# Roxul mineral wool batts: tough to retrofit



## bluefoxicy (Nov 5, 2012)

I'm ripping pieces out of them, packing them in, tearing off overly dense spots that didn't settle right and stuffing soft spots with them.

I'm trying to retrofit a poorly insulated wall. R-19 5.5 inch fiberglass, faced, 1 inch all around so convection transfers 100% heat around it and the insulation has an R value of 0. Wonderful job these moron contractors did; I don't even know what I'm doing and I did _far_ better with the 1 inch of spray foam (Foam-It Green, for the curious) I treated the entire inside of the sheathing with.

So yeah. Poor insulation job, major gaps around the batting, space between the batting and both the sheathing AND drywall (it was able to flop around, so it would sag at an angle)... and here I am trying to redo it.

My assessment so far is:


This stuff is ridiculously hard to stuff behind partially-obscuring drywall, cross-braces, and electrical wiring or conduit;
It would be far easier and better than fiberglass if I had straight open 16-on-center studs, joists, or rafters (14.5" to pack 15.5" wide batts into)

I'm using the right material, just trying to install it in the wrong way. I'm pretty sure.

Aside from that: this stuff is moisture resistant. Can I double-face it with vapor barriers? Outside has spray foam, I don't know if I can/want to tack a plastic layer or radiant barrier or whatnot over this stuff to hold it together. Encapsulation generally leads to vapor trapping and condensation.


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## Windows on Wash (Aug 30, 2011)

What type of foam you are going to spray determines what classification of vapor retarder it it.

OC SPF is not a Class I in most installations so you don't have the vapor trap you are referencing.


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## bluefoxicy (Nov 5, 2012)

It's closed cell polyurethane foam propelled by nitrogen.


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## Gary in WA (Mar 11, 2009)

You are in Zone 4; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Maryland

No interior vapor barrier/retarder is required; http://www.buildingscience.com/docu...heet-310-vapor-control-layer-recommendations/

If it were required the thickness of SPF you have doesn't require an interior vb; http://www.buildingscience.com/docu...ulating-sheathing-vapor-retarder-requirements

1. What is the wall sheathing- OSB or plywood?

2. What type of siding?

Gary


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## bluefoxicy (Nov 5, 2012)

I'm in zone 7. -10C winters, +106F summers, ridiculously high humidity.

Sheathing is plywood, vinyl siding. I used spray foam at 1/2 inch (except for a few areas I full-filled) because there was a huge draft--wind was coming out of my wall, and the wall was 55F where the adjacent wall was 74F. That issue has been solved by the application of spray foam.

It seems that the stone wool batting holds together well... it fell apart from the way I'm handling it and I stuck chunks into the weak spots where there are voids and it stays put. I don't think I'll need to staple anything in to hold it in place.


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## Gary in WA (Mar 11, 2009)

Sorry, I was relating you to Baltimore, Maryland as in post #3: http://www.diychatroom.com/f103/rigid-xps-block-wall-192169/

Zone 7 uses a vapor barrier, Class depending on the link I gave. This may help you in cutting the Roxul better; http://blog.lamidesign.com/2012/01/what-you-don-know-about-mineral-wool.html

Gary


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