How to Plumb a Bathroom in Basement

Taking second place to only the kitchen, the bath is the next most common area of the home to be either remodeled or rebuilt. A National Kitchen and Bath Association survey showed that last year (2008) there were about 8.5 million baths remodeled and around 25% were totally new construction. This year (2009) the numbers are expected to increase. With the downturn in both the economy and housing market, more homeowners are opting to stay put and make improvements on their existing home.

Having another bath can help keep the peace and sanity in your family and it can also make your home more appealing to buyers should you ever decide to sell. You don’t even have to sacrifice part of a bedroom or other useable living space in your home if you know how to plumb a bathroom in the basement. Every city has different rules and regulations, but you most likely will need to apply for a permit and then have the bath inspected to see that it’s up to code. You’ll need to check with your local building authority to see what the requirements are as far as minimum bath size or anything like that before you begin. You will then have to show a plan of your new bath to get the necessary building permit before you can install a bath.

Since the toilet, sink, shower or tub will all have to drain into your main drain line, you’ll have to locate that first. You can usually find the main waste line of your house running under the foundation or vertically down from a second story inside a wall and then into the main waste line. This is usually a 3″ to 4″ diameter pipe and you’ll be adding in a 3″ pipe for your new basement bathroom toilet. It is by far easier to add in a short pipe as opposed to a long one, so try to locate your new basement bath over a main waste line or against a wall where one runs down.

Most hardware stores or home improvement stores will have the fixtures and supplies that you will need. There also should be a knowledgeable service person there who can answer any questions that you might have or problems that you may run into when you plumb a bathroom in a basement. There are even starting to be some do-it-yourself kits that come with all the supplies you’ll need and detailed instructions on how to install them.

The basic rules to remember when you are learning how to plumb a bathroom in a basement are that every drain has to have a vent and a trap. That includes a toilet, sink and bath tub if you add all those. A vent is a pipe that runs up and the easiest way is to connect it into the existing vent system. Otherwise you will have to run it all the way out the ceiling and roof. Vents equalize the pressure in a water system and allow things to drain and not back up. A trap is an elbow pipe that traps or holds water and keeps gasses from the waste or sewer line from getting into your bathroom.

Drain pipes also need to slope, usually about 1/4″ per foot. You can ask your local building inspector or home improvement store what the specific codes are for your area.

You’ll also need to locate your main water line and know how to shut it off, drain the nearest hot and cold lines where you want to install your basement bath and then cut into those to add the new line you’ll need. These are usually copper and will have to have a pipe cutter to cut them as well as be able to solder them. You will also probably need to have a special tool that makes threads in the copper pipe so you can screw together special fittings and attachments.

Once you have located the easiest places where you can tap into the water lines, vent pipes and main waste drain, you can lay out where to put your toilet, sink and tub or shower. You will have to cut a hole in the floor to seat the toilet and fit the drain pipes and wax ring as well as the bath tub drain if you install a tub. You will also have to probably cut into a wall or two to connect your sink or shower pipes. It’s extremely important not to cut into any wiring as that could be deadly and also not to cut any load bearing or support beams in your floor or walls. If in doubt, get some professional advice before cutting.

It’s also a very good idea to cut and dry fit your pipes before you solder or glue them together. And when you are using pipe glue or cement you must have either plenty of fresh air and ventilation or else wear a respirator as the fumes are toxic and very strong. Once you are sure of the cuts and the fits you can begin to solder and glue all the connections. Be sure to follow the directions on the pipe cement or glue container.

You will also need to support any water lines or drain pipes. PVC pipe should be supported with wood, clamps or straps about every 32 inches and copper pipe should have a support strap about every 6 feet. This will keep them from sagging, banging or making a lot of noise. Also, when cutting holes for pipes to run through, make the hole a bit larger around than the pipe or else they may rub and squeak as they move when water or waste runs through them.

Once you have everything connected you can turn the water back on and test your new basement bath for leaks. You may also want to rent a professional pressure testing gauge system and make sure there are no leaks when a lot of pressure is on the connections. If everything works, you can close up any holes you had to cut in the floor, walls or ceiling.

Learning how to plumb a bathroom in the basement is a pretty major undertaking, but if you are willing to invest enough time and work you should be able to accomplish the job. Plumbing can be complicated, so don’t be embarrassed to ask lots of questions and even call in some professional help if you run into something you can’t do on your own. You want to be able to enjoy your new basement bath, and you shouldn’t feel like you’re drowning while trying to install it.


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