What is the acceptable moisture content level for drywall in a bathroom with shower/tub?

If 14-20% is too high, can anything be done to dry it out short of replacing it? There are no leaks and the only explanation I can think of is that we haven't been running the ceiling fans long enough during or after showers. Could there be other reasons for this high a level of moisture (assuming 20% is high)? We're in a dry climate.

Will running the ceiling fans for extended periods or using portable fans to blow air on the drywall achieve any results?

 

Welcome to the forums!

I've never used a meter on drywall to test the moisture and don't know what the acceptable level of moisture is. During the finishing and painting stages, drywall does recieve a good bit of moisture with no ill effects. Fresh air circulation is the best method of drying.

What is the reason that makes you suspect you have a problem?

 

Had a home inspection done.

 

I'm curious, what were the readings for the drywall in the rest of the home?

 

A home inspector actually measured the moisture content of the drywall? Yet apparently he couldn't determine if it was acceptable. How did he measure it? Did he use a moisture meter intended for wood?

If the drywall is painted and shows no sign of swelling or damage, it's likely to be OK.

IMO Just another example of a home inspector running amok.

 

The moisture meters usually used for investigating drywall at home inspections (I use a Tramex, and occasionally a Protimeter) only provide relative readings - selecting the "drywall" scale still only gets you an approximation. And even a direct contact (pin-type) meter does not provide an accurate reading on drywall unless it has be calibrated for the specific material being observed.

So what you are looking for is a pattern of relatively "wetter" drywall you can correlate with a source of moisture.

For example the Tramex on the drywall scale typically reports a reading of 8-12 on interior drywall surfaces in areas such as an interior living room wall, and usually does not report a higher reading on "reference areas" of drywall in a typical bathroom and away from sources of elevated moisture.

Once you have reference readings, you then check suspect areas (for example below an uncaulked shower arm or valve assembly) for a pattern of gradually increasing moisture.

In a generally "wet" bathroom - for example one without an exhaust fan - you would look for a pattern of elevated moisture above the shower and within the shower stall, gradually reducing away from the shower and as you moved lower down the walls elsewhere where there had been less condensation.

That said, in my experience if there has been enough water present to substantially raise the moisture content of drywall above reference for a sustained period you almost never need a moisture meter or IR camera to find evidence it's been present... paint is peeling, the paper backing is bubbling off the gypsum, the drywall is "soft", fasteners are popping, the paper backing detaching, the edges are crumbling, tile adhesion is failing, there is a "musty" smell, and the like - it's usually pretty obvious.

And if a meter reports a elevated moisture level in such areas absent any other sign of moisture-related deterioration - if it's the sole evidence that there is a problem - I would treat the meter reading as nothing more than an indication there there might be a problem, and recommend further moisture intrusion investigation, for example by drilling two 1/16" holes to insert a set of pin extension probes below the drywall as I'm doing above the window in the picture below:



Caption: Moisture intrusion inspection. Direct pin readings taken with moisture meter extension probes are used at a follow up study to determine if the elevated surface readings found on drywall at a home inspection reflect elevated moisture below the surface. In this case the sub-surface reading was not elevated relative to reference readings at other areas of the room. - Paragon Property Services Chicago.

IMO only then, if direct measurement shows an elevated reading below the surface, do you have objective evidence there is a problem which warrants steps such as opening walls behind surfaces without other evidence of damage.