I'd call that ok, due to the high humid outside. 87% RH right now in Milwaukee an no ice fog. Whew!

The elevation in the bathroom is due to showering / bathing in there + outside conditions at an extreme.

Sounds like odd ball weather is the culprit most likely.

You might help it a bit in the bathroom by leaving the door open.

Yah, I have been running a dehumidifier too. I was getting some mold in some shower caulk too based on the high humidity and lack of ventilation in there.

"At 31F outside, a dehumidifier is the only thing that has a chance of combating this."

Nonsense. And that prescription to solve a bathroom relative humidity problem for a home in a northern climate zone in cold conditions is a double dose of nonsense.

Condensation on the inside of a bathroom window occurs when the surface temperature of the glass is at or below the dewpoint of the surrounding air. Moisture is routinely introduced in air in bathrooms by bathing and showering activities and even using the sinks. Anyone who raised teenagers knows that hot showers, long showers and long, hot showers will raise the relative humidity in a bathroom. I thought my teenage son would become a tropical rainforest researcher.

Relative humidity in a bathroom is controlled by installing a properly-sized bath vent fan and turning it on before showering or bathing and running it for a long enough period afterwards to lower the relative humidity. I have a simple electro-mechanical timer on mine which runs the vent fan during showers and for 30 minutes afterwards. I like the Broan and Panasonic combination vent fan/lights which is what we install in the shower of every home we build or remodel.

That said, moisture can also be introduced by a leak. The location of leaks is usually obvious after a couple of days so I'm betting that's not the case here.

@ Charles Ross. Yah, I haven't noticed any brown spots or anything that would make me believe there is a leak.

It is 92% humidity outside right now. You thinking just lack of proper ventilation based on it being a bathroom and attached master bedroom in there?

Nonsense. And that prescription to solve a bathroom relative humidity problem for a home in a northern climate zone in cold conditions is a double dose of nonsense.

Yet the problem exists because the builder didn't do it right the first time?

There is a leak? sure mabye, but I go where the evidence leads Charles.

If it was low humidity outside, high humidity inside? Evidence as they say. This is a forum board we aren't here to make things up.

The home owner didn't say the shower spigot was dripping?

Didn't I ask if they had ever been to a hotel with an indoor pool? Common sense would tell you that a body of water will add to the humidity of a room thru evaporation?

But builders are here to chew on little non-sensical things? I don't know you tell me.

Hi, Kyle,

Relative humidity is a function of temperature. At the moment, here in coastal VA, the outdoor temperature is 43F and the outdoor relative humidity is close to 100%. The conditions inside my home are 70F and 42% relative humidity.

You noted the problem is in the master suite-- not throughout your home. That points to the bathroom as the source of the problem.

@Charles . Are you runing a forced air heating system? Wouldn't that automatically drop the humidity level?

What would you suggest as fixing the problem or do you think it is partially weather related?

A forced-air heating system would mitigate the problem if there was sufficient, continuous air circulation to lower the relative humidity. The problem with relying on a home's heating/air conditioning system to control relative humidity in a bathroom is threefold: 1.) bathrooms are typically high point-source moisture generators, 2.) building codes don't allow air returns to be installed in bathrooms, and 3.) forced-air heating systems typically cycle on/off.

For moisture generated by point sources like showers, bathtubs, cooktops, etc. it's best to deal with issue as close to the point of generation as possible. A properly-sized bath vent fan located directly over the shower is a great way to do that.

@charles My vent fan only holds up a tissue on half of it and I haven't checked to see if it is fully functioning (just assumed).

Do you think that could be the culprit of holding the humidity in there even if I haven't showered in a while (it was sitting at high 50's in there when I haven't showered or anything).

If you have a bath vent fan installed, take a look to make sure there's not an accumulation of lint/dust that could interfere with its operation either on the fan, in the exhaust duct or at the vent cover/screen. Also, have a look for stuff that might have found its way into the duct from the outside. It's not uncommon, in my experience, to find a bird nest in the duct close to the exhaust vent.

@Charles Ross Homes But do you think an issue with the fan would be the only culprit? Lack of ventilation?

The bath vent (ventilation) fan needs to be properly sized for the task. Most are not. For guidance on sizing, I look to the Home Ventilation Institute (HVI) https://www.hvi.org/resources/publications/bathroom-ventilation/

With regard to a "lack of ventilation" that would be a concern if you have a really tightly constructed home and need a source of make-up air to make up for the exhaust rate of a bath vent fan--which is typically in the range of 70 to 80 cfm. If your home isn't constructed from SIPs and doesn't have spray foam insulation, I doubt that a low air infiltration rate is a concern when operating a bath vent fan or even two at the same time. One thing I've found helpful for drying out a shower is to leave the shower door somewhat open (mine opens both in and out) and the vent fan running for 30 minutes after a shower.

@Charles Ross Homes . I did just recently get my whole house re-insulated. Not sure if that would do anything.

I am thinking I need to clean out the vent fan and or get a more powerful one. The rest of my house sitting in the high 40% and low to mid 50's just seems like it is a bathroom problem though?

Based on the "tissue test," your bath vent fan is underperforming. It's either not the correct rated capacity or there's something interfering with normal operation like debris in the duct or in the fan assembly.

@Charles Ross Homes . I guess my last question would be: Do you think a vent fan issue would cause the humidity to be peaked permanently in there? Wouldn't it just spike during shower, bathroom use?

Hi, Kyle,

Yes, I would expect the relative humidity to be at peak levels when showering. Keep in mind that sources of moisture remain afterwards, too. Those include both bulk water e.g., water on the shower door, shower floor, bathroom floor, and residual in sinks, and absorbed moisture e.g., wet towels that might be hung on a hook, a wet bath mat, moisture absorbed by grout, etc. Continuing to run the bath vent fan after a shower pulls conditioned air into the space which has the potential to absorb moisture which is then exhausted to the exterior. That's how the relative humidity is reduced. If you didn't have a problem with high relative humidity last year, it suggests something has changed. Your vent fan's performance may have declined due to one of the reasons suggested in an earlier post.

@Charles Ross Homes

I have been dehumidifying in there the last week or so to keep it under 50%. However if it was just a fan issue, wouldn't you think that after I dehumidified and hadn't showered in a while it would stay down?

What was the relative humidity in the rest of your home when the bathroom was 50% r.h.?

@Charles Ross Homes

About the same. My basement is sitting at 45-50 (without any dehumidifier running currently) and the rest of the house is at 50%ish with mild fluctuations. When cooking, the kitchen are hits 60%.

If the relative humidity in the bathroom is comparable to the relative humidity in the rest of your home, that's as good as it gets. The task is to get to that point as quickly as is practical following a shower.

Your existing vent fan is underperforming, so I'd plan to replace it with one sized per the HVI guidelines. The ideal location is directly above the shower. Run it during, and for at least 30 minutes following a shower. Squeegee whatever bulk water you can from the shower door, walls, and floor and direct it to the shower drain. Sending bulk water down the drain will decrease the length of time you'll need to ventilate your bathroom.

@Charles Ross Homes . Thanks for you insight and help.

I def think the fan is not doing well. From your expertise though, would you say a RH at around 50% for this time of year is fine?

I try to maintain my home's indoor relative humidity in the range 45% to 50% year 'round to minimize the potential for mold/mildew growth. I have a dehumidifier integrated in the HVAC system on both levels of my home which operate during "shoulder" seasons when neither heating nor cooling is required and relative humidity would otherwise exceed 50%. I do not advocate the use of humidifiers in winter.

@Charles Ross Homes .Yah, I agree with you. But you would classify early-mid November as still a shoulder time? Do you have any suggestions for houses with just boiler systems that don't exchange air like forced air systems to moderate humidity better?

I'd suggest you replace the bath vent fan with a properly sized one and a timer. Re-evaluate the r.h. issue after you do. You'll probably find there's no longer an issue, but if there is, you can report back.

With regard to a "lack of ventilation" that would be a concern if you have a really tightly constructed home and need a source of make-up air to make up for the exhaust rate of a bath vent fan--which is typically in the range of 70 to 80 cfm.

Kyle, Charles lightly touches on potentially creating a new problem for you.

Why I highlighted outdoor conditions as potentially being a contributor because you said here:

quote: I have lived in the home for about 14 months and this wasn't a problem last year.

You also said you don't have a traditional HVAC system that moves air.

Why are these important?

Because exhausting air (what ever rate it is) that air must be replaced. So what do you think is going to happen putting this room under a vacuum with a larger exhaust vent?

air in = air out.

If humidity in this bathroom is 70% RH and outdoor is 87% RH the potential to making this worse under these conditions is highly likely. Because that exhaust vent is just going to suck as much as it was designed to suck, the air it sucks has to come from somewhere... it's not coming from a vent of the HVAC because you don't have any such vents.

Ventilation can work, but the air you're replacing with has to be better than what you are venting.

It's one thing if the exhaust vent is not working, but just putting in a larger more forceful vent can introduce new problems, that Charles the builder didn't provide quite enough info for the rabbit hole he decided to run down.

@Austin Air Companie What would be your solution? Just wait and see? Dehumidify when it gets a little thick in there?

But once the cold outside 87% RH air enters the house and warms up the RH of that air will drop significantly and you end up pulling in dryer air than you are exhausting. Warm air holds a lot more moisture than cold air.
Fix the ventilation fan. Mine has a mesh filter on the exhaust to keep bugs out that needs cleaned once a year. Years ago mine stopped working and I checked in the attic and found the flexible duct had a real low spot in it that was full of water. I ended up putting a board under the duct so it would have constant slope and wouldn’t collect moisture in any one area.

Hi, Kyle,

Replacing a poorly performing bath vent fan with a new, properly-sized vent fan is not likely to cause any issues unless your home is tightly constructed as noted above. There is usually sufficient natural infiltration (leakage around windows, doors, penetrations in the sheathing, etc.) to make up for a relatively small exhaust flow rate such as a bath fan. Indeed, the 2018 International Residential Code doesn't even require make up air for larger exhaust flows like a range hood unless the flow rate exceeds 400 cfm. That's comparable to the flow rate of five 80 cfm bath vent fans all operating at the same time. If your home is tightly constructed, there was probably a blower door test performed. If you have the test report it should list the calculated natural air infiltration rate.

Now for a quick lesson in psychrometrics for anyone who slept through 6th grade science class. Relative humidity is a measure of how much moisture air contains relative to the maximum it can hold at that same temperature. So, it's a function of temperature as I noted above. As air is heated, its relative humidity decreases. When outdoor air at 40F and 87% relative humidity enters a home, it gets mixed with, and heated by the surrounding air. If it's heated to 70F--and assuming no mixing--the relative humidity would drop to around 40% Those properties would indeed make it useful for controlling the relative humidity in a bathroom at 70F and 70% relative humidity by ventilation alone. And it's why the assertion "At 31F outside, a dehumidifier is the only thing that has a chance of combating this" is pure poppycock.

@Charles Ross Homes I guess when I heat up my home to 67 (via a gas boiler) the humidity in the house sits between 47-52% usually. That seem normal? I still feel like it should be closer to 40%.

Hi, Kyle,

Homes are conditioned for 1.) occupant comfort and health, 2.) to minimize the potential for mold/mildew, and 3.) to maintain stable temperature and moisture conditions for components like hardwood floors and trim. You'll need to decide what combination of temperature and relative humidity is comfortable for you. Maintaining the relative humidity at 50% or less precludes mold/mildew growth and gives you some cushion against mold getting established (okay, maybe not in the shower.) Hardwood flooring manufacturers will give a preferred relative humidity for their product. I think you'll find the recommendations in the 45% +/- relative humidity range to minimize cupping and crowning. For what it's worth, I keep my home at 68F in winter and don't use a humidifier so the relative humidity fluctuates. In the summer, I keep it at 73 F and the relative humidity at 50% or less. I don't lose sleep unless it gets into the high 50's.

@Austin Air Companie What would be your solution? Just wait and see? Dehumidify when it gets a little thick in there?

Kyle I am not a provider of solutions from an internet chat board. I'm merely just offering suggestions. I work everyday out in the field, I don't pretend to work remotely. This isn't to be snide. I am deliberate when I say my definition of a solution is one that fixes the problem without causing new ones.

So I dropped a hint that just adding in a more powerful vent fan may cause more trouble. It's a hint. Do I know for sure? no I am not there. It is up to you or whomever you hire --- that is the realm we are in.

(It's only been about what you've said Kyle, the weather part what is going on outside is it a coincidence? -- weather related work represents probably in the range of 90% of my calls --- people don't call me to fix a furnace in the summer, don't call me to fix AC when it's 60 degrees outside *unless the house is full of people* another heat source a builder never considers. (If I rub someone the wrong way with my comments? put on your big boy pants and deal with it. I'm not here to pretend.)

So with heavy humid outdoors occuring around the same time? I am not the one investigating the problem. I am merely dropping hints.

What you say here tells me to take a pause or investigate further:

Do you think that could be the culprit of holding the humidity in there even if I haven't showered in a while (it was sitting at high 50's in there when I haven't showered or anything).

@Austin Air Companie

@Charles Ross Homes

I am also getting some mold in the grout and on the base caulk of my tiled shower in there. I am investigating the relationship between the high humidity in there and the mold issue. Wondering if the mold could cause the high humidity or they both feed off on another.

Pictures for reference.

Causes are different from effects.

Mold needs moisture to get established and to propagate; it doesn't generate moisture. In areas where bulk water stands for long time periods like a shower floor or shampoo niche, conditions are favorable for mildew growth. Proper ventilation helps to minimize it, but it doesn't eliminate the need for routine cleaning. You will be well served to use a squeegee to promote more rapid drying of the shower surfaces. If, despite the squeegee routine and routine cleaning you have excessive mold, it could be a waterproofing issue linked to improper installation or age.

As for assigning blame for the high indoor relative humidity to varying outdoor conditions, outdoor conditions are always a variable. They're not the cause of the OP's problem. The OP performed the "tissue test" and found the bath vent fan was drawing on only one side. That's an air flow issue. It's likely that the performance of the fan has declined over the 14 month period the OP has lived in their home--during which they would have experienced the full range of seasonal weather variations in their climate zone. We don't know whether the vent fan is properly sized or not nor whether it needs to be replaced or some maintenance task performed. The old adage "When you hear hoofbeats, think horse not zebra" is a good thing to keep in mind when troubleshooting. We haven't identified the particular horse yet, but we have clearly identified the horse's hind end.

@Charles Ross Homes . Ok so based on the pictures, you don't the mold is pervading behind the tile and drywall? I am trying to decide how big the issue is.

Hi, Kyle,

How old is the tile shower? Was it installed in the 14 months you've lived there?

@Charles Ross Homes . It was installed right before I moved in. 15-16 months ago.

For goodness sake, stop beating the dead horse with a stick. You know that your fan is not performing adequately. Fix the ducting and/or replace the fan with a proper one. Make sure it's vented outside and not into the attic.

Dont' listen to Austine Air Companie as they clearly don't understand relative humidity and the suggestion to run a dehumidifier in cold temperatures is ridiculous.

The orange stuff is not mold, it is the bacteria Serratia marcescens. It feeds on the fatty substances in soap and shampoo. You likely also have it at the waterline in your toilet.

Get a proper, working fan and use it.

@catbuilder . But what about the black stuff?

If there is black stuff, it is probably mold. What exactly is your question? Clean it all, get a good, working fan, and use the fan. You clearly have a ventilation problem, which you know because you pointed it out.

@catbuilder . Based on the images, I was trying to determine, if I have mold behind the tile and the drywall from a leakage issue.

The RH outside of that area is sitting in the low 50%. It is like 55% in the kitchen. It jumps to 60-70% in the bathroom area and master bath.

Humidity comes from where? The baseline outside the area of the bathroom is elevated for this time of the year. Winter is typically drier everywhere.

I am in a humid prone climate with a drafty house no less built before 1980 sitting here this morning with 36% RH in my office.

So if outside factors aren't a factor the RH in this house is in the low 50% is coming from where? Osmosis?

Well let's ignore that and just put in a bigger crapper fan. Just because I come here to provide hints, doesn't mean I am going to think for you too.

Without trying to go down further rabbit holes of cold vs warm and how much humidity is contained there in --- take some new readings over the next two days.

Take humidity readings in bathroom, and other areas of the house. The outdoors during this time is in the mid to low 50% RH outside. With this hint even still I am not doing all your thinking for you.

Is the problem only in the bathroom? yeah we don't know, do we?

Yet the rule here is to ignore all of that? Welcome to the internet.

Kitchens and bathrooms are special-purpose rooms in which normal activities produce moisture. Higher relative humidity in those spaces is not atypical. That's why cooktops and ranges need to be vented to the exterior. Ditto for bathrooms.

This thread is yet another one that makes it clear you don't understand basic psychrometrics, Ray. You might consider sitting in on a 6th grade science class to learn what relative humidity is and how it's affected by temperature.

I'm in AA's general region, although AA apparently is in a desert pocket. Outdoor here currently is reported as 46°F at 91% to 98% humidity on various personal weather stations linked to WeatherUnderground. The National Weather Service monitoring station at the county airport says 46°F at 100%. My house is 70°F at 49% on the 'stat in the family room. The cheap, mechanical-dial weather station in the master bath is 67°F at 55% (three 43"x43" glass block windows in there). I've never had mold in the shower in nearly 18 years here. I always run the toilet exhaust fan and the bathroom ceiling fan (yes, I have a ceiling fan in the master bath) for a few hours after a shower.

I'm in AA's general region, although AA apparently is in a desert pocket.

No this is more like defying the odds of physics --- the nexus of the universe type story.

ha, ha, ha. The internet is so much fun, especially when people push you into a rabbit hole and then think they are going to find a way out. (I've been doing this in person for too long.)

To the point one might think I was making it up?

Click to enlarge.

Haven't even broke 40% RH (This is considered low even for me)

I service the Katy, Texas area.

"No this is more like defying the odds of physics...."

Katy, Texas may be devoid of intelligent life, but the conditions there don't defy the laws of physics.

"I am in a humid prone climate with a drafty house no less built before 1980 sitting here this morning with 36% RH in my office."

If you understood elementary psychrometrics and knew your way around a psychrometric chart you wouldn't be at all surprised by that, Ray. According to Weather Underground, the average d.b. temp in Houston yesterday was 45F and the dewpoint was 35F That is a relative humidity of 70% If you heat that same air to 68F you drop the relative humidity to 28% The relative humidity inside your home at 36% to 39% is higher than that. If you want to bring it down, you could consider operating a bath vent fan....

If you want to bring it down, you could consider operating a bath vent fan....

Then add more problems when the crapper fan starts drowning in water?

Yeah here you go -- a solution that creates more problems I give you a link to illustrate the fun you can have here.

Bath vent fan drowning in condensation.

No wait let's argue about who understands what? ha, ha, ha.

The suggestion to use a bath vent fan to bring down the relative humidity in your home was facetious, Ray, although it would work under the specific weather conditions.

You clearly lack an understanding of psychrometrics which is fundamental to understanding HVAC. "Consumers" of the misinformation you sprinkle here on houzz will be well served to read posts like this one before looking to you for guidance.

Charles I've known builders a good number of them and how good they are at blowing smoke. My view of you is king, in that regard.

An opinion from a forum board is worth what exactly?

Wait for it... he'll change the subject again.