I have crawlspace that was encapsulated 4 yrs ago. Last yr it started smelling so finally this week we removed the encapsulation in the area that smelled see pic. When they removed it below we saw this big dip that was not there when it was encapsulated. What can cause this dip. So far we opened couple of vents to air out. Under the black channel drain it had water.
Various causes are possible with one being soil subsidence due to loose and uncompacted soils.
The source of the water can also be from many causes with one being moisture below the cover and collecting in low spots.
Where are you located as it may help others respond with common causes from your specific area.
Smell. Lack of ventilation.
You may have a point, however encapsulated crawls are not vented…but they do need to be conditioned.
For the poster, you should not have been able to pull back the vapor barrier without cutting it along the sidewall. This seam should be sealed. Is it properly sealed and conditioned (dehumidifier or AC supply/return)?
Is that a vent? If so, this crawl is not encapsulated.
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I would suspect that the “dip” is caused by pooling water. The water eventually drained down into the soil, taking some of the finer elements down with it causing the pit, like how a pothole forms in a road. Since it is your house, I suggest you check the crawlspace during and after the next big storm event to see what is going on and where the water might be coming from. The best solution is to prevent the water from getting under your house in the first place, perhaps adding gutter extensions, building a swale or installing a French drain at the exterior. The second best solution is to install a drain inside the crawlspace at that location to get any accumulated water out.
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Encapsulation by itself is not the answer. In order to have an effective encapsulation system (healthy crawlspace) you need to prevent the water from entering the crawlspace and if this is not possible or cost effective you’ll need a way of getting the water out of the crawlspace (interior drainage system/sump pumps). The second thing is that the encapsulation (plastic sheeting) be installed correctly. A lot of companies will just tape the plastic to the insulation board that is attached to the foundation walls. This is not nearly as effective as taping/sealing the plastic to the foundation wall itself. This would of course require the insulation board to be removed, plastic sheeting installed (taped to foundation walls) and insulation board reinstalled (mechanically fastened) to the foundation walls. A lot of companies install the wrong type of plastic sheeting. Do not use a mesh reinforced plastic. The glue/binder used between the two liners breaks down from moisture and will make the entire space smell like cat urine. Thirdly, every encapsulated crawlspace should have some type of mechanical ventilation. There are varying opinions on what type of mechanical ventilation should be installed. Some companies just cut in a couple registers off the main supply air trunk thereby providing conditioned air into the crawlspace. I am not a big fan of this type of install because the duct system and/or size of air conditioning unit was not originally designed to condition this space (could negatively impact the comfort levels/air flow in the home by robbing air from the system). Also, in the more moderate times of the year, where the HVAC systems are not operating as much or not at all, the crawlspace air becomes stagnant. In my opinion, a dehumidifier and/or dehumidifiers should be installed in the crawlspace.
A properly installed system is not cheap. I recently finished my own crawlspace (2 years of back breaking work) and I spent upwards of $15,000 just in material and equipment. I installed 3 commercial sump basins and sump pumps, interior perimeter drains all interconnected to all three sump basins (clay soil all hand dug and removed 5 gallon buckets at a time), Radon system connected to all three sump basins, 3 inches of pea gravel base for a drainage plane (5 gallon bucket at a time), rubber membrane placed on top of the pea gravel and then a 12 mil white plastic sheeting placed on top of the rubber membrane. Two layers of 2" polystyrene mechanically fastened to the foundation wall. I installed an Aprilaire E130H dehumidifier and 4 Lomanco foundation vent fans. This gives me the option of not having to use the dehumidifier year round. In the more moderate times of the year (spring and faill) I shut the dehumidifier off and unseal the foundation vents and turn the foundation vents on. I over engineer everything I do on my house.
Crawlspace Ninja in Tennessee is a really good source of information. I would recommend watching his videos.
Efflorescence or a high water mark would be visible on the concrete. I suspect normal settlement compaction combined with foot traffic. Appears a telecommunication line was added after. Foot traffic on newly installed soil
You should hire a good local home inspector to investigate and possible give some advise on how to resolve the problem.
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Give Chris a call and discuss your concerns with him:
So, why did you encapsulate the crawl? Did you have moisture intrusion prior to encapsulation? If so, what measures did they incorporate to manage the intrusion?
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Morning, Nolo.
Opinion; The contractor you retained graded the bottom of you crawlspace with backfill. Not happy, have questions, call them. You should have a guarantee, hopefully.
Sinkhole? Just a though. I doubt it.
Here is what I observed from one of the images you posted.
To me, it looks like the contractor did not ‘infill’ the ‘backfill’ and ran out of backfill material while ‘leveling’ the crawlspace in that area. That area in question, soil adequacy.
Soil requires classification. The contractor mixed ‘soil classifications’ at that area and did not properly finish the job. My 2 cents remember.
Look at the clean 3/4" aggregate and sized sorted stones. That material does not separate and nor do 3/4" aggregate and sorted sized stones rise to the top of the soil surface. It’s the other way around. Aggregate and Stone settle/mix into soil over time.
As well I see excavator/dozer tracks.
Questions to ask: Is that native soil to the area or backfill soil brought onto the site.(Backfill Soil - Complete Basement Systems™) for excavated building sites.?
Other than that, Sinkhole. Just a though.
Opinions:
1: Get rid of the below grade roof water discharge!!! When weep tile pipes break, that water is injected into the soil causing depressions and even sinkholes over time.
2: Masonry clearance is required. 4" above grade.
3: No porous material next to the foundation. Water percolates through porous/pervious materials into the soil below.
Evening, Nolo.
Thanks for the reply.
Much appreciated.
That is why I referred you to the exactor tracks. When a the excavation was performed the bottom soil was left like this.
Should the encapsulation contractor have mentioned this to you?
You keep referring to the vapour barrier as encapsulation. Crawl space encapsulation is essentially, sealing your dirt floor in the crawl space using a vapor barrier, insulating the crawl space walls, and installing a dehumidifier. You pulled back the dimpled vapour barrier by unsealing it at the foil backed rigid foam board insulation, thus exposing partly graded soil.
Is there a dehumidifier?
As for the thermogram. Cooler corner-effect and soil temperature. I do not see any comparative numbers. What emissivity reading did you set your thermal camera to? Plastics: 0.90 - 0.97. Aluminum Foil. 0.04.
The thermogram you exhibited does not reflect any anomalies I would consider exposing seeing I am not a certified Level inspector.
Hope that helps.
Is it large enough for the space? Small off the shelf units from big box stores won’t cut the mustard. I’ve seen these companies cut corners on these units.
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Good point, Brian. As well, how is the captured water taken away. I would measure the crawlspace RH, Relative Humidity to see the dehumidifier if effective. Circulation system, a fan should be installed.
Maybe constantly running because it is too small? And for how long was it not working?
The way you can determine if it is working effectively is if it keeps the humidity below a certain percentage. (I recommend below 55% at minimum, opinions vary but no one will likely say higher than 55 is ok)
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What was the smell? Just typical mildewy smell? Or something more intense that led you to the specific area where the dip is?
Decomposing bodies will leave a smell and depression in the soil, thus the use of caskets in cemeteries!
Just sayin’. 
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That was my line of thinking. Well, I was thinking more on the line of decomposing tree roots or similar organic matter. But the dip is kinda body shape/size. 
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