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Community and Q&A

Encapsulation in flood zone

HomeInFloodZone | Posted in General Questions on

I live near the Waccamaw River in SC in a flood zone. We just recently purchased our house less than 6 months ago. We are having issues in the crawl space with humidity/moisture. The crawl space is about 3 ft high from the ground to the floor joist/bottom of the homes floor. We plan on having the crawl space encapsulated. My question is when they put up the vapor barrier on the foundation walls what do we do about the vents in the crawl space since we’re in a flood zone? Everything I read said to cover them up but those homes weren’t in flood zones. I looked up the insulated flood vents and those are ridiculously priced at about $100 (if I’m lucky) each and we have about 12 vents throughout our crawl space! We do plan on buying a dehumidifier and there’s already a sump pump down in the crawl space. Who ever owned the home before us went down there and had no clue what they were doing and tried to encapsulate the crawl space theirselves. They used what looks like to be just a regular plastic barrier, they used the wrong glue to try to fasten the barrier to the foundation walls and it‘s falling down off the walls, they didn’t tape the seams together on the ground there just overlapping one another, they installed the installation with the paper facing the ground and not facing the floor to the house and the list just goes on of all the things they did incorrectly. Plus, I read that it’s better to insulate the foundation walls instead of between the floor joist. The house was built in 1987, it’s an all brick home and the home flooded for the first time in 2018. We wanted to raise the home on pillars but we’ve never heard of a brick home being raised on pillars 😂 Please help. Thank you for your time.

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  1. 730d | | #1

    Can you fabricate foam covers and install them like like a storm window so that they can be removed if there is a flood?

  2. Expert Member
    Peter Engle | | #2

    My favorite flood vents these days are called Flood Flaps ( They are made from plastic/rubber rather than stainless and cost about 1/2 the price of the stainless ones. Plus, they make air-sealed flaps that still automatically open in case of flooding.

    If you can't replace your flood vents or don't want to, the easiest solution to encapsulation is to insert friction-fit foam in the openings, from the inside. Foil-faced polyiso works well for this. Lightly caulk around the foam to seal it in the opening. In case of flooding, the water pressure will easily blow the foam out of the openings. You will have to replace the foam as part of cleaning up the crawl after the flooding.

    You also want to consider the cleanup process as part of your plans. Plastic sheeting becomes a nasty mess when flooded. if you protect the plastic with a thin concrete slab, cleanup consists of simply hosing down the area. I really like Dow Thermax for wall insulation if you're in a flood zone. It will float, so you have to pin it to the walls pretty well, but the aluminum facers are easy to clean. Polyiso does absorb water, but it seems to drain with no harm done.

    And yes, you can elevate a brick house. You could do it on piers if you wanted, but it would look odd. You could do concrete piers and an elevated grade beam, and set the house on that. It's more common to lift a brick house and just build a taller brick foundation up to the new elevation. Neither approach is at all cheap, but if your first floor is below your local base flood elevation you should certainly consider it.

  3. walta100 | | #3

    The way I see it you have 2 choices with a crawlspace the old fashion way is to vent it and connect it to the outdoors or you can condition the crawlspace and connect it to the indoors. Pick one or the other anything in between is very likely to sometimes have parts of the crawlspace fall below the dew point of the air in the crawlspace condense the water out of the air get wet and grow mold and rot the wood.

    The word encapsulation is a red flag it is the language of slick salesmen trying to sell you half a job.

    You may find this link interesting.


    1. Expert Member
      NICK KEENAN | | #4

      Yep, to paraphrase Yoda, "seal or not seal, there is no try."

      I don't think it's realistic to seal the space and expect it to be able to survive a flood unscathed and unchanged. I would think in terms of things that can be submersed and survive, and things that will just be replaced. Friction fit foam covers on the existing vents can be replaced.

  4. Expert Member

    You might be better off concentrating on insulating and air-sealing the main floor and leaving the crawlspace vented. Then all you need to do is lay poly on the ground inside the crawlspace to reduce the humidity, and there is little remediation needed if it floods again. There is no advantage to taping the seams of the poly if it is being used as a vapour barrier, only when it is also an air barrier.

  5. bennettg | | #6

    As Malcolm noted, you could set the air and thermal barriers at the bottom of the floor joists or the crawl floor/walls.

    I think I would start with "flooded in 2018". Hurricane Florence. To where? Above the bottom of the first floor joists? Where's the base flood elevation? If, in your estimation, the level is up into the joists or first floor, it seems like raising the house might be appropriate. How far would it have to be raised?

    Your house is "all brick". Is the foundation concrete block (CMUs) supporting the floor joists? How complex is the shape of the house?

    I watched as our rectangular ranch house was moved and relocated, including the brick chimney. The movers punched holes in the foundation, slid long beams under and cross beams every n feet, jacked it up and away it went. At the other end, the house was set on cribbing above the eventual foundation level, the new foundation built, and the house dropped onto it. I'd think something similar could happen with your house, with the existing foundation being added to, plus new steps, etc on the outside.

  6. George_7224612 | | #7

    The climate crisis isn't going to do SC any favors. We can expect flooding to be more frequent and worse in the coming years. If there's any way you can manage it, It would be in your best interest to raise the house.

  7. bee_clark | | #8

    Regarding the expensive flood vents: perhaps you only need one or two to relieve the pressure of rising flood water, while the other vents can be sealed permanently.

    Between floods, do what you can to manage humidity by taping the ground cover, maintain the sump pump, air seal penetrations, suspend a dehumidifier between floor joists.

    It seems like you already researched and made a plan. Please let us know what you do.

  8. JC72 | | #9

    Air seal the underside of first floor. Since your ground floor already has insulation inside the crawlspace I would replace sections of bad insulation and then apply 1" of foil faced insulation (seams taped) to the underside for the floor joists and call it a day. You'll seal off the floor from air leaks and would be cheaper than pulling everything out and hitting it with closed cell spray foam. By doing this you don't really have to worry about the condition of the crawlspace vapor barrier, buy a dehumidifier for the space, nor flood vents.

    HOWEVER, if flooding will reach the floor joists then I would pull out the fluffy insulation in there now and hit the joists with closed cell spray foam (ccSPF) instead. ccSPF will keep the joists dry and less likely to have to worry about mold.

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