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Coon
Nicholls St. Fan
La 56 Southbound
Member since Feb 2005
17528 posts
 Online 

New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam

We were originally going with blown rock wool but my sub is saying the company he uses to get the material is shut down currently due to weather/storm damage. He is offering blown fiberglass in lieu of blown rock wool. On my original quite, there’s also open cell foam available for $1500 more. Note: this is just for exterior walls.

I was going with blown rock wool because that’s what a lot of folks I’ve talked to recently have used. I don’t know of anyone that has used blown fiberglass.

What’s the H&G opinion of going with blown fiberglass and/or if I should go with open cell foam instead?

Attic will be blown fiberglass.


notsince98
Missouri Fan
KC, MO
Member since Oct 2012
10750 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
Blown anything for above ground walls will give you a better product than sprayfoam, IMO. Spray foam has the worst sound attenuation of all the insulation options and sprayfoam doesn't really have much if any payback compared to blow-in options.

I have BIBs in my house (blown in blanket fiberglass). No real complaints. Much better than batt insulation.

I only wish I would have went blown cellulose. Is there a reason you aren't considering cellulose?


Coon
Nicholls St. Fan
La 56 Southbound
Member since Feb 2005
17528 posts
 Online 

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
i was under the impression that rock wool and fiberglass were both better than cellulose. Issues i've been told with cellulose is that it settles. is there any fire retardency with cellulose?


notsince98
Missouri Fan
KC, MO
Member since Oct 2012
10750 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
quote:

i was under the impression that rock wool and fiberglass were both better than cellulose. Issues i've been told with cellulose is that it settles. is there any fire retardency with cellulose?


A couple answers:

- Better than cellulose? Not sure any one is specifically better. Cellulose will have better infiltration reduction than fiberglass, not sure on rock wool but it is probably cheaper than rock wool. Cellulose is a lot quieter than fiberglass, not sure on rock wool.
- settling: All blown insulation can have settling problems IF it is not installed properly. All blown insulation needs to be "dense packed." This means the blown insulation needs to be packed to the point its density is greater than the settling density. If any blown insulation is not packed above settling density, it will settle. If it is blown to a density higher, it cannot settle.
- Fire retardation: Cellulose is a better fire retardant than fiberglass. I'm not sure on rock wool but I would think rock wool might be better fire retardant than cellulose. There are some great videos on youtube comparing fire tests of cellulose and fiberglass. Fiberglass goes up like a tinderbox.
- Pests: Cellulose has better pest repelling capabilities than fiberglass. Not sure on rock wool.

Cellulose is a nice heavy final installation setup in walls. It reduces infiltration to very low levels. If you go any lower you have to get into HRV/ERVs.

I need to look more into rock wool. When I was looking into things for my house build, I never once ran across blown rock wool. I know rock wool makes a very good insulation, especially when considering sound. I used it in my basement ceiling. But that is all I know about it.


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VABCHTIGER
LSU Fan
Virginia Beach
Member since Sep 2007
198 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
I've read many places that dense pack cellulose is just about the best besides foam, and the mineral wool batts are also good.


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slapahoe
LSU Fan
USA
Member since Sep 2009
6983 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
I will be building within the year and have gone back and forth on spray foam and blown cellulose.


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LSUtigerME
LSU Fan
Walker, LA
Member since Oct 2012
2145 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
I couldn’t find anyone to do the blown cellulose. I went with open cell foam and have been very happy with it.

Rock Wool is very good and would be my first choice.

Rock Wool > Foam > Fiberglass


Coon
Nicholls St. Fan
La 56 Southbound
Member since Feb 2005
17528 posts
 Online 

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
Damn. So I should pass on fiberglass??


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slapahoe
LSU Fan
USA
Member since Sep 2009
6983 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
size of house and price to do the job?


Coon
Nicholls St. Fan
La 56 Southbound
Member since Feb 2005
17528 posts
 Online 

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
Ok, I’m going to source another sub to see if anyone else has rock wool.


Shoulderchoke
UNO Fan
Swamps of Lafourche
Member since Aug 2008
7467 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
We used blown rock wool and it has worked incredibly. Our house is around 2800 living (I know, I’m OT poor) and our electricity bill is around $150 per month.
Why cant he find it from a different supplier?
This post was edited on 9/12 at 5:59 am


fishfighter
LSU Fan
Baton Rouge
Member since Apr 2008
34005 posts

re: New construction Wall Insulation: Blown Rock Wool, Blown Fiberglass, Open Cell Foam
Have rock wool blown in my walls and attic. After 25 years, very little settlement in the attic. Very happy with low electric bills.

Oh, one other thing. The rock wool I have was treated for bugs. In 25 years, I had never saw any bugs in my house. Do check on that treatment. Don't know what they used.
This post was edited on 9/12 at 8:09 am


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