Crawlspace Moisture Barrier - Humid House

[jc4]

How fancy do I have to get on a vapor. Can I just roll it out, overlap 6" and call it a day? If I can get 90% of the value with 10% of the work, I'd do that.

There's tons of articles showing to tape all the seams, stake it down, run it up the walls to the joists etc. How much utility do I lose for the basic method? Does it ruin the whole job?

For reference, our house is 100 years old and very humid. As in our coasters, shoes, furniture, etc grow straight mold. As a mustacian, we limit the AC, but that's working against us here.

Getting a decent dehumidifier is on the to do list as well.

[zolotiyeruki]

Running the A/C may very well be a better option for you than a dehumidifier.  They're basically the same thing, albeit on different scales.  It's just that the air conditioning will also dump the excess heat outside the house.  If you're trying to not run the A/C in order to save on electricity, I'd suggest you simply set it to a higher temperature.  That way you get most of the dehumidification without all the expense of cooling.

[Papa bear]

If you have an electric h20 tank, consider switching to a heat pump unit.  It will dehumidify while heating your water. 

As for the vapor barrier, I would spend the extra couple hours and $50+ on some tape and do it the right way.


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[Jon Bon]

For reference, our house is 100 years old and very humid. As in our coasters, shoes, furniture, etc grow straight mold. As a mustacian, we limit the AC, but that's working against us here.

Getting a decent dehumidifier is on the to do list as well.

This seams odd, if it was growing mold for 100 years it would have rotten down to nothing at this point, did something change?

FWIW dehumidifying is treating the symptoms, removing the source of water  infiltration is the disease.

How are your gutters/grading? Where is the water coming from in the first place?

[lthenderson]

I'm with Papa Bear and Jon Bon on this one. Dehumidifying the air is treating symptoms and not the problem. You become reliant on a machine to work in order to dehumidify the air. If I was going to install a moisture barrier, I would spring for the tape and time it takes to do a good job.

[El_Viajero]

Step 1: Get rid of any problem water. This could involve grading improvements or upgrades to gutters, downspouts, and drainage systems. Still got a problem? Well then...

Step2: Add a vapor barrier in the crawlspace and install it properly. Still got a problem? On to step 3...

Step 3: Supplement your AC with dehumidification (standalone or whole house unit) OR get new central AC with a variable speed blower.

Some people might recommend doing a full crawlspace encapsulation either after step 2 or step 3. I'm not too big on sealed crawlspaces, though. I have one. It solves certain problems and creates other ones, such as increased risk of radon in your home.

[Sibley]

I too have a 100 year old house. You, or someone previous to you, did something to cause the humidity problem. Did someone insulate the walls without compensating for the reduced air flow? Is there significant water sources somewhere there didn't used to be?

In the meantime, stop being cheap and turn on the a/c (assuming it's still hot where you are). You don't have to run it at 62F, but a properly functioning a/c will dehumidify the house, and that is much cheaper than destroying the house with mold.

[former player]

I too have a 100 year old house. You, or someone previous to you, did something to cause the humidity problem. Did someone insulate the walls without compensating for the reduced air flow? Is there significant water sources somewhere there didn't used to be?

In the meantime, stop being cheap and turn on the a/c (assuming it's still hot where you are). You don't have to run it at 62F, but a properly functioning a/c will dehumidify the house, and that is much cheaper than destroying the house with mold.

If you are not runnung the air conditioning you need to be opening the windows, in every room every day for a few minutes at least.  If you can get a breeze running through the house so much the better.  If you have old-fashioned sash windows you open both sashes a little so that warm humid air goes out of the top gap while fresh colder air comes in the bottom.  It will be opening the windows on this schedule that has kept the house from rotting before air conditioning was installed.

Also, think about sources of humidity.  That will be you in your bedroom while sleeping: always air out the room first thing in the morning.  It will be cooking in the kitchen: use an extractor fan if you have one when heating anything in the kitchen.  It will be the bathroom: again use an extractor fan or open a window and let the steam out/dry the fixtures after bathing.

If you live in an area where the humidity outside is such that these measures are not enough then there is no alternative to running the air conditioning or a dehumidifier.  It will stll be cheaper than ruining your possessions and your health by living in a moldy environment.

[jc4]

Thanks for all the input. I’ll try to respond to everyone together.

Source of moisture: humid region with lots of rain. We’re on a giant hill with retaining wall up from and step slope on front and sides. I doubt it’s a grading issue. That said the joists are 6” above the dirt in the bedroom. The gutters are mediocre but I have a 24”+ overhang so the water lands a decent distance off the house.

Not an new issue. No insulation in the walls. Only new is I added a ton of blow in insulation in the attic. Been this way every year and there are certain signs of water issues. Prior owners replaced a huge section of floors in the living area because they rotted straight through

Appreciate the idea to deal with the crawl first then dehumidifier. We’ll do the tape and take some time. The crawl space sucks. Like I said it’s too short and there’s tons of old construction debris. Old path and plaster with nails and all kinds of stuff. . I’m a smaller guy and not prissy and I hate it down there.

Gas h20 and it’s in an outside utility closet.

I may try setting the ac to the in for an hour a day next summer. Other ac problem is it’s 48 degrees outside right now and it was 70% humidity today in the house.

I didn’t think about the windows. Would that still help even if it’s really humid outside? I figured if it’s just as bad outside it wouldn’t make a difference so I hadn’t tried.

Also thanks for all the responses so quick.
 

[former player]

Opening the windows won't do a lot if there is high humidity outside but might still help if you can get a breeze going through the house - but if the house is dug into the hillside that will be more difficult.

One other thought: do you have a working fireplace?  If you can find a cheap source of logs (word of warning: logs need to have been cut long enough ago, at least a few months, to have dried out) then an open fire is a great source of dry heat and will draw moisture out of the house through the chimney.

[Sibley]

Yes, airflow, even if still humid, will help. But really you need to get dehumidifiers in place. Get good ones because you'll likely be running them year round. They will output some heat, and try to set them up as self-draining if possible otherwise you will constantly be emptying them. Ideally you'll get the relative humidity to around 40%, that may not be possible in your climate but at least you can help.

Forced air furnace heating will help with humidity if you have that as well.

[BudgetSlasher]

What I would do.

1) ID and address any easy to correct sources of moisture first. Things like leaks, gutter, drainage, water entering the foundation, or poor grading.

2) Control humidity mechanically with your choice of system, central A/C, mini-split A/C, mini-split style dehumidifier, central dehumidifier, or other.

I live in an area of the country where people are adding climate control as the outside climate seemingly becomes more humid, stays warm for a longer period of time, and doesn't cool as much overnight; the housing stock here has many houses that are 100+ years and even 200+.

We added central dehumidification last year. We tried to address moisture first, but for us the majority of it is the humid of the outside air. We have done air sealing and weather stripping upgrades. But, to really address it we would have to replace the siding on the house and address the envelope itself. The cost of that makes it a non-starter at this point.

[joenorm]

Funny saying this in a DIY section but I would shell out a pay a company who specializes in crawlspace remediation to fix it. There are lots of them out there because they know everyone hates that work. A good company will make sure their workers have proper PPE also.

Living in a house that is literally rotting from below does not sound healthy at all.

[Kem]

Our community water paths where altered.  This has caused a significant increase in soil moisture levels over the last few years.  Last fall I discovered my crawlspace looked like a set out of stranger things.  I fully remediate the mold.   At this time, the crawl has 6mil poly tossed over gravel and debris.
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This fall the mold had returned in force, and after a summer of persistent daily allergies I pulled the trigger on a better fix.
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Quotes to fully encapsulate and dehumidify came in at over 20K.  For 5K I removed the debris, wet borax blasted all surfaces, leveled the stone, layed down 2 layers of puncture resistant geo stabilization cloth, topped with 25mm void free poly, poly caulked the seams and taped the edges, and installed an aprilaire dehumidifier.  I still have the skirt to seal.
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Encapsulating 3/4 of the ground resulted in 20% reduction in humidity.   Encapsulating the remainder and installing the dehumidifier dropped another 15% - keeping it at 45%.
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The family allergies are gone.  My wife is coming off her blood pressure meds for the first time in over a decade.  My youngest daughter no longer wakes up crying.
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Super hard work, but some of the best outlay I've layed money on.

[YankeeSaver]

What others said, and I would additionally check your roof ventilation. Continuous soffit vents plus a ridge vent is the best system. You also want insulation baffles to prevent the soffit vents from being blocked by insulation.

If you just have a small gable vent or other minimal ventilation, it may not be enough and may be contributing to your problem.

I used to own a house with no roof ventilation (yes, none) and had problems similar to yours. It probably had gable or some other kind of vent at one time, but it was eventually asbestos sided and the soffits were completely wrapped in metal.

[Model96]

Here in humid Sydney Australia it is very popular to improve subfloor ventilation with added vents, and with bigger problem situations some ducting and low current fans on timers which extrct from under the house. Is this an option worth exploring for you in your area?