I'm adding on a bathroom upstairs. My question is what precautions should I take to waterproof it. I'll have new copper, PVC drains and the floor itself I'm worried about. It's sitting half above a bedroom and the pipes will be running around the studs.

1) Is there anything I should do to the studs/drywall underneath to minimize issues in case of a leak in the PVC/copper supply plumbing?

2) What's best to put on top of the sub floor. I was thinking of doing one piece of laminate flooring, should I put something underneath it, are there certain products that are better? There will be a pre-fab shower and I'd rather not do any tile in this bathroom.

3) Should this flooring run completely under the shower? Anything special I should do while setting the toilet/sink to keep it waterproof.

  • When you say one piece of laminate flooring, do you mean Linoleum instead on Laminate?
    – Tester101
    Jan 27, 2012 at 18:39
  • Yes I was thinking linoleum, would that be better than laminate tiles...
    – RLZaleski
    Jan 27, 2012 at 23:47
  • In my opinion, laminate should not be used in kitchens or bathrooms. It's not a good idea to use it in any situation where water can easily get under it, since water can cause it to swell or become trapped beneath it leading to mold. Linoleum is a common choice for kitchen and bathroom floor coverings.
    – Tester101
    Jan 28, 2012 at 15:49

2 Answers 2


Most of the floor of a bathroom should not see any great water leaks or standing water. The average puddle you make getting out of the shower before you can towel off will not pose any great threat. If your plumbing work is up to code, that shouldn't be a concern either. However, a plumbing emergency can pose a greater threat.

For laminate floors, it is generally a good idea to lay down a layer of moisture barrier, like Tyvek, between the sub-floor and laminate, and if the sub-floor is over concrete (doesn't seem to be the case here) another layer between the concrete and the subfloor. This prevents the transfer of liquid water between the layers of the floor, while still allowing the layers to adjust to changes in humidity without forming condensation. For the majority of the bathroom floor this should provide ample leakage protection if properly installed.

Make sure that the laminate, once installed, is well-sealed; laminate's great for providing a wood-like floor, but if water gets under the waterproof (or water-tolerant) top layer of the laminate and into the particle board underneath, the boards will swell and your floor will be ruined. A poly or acrylic topcoat will seal the cracks between planks and help protect the flooring; your flooring dealer can probably recommend a product that's compatible with your particular brand of laminate.

Where you really need to take care is in the shower area. If you have a tiled shower, behind that tile needs to be a waterproof barrier which will contain water that gets behind the tile grout (not waterproof) and direct it to the drain, instead of letting it contact the drywall or subfloor. It is not a terrible idea to install the same type of membrane everywhere in the bathroom, but it's probably overkill especially since you'll be wanting to prevent water even getting that far.

The main source of water leakage out of a bathroom, which you will likely not be able to prevent, is inside the walls. You probably won't know there's a problem until you hear water dripping onto your ceiling, or see that telltale tea-stain on a ceiling or wall. There is not a whole lot you can do to prevent this once the walls are up; the keys to prevention are in proper installation of the pipes in the first place. Minimizing joints in supply pipes, which can swell and shrink at different rates with temperature, and making sure all joints on all types of plumbing are well-sealed, are key to minimizing leaks. Any plumber worth his salt will use the appropriate joining materials liberally (solder and flux for copper pipe, glue for PVC/HDPE, rings and cement for PEX).


If there's just wooden studs at the base, I've done: (From the top to the bottom layer)

  • Your laminate [what everyone will see]
  • cement board. [comes in 4x8 sheets, different thicknesses, I'd go with 3/8 or 1/2'][dark gray][There are screws designed to be used in concrete board].
  • a sheet of plywood (maybe 1/2 inch ?)

The plywood would be laid for the entire floor; the concrete board and laminate only for the areas not covered by the shower. As Keith mentioned, the biggest concerned with water damage from leakage (since this is a prefab shower), is ensuring your plumbing is done correctly, properly sealed and the right piping used.

If you want to be extra cautious, you could also install an underlayment, something like "Roberts 70-025 Unison 2-In-1 Underlayment", between laminate and concrete board.


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