Sealed Crawl Space

[9outof10mms]

I believe the topic has been “touched and go-ed” here on the forum as part of other topics, but I’m looking for specific discussion on sealed crawl spaces.

When we bought our current house, the only thing the inspector found was a mildly damp crawl space. The house, built in 1980) has a traditional southeast US crawl space design of an open and ventilated plan (small rectangular vents every 10-15’ around the perimeter). The previous owners took good care of it themselves and hired a good handyman to do things they couldn’t, like keep the ground covered in thick plastic in the crawl space.

The inspector said to get a fan that mounts in the vent opening to force more outside air into the crawl space, one with a humidistat would be best. I bought one and ran out of steam when we moved in, so I never put it in. Fastfaroward to yesterday when I had some time and a productive wild hair to do it...

I was Googling what setting to put the humidistat at and I fell into a plethora of articles and advice to NOT force outside air into the crawl space—in fact, the new prevailing thought seems to be to convert the traditional “old” design of the space to a sealed crawl space.

Without knowing too much about these folks (and acknowledging that they seem to be a for-profit company, so there is likely bias), this website has some informative info: https://www.advancedenergy.org/portal/crawl_spaces/
Particularly a detailed guide: https://www.advancedenergy.org/port... Spaces_An Introduction for the Southeast.pdf
And a quick reference: https://www.advancedenergy.org/portal/crawl_spaces/pdfs/Closed Crawl Spaces_Quick Reference.pdf

I took a building systems design course, but humidity and air temps and such have always been at the edge of my understanding—I know less than enough to be controllably dangerous. When it comes to the well-being of my house and its occupants, I’m not too inclined to experiment.

On the surface, the idea of pumping warm and humid air (which is NC’s air type for 75% of the year) into a cooler crawl space does not seem to make sense. So before I read the first piece of “science” on the topic, I’m already a bit cautious.

The sales concept seems to make sense, but I see some challenges with it:
- Maintaining a truly sealed space
- Knowing all the little nuances of leaving exposed areas (i.e. termite inspection spots) and/or expansion spaces...you know, those little topics that seem to be easily blamed in a forensic analysis of why a house had a major air problem

Does anyone have any experience with this? Is it just a new fad/trend that is unproven, unnecessary, and/or not fully thought out? Or is it really a good way to not just retrofit a traditional space, but that we should be looking to for all new construction from here on out?

Back to my crawl space...
There aren’t any major issues. There is some condensation on the water pipes, and a little bit of dampnessunder the plastic in spots. There’s a French drain around the house on the uphill side. The inspector saw some “dark growth” on the joists, but not enough to freak out about. My inspection yesterday didn’t see much either.

I’d like to do something to try to dry it up a little more. I thought I’d follow the inspector’s advice of installing the fan, but now I’m hesitant given all the chatter on the web about that method. Should I convert the space to sealed?

 

[fieldgrade]

They are starting to completely seal, and heat/cool the crawl spaces in some new construction I've seen recently around the greater RTP area.

 

[Jeppo]

I sealed mine and put in a monster dehumidifier. It is 38% RH and 76 degrees under there at this moment.

 

[12151791]

I sealed mine and put in a monster dehumidifier. It is 38% RH and 76 degrees under there at this moment.

I did the same plan ^^^^ - sealed all of the rectangular vents and installed a dehumidifier: https://www.santa-fe-products.com/
I also installed a wireless hygrometer/thermometer combo to keep an eye on temperature/humidity in the crawl space.
Side benefits, little critters don't like dry air so they stay away from your crawl space.

 

[railsplitter]

If the following apply:

1) your crawlspace is at or above outside ground level
2) outside ground slopes away from the foundation wall all the way around your house.
3) you have a functioning foundation drain
4) your crawlspace doesn't seem overly wet
5) you have the recommended number of crawlspace vents.

Then I'd just put down a vapor barrier, open the vents in the summer, and close them in the winter - done and done.

If using a fan, do not positively pressurize the crawlspace. Use fan to draw air out instead (-0.04 in.w.g. of pressure is plenty).

Sealed crawlspaces and dehumidifiers are nice, but I just don't see spending the money if it isn't necessary.

 

[Jeppo]

I did the same plan ^^^^ - sealed all of the rectangular vents and installed a dehumidifier: https://www.santa-fe-products.com/
I also installed a wireless hygrometer/thermometer combo to keep an eye on temperature/humidity in the crawl space.
Side benefits, little critters don't like dry air so they stay away from your crawl space.

Same here. That's how I know the conditions below without going down there. This is the unit I installed, https://www.santa-fe-products.com/santa-fe-max-dry-dual-xt/.

 

[GymB]

I just had this quoted, it’s more than I want to pay, about $4.50/sqft.

Water under the plastic is not something to worry about.

When they seal it they put down something like 10mil vinyl, I don’t know what vapor transmission is vs 6mil poly from Lowe’s, but I’m going to put that down, overlap and tape the edges and make sure it goes to all the walls.

For my quote they were just going to cut pieces of foam board to put in the vents from the inside and then seal with spray foam, haven’t decided about that.

Last thing, if you have an open flame furnace or water heater in the crawl then you have to leave a vent open so it can get oxygen and push CO out the exhaust, otherwise it might dump fumes in the crawl.

 

[Jeppo]

For my quote they were just going to cut pieces of foam board to put in the vents from the inside and then seal with spray foam, haven’t decided about that.

I didn't know that was "the way". I made it up as I went along. Thick pink foam sheets from HD, cut slightly oversized, wrapped in heavy plastic sheeting, pounded into place and then spray foamed.

 

[CZfool68]

Not sure what it is, but my wife's Dad sealed a basement/crawl space in a cabin that was built in the late 1800's. Uneven dirt floor and kind of nasty. He used some soray foam type stuff that hardened into an almost white, cast like substance. It's been done for at least 5 years and has worked well. No ventilation down there since the cabin is so old. Pretty much like you'd imagine an old dungeon. Except now it had the cool white stuff over the dirt.

 

[GymB]

I didn't know that was "the way". I made it up as I went along. Thick pink foam sheets from HD, cut slightly oversized, wrapped in heavy plastic sheeting, pounded into place and then spray foamed.

Believe that the pink stuff, extruded polystyrene, is closed cell so the plastic wasn’t really needed, but shouldn’t hurt anything.

Not sure what it is, but my wife's Dad sealed a basement/crawl space in a cabin that was built in the late 1800's. Uneven dirt floor and kind of nasty. He used some soray foam type stuff that hardened into an almost white, cast like substance. It's been done for at least 5 years and has worked well. No ventilation down there since the cabin is so old. Pretty much like you'd imagine an old dungeon. Except now it had the cool white stuff over the dirt.

So I’ve wondered if you could basically spray down a thin layer of gunite, the concrete they use for swimming pools. If you figure out what he used please let us know!

 

[CZfool68]

Believe that the pink stuff, extruded polystyrene, is closed cell so the plastic wasn’t really needed, but shouldn’t hurt anything.



So I’ve wondered if you could basically spray down a thin layer of gunite, the concrete they use for swimming pools. If you figure out what he used please let us know!

Just sent him an email. Will let you know as soon as he gets back to me. But he's 80 so he moves kinda slow.

 

[Carolinatlc]

My dad just had DryPro seal up his crawl space and was very happy with their service. He also installed around 10 or so LED strip lights to a common switch at the door. The covering they use is white so with the LED lights on, it’s like daylight down there.

 

[JimP42]

I had mine sealed when I moved in. Love it.

Much better for all the equipment and insulation. Bonus is lots of conditioned storage space if you have usable height under there.

 

[Jeppo]

Believe that the pink stuff, extruded polystyrene, is closed cell so the plastic wasn’t really needed, but shouldn’t hurt anything.

The sheeting, being a bit slippery, made shoving the foam "plugs" into the vent openings easy.

 

[9outof10mms]

The pics and specs I’m seeing make it look like a heck of a lot more undertaking than just blocking the vents. They’re showing bringing the ground poly up 12-18” onto the walls and for stripping it into place; styro insulation on the masonry; sealing any and every joint/crack/space to the outside.

Am I understanding you guys correctly? Some of you have just solidly closed the vents and made sure your ground cover is good—and that’s it?

I’m trying to get as much info and experiences here as I can before making a move. Like I said: I don’t have a screaming problem down there, but I’d sleep better if I knew it was a little more dry.

 

[Stick]

A few thoughts.
First, I really don't like to bash Home Inspectors, I am one, but whoever your inspector was, he needs to go back to school. Your instincts are right on the money, DO NOT pump hot humid air into a crawl space! That being said, air movement under the house is good, and can help reduce condensation, but will not reduce humidity levels below what it takes for mold to grow, and will do nothing whatsoever to reduce cooling costs.
Second, you hit a home run with the Advanced Energy web site. Those guys are national leaders in the building science field and know their stuff. Here is a chart Bruce Davis did a few years back when they ran energy diagnostics on a series of homes with standard vented crawl spaces, closed and dehumidified with R-19 floors and closed with perimeter foam insulation:


If you decide to go with the perimeter foam, be sure it is the foil backed material and seal the edges with foil tape.

The sales concept seems to make sense, but I see some challenges with it:
- Maintaining a truly sealed space
- Knowing all the little nuances of leaving exposed areas (i.e. termite inspection spots) and/or expansion spaces...you know, those little topics that seem to be easily blamed in a forensic analysis of why a house had a major air problem

Again, good questions. First, there is no such thing as a truly sealed crawl space, no matter what some salesman tells you. The proper term is a closed crawl. You seal around vents and weather strip the access door as best as you can, but there will always be at least a little air getting in, and during wet periods soil moisture will work it's way up through the vapor retarder and wick up though foundation walls. There is also a near 100% chance that, eventually, there will be some kind of a plumbing or HVAC condensate leak. That is why if you close a crawl space you need either a dehumidifier or a conditioned air source under the home.

A lot of the builders around here are going with semi conditioned crawl spaces now, where they open a 4" air duct into the crawl and bleed off a little conditioned air from the HVAC system. This actually works pretty well and is cheaper than a commercial dehumidifier, but if you go that rout be sure to air seal around all wiring, plumbing and HVAC penetrations into the crawl. Having a humidistat installed to let you know if there is a problem down there is inexpensive and a good idea.

Without having seen your crawler, I can tell you that condensation and mold problems are less related to foundation leakage than weather conditions. You don't see much down there now, but wait till August. Headroom under the house also makes a huge difference, as does the presence of heat ducts and areas where air movement is restricted. Really, if you have a nice open crawl space with over 3'-4' of headroom and decent air circulation you are unlikely to have a serious mold problem. If it is a low space with bad air circulation (heat ducts in the way, dropped girders, garages and porches where vents can't be installed, shrubbery blocking the vents), the house is designed to fail.

So in short, there are two reasons to consider a closed crawl, moisture related issues such as mold and indoor air quality and energy conservation. Generally, if you can do the work of closing it yourself and do it properly (follow the instructions at the Advanced Energy site and you will be good), even if you don't have mold problems a closed crawl can pay for itself within about 5 years. If you decide to let someone else do it for you, be careful. There are some badly overpriced contractors out there who really don't know as much as they think.

 

[GymB]

The pics and specs I’m seeing make it look like a heck of a lot more undertaking than just blocking the vents. They’re showing bringing the ground poly up 12-18” onto the walls and for stripping it into place; styro insulation on the masonry; sealing any and every joint/crack/space to the outside.

Am I understanding you guys correctly? Some of you have just solidly closed the vents and made sure your ground cover is good—and that’s it?

I’m trying to get as much info and experiences here as I can before making a move. Like I said: I don’t have a screaming problem down there, but I’d sleep better if I knew it was a little more dry.

I think that like anything else, 80% of the cost is to get the last 20% of the benefit.

Our quote was to cover the ground going up the walls and pillars and to seal the vents and to weatherproof the door and finally to add a dehumidifier.

Maybe I’m dumb, but covering the floor well, sealing the vents, and oversizing the dehumidifier will likely get you 80% of the benefit for less than half the cost of doing the full encapsulation.

I did learn that NC requires insulation in the crawl, either against the floor (crawl space ceiling) or against the walls. Walls is appealing to me, but it is more complex than slapping up some pink stuff.

 

[Jeppo]

I didn't run the vapor barrier up the foundation walls only because it was more work than I was willing to do. Wish I had.

 

[9outof10mms]

but whoever your inspector was, he needs to go back to school.

I’m gonna give him the benefit of th doubt in that he was likely trying to improve the current setup without freaking me out by recommending a $4,000 closed space fix (when it doesn’t require it). Ideally, the vents work in the manner that the vent fan would help induce (letting outside air in). I’m not mad at the guy.

I appreciate your input, @Stick .

I may try to go a home brew route by redoing the ground cover (bringing it up 12-18” above grade and insuring 100% coverage), adding foam insulation to the masonry exterior walls, blocking off the vents, and sealing the access door. My space is a wedge shape: the front being tall enough to stand, the back being about 18-24” tall—and the back is where the moisture levels are higher than desired. There’s a dehumidifier in there now (from the previous owner), but I see it as trying to dehumidify the earth with the open vents. Maybe it’ll really make a difference with a closed space.

I guess if the closed solution doesn’t work (as in, I make it worse somehow), I can always reopen the vents and make it breathe again.

 

[Jp8819]

One of the biggest things you can do to help a crawl space is be sure grading and gutters are working properly around your home first to keep water away and landscaping is not holding water in. If you do not have that going for you to start you could be fighting a losing battle.

 

[foopid stucker]

i encapsulated my crawl years ago. 20 mil plastic up the walls and such. bricked in the vent holes, nice and clean and dry. you need to keep a 4 inch viewing area of brick beneath the wood band/ joists to inspect for termites. I put a 4 inch vent off the plenum for conditioned air and there is a single vent opening for gas furnace feed air that comes through a vented closet in the garage. I may be wrong but I put a cheap dehumidifier down there since once the area was " sealed" there should not be much humidity coming into the space.. I did pull all the insulation down off the floor so they are vaguely "heated" in the winter months. my only issue is some shrinkage of the wood flooring at times...HTH

 

[9outof10mms]

i encapsulated my crawl years ago. 20 mil plastic up the walls and such. bricked in the vent holes, nice and clean and dry. you need to keep a 4 inch viewing area of brick beneath the wood band/ joists to inspect for termites. I put a 4 inch vent off the plenum for conditioned air and there is a single vent opening for gas furnace feed air that comes through a vented closet in the garage. I may be wrong but I put a cheap dehumidifier down there since once the area was " sealed" there should not be much humidity coming into the space.. I did pull all the insulation down off the floor so they are vaguely "heated" in the winter months. my only issue is some shrinkage of the wood flooring at times...HTH

Over-dehumidifying. I don’t want that either. My last house had squeaky floors. It was like a video game of “don’t squeak the floor” every time I wanted to tip toe around in the early morning getting ready for work.

 

[Stick]

There’s a dehumidifier in there now (from the previous owner), but I see it as trying to dehumidify the earth with the open vents. Maybe it’ll really make a difference with a closed space.

I would say that was rather counterproductive. Yes, close it up and see what happens. If the dehumidifier works there is no way you will make anything worse.

i encapsulated my crawl years ago. 20 mil plastic up the walls and such. bricked in the vent holes, nice and clean and dry. you need to keep a 4 inch viewing area of brick beneath the wood band/ joists to inspect for termites. I put a 4 inch vent off the plenum for conditioned air and there is a single vent opening for gas furnace feed air that comes through a vented closet in the garage. I may be wrong but I put a cheap dehumidifier down there since once the area was " sealed" there should not be much humidity coming into the space.. I did pull all the insulation down off the floor so they are vaguely "heated" in the winter months. my only issue is some shrinkage of the wood flooring at times...HTH

If your dehumidifier is holding relative humidity between 50%-60% that is all you need and should keep wood shrinkage to a minimum. If the crawl space has been really wet and you dry it out, then, yeah, there's going to be some noticeable wood shrinkage. That beats the alternative of a wet moldy crawl space and in the worse case, wood rot.

 

[Exile_D]

My dad just had DryPro seal up his crawl space and was very happy with their service. He also installed around 10 or so LED strip lights to a common switch at the door. The covering they use is white so with the LED lights on, it’s like daylight down there.

Would you mind sharing how much that cost and sq. ft.? They were referred to me by a friend a while back, but we never got around to doing it, mostly because everyone said it is fairly costly.

 

[railsplitter]

Something was said upthread to the effect that weather conditions have more to do with crawlspace moisture than does water penetration through the outside wall. I'm not trying to get into a peeing contest and maybe I misunderstood, but that is flat wrong given the context I interpreted it in. If water is entering a crawlspace due to one or more of the below reasons, then anything you do before fixing it/them is a band-aid.

1) your crawlspace is below outside ground level
2) parts or all of the yard is level, or, slopes toward (not away) the house.
3) lack of -or- non-functioning foundation drain
4) inadequate number of crawlspace vents.
5) stopped up gutters or gutters that discharge at/near the foundation wall

Assuming you have none of the above issues, then the normal humidity of southeastern air alone is not enough to cause a long term humidity concern in the crawlspace IF you have a vapor barrier and use the vents properly. It is actually preferable to have a certain amount of moist air in the crawlspace to keep the wood from getting too dry.

If it is cheaper to seal the crawlspace than to address items 1-5 above, then that would make more sense if money is an issue. But then again, you'd be treating the symptom and not the cause.

I can't believe the number of new homes I see built where items 1-5 above are not taken into consideration during construction of the foundation.

 

[GymB]

Something was said upthread to the effect that weather conditions have more to do with crawlspace moisture than does water penetration through the outside wall. I'm not trying to get into a peeing contest and maybe I misunderstood, but that is flat wrong given the context I interpreted it in. If water is entering a crawlspace due to one or more of the below reasons, then anything you do before fixing it/them is a band-aid.

1) your crawlspace is below outside ground level
2) parts or all of the yard is level, or, slopes toward (not away) the house.
3) lack of -or- non-functioning foundation drain
4) inadequate number of crawlspace vents.
5) stopped up gutters or gutters that discharge at/near the foundation wall

Assuming you have none of the above issues, then the normal humidity of southeastern air alone is not enough to cause a long term humidity concern in the crawlspace IF you have a vapor barrier and use the vents properly. It is actually preferable to have a certain amount of moist air in the crawlspace to keep the wood from getting too dry.

If it is cheaper to seal the crawlspace than to address items 1-5 above, then that would make more sense if money is an issue. But then again, you'd be treating the symptom and not the cause.

I can't believe the number of new homes I see built where items 1-5 above are not taken into consideration during construction of the foundation.

Agree entirely about fixing the problems if you can. My crawl is a few inches below grade, hate the builder and should never have bought the place.

 

[foopid stucker]

a problem with the vents is the ambient humidity can condense on the water pipes and cooler duct work and almost keeps them constantly damp if not dripping. mold needs moisture and an organic food to grow. remove the moisture and the mold cannot actively grow. once dried, I used a brush attachment and vacuumed it all off of the exposed wood....

mind you I had an uneven crawl floor on a sloped lot causing standing water. so I put a sump and pump in that area

 

[LesBaer45]

https://buildingscience.com/documen...space-construction-performance-and-codes/view

https://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

 

[Jeppo]

Working outside today, I saw one of my "plugs" and remembered another reason for wrapping them with black plastic. Looks a lot better from the outside than pink foam.

 

[fishgutzy]

Our crawl space was awful.
Poor drainage resulted in water accumulating at the low point.
We had the space given the seal treatment.
Light added and humidifier.
Replaced the drooping insulation.
TheY did the drainage around the interior and drained it to the outside.
When it was all done, we had a space that was white, easy to crawl in without getting muddy. Came in Handy when i had to replace the blown exterior water faucet.

Yes, when we sold the house the tenure inspector noted that they couldn't complete it because of the covering in the brick. But the framing was still visible.

To me, the advantages outweigh the minor objection of termite inspectors.
How is that any different from finished walk out basement? Same thing. (Granted we found past termite damage in our current home when we had to repair a foundation leak)

Sent from my SM-G935V using Tapatalk

 

[Tailhunter]

They are starting to completely seal, and heat/cool the crawl spaces in some new construction I've seen recently around the greater RTP area.

This is the only way to fly. or crawl.