Crawl Space Encapsulation, Drainage, & Dehumidify

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Jan 3, 2004
northern Alabama
I would appreciate input on the general idea of crawl space encapsulation & things to look out for as well. Our house has a half basement ~1400 ft2 & half crawl space ~1300 ft2. You can walk upright in the crawl space so access is good. It's not monolithic as the hollow block wall & 4000psi concrete slab are separate. Would it have been beneficial to use 5000 psi concrete (waterproof)? Anyway, the trench in the area between the crawl space & basement (where the wall of separation is located) is subject to water infiltration after heavy rains. I assume this is from an increase in the water table. The "fix" for the previous decade has been a 1/2 HP Zoeller pump with 2" PVC pipe ~ 60' away. However, this isn't the optimal solution for several reasons. One is that I don't want standing water even where the pump is as that creates too much moisture in the crawl space area. I don't have a good backup system for when the primary pump fails. There are 3 main contractors in my area that are viewed as doing it right for quite some time now (wished I had known when we built the house 10 years ago). Contractor A: $13,650 Contractor B: $7,800 (used to work for Contractor A) Contractor C: No return call although it's possible that I provided a bad number but they do have my email address. Giving them another chance this week but red flag already. I would also appreciate any particular advice on the subsystems below. Interior drain system around the crawl space interior perimeter: Both use NDS EZflow which is a gravel free French drain, i.e., fabric, lightweight gravel substitute, and pipe all in one package. It is made of 3 or 4 slotted corrugated pipe, surrounded by NDS poly-rock, and wrapped in a geotextile fabric. The NDS French Drain has been designed to take water out of the soil and pipe it to a safe discharge point. Encapsulation: along floor & up concrete wall afixed with butyl tape, fasteners with washers, & adhesive leaving a 4-6" gap at the top for pest control Contractor A: Basement Systems CleanSpace 20-mil moisture barrier Contractor B: WhiteCap 20-mil moisture barrier Foundation vent covers will also be installed like this from Basement Systems Sump pump: Plumbed separately to outside following slope of land ~ 30' away from house Zoeller 1/3 & 1/2 hp backup sump pumps vs. Liberty 1/2 HP sump pumps Pro Series model ST1050 Contractor A: Basement Systems Triple Safe (TSL) basin with lid but won't use the battery backup as the pumps are backed up by a propane generator Contractor B: 24" diameter by 36" deep plastic sump pump basin with lid Dehumidifier: Plan is to place one in the basement & duct to the crawl space with separate hygrometers to see if that can handle both areas (rated for 2,900 ft2 so possible). If not, then I can add another smaller one to the crawl space. Contractor A: SaniDry XP vs. AprilAire 1870F Contractor B: Sante Fe Classic vs. Sante Fe Force I don't see any point in insulating the basement walls as I'm in northern Alabama which neither contractor suggested. Contractor A also wants to sell a $350 EverLast PVC plastic door to better separate the crawl space & basement. However, I think that seems to be a waste as both areas should have the same environment once the crawl space is encapsulated. Thank you.
When dealing with hi water table the best way is to raise the level of the floor above the water table several inches i.e.. backfill with dirt , dig a sump pump pit then pour 4" concrete slab. Get a Zoeller pump plumbed to outside and you are done. The interior drain system when dealing with a hi water table, the pump will be running constantly as the pipe will be sitting in the raised water and you will be pumping against the tide. French drains clog.
I have to think that any solutions will have to done on the outside perimeter of the house/crawl space so that the water doesn't come in the first place. If you have a high water table then I don't know what to do there. Do you have a perimeter drain all around your basement walls? Perhaps framing in a parallel wall that would seal off the crawl space might help. If there is a perimeter drain then leave the corner of that wall open? If water is no issue elsewhere in the basement then no need for the opening. You are losing heat out through that crawl space as well. Just a thought. Without seeing it, figuring out a solution is difficult.
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Ben, sorry if I missed it, but is your goal to use this crawl space as living space?
Vapor barrier under any concrete slab for sure. If you're exposing the foundation walls slap some waterproofing on the concrete while you're there. Water table is easy, dig a hole outside. Unless you're waterfront I sincerely doubt that though.
I agree with Pimtac. Do you have a place on the exterior you can slope to a discharge point, i.e. a storm inlet or creek or street?? I would get a price to put a French drain on the outside of the house. Excavate down to the foundation with a trench 24” wide. Wrap the ditch with filter fabric, install perforated pvc pipe (not that slotted plastic black junk) and backfill with stone to within 6” or so of final grade and if there’s no place to slope buy a prefab sump and put in a pump.
Q: What's a basement? A: It's when you dig a Well, then spend the rest of your life trying to keep water out of it.
I have a lot of experience in water in basements. I live in Minnesota, probably 1/3 the homes have some type of issue. If I were you, I would have them excavate around the perimeter of the foundation, then pipe and gravel to one central location, pump away from there. Don't do the interior thing, by then you have water right under your slab. You want to capture and pump it away before it is under your home.
The biggest thing about an interior drain is to ensure that the pipe is laid deep enough and can draw the water to an acceptable point. I find this guy's series of videos to be enlightening.
Sorry for the delayed reply. There is a block wall between the crawl space & basement with a plywood access door. georgemiller, How will the pump be running any more after this work than it does now? I don't quite understand your comment. Are you saying to concrete the trench in the crawl space? Would monolithic foundation averted the problem? JTK, 1st goal is to prevent fungus & mold from having a hospitable environment. 2nd goal is to have a good sump pump system with proper sealed basin & backup with dual pipe outlets. 3rd goal is to remove musty smell from basement. 4th goal is to use the crawl space as storage & better utlize the basement with less fear of flooding. DdDd, Foundation walls already had waterproofing applied when the house was built. I don't understand your comment about digging a hole outside. How does that help? bcossa, French drain was installed around perimeter of house. Not very feasible to dig outside the house as that would require demolishing a $15k deck & replacing. I would prefer to fix from the outside as well & that was my first thought, but price approached $30k quickly.
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Anyway, the trench in the area between the crawl space & basement (where the wall of separation is located) is subject to water infiltration after heavy rains. I assume this is from an increase in the water table.
Are you sure it's a high water table vs. surface water moving towards the basement wall? I eliminated our block wall basement water leaks by simply diverting all outside water away from the house. Labor intensive, but only about $300 in materials. - I installed a 2' wide "flashing" around the house perimeter, made of pond liner covered in stone, with a 10% grade (2"). - I made sure that all water beyond that 2 foot apron also drained away from the house. - Of course, gutters with good downspouts are required. Get rid of foundation plantings. Is the under deck area properly drained?
No I'm not really sure of anything. smile I don't think that this crawl space solution proposed is really the best option. The water intrusion doesn't happen when it's dry outside but rather once there has been a substantial amount of rain, say > 2" & ground is already saturated. The under deck area is closed in which I now understand needs to be open. All downspouts are routed well away (at least 30') from the house.
I see lots of people do landscape projects at the base of their home that essentially creates a gutter there to collect rain water and divert it down towards the basement wall: [img][/img] Take a close look at every nook and cranny around the outside of your home. Lots of examples if you Google "water draining towards house". I wish you the best in finding a simple, affordable solution. Take care.
Yeah, we have nothing on that side of the house where the water infiltrates as it faces the woods. I wonder if the poor drying of the area under the deck causes it to be worse? I don't think it would be the root cause as water shouldn't get in if everything is working properly. And that makes me think that the footer drain is not working properly.
Some photos would help. Don't have basements here in Cen. Tx. However I've never liked that black, corrugated "flex" pipe. First, it is too easily crushed by clay + rock "soil" here. Second, without a perfectly graded base, it'll form divots, low spots which will collect water. Rigid PVC won't do this. Third, the small "corrugations" collect water and increase resistance to flow. Smooth pipe won't do this. Further, those little corrugations will collect water & mosquitos will breed there. Very bad here; maybe not in your area. Even thin-wall PVC is unable to withstand the heavy load of rock + clay + hydraulic pressure here. I had to replace such a pipe leading from the septic tank to the drain field junction, about 22' away and 2' deep. The above combination had just crushed it; looked like binoculars when viewed edge on. Pipe completely collapsed. Replaced with 4" Sch40, properly graded and backfilled with sand. Caveat Emptor.....
I say that there is a French drain around the footer, but I'm not so sure of that. If not, then that would seem to be the root cause, but I would expect to see water intrusion all around so perhaps that's not it. Photos of water leakage, sump setup, or what?
I'm in North Alabama and had this done this summer. I can probably name the ones you have talked to. I used Crawl Space Doctor in Madison, Al. It was probably overkill, but I sleep better and feel like they did everything agreed on. The really big company I decided against after doing as much research as I could. Your mileage may vary. You need to take a good look and determine if it's water table rising, water running down a slope and hitting your foundation, french drain may help this, are down spouts dumping water back against the foundation? They are all going to try and sell you as much as possible so take your time. Hope this helps and I will answer any questions I can.
AFS is the big company. Allied Crawlspace in Decatur is another one. He was really good about not trying to sell more but rather let's just try Phase A & see if that fixes it & doesn't require Phase B type of approach. I've tried Ram Jack but no dice yet. I'll try Crawl Space Doctor as well. Thank you. Down spouts aren't dumping water back as they are piped well away to a (slight) downhill from the house.
If the water table reaches above the floor of the basement, and it is a deep water table I don't think anything done on the outside is going to stop it. The water will creep up from below and go where it wants to go. At least that was the consensus of everyone we talked to for our house that had that exact situation (and we talked to quite a few contractors). It was a weekend home by the shore. I had a couple of commercial sump pumps that ran 24/7 in the several months of the wet season (some years it was more than a few months). The pumps needed replacing after 5 years or so. Eventually I sold the home with full disclosure on the water intrusion. It was a hot real estate market, so the price didn't suffer. However it took a while to find a buyer who wasn't turned off by the situation. If we had wanted to keep the home, the proper solution would have been to move the mechanicals to ground level in an attached structure to the house and fill in the basement with some sub soil.
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