Best way to dehumidify this crawlspace / basement (to remove damp smell)?

[Owen Lucas]

There is a crawls space which is accessed by a basement. It appears to be filled with sand, there is a room above it. There is a loose vapor barrier above the space, looks intact, I cant tell if it's a good job but it is intact.

The basement has a cat urine smell / damp which appears to be coming from this crawl space since it is stronger int his area. There are no cats and though the previous owner had one, this area is closed off with a board.

I am thinking of digging a pit, lining it with expanded steel, and connecting a radon fan to suck the air out in order to dehuminify the soild and move air out of the basement area.

This is a 20 year old house.

What

would you do?

 

[JohnnyG]

The basement in my last house had a radon system, and the PVC pipes ran UNDER the vapor barrier plastic. It worked well, kept out the moisture and the radon without overcooling the area in winter.
On that note, I don't see any ventilation in that space. Mine had those grill/screened vents with louvers on the outside that replace a single concrete block, so there would be some cross ventilation. I'd close the louvers in the winter.
MANY styles and prices to choose from.

 

[Owen Lucas]

The basement in my last house had a radon system, and the PVC pipes ran UNDER the vapor barrier plastic. It worked well, kept out the moisture and the radon without overcooling the area in winter.
On that note, I don't see any ventilation in that space. Mine had those grill/screened vents with louvers on the outside that replace a single concrete block, so there would be some cross ventilation. I'd close the louvers in the winter.

There are no vents, which I thought was weird for a 20 year old house.

I have yet to install a radon system in the sump, which is lower than the crawl space int he actual basement. I was going to run the PVC it through this crawl space out the side to vent.

 

[Pablo]

Is there a functional footer drain? Been code for awhile now.

 

[Fattylocks]

First thing I would do is inspect the walls behind the foam sheets. If that looks clean I'd put a dehumidifier and a fan down there and run it for a week.

 

[Owen Lucas]

Is there a functional footer drain? Been code for awhile now.

I believe so, would a foot drain mean drain tiles? The downspouts go to drains outside the house which i presume feed into the drainage system.

The sump needs some tlc and I want to overhaul the entire system. The water appears to be too high with one of the drains being perpetually full, maybe that has something to do with the musty smell?

The humidity in the regular walk in basement is 29 - 34% humidity which seems pretty good. I moved the sensors to the crawl space so I'll see what they register in a few hours.

First thing I would do is inspect the walls behind the foam sheets. If that looks clean I'd put a dehumidifier and a fan down there and run it for a week.

Sounds good. I don't want to blow the musty smell into the regular basement but I have an unused dehumidifier which I am tempted to lug up there.

A fan would be on the menu once I figure out what I am doing with the radon plumbing. Maybe I would install an extra vent for an exhaust.

 

[Snagglefoot]

I have seen a few crawl spaces that look exactly like that. In fact I had to check that it wasn't one of my photographs, LOL. The foam insulation is totally common and the correct thing to do. I would have a radon company do a test. You could install a vapor barrier along the underside of floor and then place fiberglass insulation between the joists, held in place with slats of wood. The temperature of 60 degrees in the crawl space indicates to me that the floor should be insulated. Definitely if you decide to vent to the outside you should be insulating that floor. My two cents. Good luck.

 

[Fitter30]

A fan will only raise the RH level by bringing in outside air uncondition. Box store dehumidifier are rated at 95° at 90% RH. AHAM rated is rated at 80° at 60%. Most crawl space dehumidifiers are rated AHAM.

 

[Pablo]

Footing/footer drain

https://duckduckgo.com/?q=footer+dr...2c-4af6-ad4a-47a0bba9a011/dcp00919.jpg&t=ffab

https://www.basementsystems.com/bas...asic-construction/exterior-footing-drain.html

You need #1 to stop the water from getting in, no drying method will help that

 

[Owen Lucas]

I have seen a few crawl spaces that look exactly like that. In fact I had to check that it wasn't one of my photographs, LOL. The foam insulation is totally common and the correct thing to do. I would have a radon company do a test. You could install a vapor barrier along the underside of floor and then place fiberglass insulation between the joists, held in place with slats of wood. The temperature of 60 degrees in the crawl space indicates to me that the floor should be insulated. Definitely if you decide to vent to the outside you should be insulating that floor. My two cents. Good luck.

Thank you, I have a radon meter running and its elevated in the basement, outside the basement Radon levels are 1 or less. Good point about insulating the floor w/vapor barrier. I can do this job my self.

A fan will only raise the RH level by bringing in outside air uncondition. Box store dehumidifier are rated at 95° at 90% RH. AHAM rated is rated at 80° at 60%. Most crawl space dehumidifiers are rated AHAM.

Interesting, I was not aware of the different ratings systems. I'll search for a a dedicated crawl space dehumidifier then.

Footing/footer drain

https://duckduckgo.com/?q=footer+drain&iax=images&ia=images&iai=http://www.alliedwaterproof.com/cdn2.assets.sites.launchrocketship.com/52358f35-5201-4550-8d61-c316e0b0a49a/files/4a52a342-992c-4af6-ad4a-47a0bba9a011/dcp00919.jpg&t=ffab

https://www.basementsystems.com/bas...asic-construction/exterior-footing-drain.html

You need #1 to stop the water from getting in, no drying method will help that

View attachment 266962

I wish I had the house blueprint to confirm the construction method. I can see a layer of tar on the exterior cinder blocks above the ground and the house is surrounded by pebbles though I think this is just aesthetic.

 

[Fitter30]

Have a crawlspace I'm very rural. Used fiberglass between the floor joist. Mice luv it all insulation to nest in it.
https://www.google.com/url?q=https:...4QFnoECAkQAg&usg=AOvVaw2A7IvjNP48x-EtZdkRXMQM

 

[JohnnyG]

There are no vents, which I thought was weird for a 20 year old house.

I have yet to install a radon system in the sump, which is lower than the crawl space int he actual basement. I was going to run the PVC it through this crawl space out the side to vent.

Don't forget to check your local requirements on Radon systems. Most require the outlet to be 3 feet or mare above the roofline.

 

[Hohn]

Have a crawlspace I'm very rural. Used fiberglass between the floor joist. Mice luv it all insulation to nest in it.
https://www.google.com/url?q=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1184&context=coopext_swine&sa=U&ved=2ahUKEwjWgdaew_uLAxV-k4kEHYrEJA4QFnoECAkQAg&usg=AOvVaw2A7IvjNP48x-EtZdkRXMQM

sounds like you need a crawlspace snake.

 

[maineiac]

Just a few thoughts from someone who has actually done this job on houses we've rehabbed - maybe some of this will be useful to you.

I would start by encapsulating the entire crawl space - something you can easily do yourself though it's not a fun job. You need to be scrupulous about the details like taping/sealing your posts/penetrations and taping all the seams (with 6" overlaps) and sealing the ends of the plastic at the tops of the walls. You need to approach this with the idea in mind that you're trying to create a swimming pool liner... no leaks! Use quality, thicker plastic with an imbedded scrim - it'll last forever. If you use this thicker plastic (google "basement encapsulation"), it is also a RADON BARRIER - and that's a big bonus in your case. Oh, and use a seam sealing tape with an acrylic adhesive (like Zip or 3M flashing tape) - it won't let go... ever. The tape the encapsulation vendors use is cheap and won't adhere long term. Your labor (if you DIY this) is disrespected by using cheap materials

Do NOT vent your crawl space - that is ancient and incorrect thinking with respect to your objective of eliminating moisture. As was pointed out, above, you'll be introducing moisture vapor into your crawl space by doing that and it'll condense on the relatively cool surfaces down there - no bueno! Make sure those block walls are inside the encapsulation, too. Tops of knee walls/rim joist should ideally be sealed with closed cell foam (with your encapsulation "vapor barrier), terminated underneath that foam. They make top-sealed plastic sumps to minimize moisture from that source, but you could probably jury rig something with yours.

Finally, add a humidifier that drains right into your sump for ease of maintenance. With this method, you'll minimize the dehumidifier run-time and save a lot of $$ on your electric bills (unless you get a very $$ high-efficiency dehumidifier like a Quest, dehumidifiers are energy hogs).

This is really a 2 person job - it makes unrolling/fitting and taping much, much easier if you can recruit help. It can be done solo, but I wouldn't recommend it - it'll make the job 3x harder. JMO, good luck!

 

[maineiac]

paragraph 3, 3rd sentence should read, "...outside the encapsulation..."

sry for the poor punctuation, (I was pressed for time) but I think the ideas are still intelligible

 

[BMWTurboDzl]

There is a crawls space which is accessed by a basement. It appears to be filled with sand, there is a room above it. There is a loose vapor barrier above the space, looks intact, I cant tell if it's a good job but it is intact.

The basement has a cat urine smell / damp which appears to be coming from this crawl space since it is stronger int his area. There are no cats and though the previous owner had one, this area is closed off with a board.

I am thinking of digging a pit, lining it with expanded steel, and connecting a radon fan to suck the air out in order to dehuminify the soild and move air out of the basement area.

This is a 20 year old house.

What would you do?

 

[Owen Lucas]

Wow very helpful, thank you! There is sheathing on the soil but it doesn’t go up and under the foam. I guess I was on the right track with the sump, that shouldn’t be too hard to install.

 

[Donald]

Most people seal up the crawlspace and install a crawlspace dehumidifier from Aprilaire. Or one of a few other manufacturers that make one designed for a crawlspace.

Some vapor barriers are plastic reinforced with string kind of running in a mesh. I believe if this string gets wet it can smell like cat urine.

Deal with standing water before you do much else.

I believe you can use a crawlspace dehumidifier to get the RH down to 45% to 50%. I don't think you need to spend $15K on a perfect encapsulation. Just a decent vapor barrier and a crawlspace dehumidifier.

Remote RH sensor(s).

I have 2 RH sensors, 2 water detectors and a smart outlet all connected to Samsung SmartThings. I can tell a lot of things including if dehumidifier is fan only or compressor is on also. Alerts to my phone if RH gets too high.