[Greenbuilding] Best bang for the buck in wall insulation

Tue Mar 25 18:32:50 CDT 2014

Adding to to Jason and RT's information, and the description of Roxul 
and it's use, I would add that Roxul has all those good qualities that 
they've mentioned,
but is entirely dependent upon the skills of the installers to be a good 
fit.
The Roxul Comfort Batts, made for the interstices between 2x4 studs, can 
be accurately sliced off using a sharrpened, long bread-knife, and if 
the cuts are square and accurate, the resulting piece will fill and seal 
the wall cavity quite well.
If not cut square and accurately, the result is worse than the use of 
fiberglass batts, which will "stretch" a bit to fix a poor cut and 
measure. Roxul does not "stretch". It crumbles.
Good carpenters are required, so that good results can be expected.

The Roxul Comfort Board, made to be applied outside of the studs, also 
requires care, as it too can degrade with poor installation techniques.
I love the stuff, but it takes a lot of thickness to add up to R-50 or 
so in the wall system.

Side issue: Each person is different, and I know two different people 
who can not tolerate being around the application of the Roxul Batts. 
Dust is not the issue, but some sort of chemical intolerance is the 
issue. Perhaps the batts are formed using formaldehyde as the stiffener? 
At any rate, there is a fume to be concerned about, for some people.

Perhaps with 2x6 framing, and R-22 batts, layered over the exterior, 
with two layers of 1 1/2" Comfort Board, at R-6 per 1 1/2" layer, we get 
a total of R-28. If we add another 1 1/2" Comfort Board on the inside of 
the wall frame, and strap it with 1x4 furring strips, as a substrate for 
dry wall or plaster lathe, we still only have a total of R-34 or less 
for the wall system.  R-34 is not enough for your purposes.
..................................................................................
Deva Racusin, from Vermont, has built some beautiful straw bale combined 
with Roxul Drainboard, and dense-packed cellulose to achieve R-60 
overall, which is a happy combination, too. I co-wrote a presentation, 
Building For A Cold Climate, with him a few years ago, and his system 
looks good. See this wall system in his book, "The Natural Building 
Companion".
..................................................................................
But if straw bales are too intimidating, then double-stud framed with 
dense packed cellulose is the very best possibility to achieve R-60.

I'm with Topher.
Without hesitation.
My favorite choice has been 2x4 frame loadbearing wall. Quick. Easy. 
Minimizes lumber use. Strong enough and meets code.
See the attached photo.
Describing the layers in this system:
 From the outside moving towards the inside:
~ Vertical wood board siding, (vertical provides good drainage) 
something like board and batten, or, Fraser Board Contour Siding, or 
hardee board;
~ horizontal 1x4 furring strips@ 16" o.c., as substrate for vertical 
siding;
~ attached to studs with #8 x 4" yellow zinc screws,
~ through 1 1/2" Roxul Comfort Board,
~ over 1/2" poplar plywood as a wall sheathing, (Pure Bond Ply, with no 
formaldehyde glues),
~ into 2"x4"@ 24" o.c. load-bearing studs,
~ with a similar 2"x3" @ 24" o.c. non-load-bearing studs framed parallel 
to the outer wall frame, on the interior,
~ and spaced a full 14" inside of the outer plywood sheathing. Allows 
14" of dense packed cellulose, @ R-45

This inner frame will be covered with MemBrain, by CertainTeed, variably 
permeable membrane vapour retarder, stapled to 2x3 studs, and covered 
over with 2"x2" horizontal furring strips @ 16" o.c., as a substrate for 
drywall, or, plaster lathe.

After strapping over the membrane, the dense pack process can begin, 
through the membrane, and it is easy to visually see how well each 
cavity is filled under 3lbs+ pressure.
Total R-Value of the system is R-52. or R-60 @ 18" of cellulose with 
half inch plywood and 1 1/2" Roxul Comfort Board exterior.

The electrical wires and boxes can all be fastened to the 2x2 strips, 
and wires run through the 2x2's, with no puncturing of the vapour 
membrane at all, and no need for fussy "booties" around each electrical 
box, and still achieve 1 1/4" set-back for safety behind the plastered 
or dry-walled wall surface.
For maximum thermal mass, inside this very warm wall system, 5/8" 
drywall or, 1" plaster works just great to slow the diurnal temperature 
swings, when using firewood and solar gain as heating fuels.
Total wall thickness still adds up to similar to a well-built straw bale 
wall system, but R-value is higher.
Embodied energy is also higher, but most all materials in the system are 
benign to the environment, expecially using earthen plasters on the 
interior, (except the MemBrain ... hard to get around using plastech! as 
a vapour barrier, with most wall systems).

Hope this helps, Lynnelle. (More choices? Oh no!)

Frank Tettemer
Living Sol ~ Building and Design
www.livingsol.com
613 756 3884

On Tue, 25 Mar 2014 15:56:08 -0400, Jason Holstine 
<jason at amicusgreen.com> wrote:

>
> Roxul ... doesn¹t burn (made of recycled steel and volcanic rock), deals
> with vapor and water nicely,

>  Only downside is availability in your area may
> still be dicey.

I understand that economy of words is a good thing but in Jason's case, 
a few more wouldn't have hurt.

As far as I'm aware, Roxul is not made of recycled steel.

For the last 30-odd years I've been under the impression that the 
materials used to make Roxul are basalt and slag (a by-product from the 
blast furnace cycle of iron or steel production). Some of you may 
remember seeing chunks of the stuff when you were a kid, playing where 
you weren't supposed to be playing, alongside railroad tracks.

Roxul may still be relatively new to Murricans but it's been widely 
available in all building supply outlets since at least the early 1980s 
if not 1970s, in batts and rigid boards.

The Roxul area rep would often set up a table in the local building 
supply store and entertain passersby with his demonstrations of Roxul's 
fire resistance (destroying other insulations with a propane torch while 
gleefully achieving nothing with the same torch held onto a piece of 
Roxul) ... Roxul's ability to repel and float on water (even after being 
held underwater for an extended period of time and Roxul's ability to 
drain itself dry after water was forced into it under pressure.

Best of all, it doesn't make you itch all over or make you spit up blood 
when installing the stuff, like fibreglass does (makes me cringe just 
thinking about that F-G-ing stuff). Slightly better R-value than the 
same thickness of F-G too.

Guess I went a bit overboard with the words when all I really wanted to 
say was "Not recycled steel".

-- 
=== * ===
Rob Tom                    AOD257
Kanata, Ontario, Canada

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