A friend that lives in the Northwest is asking about insulating their home that they just purchased before winter kicks in. They have done a little research and called a few contractors for estimates but they are still not completely sure which material is best for their situation.
They will be insulating both their walls and their attic space and the home is already built so the wall insulation will mean having a contractor blow insulation into the voids.
A lot of people have given concerns about fiberglass and health situations but cellulose will also cause heath problems if you breath the particles. No fine material is actually safe because it is not the actual material of fiberglass that is the problem it is the physical size of the particles that can cause respiratory problems. The way this happens is that a particle of very small size will be breathed in and out of your lungs just like a large particle but when the particle is within a specific size range it will stay in your lungs much easier. It is somewhat like but not exactly like this example… small smoke particles are easily inhaled and exhaled and mucus in your lungs will come out from coughing. But some things will stay in there and inflame the lungs and cause problems. So its not just the material because Fiberglass is Glass which is pretty much inert but it can still cause problems. If you have any question about this do some research on reliable medical websites. And I will say many of these studies are inconclusive and not yet to the thoughts about asbestos which is also a problem because of the size of the particle.
Bat insulation over blown insulation means that the material will normally hold its shape over time while blown will settle. It is a common practice for insulation installers to fluff as its blown in and not give you the full density of material needed to retain its shape over many years.
Cellulose will also hold moisture much longer than fiberglass and living in a high humidity area this is an issue for you as much as it would be in south florida. Maybe even more.
another factor is Cellulose can be installed with a blower by a do it yourselfer but fiberglass normally requires a professional to blow it in .. Bats on the other hand are very easy to work with and can be placed over other bats or blown in insulation.
Personally a combination of both is probably best but for best situations an R60 using two crossed layers of R30 insulation in Bats will retain its shape much longer. In your area you can probably get away with an R30 to R40 for maximum coverage and for blown in insulation that is a lot of material to blow in. You will basically lose your entire attic.
It is a difficult choice but given all of the money in the world and an empty attic or house without drywall I would probably first look at using a foam insulation to seal off air infiltration and then install bat insulation for the primary insulating material and then finally in areas that are difficult to cover I would blow in or use loose fill to cover those areas.
In my own personal decision I would most likely stay away from sprayed foam insulation within wall voids because in my opinion it renders the wall completely useless once sprayed. You can no longer easily run wires or service the area and if there is a problem its extremely difficult to work with. On the other hand spray foam in specific hard to handle areas can be amazing and also when used to seal things like gaps between vent or plumbing pipe. But in my opinion it should be used in very limited situations.
Final Note
The materials you use and the methods that they are installed mean not only initial savings but you must evaluate the long term use of your home and the longevity of the materials you install.
Blown in insulation is a quick way to fill an attic or retrofit walls with insulation but it is not always the best solution. For example I gave the thought on foam insulation in wall voids. Well the same is true for blown insulation in attics. Where you can easily remove and replace bat insulation if you need to work in your attic to install or fix a fan or wire or fixture… digging through a pile of blown insulation can be a nightmare. its like the difference of folding back a comforter vs trying to hold a million marbles in your hands.. can’t be done without a mess.
So, in my home I don’t just seal off the attic and forget about it. I normally have projects going on where I need to get up there every few months and I also value the storage. This is another reason I suggest Bat insulation over blown in insulation but everyone has their own considerations. For me I want to be able to get to my antennas and check for any leaks or problems in the roof or whatever I need to do. For other people they will never enter that space and they will call contractors to do everything for them. Hopefully those contractors have tyvek suits and respirators.