How to Install an Attic Bathroom

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

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Updated on 08/07/22
Reviewed by
Johnathan Brewer
Johnathan Brewer
Reviewed by Johnathan Brewer
Johnathan C. Brewer II is a licensed general contractor specializing in kitchen, bath remodels, and general construction with two decades of professional experience.
Learn more about The Spruce's Review Board
Fact checked by
Jessica Wrubel
Jessica Wrubel
Fact checked by Jessica Wrubel
Jessica Wrubel has an accomplished background as a writer and copy editor, working for various publications, newspapers and in public libraries assisting with reference, research and special projects. In addition to her journalism experience, she has been educating on health and wellness topics for over 15 years in and outside of the classroom.
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Attic Bathroom

Johnny Greig / Getty Images

Project Overview
  • Working Time: 1 - 2 wks
  • Total Time: 1 - 2 wks
  • Skill Level: Advanced
  • Estimated Cost: $4,000 to $17,000

Many homeowners expanding their families or simply interested in more space often look to that neglected area above their heads: the attic. Just like basements, attics are spaces that are ripe for expansion because large-scale structural building is kept to a minimum. Much of the building structure, consisting of exterior walls, roof, joists, and other expensive contractor-driven features, is already in place.

One feature that makes an attic bedroom so valuable for homeowner use and eventual resale is a bathroom. An attic bedroom without a same-level bathroom can be a tough sell, both for current occupants and for potential buyers. Learn the general outlines of installing a basic, lower-cost attic bathroom, whether this is a do-it-yourself project or one that you feel is best left in the hands of a building contractor.

Warning

Unlike upgrading an existing bathroom, installing a new bathroom can involve heavy plumbing and wiring work. This is not a project for beginners or anyone who is not a home improvement veteran. For an addition or renovation of this degree, our experts strongly recommend hiring a professional.

Assessing and Planning Your Project

Full bathrooms, consisting of a toilet, sink, and bathing facilities, add maximum utility and value to your attic. Full baths are also the most costly and labor-intensive type of bathroom to create since a bathtub or shower adds significant weight to the flooring, as well as creates more complications with water supply and drainage lines. Instead of a full bathroom, many homeowners decide to install a half-bathroom: sink and toilet only, with no bathing facilities.

Consider the placement of your attic bathroom. The highest possible ceiling for an attic bathroom is usually afforded by situating the room closer to the center of the home, where the roof peak is at its highest. Consider the vital services that are necessary for building a bathroom: electrical supply wires, water supply lines, branch drainage lines, sewer line, and vent stack. Since these services are found in the bathroom or kitchen on the floor below, it makes sense to locate your attic bathroom directly above either of those rooms, preferably a bathroom.

Developing a solid bathroom floor plan is critical to fitting all of the necessary items in this tight space. Begin by considering the largest item that will be installed in the space and working downward in size. If this will be a small full bathroom, a standard alcove bathtub size is 60 inches long. This means that the tub must be bounded by three walls, and the tub will fit tightly against the walls. Next in size is the bathroom vanity. If two of the walls are 60 inches long, then the other two walls should be longer than 60 inches to create a rectangular space that can fit a sink and vanity combination ranging from 24 inches to 36 inches wide. If room is at a premium, you may wish to install a space-saving pedestal sink.

Tip

Hiring a licensed contractor and bathroom designer are good investments when embarking on a large-scale renovation project.

Codes, Permits, and Regulations

Due to safety concerns, attic conversions of any type are controlled by building code. Check with your local permitting office about the types of permits you will need to apply for before building living space within your attic. In addition, bathroom additions in any section of the home always come with code restrictions and permit requirements.

Before You Begin

Costs for a DIY attic bathroom, like a contractor-built space, can vary enormously depending on its size, the features you choose to include, and the quality of the building materials you choose. In most cases, a skilled DIYer can do the work for about half of what it would cost with a contractor. But a simple bath with sheet vinyl flooring and prefab shower stall will be far more affordable than one with designer marble floor tile and a special-order whirlpool tub.

What Is Live Weight, Dead Weight?

Unless built expressly for the future addition of living space, the ceiling joists or rafter ties will need to be strengthened for the bathroom flooring. Attic floors often are built to accommodate only a maximum dead weight load. Dead weight essentially means an attic that is only used for storing boxes and for very limited traffic. Live weight load refers to the total weight carried by the floor, including furnishings, occupants, and all other permanent and temporary objects. Flooring joist span tables will assist you with information about whether you need to strengthen your joists. Better yet, consult with a structural engineer or a qualified contractor.

What You'll Need

Equipment / Tools

A wide variety of tools will be necessary for this addition. Make sure you have a fully stocked tool shed before embarking on creating an attic bathroom.

  • Saws of various types
  • Screwdrivers
  • Wrenches
  • Hammer
  • Measuring tape, square, and other measuring tools
  • Level and chalk line

Materials

The supplies you need, and how much of each you'll need, vary depending upon your final design.

  • Toilet
  • Subfloor: 1/2-inch or 3/4-inch thick A/C-graded plywood
  • 2x4 lumber
  • Floor covering, such as luxury vinyl plank
  • Water-resistant drywall
  • Drywall screws
  • Drywall compound and sanding sheets
  • Bathroom vanity and sink
  • Bathtub (optional)
  • Bathtub/shower direct-to-stud surround kit (optional)
  • Electric cables: 14-gauge and 12-gauge
  • GFCI outlets and electrical boxes
  • Plumbing supply and drainage pipes

Instructions

  1. Build the Subfloor and Interior Walls

    Use full sheets of 1/2-inch or 3/4-inch thick A/C-graded plywood laid across the strengthened joists to form a base for your floor covering.

    Interior, non-load-bearing walls will need to be built within the attic to form the bathroom space. Use 2x4s to build walls with the studs spaced every 16 inches on-center. Electrical wires and plumbing pipes will run through these walls. Because of the unique triangular structure of attics, short walls called knee walls are used to enclose the lower section of these triangles.

    Face the stud assemblies with drywall fastened to the studs with drywall screws. After applying drywall compound, let the compound dry and then sand the compound smooth.

  2. Install the Bathroom Electrical Circuits

    The attic bathroom will need electricity to supply at least two 20-amp GFCI outlets and one switch-controlled ceiling light. Bathroom exhaust fans are not required by most codes. In lieu, a window 3 feet square or more, capable of being opened at least halfway, will suffice. However, due to the difficulty of adding openable windows in an attic, a bathroom fan is strongly recommended.

  3. Install the Plumbing

    Attic bathroom plumbing can be tricky to install. While it can be moderately easy for a do-it-yourselfer to extend water supply lines up from a lower floor, drainage and venting can be more difficult to plan and install. Stacking one bathroom above another bathroom (or kitchen) does not necessarily mean that all of the plumbing continues vertically in a linear fashion.

    Cutting the attic drain into the line directly above a lower bathroom may create drainage problems due to hampered venting. It may be necessary to cut the drain in at the lower floor or even continue all the way down to the crawlspace or basement to ensure proper venting. Because of these concerns, it is highly recommended that you enlist the help of a licensed plumber for attic bathroom plumbing.

  4. Install a Shower/Bathtub and Surround

    Prefabricated shower/bathtub and wall surround units provide the easiest, fastest method of installing bathing facilities in your attic. Due to weight concerns, tiled units aren't recommended, as they can be extremely heavy.

    Acrylic or fiberglass prefabricated units are vastly lighter than tiled units. Direct-to-stud wall surround kits eliminate the need for installing lower levels of cement board or water-resistant drywall. As the name suggests, these surrounds are caulked and screwed directly to the open studs that form the attic bathroom's walls. Because attic access can be difficult, it may be necessary to use three- or five-piece wall surround kits rather than single-piece kits.

  5. Lay the Floor Covering

    To reduce weight, consider installing a lighter-weight floor covering for your attic bathroom. Luxury vinyl plank, vinyl tile, and sheet vinyl flooring are much lighter than ceramic or porcelain tile. Not only that, luxury vinyl plank and tile lend themselves to do-it-yourself work. Even if you are having a contractor build the bathroom, you can save money by doing this part of the project by yourself.

  6. Install the Vanity, Sink, and Toilet

    Install the bathroom vanity and sink and connect to the plumbing stub-outs that were put in place earlier during the plumbing rough-in.

    Install the toilet by setting the wax or silicone ring on top of the toilet closet flange. Carefully place the toilet on top of the closet flange, then screw it into place with the included hardware. Do not screw too hard or you risk cracking the toilet. Connect the water supply lines to the toilet and turn them on.

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