I've got an old house. It's brick with 2x3 studs, plaster and lath.
While the kitchen is gutted down to the studs and brick right now, I'd
like to add some insulation - you know, the "while you're in there"
The minimum insulation I know of is 3". While it's R value isn't
great, I figure it's better than nothing, right?
I am wondering if compressing it into a space that is only 2.5 inches
deep will reduce its effectivness to a great degree
By the way, I do not want to go as far as building out the studs to 4
inches because I'd have to build out all the window jambs and rip down
the cornice of the tin cieling and move it an inch too. Just not
One last question, if I use the Kraft paper backed batting, do I need
to also put up a polyethylene vapor barrier?
Thanks, in advance, for your thoughts on this.
Compressing the glass fiber insulation a bit should * increqase * its
This according to building researcher and Journal of Light
You might want to check the Building Science Corporation web site.
It includes climate specific information on vapor barriers and so on.
My first reaction is to question how the separation of brick and
insulation is to be done.
Brick walls do let in water.
You might check the BIA (Brick Industries of America) web site.
Shouldn't make a noticible difference. I would go with the batting with no
paper and use the poly over it. You have wood over your brick right? If not you
may want to put a barrier over the masonary first then batting then another
barrier. But that may trap moisture hmmm!
Knaupf makes an R7 fiberglass insulation, 15" wide by nominally 2 1/4"
thick which leaves room for venting off moisture. The model number is
R-7U-MHR-15. Fiberglass itself is not what provides insulation, it's
the trapped air, so I would not compress 3 1/2".
Where do you live - north or south? I.e., do you principally use heat
or air conditioning?
I think it would depend. Polystyrene foam has (or at least "had") an
R value of 5 per inch and Polyurethane 6.5, so both are better
insulators, but when last I checked (which was several years ago),
polystyrene while not flammable gave off poison gas when burned, and
polyurethane was flammable.
In addition, there was available a non-expanding foam based on urea
formaldehyde. The "gotcha" there was that it apparently out-gassed
fomaldehyde vapors for a long time and many folks had adverse
reactions to it. I'm not up to date, but if that's been cured, it
seemed like a very effective insulation. You'd want to know if it was
open or closed cell however, and OP would still need to mention his
location and whether his primary need was air conditioning or heating
or some combination of both before water migration issues can be
Just curious, Chris, are you opposed to it because of the negative
impact on the value of your home due to the perceived problem, or
because there are other technical problems with the stuff? We never
used it because of a possible sensitivity to formaldehyde, but it did
look appealing. No expansion and a possible shrinkage of under 1% at
least at the time.
Taken in isolation, UFFI application and insulation characteristics are
In the past, MOST UFFI problems were probably due to poor mixture
control and perhaps even poor QC on the production of the stuff.
Ie: if it didn't mix completely, you wouldn't get 100% chemical reaction
completion, and you'd be left with localized hotspots of (toxic)
Secondly, there are "treatments" for problematic UFFI - air-to-air heat
exchangers and there are apparently ways to "force" uncombined volatiles
out or to reaction completion (expensive, but a whole lot cheaper than a
whole house tearout).
And thirdly, "problems" usually only arose with the unduly sensitive. But
formaldehyde and related chemistry are nasty beasts, and long term dosages
too low to cause problems themselves can trigger more generalized chemical
Its troubled past, plus uncertainties about whether my contractor might
goofup and leave me with unmixed bits, plus the remote possibility of
the kid becoming chemically sensitized makes me say no, entirely aside from
And even now, a UFFI installation can be a real-estate deal or mortgage killer.
My aunt and uncle bought a beautiful century home with UFFI. We didn't tell
them to run away as soon as they possibly could - they didn't have kids.
Just pointed out that they will probably have difficulties selling later.
There are apparently new foam technologies that don't have anywhere near as
much trouble, but I've never been tempted to research them.
Unless foam has changed, then, I"d use the Knaupf I mentioned earlier
and quoted below. I'd use foil backed. It's just a tad better than
kraft in that it reflects radiant heat sources inwards, but with
smaller studs, you really need all the help you can get. I don't
think you need plastic over it.
Sorry about the guy/gal stuff.
I got a few repsonses in alt.building.construction about fiberglass
and brick being very compatible. Specifically that the brick allows
moisture through and if fiberglass was against it, it would become
sodden. Perhaps even push out the drywall if it expands due to having
been compressed (although I know you are recommending to NOT compress
What are your thoughts on fiberglass and brick? Perhaps I should use
furring strips on the brick to keep the fiberglass from directly
touching the brick?
oh, and don't worry about the guy/gal stuff - I've got a good sense of
humor and it didn't bug me! And besides, "Rogue Petunia" is just a
posting nickname, so how could anyone tell based on that, right?
Funny...I took it as being your first and last name...and that you
were of a nationality with a unique, unusual first and last name. And
Rogue sounds masculine...or at least neutral.
Have a nice week...
Fighting for peace is like screwing for virginity!
I think it's important to note that proper installation of any
fiberglass insulation leaves the external surface NOT in contact with
anything else, brick, wood, whatever. There is always supposed to be
an air space and it should be vented. I am guessing that this applies
even more so to brick since, as you say, it does provide a cool
surface upon which water can condense at some point in the year.
Fiberglass will not expand when wet, but it will lose substantial R
Hopefully, this explains the problem: In the winter, you have cold
dry air outside and warm, relatively (to the outside) moist air
inside. At some point, the moisture in that moist air would condense.
What you are trying to achieve is twofold: most important is to keep
the moisture out of the insulation and keep the dewpoint within the
dry area. Since there is no moisture there to condense, there is no
problem. This is one of the best reasons for using a closed cell foam
- you guarantee that the dewpoint will occur within the medium and
there will be no moisture to condense there. If only it weren't
poisonous when burned (in the case of polyurethane) or outgassing
(urea-formaldehyde). You keep moisture out of the wall with kraft or
foil facing. Obviously you might want to be extra careful around
outlet boxes. There you might want to wrap the outside of the box in
plastic and tape the plastic to the foil or kraft facing.
So, the long and the short of it is this - if you use Knaupf or
similar insulation, it will not touch the brick and you'll be fine.
That said, I am a bit confused. Normally, brick is applied as a
veneer against sheathing (nominally 5/8" plywood). I think you're
saying you have masonry walls of some substantial thickness with 2 x 3
studding directly against it. Those 2 x 3's provide structure for the
sheetrock only - is that correct? If that's the case, you won't be
able to vent the insulation without some major surgery. That would
make me be especially careful about keeping moisture out of the cavity
between the studs.
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