You do not need a vapor barrier for attic insulation provided the attic is ventilated. Any fiberglass insulation you do installed over existing blown insulation should not have paper facing on it. Vapor barriers belong directly next to the drywall when used.

It is necessary to install rafter vents in every rafter space at eaves to assure proper ventilation.

You could check your soffits vents from the exterior by removing the soffits.

Air infiltration can account for up to 50% of all heat loss/heat gain even when a structure is adequately insulated....and can account for rapid temperature drops...

Sealing the structure can do more for energy savings than adding insulation.

It is interesting to note that various research as shown cellulose provides the best insulation for the dollar. The November 2004 "This Old House" magazine does an excellent job of comparing all types of insulation. On page 60 they compare all insulation options. Cellulose has an R-value of 3.8 per inch of tickness at a cost of $0.17 per sq. ft. Made from pulverized newspaper and treated with boron to resist fire ants and pests. Blown into place, an adhesive reduces any settling.

Regarding fiberglass batts, it lists an average cost of $0.38 per sq. ft. producing an R-value of 3-4 if not compressed. It says the fibers offer little resistance to air movement and convective heat loss. They suggest batts that are held together with a nontoxic acrylic binder instead of the typical formaldehyde-based binder.

Check with your local utilities to see if they offer offer heat loss analysis and maybe offer financial incentives for improving insulation. About two years ago we had 12" of cellulose blown in over old rock wool. The total cost was $1,000. Texas Utilities reimbursed half the cost resulting in a total cost of $500. We have a 3,000 sq, ft. home in hot summer Texas. Our highest electric bill in July/August was $274.

It might be easier to buy R-25 in 8 ft. batts. Run these batts across the joists and you will be able to easily push them into the eaves. A big plus to this approach is that if you ever need to work in the attic it's very easy to move these batts out of the way

i am doing the exact same thing. our house is really old and the circa 1940's insulation just doesnt do the trick. the rafters are origional to 1892 and have the simple triangle design and are 6" studs. the blown in had settled to a thickness of 2 inches. i added 4" unfaced in betweeen the studs and 8" running perpendicular. i suspect we have an r value of approx 45-48 now and noticed a HUGE difference.

Thanks for the input. I didn't realize you can remove the soffits from outside. That makes things wicked easy.

As far as the insulation goes, now I'm back to wobbling about whether to do rolls or blown in. This is almost like the Ford/Chevy debate. Both sides very loyal to their own brand. I know people with both, and both say their results are great. Maybe I'll just make this a straight cost decision.

It would be nice of This Old House Magazine to tell us what their insulation costs represent, per s.f, per inch thickness?, installed?; none of the prices make sense to me, at least in the online version. And whatever the percentage of heat loss to air infiltration, it is always more cost effective in the northeast to add attic insulation than to substantially tighten up the envelope of an existing house.

You won't find that there is much difference between the performance of the materials. The material cost of the fiberglass batts should be enough more than cellulose that you might be able to get the cellulose blown-in for the cost of the fiberglass uninstalled. Don't assume doing it yourself is necessarily a big savings. It's great to not have to handle insulation materials.

Push cardboard insulation baffles between the rafters down into the eave against the roof deck if a baffle isn't already there. A professional installer would probably automatically include that in the price.

While you are at it, seal any penetrations in the ceiling including the access door and insulate the door as well.

Thanks, I have been trying to seal the pulldown stairs to the attic. It amazes me that they can install a heavy metal ladder onto a 1/4 sheet of plywood and expect it to hold up over time. I recently put some weather stripping around the perimeter and a latch to keep it shut tight. I'm not sure what more I can do to insulate that part.

I've sealed up as much of the house that I can afford. I still have some windows and a door left to replace. They have plastic and/or weather stripping on them for now. Luckily I have a good wood stove to keep the temps up even though I'm sure a lot of the heat is going right back outside. At least I'm not wasting oil while I work on getting my house all sealed up.

I am a cellulose fan. Jus had R38 blown in and replaced very old (1957) fiberglass that was deteriorated into crumbling dust. I pulled all that out, a smelly mess. But the cellulose job took maybe 2 hours to blow in 2600 sq ft. The low cost of cellulose combined with better R value year round makes the decision easy for me. One caveat mentioned earlier was that fiberglass gives you better or easier attic accessability should you later ever need to do some additional attic work.

one of the reasons i chose to go with fiberglass bats is because in a year or so we are going to be renovating 2 bedrooms. we plan to COMPLETLY gut them, including the ceiling. the less blown in, the better for that job! been there done that got the tee shirt, dont want to do it again. 2 inches of blown in is enough to handle while gutting the rooms. maybe after the remodel is done blown in is an option.

If you have blown-in insulation that is terribly compacted or otherwise no longer desirable shop around and you will find an insulation company that can vacuum it out. Yes, they have large centrifugal vacuums designed to remove insulation. I had a contractor take out the blown-in above my large master bath so I could replumb and rewire. He showed up with a flab bed pickup with this vacuum thing on the rear, 150' of 6" hose, large "vacuum bags" holding 500 lbs of insulation and a small helper. 3 hours later they were gone (and most of the three hours was setup and teardown.

I don't know how many hours this saved me, but I was able to do 95% of the ceiling work (recessed lights, plumbing, wiring) from a small aluminum platform on the floor. Now, this cost me about $350 for 400 sq. ft., but this was for a very small job and was worth every penny.

Rick

How important is it that the insulation be one depth in an entire attic for overall performance. Due to a large amount of flooring it is difficult to maintain the same depth through the entire attic.

Keeping the insulation uniform we can achieve a 19 to 21R value and we would like to get it up to aprox 39. Some people say the insulation has to be one depth only and others say it can be varying depths.

Sure you can have varying depths, but gaps and/or improper installation will reduce the overall R by 1/3 at least. Its not cost effective if its not uniform. You can pull up 1 or 2 floorboards to blow into the joist spaces; drill holes in them, even blow over them if needed. The bottom line is do what is cost effective. If its easy to blow R49 and cheap, do it. If its not uniform then dont waste money trying to blow more for one spot, the conductive heat loss will just be greater at a place it finds lower R value. Kind of like water leaking thru a hole or a sieve.

What do you have to watch out for, if anything, as far as covering up the part of the light fixtures (electrical boxes) that are in the attic? and are there any other things to be careful of?

I'am remodling my kitchen. My house was built in 1957 and I'am the second owner. I'am constructing a raised reflective ceiling. I have exsisting fiberglass batts. I pulled back the batts and noticed a powder like substance(looks like baby powder). Could this powder/dust be from the old blown in insulation? Does this contain asbestos?

Given what you plan to do in the future (and I'm a big fan of planning ahead) I think the idea of vacuuming out is a great one - why not consider - vacuum out all old insulation (who knows what it was made of and if it's cellulose, I have heard it loses fire rating over time) then add fibreglass batts, plus the soffit vents (usually styrofoam) THEN when you do your renos you are just shifting fibreglass batts, when finished, you already have the soffit vents, then get blown-in cellulose (and do look for subsidies, they offer them in my area too) added after. Best of both worlds that way.

As for whether something contains asbestos, err on the side of caution, don't disturb it, and have it tested. Don't treat fibreglass as harmless either, always wear long sleeves, gloves and a real mask (rubber/silicone with filters, the reason why people don't wear paper masks for long is they get too hot) I've seen people insulating right beside me with no mask, ten minutes later I'm still working, and they're coughing up a lung. Silicosis is the next Asbestosis.