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Maxwell Robinson
Posted: Jun 27, 2011 11:19 AM
New build. Foam questions
I am building a new home on the Gulf of Mexico in Louisiana. It is on pilings 14ft off the ground.First floor is 1600 ft and second is 1000ft. I have 3 1/2 tons of a/c on firat floor and 2 1/2 on second floor. Exterior walls are 2x6. The roof is metal. I have asked at least ten insulation companies and individuals how to insulate this home and gotten ten different answers. From all closed cell , or all open cell , or closed cell under house and open cell in walls and fiberglass on ceiling of second floor. That i must leave ventilation and i must close all ventilation. Please help.At this time , unless i get some clarity, my only option is to go all fiberglass.
Posted: Jun 27, 2011 01:33 PM
I am in new Mexico and primarily spray open cell foam. But in your case you would definitely want to go all closed cell foam, in the roof the walls and the floor. You are in a very humid climate and would have moisture issues with open cell foam or fiberglass I am afraid. If it was my house, I would use closed cell foam.
Terry Adams
Posted: Jun 27, 2011 02:23 PM
Closed cell 2" under 2" in the walls and 3" in the roof is the best option, however if its between open cell or fiberglass go with open cell.
Make sure your a/c contractor sizes for foam, 6 tons for 2600sf is high. Scratch any contractor that does fiberglass and cellulous off your list because they just want to sell you anything they can. Get references.
Maxwell Robinson
Posted: Jun 27, 2011 03:25 PM
If I am locked in on the 6 tons should I go with a different insulation?
John Shockney
Posted: Jun 27, 2011 07:47 PM

There is another concern besides moisture in your location: Hurricanes and because of that I would recommend 2# closed cell foam because it will add the structural strength that is needed to make your home as hurricane proof as possible.

After the last hurricane that hit Miami their research lead to the new 100mph 2x4 test standard that is now required there. That is all: doors, windows, and walls must survive an impact with a 2x4 traveling at 100mph without it opening a hole, this is because they found in their research that when wind carried debris opened a hole in a wall the pressure would then lift the roof off the house and the resulting water damage from rain caused more homes to become total losses.

2 inches of 2# closed cell in your walls will pass the 100mpn 2x4 test!!!

The foam under the elevated floor should also be closed cell due to the possible moisture issues.

Due to the possible high winds I would recommend spraying foam on the underside of the roof in a sealed attic system this also reduces the wind lift and possibility of the roof blowing off, this could be done with open or closed cell foam but I would probably spray one inch of closed cell to glue everything together followed by open cell to achieve the required R-value.

From my 30+ years in the HVAC industry I will say that with spray foam 6 tons of A/C is probably overkill and the system may not run long enough in mild weather to properly remove the moisture from the house, but since there are two systems you can compensate for this by only running the upstairs A/C and just running the fan constantly on the downstairs unit. But it would be best to install 2-two speed heat pumps with a dehumidify cycle and programmable thermal humidistat. But if you are locked in on the A/C units please don’t skimp on the insulation you can live with the A/C for its ten or so life and replace it but it is hard to replace the insulation!!

You can email me directly at airpro@gotsky.com if you need advice on your HVAC system or anything.

Maxwell Robinson
Posted: Jun 27, 2011 09:55 PM
The A/C they installed yesterday are as follows, 1st floor (1600 sq ft) is 3 1/2 ton two speed with a humidity setting. The 2nd floor (1000 sqft) is a straight 2 1/2 ton unit. Both use heat strips. We do not have much need for heat at a summer fishing camp. I'm worried about moisture when we are not using the house and if we should run fresh air to the intake. I could possibly get them to install a 2 speed on the 2nd floor if that would solve the problem. The A/C installer is a friend, but has not done any foam homes, only commercial. I started researching foam insulation a little late in my build process. I wish I would have planned from the beginning.  
Terry Adams
Posted: Jun 28, 2011 12:26 AM
I was thinking the same thing but not being a a/c guy like Airpro didn't want to steer you wrong. Would a dehumidifier running when you are not using the camp work (Airpro)? Is your camp in the rigolets ? I have done work in that area before. www.nexgeninsulators.com
John Shockney
Posted: Jun 30, 2011 03:24 PM
By using a two speed A/C it would be very hard to be oversized and the electric heat strips will come on in stages too so you should be ok. Making the upstairs unit a two speed would make the system ideal.

You can control moisture by two ways one is ventilation and the other is by mechanical dehumidification, this is done by you’re a/c or a dehumidifier.

The biggest problem with a summer fishing camp is when you close it up for the winter and if you don’t heat it to the same temp that that it was when you leave you could have condensation/moisture problems during the unoccupied winter time. If the house is 70deg and 50% humidity when you leave and you set the temp for 50deg through the winter as the house cools the humidity will go up to over 100% (dew point) and the water will condense on all the cold surfaces.

Probably the most economical way to control the moisture in the house is to use one or two portable dehumidifiers making sure that you can route the water to a floor drain. The dehumidifier will remove excess moisture and add some needed heat to the house.

Also I would point out that by using spray foam you will create a closed environment like the inside of a refer that will be easier to control the moisture and I would not recommend going the ventilation route to control moisture in an unoccupied house too many times the weather conditions will cause more moisture to be brought in than is vented out.

Hope this helps


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