Which is best? Batts or rolls?

I think it's called (something like) Roxcel. It is presumably made from lava rock or some very strange thing.

The benefits: not itchy; is dimensionally stable; is not affected by moisture; little critters don't seem to like burrowing in it; higher burn point.

Anyway, it's worth asking after at your local building supply.

I prefer batts and just squush them in a bit for a good seal. Also, I would check on vapour barrier. I think (but could have it backwards) if you put it against the joists, under the insulation rather than on top, you should be okay.

as The Band would say. In fact batts sometimes come bundled up in what looks like rolls, and sometimes in big plastic bags (in which case you either have to get rid of the big plastic bags, or use them for drop cloths and other things).

The roof should extend past the walls (overhang/soffit). There's no point in extending the insulation past the walls, and don't block any ventilation there or vents in the gable walls. If you don't know how it's vented, you may be in for trouble, as it doesn't sound like there's any vapor barrier above the ceiling. Just butt the batts or rolls together all around - no tape.

I've done it with a well-vented attic/no vapor barrier and didn't have a problem. My sister bought a house with an unvented attic that the previous owners added insulation to, and large chunks of ice formed in the insulation and then leaked through the ceiling in spring. Both were in WI. Most old houses probably aren't sealed that well. YMMV. (Apparently you don't have a problem now)

How to cut: put a length of 2x6 or 2x4 or plywood (width of the roll or a little more) under the roll. Take a second 2x4 and press down the roll onto the first board, offset slightly to leave a backing surface to cut against. Cut with utility knife (although a large kitched knife works really well too).

...if I do say so myself.

Don't walk, but run....er--surf to Make It Right Tips and Tricks, by Mike Holmes, of the frigid wilds of Canada.

And a nice review of Holmes on Homes, from The Whispering Crane Institute.

I hope that helps. Happy winterizing, y'all, from
Zone 8A.

First on too much insulation to walls and ceilings: there is a point where adding just isn't worth the effort; for example, at higher R-levels. An R35 roof will perform only marginally worse than an R40 roof, though you may spend a ton of money getting those five extra points. However, going from R20 to R30 in your roof is worth it. Has to do with thermal resistance, dew points, and crap like that. As I recall, you also want to make sure that a roof especially ie evenly insulated---no creating areas where R-value drops too much.

I read that months ago, but I can't remember where. Sorry, no linkiness.

One key is to properly seal and ventilate the space. Areas of concern are any connections---rafters to sheathing, framing to sheathing, openings for plumbing, electrical and mechanical systems, and so on. You can have an R50 wall, but if there's a void where cold air from outside and warm air from inside can mix, you'll have condensation. And that can lead to bad bad things.

So seal those openings. I know you don't like the foam, but they have the stuff you can get in cans from your local Home Depot or Lowe's you could try and see if it bothers you. Or use caulk (I like Big Stuff, but any good quality caulk will do) and a 2" drywall knife on the seams. (Also, the NEC (the electrical code) requires all electrical pass-throughs be sealed to stop fire spread.)

Also, if you have any pipes coming through, get that foam pipe wrap stuff, matching the inside diameter of the foam to the outside diameter of the pipe exactly. It sells at Lowe's here for like $2 for a 6' length. Pipes with hot water are required by code to be wrapped: there has to be a thermal break at the wall to stop condensation rom causing water damage and to stop anyone from getting burned. But if you have cold water moving through, wrap those pipes, too. Hot air and cold water will cause condensation on the exterior of the pipe.

The point of sealing well is so your ventilation system* controls the movement of air into and out of the structure. This is a big deal as you're actually trying to control two-way traffic. There's the air from outside that can produce drafts and moisture, or condensation if it mixes with warm air. But you're also trying to vent the warm moist air from inside your house (and replace it with fresh air). That indoors air is warm and moist from your heating system, showering, cooking---and from breathing. You want it to move outdoors in a controlled manner so it doesn't hang around and wreak havoc.

*Ventilation system means anything that controls air flow---opening and closing windows, vents, fans, or a fancy energy recovery ventilation unit (ERV) like certain people installed in their houses, complete with duct work and swearing. The key is to consider how you're going to move air in and out intentionally to keep moisture from calling the shots.

I don't like fiberglass much, but there are a few tricks. Yep, just roll it into the bay. Don't mash it in---use a sealing product. Insulation works by trapping air in it's spaces and slowing down it's movement from one side to the other. Mashing gets rid of the voids built into the material and you lose R value. Keep it nice and fluffy with as few breaks as you can. You can tape the seams if you have to butt them to fill a bay---I would. But I'm crazy.

After you're done working for the day, wrap some cheap duct tape inside out around your hands and pat any skin that was exposed to the fiberglass. That picks up most of those little tiny slivers.

Rockwool, like Roxul http://www.roxul.com/sw16796.asp, I've never worked with but I know people who like it a lot. I've considered using perlite, which is another mineral, to pour into some top plate bays and between stem walls. Perlite is bug resistant, has no food value, is fire resistant, and because it's small and loose, fills in a lot of stuff. If there's a local source, you may want to look at the cost---check a gardening supplier. Very easy to work with and you can use it to create a potting or starter soil for your plants (or in soilless gardening), too. But it goes everywhere, so don't be surprised if you're vacuuming up little white puff balls for the next month or so.

recycled blue jeans insulation.

is correct as far as the eaves go. I wouldn't tape the batts together a)because it'd be a real pain in the ass to do and b) while you should get a reasonably tight fight just butting the edges together, since you're operating without a vapor barrier, a small amount of air/vapor movement through the insulation probably is a Good Thing.

Ice dams happen because warm air from the house melts snow. When the melt water runs down the roof to the lower parts which are colder (sometimes past the overhang), it freezes. Typically, it then backs water uphill under the shingles (they're designed to be waterproof only in the downroof direction) where it leaks into the attic, soaks the insulation and spots or destroys your ceiling.

I can't see why insulating would create ice dams, since it'll keep the roof colder - the eaves/overhang will always be cold. What it will do is allow snow to stay on the roof, so hopefully the rafters will support the snow load, and the snow won't fall off the roof and kill kittens or damage cars (both of which have happened around here with metal roofs, but not to me).

What I'd do about the eaves is this: go up into the attic during daylight hours. Look around the edges - if you can see daylight someplace, your eaves (soffit actually) are part of ventilating the attic. If that's the case, keep a clear path for air from the daylight into the attic proper (by holding the insulation back from the edge, or thinning it at the edge). Don't push it tight to the roof at the edges. At any rate, there's no reason to extend insulation beyond the wall below.

AT1.4 here is a good picture of baffles: http://www.energytrust.org/TA/hes/weathe...

http://www.buildinggreen.com/auth/produc... has an array of green insulation baffles, though I've seen them made out of cardboard. IRC says you need minimum of 1" between the insulation and the sheathing. I'll bet 2" would be better, though the only reason I think that is because that's what my dad does.

There are baffles you can also buy for sloped ceilings that are stapled to the sheathing and run to the ridge as well. I've never seen those, just the other kind. And since the baffles handle the ventilation, you can shove the insulation right up against them them. But badger is right in that you do not want to block the sofft vents or birdblocking or anything like that. IRC says 1" back from vents, so that just means you either foam or staple the insulation around the vents 1" from the opening.

To expand on the damned dams, the idea of the baffle is that you're letting the air constantly sweep from soffit to ridge vent, keeping the temperature within 10 degrees from inside to outside on the exterior side of the insulation directly under the roof. No ice forms because there's not enough heat escaping from the inside of the house to cause the snow to melt, run down the roof, and freeze as the water passes over the eave where there is no insulation or anything else.

Brrr. And that's why I left Minnesota.

But this assembly works only if you also create a continuous air barrier on the other attic side of the baffle. You do that by sealing all penetrations to stop air from the conditioned space below and add insulation to stop heat loss from the framing and ceiling materials. This is where that foam/caulk and taping all intersections comes in. And adding non-paper backed fiberglass batts on the floor of the attic running perpendicular to the bays. But as I said, I'm crazy and I would do all this. Monk is right: mental illness is a blessing and a curse.

So in answer to your header, I'd get continuous roll fiberglass insulation as there will be fewer areas to splice and tape along the bays.

FTR, basically, you're looking for detailing here and I'm not a builder, engineer, or architect. I think, though, that you're going to have to maintain the ventilation along the roof sheathing using attic insulation baffles. (Our roof is unvented cathedral style and it's detailed differently.)

Even if insulating the attic floor, you could put a baffle (maybe a foot long) between each pair of rafters above the wall. Cardboard would be all you'd need. Just measure the space between the rafters, cut a piece of cardboard 1 foot long by the measured distance plus 4 inches, fold the extra 2 inches on each side into a U.

Stick the U (open side up) between the rafters and shove the batt against it to hold it in place (even compress the batt a little under the cardboard). If needed, a staple on each side would hold it. What you've made then is a kind of duct to keep the air flow open and still able to get insulation coverage all the way over the wall.

You can probably do it without that (although you might end up holding the insulation back farther), but it's a cool idea.