It’s time to put up some walls in the bathroom – which puts me squarely back on one of my favorite building topics: moisture management and indoor air quality (IAQ).
A bathroom, in building science terms, is considered a wet room. Splashes, drips and leaks are inevitable, and can over time lead to structural problems, but also IAQ issues such as mold with negative health impacts on the occupants.
This and any associated durability issues are easy to avoid by falling back onto a few simple moisture management strategies.
One of them is to employ floor drains. We documented the installation of the 1st and 2nd floor bathroom drains in a previous post, and there is more to come in one of the next posts.
Another strategy is to use cement board or fiber cement board as a wall cover in shower stalls, bathtub enclosures, and behind lavatories and toilets.
To give you an idea how water resistant cement board is… I had a leftover piece sitting in the yard for one and a half years, exposed to the elements. It was still in perfectly good shape and I ended up using it for one of our window sills in the basement.
Do not use green board or any other kind of paper-faced gypsum board product. These things are not suitable tile backer products and can turn into big mold traps.
See also Building Science Corporation, Info-306: Interior Water Management
What about the areas that don’t receive tiles, such as the ceiling and the upper half of the wall behind the lavatory and toilet?
Regular drywall will do the job, at the cost of around $6.00 per sheet. The green board products run twice as much (around $12.00 per sheet).
But what about the green board’s mold resistant property? Wouldn’t it prevent mold formation on the walls and in corners? Isn’t that worth the extra cost?
I would say no. Because if a bathroom requires such mold resistant product, there is an insulation/condensation and ventilation issue. And the extra $6.00 per sheet for green board won’t solve those problems, just prolong the denial about the real issues for a little longer.