Plumbing and Ventilation 1: Plumbing Rough-in Dimensions and Instructions


I'll give you the usual heights and dimensions for plumbing fixture drains and supply lines for home improvement rough-in. Follow the directions that come with your new plumbing fixtures. Try to get an idea of the plumbing fixtures you want to install before the house framing stage since some plumbing fixtures will need backing to support them.

I'm really partial to the plastic piping that can be used for hot and cold water supply lines, rather than the straight copper pipe with solder joints. Less expensive, too. They use copper or brass crimp on fittings so no soldering is needed.

The plumbing rough-in stage is made easy with stub-out elbows which are sealed so the water can be turned on for checking for leaks before the walls of the house are sheeted. These usually are available in your local home improvement stores now. A crimper is required but can be rented for a nominal amount, $10 to $15 per day or purchased, of course. They are not cheap to purchase though, ranging from $200 to $300.

After the wall finish is applied and painted, the water is turned off, the stub-outs are cut off to the appropriate length and escutcheon plates and shut off valves are installed. The shut off valves can be 5/8" OD compression fittings rather than the solder type.


Toilet Floor flange: 12" from finished wall to center of the toilet floor flange, screw down the 3" ABS flange on the sub-floor with stainless screws. A 3" ABS 90 degree elbow is usually connected to the floor flange. This is the only time you can use a 90 degree bend in a waste system, as a vertical 90. When turning a 90 laterally, use two 45s.

Vent: Keep the vent within 5' of the floor flange, the vent can be 1 1/2", usually on top of a 3" stack.

Cleanout: The toilet itself can be removed quite easily so a cleanout is not needed. Put a cleanout at the bottom of the 3" stack, along with an expansion joint if the stack enters a concrete floor in the basement or crawlspace.

Supply: One supply for cold water is installed 9 1/4" from finished floor and offset 6" to the left of toilet center. This is terminated with a shut-off valve with a 3/8" O.D. (outside diameter) compression fitting. A closet supply tube is attached to this fitting complete with compression ferrule. The other end is a closet tapered fitting attached to the supply tube from the toilet tank. No washers required.

Countertop or Drop-in Lavatory:

Drain: Set the drain on center of the sink and 18 1/2" from the finished floor. Usually the waste through the sink is 1 1/4" so use a 1 1/2" hub x 1 1/4" ABS slip joint adapter onto the tailpiece coming through the sink.

Vent: Keep the 1 1/4" or 1 1/2" vent within 5' of the p-trap, usually the vent pipe goes vertically up the wall behind the center of the sink and is attached to the sink waste with a sanitary tee.

Cleanout: A cleanout must be provided past the p-trap. The easiest way is to use a union p-trap and slip joint adapter, rather than a cleanout adapter which has to be provided an access hole outside the wall.

Supply: Install hot and cold supplies on the sink centerline at 8" centers and 21" from the finished floor terminated with a shut-off valve with 3/8" compression fittings. Lavatory supply tubes or risers, smaller than the closet tube on its ends, are attached to the sink faucet. Some faucets are supplied with risers for the standard 3/8" compression fittings.

Pedestal Lavatory:

Drain: Since the tolerances on a pedestal sink are very limited, I usually go by the actual sink itself. There are a lot of off-shore pedestals out there without any standards. For a sink with the top of the rim at 32" above finished floor, set the drain centered with the sink and 18 1/2" above the finished floor

Vent: Same procedure as the drop-in lavatory. I usually go with ABS, but for a high-end unit go with chrome. Most of the drain is hidden in and behind the pedestal.

Cleanout: Same as the drop-in lavatory.

Supply: Same as the drop-in lavatory, but go with 4" centers on the shut-offs. Since a pedestal sink is wall hung install the necessary backing during the framing stage.

Bathtub and Shower:

Drain: Set the drain to the particular bathtub, access is needed through the floor. The 1 1/2" drain goes through the floor and is connected to the stack with a sanitary tee from inside the joist space or below it depending on which way the floor joists run. The drain for a shower only is 2". It is tough to replace a bathtub if the ceiling below is finished, I usually access the floor through a wall rather than the ceiling. Choose the lesser of two evils to repair. The drain is connected to a waste and overflow (W&O), which is bought separately from the bathtub and connected prior to installing the bathtub. Choose the particular means of stopper: plug, twist and turn, push button, etc. Follow the instructions that come with the bathtub, usually these are very good. With a bathtub that comes with the surround as a one piece, install this on the sub-floor prior to framing up the walls so you can get it in place. It won't fit through doors, that's why they make a renovator bathtub and enclosure in two pieces, so you can get it through the doors, then install it after attaching the two pieces together. If the unit is against an outside wall, insulate and vapor barrier the wall before installation.

Vent: The stack can be used as a wet vent if it is within 5' of the p-trap, otherwise use a 1 1/2" vent through the wall similar to the vent on a lavatory.

Cleanout: This is a tough one, check with your local building codes. Usually the ceiling and walls are finished around a bathtub so there is no access. This holds true especially if the supply is on an outside wall, to be avoided if at all possible. The p-trap must be glued at both ends since it is in the floor without access. If accessible a p-trap with cleanout may be installed. Usually, we can remove the drain screen or pop up mechanisms fairly easily and remove hair and assorted good stuff from inside the bathtub.

Supply: The control valve is part of the rough-in before the walls are finished. Install the control 15" above the rim of the bathtub and 54" above the finished floor for a shower only. For a bathtub without a shower the control should be placed 10 1/2" above the rim. Modern controls have the spout separate. For a bathtub and shower install a spout with diverter 4" above the bathtub. For a bathtub only install the spout at 4" above the rim, as well. The shower head is connected to the control with appropriate piping at a height of 78" from the sub-floor. The hot and cold water supplies are connected directly to the control valve. Standard connection is hot on the left, cold on the right when facing the bathtub or sink. Some valves have threaded connections, others have solder type fittings. Remove the innards of the control when soldering fittings to it. Usually the innards are made of plastic and rubber parts. When finished the connections, turn the water on to check for leaks, before the walls are covered.

Curtain Rod: Install the curtain rod brackets 76 1/2" from the floor centered on the curtain rod. Friction fit or spring loaded curtain rods are also available.

Kitchen Sink:

Drain: Set the 1 1/2" drain 16" from the finished floor, centered for a single bowl, offset 8" to the left of center for a double bowl. I prefer to make up my own ABS waste connections between bowls, you can purchase these but they are expensive.

Vent: Same as the bathroom lavatory.

Cleanout: Same as the bathroom lavatory, use a union p-trap with slip joint adapter attached to the tailpiece connected to the basket and strainer coming through the sink. Usually most brands of stainless steel sinks come with the basket, strainer and tailpiece included.

Supply: Install the hot and cold supplies at 8" centers centered on the sink and 23 1/4" above the finished floor terminated with shut-offs. The risers from the shut-offs to the kitchen faucet are the same as the lavatory risers. Some are supplied with the faucet so check that out. When ordering a kitchen sink be aware of the number of holes in the faucet deck. Usually three hole sinks are common with a fourth hole for a sprayer or soap dispenser. Match the number of holes with the faucet. For single lever faucets, usually a mounting plate for a three hole is included.

Bathroom Accessories:

Toilet Tissue Holder: Install this about 24" high from the finished floor, centered on the toilet roll and even with the front face of the toilet bowl.

Towel Bars: Install these 45" to 48" above finished floor.


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