/pipe always fit together differantly once you glue them. :spit:

zmaxmotorsports · Oct 10, 2015

gregtwojeeps said:
I think he means the toilet drain rough in from the finish wall surface like this : Pardon my drafting skills

What kind of toilet do you use an external trap on? Must be french. :lol:

zmaxmotorsports · Oct 10, 2015

Todd.Brock said:
I read that you have to run drain line upstairs then tie in to an existing stack? What about vent line ? Does that need to done too ? I would consult with a plumber if that isn't in place. It's one thing to tie in and finish.

But if all that's in place, I believe six feet to a vent is rule of thumb I was taught, account for backer board mortar and tile height when setting toilet flange , be consistent with your stub out heights. Don't plumb hot water to the *******. ...don't ask me how that happened...try to tap into a hot and cold line that will support a ****, shower and shave all at the same time. When drilling through joists , be aware of rules for large holes- middle third- no more that X percentage or total height. Will have to google it but you get the idea. But a good hole saw.

Your venting depends on where youre located.

zmaxmotorsports · Oct 10, 2015

Big Bad Dad said:
In addition to the dimension of the toilet flange from the rear wall, keep in mind that the minimum allowable dimension from a side wall or vanity, etc. is 15" from the wall surface to the centerline of the toilet. (That's for us big guys so we dont get stuck.....)

A 30" space for toilet only is common.

zmaxmotorsports · Oct 10, 2015

Try and keep the plumbing on interior walls,Insulate the hell out of garage ceiling under bath where any plumbing is run.

Rough Plumbing a Bathroom: What do you wish you knew before you started?

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