rock wool insulation questions

[1redTA]

I line in Pensacola Florida in a house made in 95. The living room has a vaulted ceiling that is under the southern facing side of my roof. The trusses are on 24” centers and currently the ceiling is insulated with rolls of pinks insulation that is unfaced. In the summer this room, houses the thermostat, is several degrees hotter or colder than the rest of the house.

Can I put rock wool over the existing insulation or should I remove the pink and lay the rock wool on the bottom and refit the pink insulation.

or should I just add some r30 pink instead? The helicopter field is close by and the th57s can be a little loud depending on how much the pilot torques the rotors;-)

 

[bored350]

Rock wool only provides a small improved R/inch insulation property gain over fiberglass but it will certainly deaden the sound much better. You mentioned vaulted ceilings and "a few degrees warmer" buy nothing specific. I think you need to start with two specific measurements. First gather the temperature and humidity information from that room vs. the other parts of the house that are cooler. Second, evaluate exactly how much insulation you have over the living room vs. what your area calls for. I suspect you could benefit from air sealing in the living room in addition to more insulation.

Based on your description, see if your local power company has a blower door test/energy audit agreement in your area. Here, the PoCo will perform an evaluation for $100 and if you perform at least $100 in improvements, they will reimburse you the cost. The blower door test will tell you where to air seal and the audit will make insulation recommendations. Once you air seal, the most efficient solution will likely be to blow in cellulose over the finerglass. This will increase your R value and provide the sound deadening you are after.

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[yeldogt]

What is on the ceiling -- drywall. How thick is the the insulation?

closed cell foam is the answer ....

 

[e36jon]

Greetings from sunny / foggy / sunny CA (I'm a few blocks from the beach, so it changes every 20 minutes)...

I have been using ROXUL mineral wool on my remodel and have been impressed (Now available at Home Depot Pro.):

1. Way less / maybe even zero itching when working with the stuff.
2. Won't hold water or support mold.
3. Has enough mechanical strength to be self supporting. You actually press it into stud bays so that it seals against both studs.
4. I'm going to flub this one, so be gentle everyone: Is rated as a draft-stop / air barrier? I don't think it's vapor barrier...
5. Is essentially fireproof. Yeah, we have wildfires around here that will melt a cast iron stove, so 'fire proof' is subjective.

ROXUL also makes a product called "Safe-N-Sound" (Or something close) that isn't rated for insulation but has better sound absorption and fire barrier properties. I'm using this in the ceiling between my garage and upstairs living space, as well as in the wall between my place and the neighbors (It's a row house, so we share a wall.). Going from nothing (My place was built in 1946, so no insulation, or plywood, anywhere.) to this stuff makes a non-trivial acoustic difference.

Anyway, Go Roxul! Woo hoo! Foam may totally stomp this stuff. I have no idea.

Good luck!

Jon

 

[1redTA]

the ceiling is drywall, no barrier, just the pink insulation in between the 2x6 that sits flush

 

[Kaizen]

the ceiling is drywall, no barrier, just the pink insulation in between the 2x6 that sits flush

Figure out the cost to add vs spray foam per foot. Safe and sound is what I used in my garage on the side where I’m close to neighbor. Definitely deadens sound but about half way between foam and fiberglass.
If you do roxul or more glass take it out and air seal everything. Some good YouTube vids showing similar. Big payoff for a couple cans of foam.


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[jvitez]

I love Roxul, have used it in my attached garage and a detached structure. I concur with everything e36jon said. It is not a vapour barrier however.

To the OP: high density closed cell "2 lb." spray foam would be the best insulation. Expensive but ~ R6-7 per inch and a total air barrier. It doesn't have any sound deadening properties.

Open cell "1/2 lb." spray foam is cheaper but only ~ R3.5 per inch and has no air sealing properties.

Roxul is a much better product than fibreglass, but again no air sealing properties and only about 10% more R value than fibreglass per inch.

If it were me I'd go with closed cell spray foam.

 

[Showkey]

My daughter in Texas just got an estimate to increase the 35 year old 6” rock wool to today's standard in the ceiling of a two story appox 2200 of ceiling space on two levels. 3000 sqft home all in.

Two choices:

Remove rock wool and Spray foam Was $6000-$8000 ( did not see the details suspect depth was the variable in price).

Add 12” of blown in fiberglass or cellulose was $1200

She went with the blown in........pay back on $7000 Investment was not computing.

 

[99LeCouch]

Is the roof currently vented, or is it a "hot roof"? Another option might be flash and batt, where 2" of spray foam is applied to a cavity for air sealing, and the bulk of the insulation is provided by batts.

 

[yeldogt]

The OP has a vaulted ceiling -- this is a difficult insulation detail especially with AC in a hot climate. It's even more of a problem with a shed roof ..

With a typical attic where the ceiling provides the insulation and the attic is empty -- pumping a lot of cellulose on top of what is there is typically the best return. This can't happen within a rafter system of a shed or vaulted -- unless you have a scissor truss and you hold in the insulation.

Nothing stops solar gain like foam -- even 2-3 inches on a hot day .. it's eliminated

 

[99LeCouch]

Too bad Florida is so hostile to rooftop solar. South-facing roof with lots of direct sun? Slap a solar array onto it. Not only does 20% of the sun's energy get captured outright, the array itself would shade the underlying roof. The gap between the array and the roof would make a natural chimney that would convect hot air up and away from the underside of the array. That would also cool the roof underneath. Like a safari roof on an old Land Rover.

Wacky idea. But, if spending $8k on spray foam is on the table, why not intercept the sun before it hits the roof?