Before you remove the batts, make sure they are not being used as your vapor barrier. In other words, if the batts are faced with paper on the bottom side, I'd leave them in place.

And, before you blow in any insulation, purchase some of those cardboard or styrofoam boxes that connect the eave space with the attic space. These conduits will maintain the ventilation between attic and eaves. If you don't do this, the blown-in insulation will fill the space between the attic and eaves.

 

I think your idea to use blown insulation is a good one. It'll take you about an hour or so, really improve the insulative value of the house and make you look like Santa.
Definately do your best to install the thingies that Cabin mentioned. They are made of styrofoam or cardboard, are as wide as the space between the rafters. they are to be nailed to the sheathing. they provide a space for cool air to come in under the eaves and up into the attic. they prevent the build up of moisture against the roof sheathing/ prevent the insulation from resting against the roof sheathing and provide fresh air to the attic. they can be installed with a slap stapler or a staple gun. It's kind of a short term pain to install them, but it is a really good long term benefit in helping preserve the roof and the house.

 

I'd let whatever protrudes do so. You're not going to have as much control over it as you think you will in the abstract. Been there, done that. DO wear a mask! I would definitely NOT cover the ducts so deep that you can't locate them if needed for repair. Have fun.

 

I'd insulate the ducting too by either wrapping it in fiberglass before you blow in or mound the blowin over them.

If you don't they will loose alot of heat to the attic space.

 

Thanks guys. Yep, I've already thought of the venting. Do I need to do every rafter bay, every other, every third? I am WELL aware of the mess LOL, worked one summer in H.S. at a manufacturing plant where we made the blown cellulose (news paper) insulation. My job was mixing the chemicals to make it flame retardant (borax or ?boric acid?, hydrated alum and another chemical I can't recall at the moment) in a big hopper. Man that stuff got everywhere. I did help a friend do his attic with the blown fiberglass but I got lucky on that job, I got to stay outside and "feed the monster".....He got to crawl over and through everything. Role reversal on this one.

 

....I've already thought of the venting. Do I need to do every rafter bay, every other, every third?....

On one hand, you could never put in too many. On the other hand, there is no reason to put more of these "attic ducts" in than what you have for soffit vents. In other words, if your soffits have the continuous vents, I'd be incline to put these attic ducts in every other space between the rafters. If you have the typical 6"x12" soffit vents, I would use 1 attic duct for each of these soffit vents.

 

Typically you shouldn't have a vapor barrier in your ceiling, that where the majority of the moisture in your house exits at. I live in eastern Washington state and we don't very often get below 20*'s, when I blew insulation in my attic I put up to 3 feet in and left just enough space on the eve's for ventilation (don't have vented soffits). It will settle quite a bit over the years so I put in quite a bit more than was needed.

Bobg

 

You want proper [that's what they are called] vents in every rafter chase. Otherwise you get hot and cold spots, condensation, water and ice damage. You want the roof itself to be uniformly cold.

Don