Persistent Crawl Space Odor

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  #1  
Old 08-03-08, 08:44 AM
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Unhappy Persistent Crawl Space Odor

We built a house having a crawl space 3 years ago and have had an odor from the time we moved in. I was the contractor on the project so I canít blame anyone else. In the crawl space there has been a distinct odor which my wife says is s musty smell. I have thought it spelled something like sewer gas. An independent plumber has verified there are no leaks from our septic system into the space. When it rains the odor comes in stronger in the house. When we excavated the lot, there was a wet area and in one corner of the crawl space.

I know our gutter system is imperfect due to a architecture that canít avoid some bypass. All downspouts do tie in to piping routed away from the home. There is a footer drain.

We have done significant work to eliminate the smell but nothing seems to work. 1st we had the entire crawlspace trenched around the inside parameter and drained at $4500. The outlet in the yard weeps nearly constantly. This work also included applying plastic sheathing over the dirt. All work was done by a capable crew. The smell seemed to be somewhat less after this work and even less when we took up the plastic. But when it rained the smell was present in the house.

Next we had humidity controlled power vents installed and all the wood rafters, sub floor and seal plates sprayed with a fungicide and again installed the plastic, $3500. Now the smell is worse than ever showing up in rooms that had not smelled in the past.

The front of the house has a concrete floored porch so no venting is possible, however the (3) power vents were used with ducting attacking this dead spot.

Iím now contemplating sealing the 1st floor in the crawl space with plastic sheathing and sealing all joints. Maybe concreting the crawl space (my wifeís idea) I know I am talking extraordinary measure but this is a big investment and is our dream home. My wife says if we can not eliminate the odor she wants out.
 
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  #2  
Old 08-03-08, 04:38 PM
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Is there any discoloration on the walls of the crawl space? How much of the crawl space is above ground, if any? Do you have any idea how high the water table is? Is there a vent for the main drain? Is the main drain cast iron or PVC?
 
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Old 08-03-08, 04:54 PM
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Do you no what the RH is in the crawl. Only way to keep odor and mold from growing is to have a dehumidifier and keep Rh under 50 %.
 
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Old 08-04-08, 05:55 PM
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The crawl space is 5' high in the back and 3' high in the front. Walls are cinder block all above grade.

Do have a large dehumidifier but not sure how much help it has had. Very low RH in the winter. Now the vent fans run with high humidity.

The house is on a hill. Main drain is PVC. The stack is vented to roof. I notice that there is some condensation on the HVAC plenums in the heat of the summer. These supply the 1st floor.

No discolorization on walls. All surfaces look new.
 
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Old 08-04-08, 06:04 PM
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What about installing an exhaust fan in the crawl space? Is there room for that?
 
  #6  
Old 08-04-08, 06:10 PM
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[QUOTE=bad-smell;1408659]The crawl space is 5' high in the back and 3' high in the front. Walls are cinder block all above grade.

Do have a large dehumidifier but not sure how much help it has had. Very low RH in the winter. Now the vent fans run with high humidity.

Having a fan will only pull in more RH if you are in a green grass state.

The house is on a hill. Main drain is PVC. The stack is vented to roof. I notice that there is some condensation on the HVAC plenums in the heat of the summer. These supply the 1st floor.

Condensation is because the RH is to high. A good dehumidifier should be able to handle this.
 
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Old 08-05-08, 06:06 PM
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Have thought about a large volume fan but it would be a job to put it in, though not out of the question iby any means.

Regarding the dehumidifier........you are probably right I should try it again. One would think that if it is bone dry, there would be no odor except for earth. The crawl space is 45' by 60' so in order to feel assured of the desired result, I would need 2 or 3 or more with positioning throughout the space. Perhaps having only one is why I didn't see the benefit. I understand that mold/mildew spcies can not propagate below about 40 RH. However I would have thought the biocide/fungicide would have destroyed any odor. I'm convinced though that this is something I will definitely try. As before I will drain them into the existing trench system which is now under plastic in most areas. I wonder what the cost is to power these, I can find out when I buy them.

Appreciate any other ideas you may have. Is it acceptable to seal the underside of a home with plastic? I have been considering this.

I'm not sure how the passive temp vents work. I assume they open with high temperature? And the power vents come on at high humidity. I can simply turnoff the power vents totally (6) in number but will have to accept the temp vent positions.
 
  #8  
Old 08-05-08, 06:14 PM
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Vents will only add to the RH! Fans will only add to the RH! No vapor barrier will add to the RH! Vapor barrier that is not sealed will add to the RH! One GOOD dehumidifier will be able to keep the RH under 50%! No need for three!
 
  #9  
Old 08-05-08, 07:05 PM
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I notice from your other postings that you are a strong avocate of a sealed crawlspace. Do you have 1st hand experience with this? In most cases and for hundreds of years vented crawl spaces have been successfully used in non-bent grass states. In my case though, I am grasping at straws with odor problems.

As I said a humidifier simply doesn't circulate enough gas for me to be assured of it's efficacy. If I am to proceed I will over engineer, what is a couple $200 humidifies when I have already spent $8K.

Thank you for the comment relative to the barrier; mine is neither taped or sealed to the walls. Perhaps this is where I should start?
 

Last edited by bad-smell; 08-05-08 at 07:25 PM.
  #10  
Old 08-06-08, 04:54 AM
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Stay away from the $200 junk dehumidifiers and buy a good unit designed for low temp operation like a crawl space. One Therma-stor dehumidifier will remove more RH and use less electricity than two conventional dehumidifiers. I have worked in the IAQ field for over 12 years now so I have seen a couple of crawl spaces over the years!! Venting used to work ok when there was lots of ventilation. Now days with most homes having under 10 vents they just can't get the airflow needed. If you add a fan to help ventilation in a home with to few vents it will still grow mold because there will be so many areas where the air is stagnant. Only way to keep mold from growing is to seal it up and to add a dehumidifier.
 
  #11  
Old 08-06-08, 01:14 PM
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WOW! I got a sticker shock on the Therma Stor. What size do I need for 10,000 ft3? Can I run it to the trench like the cheapies?

Just for discussion; the problem is significantly less in the winter due to the lower outside RH due to cold temperatures. Maybe I should seal the crawl space and use cheapies and accept low performance at cold temperatures or until I have proven the overall approach. In this way I can hedge the risk.

Sorry for any skepticism its just that this is a major about face for me. With the vent fans running the 1st thing I notice are puddles under the HVAC lines that support your hypothesis.

Damn, I wish I could pinpoint the source of the odor just to know what is generating it.
 
  #12  
Old 08-06-08, 01:57 PM
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10,000 square FT! You sure that is wright? They will tell you how much capacity they have to the right of the screen. In a crawl space it will take some where around 3 dehumidifies to equal the capacity of a unit designed for a crawl. then add up what it will cost you to run the 3 an the average life around 5 years for the cheap ones. Now the grand spent in a good one doesn't sound bad. Yes RH will be less in winter. If you are still running the vent fan this needs to be removed and sealed.
 
  #13  
Old 08-06-08, 02:34 PM
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The Crawl space is 60*40 with 4' average height..9600 ft3 not square ft. It is 2400 square ft. I see the Sante Fe HC Crqwl Space Dehumidifier model 4025081 fits the bill at about $1600 at one site. The model operates from 55 to 95 degrees F. Don't know what you were referring at left. This model is touted to serve 1500 tp 3000 ft2 spaces.

I have lined up the contractor to seal the floor last week in August. He does not usually seal his poly but he is very good. He is pondering materials. He uses 6 mil poly. What do you recommend for tape and sealant on the walls?

Thanks for the help.
 

Last edited by bad-smell; 08-06-08 at 03:16 PM.
  #14  
Old 08-06-08, 06:11 PM
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Spray glue is what we use and is very good!
 
  #15  
Old 08-07-08, 06:28 AM
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I too am having a musty smell from a two year old house, and have been reading elsewhere about closing the vents in high humidity. Would you advise to go ahead and close the vents now with the smell still there and trapping in the moisture?

Also, the crawl space has a hole dug in the low end of the house. There is a hole in the foundation there. This area stays wet most of the time - not standing water, but ground is clearly wet. Is this right?

Thanks,
Kentucky Resident
 
  #16  
Old 08-07-08, 06:32 AM
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I never advise closing any vents unless it's to keep out the cold. The foundation should be sealed.
 
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Old 08-07-08, 08:30 AM
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Originally Posted by Pulpo View Post
I never advise closing any vents unless it's to keep out the cold. The foundation should be sealed.

How does one both seal the foundation (crawl space?) and not close vents. You either close the vents and dehumidify to seal or open them wide and vent.
 
  #18  
Old 08-07-08, 03:07 PM
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Originally Posted by channelscanner View Post
I too am having a musty smell from a two year old house, and have been reading elsewhere about closing the vents in high humidity. Would you advise to go ahead and close the vents now with the smell still there and trapping in the moisture?

Also, the crawl space has a hole dug in the low end of the house. There is a hole in the foundation there. This area stays wet most of the time - not standing water, but ground is clearly wet. Is this right?

Thanks,
Kentucky Resident
1) Does the odor enter the house? If not, how much does it matter?
2) Does it go away during the coldest part of the winter? If so, that could be because this is the lowest relative humidity of the year.

If you have definite wet areas in the CS you probably need to get it out. In my case this required significant trenching all of the perimeter.

Now I am faced with 2 ways to go..either seal and dehumidify or vent vent vent. But I have already gone the vent vent route.
 
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Old 08-07-08, 03:23 PM
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bad-smell I was answering channelscanner who said he had a hole in the foundation. We have two people here with similar problems but they aren't exactly the same.

Any foundation has to be sealed to stop water entering it. If only dampness in entering, products like Drylock from Home Depot are available. If something like that isn't enough, I would dig down to the footing and seal the entire foundation from the outside. I have done many of them as part of a crew. Once we got to the footing we would dry the wall with a torch, paste a membrane that came on a roll to it, threw #8 gravel at the bottom and backfilled. We always dug a little lower than the footing to let the membrane overlap. That should solve 80% of the problem or more.
 
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Old 08-07-08, 05:04 PM
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Missunderstood, Pulpo, please sxcuse.

I have used drylock in the past for a basement. If the crawl space wall is above grade, is this unneccesary or useful?
 
  #21  
Old 08-07-08, 05:48 PM
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Originally Posted by bad-smell View Post
Missunderstood, Pulpo, please sxcuse.

I have used drylock in the past for a basement. If the crawl space wall is above grade, is this unneccesary or useful?

That's a good question. My first guess would be that it's not needed but I don't know for sure. If the walls are above grade, what is the house sitting on? Now that you mention that, I'm starting to think that the problem is originating below grade.

Is there anyway, you can post some pictures, inside and outside?
 
  #22  
Old 08-07-08, 06:18 PM
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Would help(SOME)> help keep the water vapor from going up the block and into the crawl. Put then you have all that RH on the sill. So [email protected]# if you do and D (well you know how it goes)
 
  #23  
Old 08-08-08, 01:15 PM
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If you guys can point me to how I can attach photos I'll happily to that. You guys are definitely helping me out. I'm eagar to see how it smeels after the floor sealing is complete.
 
  #24  
Old 03-30-11, 04:54 AM
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just signed up to this sight and read your problem..really curious on how it turned out..i'm no expert but it sounds to me if you put in just a few open vents in the crawl that would have helped alot..i no you said had poured porch on front but what about the sides..with a dehumidifier running..the dehumidifier still works with open vents..just dont put in to many..and the main purpose of few vents is to just let in some fresh air..its like finding something smelly in your car with the windows up it smells really bad but with just a crack in the window it drastically reduces the smell..same ass a basement it just needs to breathe a little
 
  #25  
Old 03-30-11, 05:53 PM
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Wow opening a 3 year old thread. Open vents in a crawl is a bad idea
 
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