Since you don't give any details about the age, style, or construction of your home, it's difficult to say if batt or blown fiber is the best insulation solution for your needs. And you say that you are going to insulate your "roof," but are you actually referring to the attic floor? Or do you have a cathedral ceiling where the insulation will be directly against the roof sheathing?
There are a lot of variables which influence the proper recommendation. If you want to reply below with some more details, I would be happy to fine-tune the answer for you a little further.
But in lieu of those details, here's what I can answer for you:
Recommended R-Values for Your Climate Zone
In Mechanicsburg, Penn., you are in Climate Zone 5 according to the 2009 editions of both the International Energy Conservation Code (IECC) and the International Residential Code (IRC).
- As such, the recommended R-value range for an open attic area is R-38 to R-60.The recommended values for a cathedral ceiling installation are R-30 to R-38.
- Since you are just barely into Zone 5, you should be good staying around R-38 in either scenario. You can always do more if space permits, but that's also dependent on your budget and goals.
Fiberglass and Indoor Air Quality
Regarding fiberglass and indoor air quality (IAQ), there are two factors which will affect your project:
- how the fiberglass is made, and
- how it is installed.
How the fiberglass is made. The primary issue with fiberglass insulation when it comes to IAQ is the formaldehyde that it typically contains (regardless of brand). However, there are now formaldehyde-free products on the market in batt, blown loose-fill, and spray-in versions.
- Johns Manville is the market leader for these products.
- There are two other manufacturers of "formaldehyde-free" products available in the U.S., but one (Knauf) makes their "free" product on the same equipment as the regular line and the other (Dow) has several "red flag" substitutes for the formaldehyde -- so it may not be any better.
There is also still the issue with the potential for glass fibers in the air, which may irritate your son, but the primary chemical issue of formaldehyde can be removed from the equation with the JM products.
How the fiberglass is installed. The choices are:
- blown loose-fill, and
Batt installation is the least disruptive and creates the least amount of airborne particulates, including glass fibers. However, it can also leave the most voids and large air gaps, so it is usually the method of last resort from an energy efficiency standpoint.
The link above is for a product which is encased to even further minimize the particulates during install. Note that for an attic situation the product is available without the vapor barrier encasement if specified that way. That's most likely what you would want in a batt product (again without knowing your building's specific assembly profile).
Blown Loose-fill Insulation
Blown loose-fill will create the most airborne particulates of the three versions.However, it does not use any adhesive blowing mediums, just forced air, to distribute the product.
- It is also lower-cost than sprayed-in, but typically more expensive than batts.
- This product does a great job of filling the gaps and hard-to-reach areas.
If you select this type of insulation, you may not want to be home during the install. You should also be sure to turn off your HVAC system before the installation starts and leave it off for at least 24 hours afterward. This will help you avoid getting the particulates in your ductwork and then blown around the rest of the house.
Finally, you have the sprayed-in option. Like the other two options, this is also fiberglass and also formaldehyde free. In your situation, the primary advantage of this system also has the potential to be the primary drawback. Specifically, this product uses an adhesive during the blowing process.
- This enables the product to grab onto the framing of your attic and/or roof and stay put.
- The adhesive helps prevent settling over time and wind-washing depending on the air movement in your home.
If you can avoid those two issues, your insulation will come closer to achieving its target R-value over its lifespan. It also means that the airborne particulate fibers caused by blowing are drastically reduced because they are essentially being glued in place as they come out of the hose.
So, if you can deal with the adhesive, this product will perform better in the long term and go in with less "dust." The big question is how your son may or may not react to the adhesive chemicals.
- Here is the Material Safety Data Sheet (MSDS) for this product. Since they don't want to give away any trade secrets, they only state that it uses "Hydrolyzed Polyesters."
- If you have an ENT or allergist who sees your son already, they may be able to clue you in better about possible reactions. Section 2 of the MSDS is pretty benign compared to many of these sheets I've read, but it does show the possibility for some irritants, so it may not be an option for you.
- There is also an 800 number on the top of the first page for Chemtrec. They may be able to answer more questions for you.
Non-fiberglass Blown-in Insulation
And while you asked specifically about fiberglass, there are also other blown-in options to consider, entirely apart from fiberglass. All of these will cost more than fiberglass, but each has its advantages. These include:
- cellulose, and
- mineral wool (aka rock wool).
From a chemical sensitivity point of concern, rock wool is the most inert of the bunch (primarily because all the others have to be treated with something to prevent mold, critters, fire hazards, etc.). However, it can also be the most costly; it can be harder to find in some markets; and trained installers can be harder to get.
But if it's an option in your market (and in your budget) you may want to strongly consider it.
Rock wool is my first preference, when available, for a variety of environmental and long-term performance reasons -- chemical sensitivities being one of them.
For more information:
Check our best attic insulation Q&A to see what other homeowners and contractors are saying about fiberglass, foam, cellulose, etc.