Insulating under floor

Got my crawl space dug out so I can move around. Want to insulate w/ R19 bats. Joists are 2x6 approx. 24 inches on center. What's the best way to hold up the insulation? Can't staple the flanges since they need to face up towards the heated surface. Can't use the "wire struts" since the 24" on center is only approximate. ( 1/2 inch). Was considering cutting strips of Mylar and stapling them to the studs under the insulation.
Any other thoughts????
Thanks!!!
Ivan Vegvary
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The wires don't need to be precise fit. They bend, spring like. All you need are wires longer than the largest distance. You can even use them diagonally.
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The -1/2 is no problem, but if the spacing is over 24 those wires don't hold well. How about stapling chicken wire across perpendicular to the joists?
Jim
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wrote:

No matter how you put them up, you need chicken wire with small openings stapled over the insulation to keep small animals out as they love to nest in accessible insulation. The paper flanges won't keep anything out. They can make quite a mess.
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If you EVER have moisture issues, fiberglass batts are a bad choice. once they get moist their R value drops a lot.
closed cell expanding spray foam costs more but isnt effected by moisture
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With fiberglass R value drops proportionatly as it gets colder below 32f, at -20 it might be 20-35% less effective, Foam excells in keeping R value stable, it also doesnt settle. R value can be double that of fiberglass, it keeps out moisture from your home and cold or hot air infiltration. It should be painted to keep from oxidising and covered in small wire as rodents will burrow. R 7 foam may be 3 times as effective per inch, than fiberglass at cold temps. But there are many types of foam to pick.
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The flange is stapled and at the bottom you keeping moisture from entering, dont think everybody has beeen doing it wrong on millions of houses for decades.
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wrote:

The flange is stapled and at the bottom you keeping moisture from entering, dont think everybody has beeen doing it wrong on millions of houses for decades.
Thanks Ransley, This is in a crawspace between the first floor and earth. I would love to simply staple the flanges BUT have been told the 'paper' always goes up toward the conditioned (heated living space) side of the space. What gives? Can I install it "paper down"?
Thanks,
Ivan Vegvary
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In the attic heat rises so does moisture, in a damp crawl moisture and cold incomming air rises to your inside. Ive seen quite alot of crawl spaces and open buildings where it was done this way with no issues, and mine maybe 80 years ago, but crawl spaces were dry, its the only easy logical way to do it, and the paper down keeps air from going up through easily. Read about how fiberglass looses efectivness at very cold temps, paper down could help that issue. The Attic issue is to keep attic wood dry so you dont mold then rot your roof away in a few years with tight attics. Celulose and unfaced insulation without vapor barrier are used all the time in attics. Staple it and be done, but foam is really best if you have the $
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Ivan Vegvary wrote:

Hi, Friction fit will do. I did it at my cabin crawl space and no bats fell off. I used R20 fiberglass bats 16 in. OC between joist.
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Polystyrene or similar pushed in as a tight fit will do the job. You need at least five inches thick to do a proper job.You must ensure that you leave no holes, as heat always moves to cold and your heat will move out through those holes. Then the problem is that the floor and joists are poor insulators in comparison to polystyrene and your heat will leak out through the wood joists. The best solution the that is insulate above the floor. Perry
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Wood had a fairly high r value it is not a poor insulator. Insulate above the floor, that idea is a laugh. His heat wont "leak out" the joists, even less so than fiberglass batts. Go look at log home R values. He has about 6.5" of wood.
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1x2s work good. Or even some landscape fabric. It breathes well. or both
s

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