How support roxul 27" OC joist


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Old 01-28-19, 07:46 PM
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How support roxul 27" OC joist

I want to insulate the underside of my floor between the floor and the crawl space.
I'm going to use 6mil vapor barrier on top of the joists with osb on top. I will then put roxul underneath. Roxul only comes in 24" or 26" but my joists are 27" OC. How can I support the roxul so it start up and also fit it into this spacing?
 
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Old 01-28-19, 08:11 PM
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They make fabric you can staple up to the bottom of the joists first. It's breathable. If you can't find it, certain types of woven landscaping fabric work well. I would do that first and then do the osb after the floor is insulated.
 
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Old 01-29-19, 07:29 AM
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For odd dimensions I cut the Roxul to the desired length (plus a 1/2" or more) and fit them crosswise. Roxul fits together nicely and should stay in place until you get some support from below.

Bud
 
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Old 01-29-19, 10:33 AM
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The joists are 12" deep.
should the net be halfway up the joist to hold the wool close to subfloor or at the bottom?
 
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Old 01-29-19, 10:42 AM
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I would staple it to the bottom and fill it up!
 
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Old 01-29-19, 01:33 PM
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That`s a lot of roxul! Is roxul 3inches thick? 4 layers of roxul in that space x a few hundred sq ft
 
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Old 01-29-19, 01:54 PM
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Well is the crawl space insulated? If not you want all the r value you can get!
 
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Old 01-29-19, 06:24 PM
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It's a crawl space where you open the window vents in summer. I've read many articles but it's not clear whether I should insulate the wall or the floor.
many of these articles say insulating the floor won't help?
 

Last edited by qwertyjjj; 01-29-19 at 07:17 PM.
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Old 01-29-19, 06:29 PM
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Yes, well I see the answer is "no, the crawlspace is not insulated."

That means you put as much R-value in the floor as you can to keep everything above the insulation warm during winter months.
 
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Old 01-29-19, 07:17 PM
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Will fiberglass be ok instead of roxul? It's half the price.
 
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Old 01-29-19, 07:42 PM
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Its your project. You have to decide. Roxul has more r-value per inch, but if you want to save money, yes, Fiberglass is less expensive. I doubt you will be able to feel the difference between R-38 and R-48.
 
 

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