After the flood…A Sealed Crawlspace?
I recently posed a question about a few homes damaged by Superstorm Sandy in New York.Homes are near the coast,but neither experienced flooding for at least 50 years prior to the previous 2 years,this year being severe,flooding the main levels of the living area,causing major material damage,not structural.Both homes are built on crawlspaces with poured concrete foundations with a couple of cast-in-place vents.They have concrete “rat slabs”,which I was to find out were actually retrofitted long after the houses were built in the 1950s. Both of these “rat slabs” are approximately 18 inches feet below grade. The wood lumber floor joists are approximately 28 inches above the slab. Both homes were insulated with r-19 fiberglass insulation in the joist bays,but in some areas it was completely missing.The soil in this area is sand,it drains extremely well.When these home were flooded with about 4 feet of sea water,the water came in,and just as quickly,went out,leaving behind a full crawlspace of water and about a foot or two on the main level.Within a few days 75% of the water had drained downward in the crawlspace,with only less than a foot to be pumped,once I got around to getting a gas powered pump (electric was out for weeks,and gasoline was scarce).These crawlspaces are not designed to be “flow through”,as may be required of a structure built on the immediate shoreline,but more or less a mini basement.
Having giving it some thought for a while,I think the smart move would be to remove the vents,seal them up with concrete,ditch the fiberglass and insulate on the inside of the foundation walls,air seal everything,and connect the crawlspace to the conditioned space with vented openings.Then ventilate the crawlspace with a small continuously running fan from the crawlspace to the outdoors.I will be removing and replacing the subfloor also,so access will be good.One thing I may not have,that is recommended for this system is poly on the floor(it is not under the rat slab,and not having it actually helped the flood water drain downward,I believe.Neither crawlspace was damp this winter.
I would appreciate suggestions.
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