Insulation, Radiant and Vapor Barriers - Insulating walls in a flood zone

I am going to purchase property next to my cottage that is located in a flood zone. The house has had water( 26 inches) in it twice in the last 16 months. Most of the house will be torn down except for the garage and two other rooms. I am going to fix up the two rooms and would like to insulate the walls with something that is waterproof in case the river rises again. Hopefully I can just wash the mud off. Also looking for suggestions on what I can put on the walls (up about 36") that can be easily removed cleaned and put back, and is also water proof.

Closed cell spray foam for insulation and 4x8 sheets of that plastic stuff they put in food prep areas.

I spent about 5 months in Louisiana and Mississippi looking at damage and estimating repairs. I evaluated over 600 homes plus the neighboring homes and those I drove past or saw on "sight-seeing".

What I learned:

1. Don't build where you know it will flood. Unfortunately some people do not think or learn. If it flooded once, you can be guaranteed it will flood again for the same reason or another one. You have apparently chosen to fight Mother Nature.

2. If you build in the wrong place, do not build at an elevation where the house itself will flood. Raise it so the floor is high enough. It is cheaper in the end. Even when flooded, the homes on piers or elevated ground came out much better than those built at the local, traditional elevation.

3. Use the right materials. If it will be flooded, do not use wood. There many consequences people do not realize. If you absolutely have to use wood, use pressure treated since the wood will never dry out due to lack of heat and circulation. Use nails and fasteners that will not rust (not just something like galvanized). The smart people renailed everything because they knew that if it did not dry out (inside the wood) in 4 to 6 months, the fasteners will rust.

Count on your loose, bulk insulation (fiberglass and cellulose) being useless. Fiberglass does not absorb much moisture, but it wll hold enogh moisture to drop the ceiling on the floor. If fiberglass has as little as 1/2 to 1% moisture it will lose over 50% of its insulating value. It wil hold enough moisture to guarantee mold on wood and gypsum board in a couple of days if the conditions are right.

The only insulation to use where exposed to possible flooding is rigid extruded polystyrene.

The only homes that came through the floods good were solid masonry or concrete. These suffered little long term damage and were the easiest and cheapest to clean up and repair. The different was even greater when it came to wind damage. - It is good that wood is a renewable resource, since it has such a short life. It is fortunate that the rest of the advanced coutries in the world do not use wood as their primary building material for residential housing or the wood price would be up 2 to 5 times what it is now.

It is sad to see how many people did not realy think about what they were doing when they built or lived where they knew it would flood. - Try not to make that mistake and at least move up in the world.

Dick

What about moisture trapped behind the rigid foam insulation? Would there not be mold and mildew issues?

The insulation was the last thing to consider after they other desireable approaches were NOT taken. Location and elevation are basic items to eliminate damage. If you don't do that, minimize the damage by eliminating moisture susceptible materials like wood and bulk insulation like fiberglass and cellulose.

The foam is more desireable than any other type of insulation, but it is still possible for the wood and sheetrock to mold. The foam just does not hold the moisture in contact with the undesireable materials (wood, sheetrock) for a long period if you allow the living space to flood. Fiberglass does not "absorb" moisture, but it will hold the moisture that is absorbed by the wood & sheetrock or causes mold.

Anytime you build where there was a flood, you can expect another and should plan ahead - good move John!

Also, if you expect a flood, locate your outlets higher or just plan on replacing all fixtures (not necessarily wiring). It was a standard thing to do in LA, MS & AL whether it was salt water or fresh water.

Dick

Outlets was my next question. How much higher? They do not look very aesthetic up high, but certainly safer.

Do you have to replace the wiring after a flood?

The reason I am curious is because I own a cabin in the mountains on a river. It has flooded once in 1985 in a 100-year flood before I owned it. Thus, I always worry.

Regarding outlets - If you raise them, it is up to the owner and the balance of appearance and likelyhood of a flood. You do things differently when you have 2 floods in 16 months than you would for one flood every 100 years.

After the hurricanes and flooding, it was common to replace all the outlets (easy and cheap), but not the wiring. More often in salt or brackish water than freshwater. Most of what I saw was water less than 4 feet deep, so switches did not get wet. If they did, they were also replaced. Smart people renailed while the wall or floor was open to dry.

I wouldn't bother to change a structure to meet a 100 year flood. If I was going to buld new one or make a major addition, I would factor a flood in regarding the location AND elevation. In any case, I would question the choice of materials. Despite or because of the frequency, Florida rebounds much faster since the common coastal masonry homes are much more storm resistant and easier to clean and restore.

Disasters are a part of life, so you just have to minimize the effects.

Dick