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Posted by on December 3, 2006, 1:50 pm
Kyle Boatright wrote:
> >
> > marson wrote:
> >> Kyle Boatright wrote:
> >> > Our 40 year old home has a mixture of insulation in the attic. 2/3 of
> >> > the attic has blown in cellulose, and the other 1/3 has fiberglass
> >> > batt's that were added during renovation work.
> >> > Can I blow in additional cellulose over the whole area. If not, why?
> >>
> >> yes you can blow cellulose over the fiberglass.
> >
> > Marson may not agree but I think blow in sucks if you ever have to work
> > up there again....
> >
>
> No doubt about that, but what I really wanted to get at was whether there
> was any major downside to blown in over batts from the perspective of
> insulation value.
Over time, blown in cellulose insulation can/will settle down
due to gravity ( reducing the air pockets between the cellulose )
and thus their insulating property will/can degrade over time.
Fiberglass batts are more likely than blown in cellulose to
maintain their insulating qualities over time. Installing fiberglass
batts takes less skill to install and less equipment than blown-in
cellulose thus making it a better DIY weekend project. ISTM
- the current cost differential between blown in cellulose
vs. fiberglass batts for most residential homes is not
substantial enough to warrant it as a decisive factor.
Fiberglass batts insulations are maintance free; blown in
cellulose insulation will require that one add/redo cellulose
insulation periodically to maintain its insulating properties.
I removed my attic blown in cellulose insulation (R20-R30)
because it was settling down due to gravity and it was losing
its insulating quality. I replaced it with new fiberglass batt
insulation last fall (R38 - the highest R rating available locally
and the thickest batt my attic could handle uniformly).
DOE has a new insulation standard for new construction
now ( see page 6 and 7 in the U.S.DOE "Energy Saver$"
booklet at http://www.eere.energy.gov/consumer/ or ask
for the booklet by calling 1-877-EERE-INF, 1-877-337-3463).
Older home may not have enough space along the
edge of the attic to hold uniformly more than R-38 of
fiberglass batts (12"-14" deep ceiling/attic cavities) so
the higher U.S. DOE recommended R-rating attic
insulation standards may not be viable -atleast using
fiberglass batts. Stryofoam panels take up less space
than fiberglass give the same insulating property so
stryofoam panels could provide a higher level of insulation
given the same space limitations in older homes.
However, a stryofoam panels insulation project is
going to cost significantly more.
HTH, Walter
>
> If there isn't, I plan to "top off" the settled cellulose between our
> rafters in the area where we store things, then reattach the decking on top
> of it. I figure that's probably 250 sf of the 1,000+ sf attic.
> I'll have another 8" or so of cellulose blown in elsewhere and may put down
> a couple of boards to facilitate walk paths for future maintenance before
> the new blown in material goes in.
>
> KB
>
> > I like f/g batts / roll / blankets best.
> >
> > cheers
> > Bob
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