HI again tammys,
Attic Moisture Problem is your related post for you and others to use as reference ...
Forget the allergy thing for the moment. Once the insulation is installed, no matter what type it is, whatever initial 'dust problem' exists, it will essentially go away. Of course, if you're up there stirring things up, that's another matter.
If your existing insulation is 'bad', it should be removed and replaced. This means temporarily removing your attic flooring. (I hope you used only a FEW screws, and not a lot of nails. You can use deck screws ...) Assuming the insulation is bad, I'd install batt insulation THAT COMES WITH a Kraft-sided Vapor Barrier.
Assuming your insulation is 'good', the what you do can depend on a couple of different things. You see, when you add MORE insulation on TOP of existing insulation (the existing insulation can get 'compressed'. WHen this happens, the R-value drops. It's DIFFERENT if the insulation is added all at one time. Whenever you compress the insulation, you drop its R-value. Soooo, adding more may not do anything. And, to boot, if your flooring is compressing what's there, then you'll have to deal w/that too when new insulation is added, to see if your flooring will compress the insulation.
ou see, the way insulation works, it's NOT to prevent air and moisture from going through it. In fact, it's the opposite. As you've already seen, trapped moisture in insulation is bad news. Insulation basically slows down the movement of air through it BUT still allows it to escape. Air is one of the BEST insulators. Ask any duck or goose. Their wings are oil-coated BUT they trap air (slow its movement down) but it still keeps them boyant in the water. It's almost the same principal with our home insulation.
In short, it may be best to have your existing insulation removed and go w/an R-30, or higher, in batt. You'll want to hire a Pro to remove (vacume out) the existing junk but you can easily install the Kraft-sided Batt Insulation yourself. You need to find out the proper R-factor for your home and area in which you live. Maybe you can talk to the COntractor that will remove your insulation for advice. Or, you can talk to your Municipal Building INspector for advice. (Perhaps you can ctc. your old Home Inspector who did the inspection when you bought the house for advice.)
My best to ya and hope this helps.
Jay J -Moderator