Hi Everyone,

I am completing a major renovation of my house on Miami Beach, FL and I am to the point where I need to decide what kind of insulation to use.  My primary concern is finding a green product in terms of health, NOT energy efficiency.  I do not want a product that contains formaldehyde, VOC's, flame retardants, or any other toxic chemicals which have the potential for degradation and off-gassing over time.  I know that many products are claimed to be inert after installation(like Icynene), but that's only tested to be true under controlled laboratory environments.  What happens over time after repeated exposure to extreme heat and moisture is less certain.

Being on Miami Beach, FL, heat and moisture are huge concerns.  To further complicate things, I have an Unvented Attic Assembly and the HVAC unit is hung in the attic.  I will have a dehumidifier installed in the attic to help keep moisture at bay.  I like to keep my house cold(70 degrees), so choosing a well performing insulation is very important.  My roofing material consists of 30# felt, TU-Plus, and a handmade natural clay barrel tile.

The exterior walls are concrete block reinforced with rebar.  The walls facing East and West are primarily glass windows and doors, and the walls facing North and South are very well shaded, so wall insulation isn't a huge concern for me.  So I am really more interested in insulating the walls to create an insect barrier rather than for temperature reasons.

In terms of flooring, I have a plywood subfloor and will be using an engineered wood for the finished floor material.  Miami Beach has poor storm water drainage, so it is extremely common for there to be a lot of water running under my house.  I would like to have some kind of insulation/moisture barrier installed in the crawl space on the underside of the subfloor. I want to keep moisture out to avoid warping problems with my wood floor, and I also want to keep bugs out.   I know of people who have used vapor impermeable Icynene, but I have reservations about its safety. 

What options do I have?  Are there any products that are actually made from all natural ingredients and which can be used in my climate for my intended purposes?  What would you guys recommend for each area(unvented attic, walls, and floor)?  Thanks for any help!

Rock wool (high density panels, unfaced batts, or blown) is likely to be your lowest outgassing material for insulation above grade applications.  It's primarily spun slag from steel-making- anything volatile was burned off during the (very high temperature) manufacturing process.  High density rock wool panels (sold as exterior wall insulation in commercial building, but more recently being used in residential) mounted on the exterior of the roof deck, with a vapor-tight underlayment between the roofing and panels would put the attic inside of conditioned space, which keeps the roof decking trusses/joists etc dry and mold-free.

Organic insulations are out, since they all require fire retardents.

For the slab edges & crawlspace walls your better bet is EPS, which is blown with pentane which outgases within days of manufacture rather than XPS which is blown with HFC245fa and takes years to outgas.  You'll still want to put a full poly vapor barrier on the crawlspace floor (or under the rat-slab) to prevent both moisture & soil gases from getting in. Sealing the crawlspace from the exterior and the ground would let you insulate the floor if you desired, but in general it's better to just insulate the crawlspace walls and "earth couple" the house to the subsoil mass from an energy-use point of view.  Vent the crawlspace to the conditioned space to guarantee crawlspace air is at the same dew point as conditioned air, and it'll have no moisture issues.

Rather than putting the air handler & ducts in the attic, it may work better to put it in a conditioned crawlspace.

Your east & west facing windows are gia-normous solar collectors with high gain year-round, since they can't be shaded with simple overhangs. That can add more than a ton to the peak cooling load for a house.  Exterior operable shades can cut that, but natural shading/screening of the low-angle E/W sun can work almost as well, but low-gain windows are mandatory, at a minimum.  If you're not replacing the windows, look into low-E storm windows as retrofit treatment.

So for the attic, the rock wool panels actually go on the outside of the roof?

Does the order of material layers go like this:

trusses
plywood
30# felt
Polystick TU-Plus
rock wool panels
barrel tile

Is that correct?

I have more questions about the rest of your post and will respond later when I have more time...thanks!

Yes, the rock wool goes on the exterior, but you need a vapor barrier (say, the Polystick TU-Plus layer which is rated at 0.1 perms) between the rock wool and barrel tile to prevent moisture from condensing within the insulation on the cool side of the assembly during periods where the dew points are high. While high-density rock wool panels fairly air-retardent, it's still air and (highly) vapor permeable. With the Polystick on the exterior you can leave the 30# felt a the roof deck. The vapor permeance of the felt is low, but still higher than Polystick.

In that stackup you would also need a layer of half-inch OSB or something between the vapor barrier and the tiles through-screwed to the structural roof decking to handle the weight & attachment of the tiles.

You could also use OSB-nailbase polyiso panels (Hunter, Atlas, et al) rather than rock wool + separated OSB nailer deck. Like EPS iso is blown with pentane and outgases very quickly. Iso isn't fireproof like rock wool is, but it's R6/inch instead of R4/inch, so you get better R value for the available space. A 4.5" nailbase panel runs about R24, (half-inch OSB + 4" iso) but performs as well or better than R30 batts between rafters or joists since it has no thermally-bridging timbers, and a limited amount of bridging through the long-screw fasteners. See:

http://www.hpanels.com/ http://www.atlasroofing.com/tabbed.php?section_url=58

http://www.greenbuildingadvisor.com/blogs/dept/musings/installing-mineral-wool-insulation-over-exterior-wall-sheathing

There are rock wool panels with exterior metal vapor & weather barriers, but I don't know how adaptable they are to use under tile roofing eg:

http://www.roxul.com/files/RX-NA-EN/pdf/ConRock_SWP_July9.pdf

From the top down the stackup then runs:

tile

Polystick

nailbase OSB

rock-wool (or iso)

30# felt

structural roof deck

Thanks. I actually already have 30# felt and Polystick installed. So the rockwool would go over that double layer, and then I would have an additional Polystick on top of that rockwool. I will have to discuss this with my roofer because I am not sure how the appearance will be altered by having the tiles sit 4.5" higher(using your example of 4.5" of insulation on top of the roof deck).

Posted By EricM on 13 Jun 2012 07:03 PM
Thanks. I actually already have 30# felt and Polystick installed. So the rockwool would go over that double layer, and then I would have an additional Polystick on top of that rockwool. I will have to discuss this with my roofer because I am not sure how the appearance will be altered by having the tiles sit 4.5" higher(using your example of 4.5" of insulation on top of the roof deck).

If you put down a vapor barrier on top a rock wool panel  as well as below it would trap water in the insulation- any moisture that finds it's way in would take forever getting out.  Better to use a roofing felt on the top.

Roofing felt is also the right choice if using an iso panel with nailbase would still be the better choice. Since there is no entrained air in the iso you never get a condensation event, and even though drying would be slow, any moisture that finds it's way into the nailbase will still eventually dry toward the exterior.

What about Air-Krete? Have you heard of this product? Any thoughts?

Air-Krete like other foamed concrete products are highly permeable to moisture, but I'm not sure how air-permeable it is relative to the very high-density rock wool products. It' fairly pricey R too. Air-Krete specifies that it be skinned in 6-mil poly (which is VERY low permeance).