Bathroom materials and layout: planning for water, air and access

Think in three zones, not one room

Grout and most tile are not waterproof on their own. Water that gets through the grout has to stop at a layer behind the tile and drain to the shower outlet. That layer is what protects the framing, and it's the part you'll never see once the job is done.

Waterproofing: the questions to ask

There are several sound ways to waterproof a tiled shower, including sheet membranes, liquid-applied membranes and traditional mortar beds with a liner. Which one is right depends on the substrate, the drain and the installer. As a homeowner, you don't need to pick the product, but you should know what's planned.

1. Which waterproofing system will be used on the walls, floor, curb and niches, and is it one manufacturer's system or a mix?
2. How are corners, seams, the valve, the shower head and niches sealed?
3. How does the floor slope to the drain, and what kind of drain is it?
4. Will the installer follow the manufacturer's written instructions, and will a flood test or inspection be done before tile goes on?
5. Which parts of the waterproofing are covered by the product manufacturer's own warranty terms, if any?

Ventilation: size the fan, then vent it outside

The EPA's guidance on mold starts with a simple point: the key to mold control is moisture control. For bathrooms, that means running an exhaust fan while you shower and venting moisture to the outdoors, not into an attic or ceiling space. The EPA recommends keeping indoor humidity below 60%, and ideally between 30% and 50%.

The Home Ventilating Institute (HVI) publishes a common sizing rule:

• Bathrooms up to 100 square feet: about 1 CFM of exhaust per square foot of floor area. An 8-by-5-foot bathroom works out to 40 CFM.
• Bathrooms over 100 square feet: add up the fixtures, at 50 CFM each for a toilet, shower and tub, and 100 CFM for a jetted tub.
• Placement: put the fan over or near the shower or tub. An enclosed toilet room needs its own fan or an operable window.
• Makeup air: the door needs a gap at the bottom so air can enter as the fan pulls it out.

Sizing is only half of it; the fan also has to run long enough. HVI recommends leaving the fan on for 20 minutes after the bathroom is used and suggests a timer so it shuts off on its own. For a steam shower, HVI recommends a separate fan in the steam room that can be turned on after use. It also notes that ventilation can instead be provided continuously at other rates, which is a design choice to discuss with whoever plans the system.

• Ask what control is planned: a plain switch, a timer, or continuous low-speed operation.
• Ask where the fan exhausts relative to where fresh or conditioned air enters, so air is pulled across the room.
• Ask whether the fan rating and the duct run were considered together; the rating on the box is measured by the manufacturer, and the installed result depends on the duct.

Fan wiring, switching and duct runs through walls or roofs belong to licensed trades. Ask whether the fan, its duct and its exterior termination are part of the scope.

Layout choices that age well

The federal ADA Standards for Accessible Design apply to public accommodations, commercial facilities and government buildings. They don't cover a private home used only as a residence. They are still a useful reference if someone in your household uses a walker or wheelchair, or if you want the option later. For example, the ADA Standards place grab bars between 33 and 36 inches above the floor.

• Blocking in the walls: solid wood blocking behind the tile near the toilet and in the shower lets you add grab bars later without opening the wall.
• Low or no curb: a curbless shower is easier to step into but needs a recessed floor and careful drainage, which affects cost.
• Handheld shower on a slide bar: useful for seated bathing and for cleaning.
• Lever handles and a shower valve near the entry: you can turn on the water without stepping under it.
• Clear floor space: keep the area in front of the toilet, vanity and shower open and the door swing out of the way, or consider a pocket door.

For everyday fall prevention, the CDC's home safety checklist for older adults suggests grab bars next to and inside the tub and next to the toilet for anyone who needs support getting in, out or up; a non-slip rubber mat or self-stick strips on the tub or shower floor; and a nightlight on the path from the bedroom to the bathroom. Those are low-disruption steps, and planning wall blocking during a remodel makes the grab bars easier to add later.

Floors, vanities and storage

• Floor tile: a textured or smaller-format tile, with more grout lines, gives more grip underfoot than large polished tile. Ask the supplier for the tile's slip-resistance rating for wet areas.
• Vanity: a wall-hung or legged vanity leaves the floor visible and is easier to clean; a cabinet base gives more storage. Particleboard cases swell if they stay wet, so plan for a dry floor under the sink.
• Medicine cabinet or niche: recessed storage works only where the wall isn't a plumbing or vent wall. Ask before you design around it.
• Lighting: light the face from the sides or above the mirror, not just from a ceiling fixture behind you.