Crawlspace and odors in living space


Old 12-05-18, 09:16 AM
Thread Starter
Join Date: Aug 2015
Posts: 16
Crawlspace and odors in living space


I have a two-story contemporary home built in 1982 located in coastal Virginia (Zone 8A, hot and humid summers). Crawlspace is 1480 sq. ft. and is approx. 28" high. The exterior walls are cinder block. There are no HVAC components or ducts down there, only plumbing.

Here's what it was like when we moved in 3 years ago:
- 7 exterior grill vents
- No living space to crawlspace vents.
- Joists had been repaired due to moisture damage, the new joists are sistered and the work was done correctly.
- There was and still is a 6 mil. vapor barrier down but it is perforated (1/2" holes every 12"), I assume it was done to allow any standing water to escape down into sand base.
- Fiberglass insulation was previously installed but had been removed from floor joists. No wall insulation.
- High humidity levels, 85% during the summer was common. Wood moisture readings were high as well.
- Some light mildew/mold (mostly white fuzzy stuff) was growing on old and new wood.
- No obvious signs of regular water intrusion, we did get 4" water in there during Hurricane Matthew but that was 15 inches of rain in 24 hours and def not the norm. We are not in a flood zone.
- Outside gutter downspouts were only draining 1-2' from foundation.

Hereís what Iíve done:
- Had 3 crawlspace companies come out to inspect. 2 recommended full encapsulation with dehumidifier, french drains and sump pump ($15k-$20k). The other recommended that I simply seal up the vents, get a dehumidifier and see how moisture levels respond.
- So I sealed the vents and got a dehumidifier with pump (Santa Fe Compact 70). It drains outside of house.
- I moved all gutter downspouts so they drain 3í-4í from foundation wall.
- Humidity levels stay between 45% and 50% year-around and wood moisture is approx. 13%.

So now hereís my issue. The inside of our house gets a musty smell, especially when humidity rises. This was not noticeable when crawlspace was vented so pretty easy to assume that crawlspace air is getting pulled into living space since it has nowhere else to go. I contacted another company to come take a look, he recommended a new vapor barrier to replace the perforated and poorly installed one and to remove the dehumidifier and vent covers. Basically go back to the way it was previously but this time with a new vapor barrier. I raised my concerns about previous humidity/wood moisture issues and he said they would be minimal and that the vents would do enough to circulate air and prevent smelly crawlspace air from getting into living space. He said thatís the only way to get rid of the musty smell.

Here are my thoughts/ideasÖ
- I realize new vapor barrier is needed and it will be replaced. Would that be enough to reduce musty smell?
- Iím hesitant to open vents and raise humidity/wood moisture levels again.
- Iím assuming air is getting pulled up into the house via the stack effect, especially when HVAC is running. My crawlspace dehumidifier has the ability to be ducted outside (it is not currently, the air is being filtered MERV-11, dehumidified and sent back into crawlspace). The blower is 150 CFM. would that be enough to reduce stack effect and reduce air being pulled into living space?

Thanks for any insight!
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Old 12-08-18, 06:59 PM
Join Date: Jan 2010
Location: Maryland
Posts: 399
Easiest fix is a new vapor barrier if you really need it and some fresh air movement in the crawl space. If you can vent the dehumidifier out side and provide an air intake for fresh new air (open a few vents). You will almost always have air loss from your duct work. AC runs, air leaks out, new air leaks in around plumbing and electrical from under the home and brings in musty smells.
You could also do the 20K (that"s a killing) crawlspace and totally seal the crawl. You still need air movement. Now when the AC runs, it will pull air around the windows, doors and down from the attic, through the dryer vent and range hood. Outside fresh air, not musty crawl space air.
There is talk of rethinking the sealed crawl spaces and going back to more of the old fashion vented foundation.
You have relocated the down spout drains but does the ground slope away from the home?
Old 12-30-18, 01:03 PM
Join Date: Dec 2018
Location: Usa
Posts: 2
Crawl space

I have decent amount of water in crawlspace would a french drain inside and dehumidifier help with moisture or would encapsulation be better since also have cold floors
Old 12-30-18, 02:54 PM
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Join Date: Mar 2003
Location: NC, USA
Posts: 18,591
I prefer passive solutions so I don't like the idea of relying on something mechanical like a dehumidifier. Whether or not to do a French drain and plastic on the floor vs encapsulation on the bottom of the joists comes down to your crawlspace. You can also do everything; French drain, plastic on the floor and vapor barrier on bottom of joists.
Old 01-07-19, 09:36 PM
Join Date: Jan 2019
Posts: 1
I live in Virginia also, and just had a complete encapsulation performed. I also had odor that was getting up into the living space of the home. What I needed to do was open up one vent and install a small exhaust fan. No more smells. The fan that I used was the Tjernlund V2d. A couple of other companies make them also. I have an extra one if you are anywhere near the Richmond metro area and want to try it out.
Old 01-08-19, 02:57 PM
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Join Date: Oct 2004
Location: WI/MN
Posts: 18,863
The vent with exhaust fan is going to do the same thing as a radon mitigation system - lower the pressure in the crawlspace so air from the home moves into the crawlspace instead of the other way around. Hard to say how much but this will increase HVAC costs.

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