Replies

1. GBA Editor
   Martin Holladay | Sep 26, 2011 02:56pm | #1

   Dan,
   No, I'm sure that the use of closed-cell foam will not contribute to a house floating away in a storm.

   If your friend's house is inundated in the future with another storm that leaves 1 foot of water on the first floor, there will be lots of damage. It is very probable that any insulation -- no matter what insulation is chosen -- will have to be removed and discarded after such a flood. However, if the flood is brief, perhaps closed-cell foam might remain -- but I'm doubtful. Especially if there is any wiring in the joist bays.

   If it matters at all, open-cell foam is more likely to absorb water than closed-cell foam. But let's face it -- any time a house is flooded with one foot of water, the house is in trouble. So don't fool yourself into thinking that choosing the right insulation will help much in the future.

   Disclaimer: I'm not an expert in restoring flood-damaged buildings, so I'd be happy to hear from an expert willing to chime in.

2. 
   user-659915 | Sep 27, 2011 08:06am | #2

   Like Martin I'm no expert in flood damage repairs but I'm not a fan of any kind of foam insulation in the joist bays, and the consequences of flooding - whether from a rare hurricane or a common plumbing failure - is one of the reasons. Pulling out sodden batts is a tedious enough task but nothing compared to scraping foam away from all the wires, pipes and other encumbrances in that space. And that's what will have to happen, because I don't see any way those joists will dry out in any reasonable period of time while they're still encased in either open or closed cell foam - leaving that stuff in place and hoping for the best would be a hidden rot and mold nightmare waiting to happen.

   Of course Irene was an unusual storm and the next flood MAY never happen. But has your friend considered that now, with the house all torn up, might be an ideal time to jack the house up out of danger? Down our way this is a common response to a home that's too low to the ground in a flood zone (this kind of work is commonly done by house-movers - and it's great fun to watch the actual lift). One or two courses of CMU, maybe combined with grade adjustments on the exterior, could keep the first floor of the home safe from the drama, cost and disruption of a repeat occurrence, and give a more functional dimension to the crawl space as a bonus - 24" is barely adequate if you have any kind of mechanical systems down there. Follow up with either batts plus foam board to insulate and air-seal the joist space - easily removable - or perimeter insulation to the foundation walls, whichever is more appropriate for your friend's situation. Spray foam is one of the most expensive insulation options out there, and the money saved by going to one of the many suitable alternatives can contribute to a more effective, long-term solution to the flooding problem.

3. 
   user-659915 | Sep 27, 2011 08:14am | #3

   Oh and by the way - if it's an older home without proper foundation bolts to tie the floor system to the foundation wall, yes, foaming the floor system could indeed contribute to displacement of the home - perhaps not so much floating away, though we've all seen the videos of that happening in extreme cases, but even a minor displacement of just a few inches can make the home much more expensive to fix.

4. 
   user-659915 | Sep 27, 2011 08:23am | #4

   Here's an excellent illustration of what can happen with spray foam and wet wood: from Carl Neville's current post on inspection nightmares.