My attic has 2x6 joists. The (ancient) fiberglass insulation between the joists appears to be matted down to about 2" thick.
Do I rip it out and replace with 6" thick batts and add more above that?
Or do I leave it, add 4" batts, and add more above that?
All opinions appreciated.
On Saturday, May 17, 2014 6:58:05 AM UTC-4, Stormin Mormon wrote:
Unless height is an issue, I'd just add on top of what's
there, probably use batts. As Bob said, 6" isn't much,for
most of the USA in winter, R30 is the minimum. That's 9 1/2"
thick. The original should have a vapor barrier and if you
use batts, then it should not have a vapor barrier.
He DID say he was going to add more above.
Matted down insulation has poor insulation value. I'd remove the old
first - and be tempted to have a spray insulation applied (about 2
inches) to act also as a vapour barrier and then fill with blown
insulation above that.
On Saturday, May 17, 2014 11:13:59 AM UTC-4, firstname.lastname@example.org wrote:
I missed that. I guess enough insulation to fill it up
to the level of the top of the joists, then loose cellulose
gives the best energy solution. I wonder what the energy difference
is if you use just thick batts? There would be some gaps
between them, ie between joists, which would cut down the
performance. Topping it with blown-in would be better from
that standpoint. Only thing about blown-in I don't like is
that if you have to do some work, eg find an electric, phone,
CATV etc cable, it's going to be a pain in the ass. But I
guess you don't have to do that very often.
Sounds like unnecessary complication to me. I agree if it's matted,
it has low R value, but so what? It's still greater than zero, and
if you put what you intend to put on top of it, you have the new plus
whatever is existing. A little more insulation and you avoid the
work and disposal, etc of ripping the old stuff out.
My question is how come it matted down? Moisture problem one time or
another? I want to make sure about this. Is there vapor barrier under
If all is good, I'd just add more insulation by any means. Here it is
R60 in the attic.
If it's like my attic it's dust piled up over the decades. I think, when
I finally get the funds together, I'm going to have old insulation left
in place with cellulose blown over it. With vaulted ceiling it's
probably the best solution. Back in '83, when they built my house, they
used some kind of rock wool insulation. Seems to work okay, but I'm sure
it's not anywhere near present standards.
House is in lower New York State.
Existing batts have been matted down over their apparent 60+year life in the attic.
I find fiberglass batts much easier to deal with than blown cellulose, so I'll stick with them.
I guess I'll leave the existing and just place more on top!
On Friday, May 16, 2014 11:33:48 PM UTC-5, email@example.com wrote:
the joists appears to be matted down to about 2" thick. Do I rip it out and
replace with 6" thick batts and add more above that? Or do I leave it, add
4" batts, and add more above that? All opinions appreciated. Regards, Theo
Any bats added above the joists should be placed at right angles to the dir
ection of the original bats to ensure there are no accidental "chimneys".
On 5/17/2014 1:10 PM, firstname.lastname@example.org wrote:
As long as they're not completely full of dirt as can happen here in the
High Plains over that period...we took over 2" of accumulated dirt out
of the attic of the house here (built in '15/'16). Most was from the
"Dirty 30's" but I'm sure a fair amount also accumulated during the
other really bad period of the 50's...
There SHOULD be vapour barrier under it, but you can almost guarantee
it is not uninterupted if it IS there - which is why I would seriously
consider removing what is there and having a thin coat of spray foal
installed before filling it with cellulose or fiberglass.
On Saturday, May 17, 2014 6:45:47 PM UTC-4, email@example.com wrote:
Let's say it has the typical vapor barrier similar houses would have.
What is going to happen that is so bad, from just adding more insulation?
If this house isn't experiencing any problems related to moisture passing
through the vapor barrier that is there, what's the compelling need to
rip out the existing insulation and do spray foam?
The house I'm living in, I'm sure the vapor barrier isn't perfect.
It isn't perfect in new construction either. But I'm not seeing
any problems from it. And if the OP doesn't have problems, I'm
not seeing the necessity of the rip out and spraying in foam.
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