Insulation in attic

Discussion in 'Remodel Forum & Blog' started by Semon, Jan 14, 2012.

  1. Semon

    Semon New Member

    Messages:
    36
    Location:
    Tn.
    I need to put insulation in the attic. I want to bring it to about R30.
    Which is better Bats or blown?
  2. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    I used r30 batts then used 6" of blown over that.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    This ends up compressing the batts, and decreasing their contribution to the total insulation level. the batts must be fluffed to their design height to provide the specified insulation level and that doesn't happen when you pile stuff on top of it.

    Bang for the buck, blown cellulose is probably one of the better choices - it fills nooks and crannies and stops convective losses through air movement (if there is any). In an old install, a quick check for air infiltration with fiberglass batts is to look for discoloration...the fiberglass is acting like an air filter. WHen this happens, you lose a lot of the theoretical performance.
  4. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,386
    Location:
    Yakima WA
    Blown in is inexpensive both to buy and to install. I discovered years ago when I wanted to insulate my garage/shop attic. I could have bought the blow in from HD, and used their blower for free, but I learned it's not only a rather unpleasant task, it takes at least 2 people. One to direct the insulation coming out of the hose, and one on the ground to feed the blower. Then I check with a local insulation company, and found they would supply the material and do the whole job for the same price as I would have paid HD.
  5. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    He asked for the best way, not one of the worst...
  6. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    What was your first clue that it would take 2 people?
  7. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,386
    Location:
    Yakima WA
    Duh! Guess I was a slow learner. LOL Actually, I really knew it would take two and that I'd have to recruit an unsuspecting friend...maybe ply him with a few beers before springing the job on him.
  8. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    You could do it with one if you're a fast runner!
  9. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    6" of blown didn't compress anything.
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    Have you measured recently? It can take awhile to compress. Or, your blown-in component wasn't very dense.
  11. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    The blown has settled down but the r30 batts are fluffy and thick. My power bill dropped after I added the blown and the A.c. doesn't run as much.
  12. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    So you didn't measure it.
  13. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Unless the power company lowered their rates over the past 3 years theres no need to measure anything but the stack of money I'm saving after I added the blown in over the batts. My power bill dropped an average of 30 bucks a month with the same hvac unit and thermostat setting at a constant 70 degrees. Hows that?
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    You're missing the point...obviously, adding insulation helps. But, putting blown in over a batt type compresses the batt. Your total insulation level wouldn't be as high as if you'd either used all blown-in, or put the batts on top of the blown in. IOW, you didn't get the full benefit of what you installed.
  15. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    I had batts only for 7 years. 3 years ago I added 6" of blown in on top of the batts and that cost 600.00 to add it. Since I aded the blown in over the batts my power bill has been an average of 30 bucks cheaper over the past 3 years. 6" of blown did not compress the batts enough to measure or matter,the benefits out weigh the negative and my power bill proves it. It took less than 2 years for the blown in to pay for itself and last year it saved me about 350.00. So now maybe you understand why I'd rather go by what I know rather than what I'm told or read.
  16. Dana

    Dana In the trades

    Messages:
    2,984
    Location:
    01609
    Not necessarily. Low density batts (the typical goods, not the high density "cathedral ceiling" batts) need a topside air barrier to actually achieve their rated R value performance, and in most attic installations the tops are left bare. But if you blow over them with a higher density product like cellulose, it actually performs BETTER, despite being slightly compressed. (And with only 6" of overblow it's a VERY slight compression indeed.) By filling in all the gaps and voids, even low density crappy blowing wools will improve the performance of the batts, but not as much as cellulose.

    With any batt installation layed down on top of blown (any density batt) or other batts you have the issue of the gaps allowing convection to rob performance.

    What I WOULDN'T use is cheap low-density fiberglass blowing wools- I'd do rock wool before that, but cellulose is even more air-retardent still. A 3" overblow of cellulose can "restore" low density batt performance to near it's ASTM C 518 test rating, but not low density blowing wools. The test plates used in the ASTM test become air barriers during the test which is why in many ways there's a labeling issue when batts or blowing wools are used in attics without an air barrier on the top side, as is usually the case.) Testing those products in the fixture with an added air gap also doesn't cut it, since the gap isn't anywhere near as deep as an attic space, and isn't vented to the great outdoors. (And attic ventilation rates will vary, making any arbitrary vent rate in a test fixture wrong.) But blown cellulose hits pretty close to it's rating, even without a topside air barrier.

    To get best results it's good to set up depth gauges and rake it all dead-even, since a few thin or bald spots can rapidly become the thermal bypass for the rest.

    I've occasionally blown insulation as a 1-person DIY, and I can testify that it's a scrambling, tiring. and slow way to do it.
Similar Threads: Insulation attic
Forum Title Date
Remodel Forum & Blog Attic insulation. Sep 5, 2014
Remodel Forum & Blog Attic Insulation with a new roof Mar 11, 2014
Remodel Forum & Blog Attic Insulation, nearly flat roof May 19, 2013
Remodel Forum & Blog Adding attic insulation over rock wool Feb 24, 2013
Remodel Forum & Blog Attic Insulation Jun 13, 2012

Share This Page