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Old 05-16-2008, 02:49 AM   #1
Floating in the Gulf
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Insulating wood floors

I have a 75+ year-old cypress house in Southern Louisiana. It is pier and beam, with a 2 1/2' crawl space, which is open to the outside world. The house has hardwood floors, but no subfloor under that. (Yep, you got it, planks of cypress, laid across crossbeams.) The floors are beautiful, and I have zero plans to carpet. There are, however, a few places where I can see daylight under my house, at the right time of day, through thin gaps between the boards. During the winter, drafts come up frome those gaps. No insulation will make wood floors "warm," but I would like to fix the draft problem, and add some insulation under the floor of my house.

Most things I have read talk about putting some type of batting insulation (ugh) with covering up under the house. I was wondering if any of the spray-foam insulations out the (i.e. TigerFoam, or the like) would work. Or maybe those 4x8 sheets of foam insulation. Though I suspect, for what I need to do, the spray foam might be a lot easier.

Any comments would be welcome... particularly if anyone else that has had this problem has some knovel solutions...



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Old 05-16-2008, 05:49 AM   #2
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I would think if you see day light through the floor now ,the spray foam will seep up into the gaps and then you will have some mess on you hands.
Personally if it was me , I would chose to use fiberglass batt insulation and then nail ridged foam across the bottom of the floor joist to keep the insulation from dropping down.
you could even cover the bottom with tyvek stapled to the joists and then the ridged foam board.


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Old 05-16-2008, 02:36 PM   #3
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Unfaced batts are the best idea because, while you can use faced batts, this type of insulation is harder to keep up and doesn't have rigid ends. Any loss of integrity will break the vapor barrier and make your wood floor insulation and the floor itself vulnerable to ground moisture. The batting can be held in place with thin metal rods, called lightening rods. Spacing the rods every 18 inches are the easiest way to hold your insulation in place. You can use plywood or lattice boards, but this will cost more for only slightly better performance. You can also use netting, but this can be a lot of work.
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Old 05-16-2008, 08:25 PM   #4
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Moisture barriers and wood rot?

Ok, so right now, there is no type of moisture barrier under the house. And I have crawled around under my house extensively, and there is no rot down there at all. Probably because the crawlspace is open, and gets good airflow? But in any case, a have to wonder if putting up anything that could retain moisture (really any type of cover that would act as a vapor barrier) would be worse than leaving it open. It gets incredibly humid down here... and I can envision a scenario where the moisture would get in between the vapor barrier and the floor... and then not be able to get back out, leading to my floor rotting. Like I said before, there is nothing down there now, the house is 75+ years old, and nothing has rotted yet...

Last edited by krankykitty; 05-16-2008 at 08:36 PM. Reason: Typo
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Old 05-17-2008, 07:38 AM   #5
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I'm no pro, but my first thoughts would be to use foam insulating board cut a little too big to wedge up against your cypress floor boards, and then spray in the expanding closed cell foam. The foam sheeting would keep the spray foam from oozing through the floorboards. Do you have to tack in little 1x1's along the floor joists for the spray foam to hold on to? I haven't used it yet, so I don't know.
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Old 10-31-2008, 11:30 AM   #6
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One of the main problem with insulating the under side of the house is moisture. If you are going to put insulation make sure you have good airflow. if you don't have vapor barrier, its okay as long as you have something to remove the moisture. Usually, if you have furnace, water heater running, then you won't have to worry about moisture because they suck the moisture from your basement through their exhaust pipe while they are running. if not buy a dehumidifier. either way you have to get rid of your moisture.
Life is tough, but it is even more tougher when a person is stupid.
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Old 10-31-2008, 01:25 PM   #7
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Ahh the south,,, I lived in Lake Charles for 5 years.

I miss the boudin and tasso!Just thinking about it makes my tongue want to slap me to death!

I would take some regular R22 installation and tack it up under the floor and then run some 1/2 exterior grade plywood right over the joist, just leave your access point for plumbing and wiring open.
This will help you control you cooling cost for those hot humid August nights and keep the cold out for the Feb weather and it will be better than the Gauthier's or the Benoit's place next door
Now if a freeze hits like it did 1997 all bets are off.
There are better ways to do this, just not many easier ways.
The ground moisture will never affect that ole Cypress.


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floor , insulation , piers

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