Rocket engine | Creeping cold | |
Recall these two infrared pictures, from part 24 when beginning to explore thermal imaging and then part 27 near the end? These were among the eye-openers to the fact that my foundation wall was still a problem as far as overall heat loss. |
In studying the problem a little further, I found this very indicative pair of diagrams in a builders' guide about foundations from a research team in Kansas. Note that they're mostly talking about completely uninsulated basements and slabs, so I was already doing a bit better with all the added stuff on the inside. But this basically illustrates the [lack of] R-value in concrete and soil. |
More insight came from a
frost heave study
and how foundation walls are affected, from our friends at Building
Science. This diagram [which I've taken a couple of liberties
with] shows rough isothermal lines, i.e. the temperature gradient,
between the outdoors and a basement insulated in a similar fashion
to mine -- walls done on the interior, but not the slab.
The rocks in a rubble wall are thermally more conductive than soil and
help pull more heat out of the ground and throw it away outdoors, with
the effect that the cold can penetrate even deeper into the dirt near it.
My discussions with some of their folks a couple of years back had suggested that visible heat from a basement wall could easily be coming from a combination of the basement and the generic earth-temperature of the soil around it, while all that mass cools down over the course of a winter. We do have to think fairly long-term about all of this. |
The exposed part of the wall was bad for heat leakage but great for
moisture control, as it would let ground dampness out through the
concrete face long before it could drift up as high as the sill.
With a solid vapor barrier formed from the configuration of materials on
the interior, anything placed on the external surface would *have* to
remain completely vapor-open or it would spell doom for the wood above.
That meant no foam, no membranes, and likely no paint. The semi-obvious
answer was rockwool, which the evident brand-leader Roxul makes in various
types of rigid boards as well as the traditional soft batts.
I figured that covering the exposed parts with some meaningful R-value
and going some nominal distance into the ground would at least help the
wall stay a little more up toward the temp of the surrounding earth
instead of the winter winds howling past it.
I started doing a little more research, mostly reading about Roxul's product offerings and application notes. But the rigid board products aren't just something you'd find in the back aisles of the Big Box; they're somewhat specialty items and most are geared more toward the commercial market. To know what might work for my not-yet-a-project I wanted to get some of the stuff in my hands, and thus began the first of my many runarounds with Roxul's customer service. After a bit of legwork I had the number of a local rep in Rhode Island, who said he could send me a small batch of "hand samples" to look at and assured me that some of the products I was considering were ideally suited for what I was thinking about. |
I also looked into adhesives. While the Dynaflex caulk worked well
on various kinds of foam it didn't seem appropriate for the more porous
and somewhat friable surface of rockwool. I needed some
serious construction adhesive
that would work on concrete and various kinds of
stone, because basically I'd be sticking rocks onto other rocks.
I had some experience with the PL series from Loctite, and spending a while
reading labels in the caulk and adhesives aisle seemed to suggest their
"8X Fast Grab"
product as the best option.
A little experimentation with that and some other sticky stuff revealed that the bonding strength of the rockwool board by itself wasn't actually that good, but I had already thought of a hack to improve that. Basically, to prevent a small patch from ripping right off the surface, more of the fibers around a glued area need to be brought into structural play. Now, what product did I already know about that could soak way into a porous substrate and then solidify into a strong supporting matrix? Wood hardener. I was pleased to find that it would create a much larger and more rigid region around wherever it was applied to the surface of the rockwool. In the foreground above, therefore, is my research tool: a small piece of cinderblock with little rockwool cubes glued to it, with and without the wood-hardener trick, that I set up and left to cure for a couple of days. |
On a cold evening a while later, though, I got a pretty good hint about the effect this might have. I left one of the sample blocks in the middle of the assembly unadhered and just held in by friction against its neighbors, with a couple of long screws sticking through from the back so I could gently slide it out and expose the wall behind. When I did that and shot the infrared, I could clearly see that the test patch *was* keeping the wall a bit warmer. Not fully up to earth-mass temp, certainly, especially with all the rest of the cold exposed wall not that far away through the abysmal R-value of concrete, but definitely helping protect it somewhat against the ambient. And I *thought* I could see a slight difference up in the basement joist bays that were behind the test patch as opposed to the ones outboard of it. Hard to tell there, however, as those joist bays have the disadvantage of the flashing-metal "heatsink" connected to the other side of the sheathing that forms their ends. |
Time passes ...
I left the test patch in place and did nothing further on this for about
a year, over a winter and summer cycle, and simply observed.
The timeframe on the entire idea was long and governed by cautious research;
I was in no particular hurry for answers and had to be sure, knowing that
to go beyond this and wrap the entire outside of exposed foundation in a
cozy blankie would be a substantial piece of work if it was worth doing
at all.
While the patch was too small to have any notable effect on the overall house energy demand, it survived its test in the outdoors just fine. Nothing came along to molest the fiberglass and it didn't get soggy, just a little dirty on the surface which the wall does anyway. |
As I became more confident that the scheme had merit, I took a few
measurements around the house and started a plan sheet, if for nothing
else than to determine how much material I'd need. I could see
immediately that there would be quite a few fiddly-bits and places where
partial pieces would be needed, so I arrived at a generous estimate.
I also stopped by the contractor desk at my usual local big-box to chat
about sourcing the Roxul rigid board, and the guys there assured me
that they could get it in convenient 3-packs through a supply-line
called Primesource and even gave me an SKU number.
Roxul mentions this partnership on their
where to buy
page, so I squirreled that information away for when I figured I might
actually want to act on it.
Which, cutting somewhat to the chase, finally happened about a year after the patch went on. It was actually not an easy decision, because it was already late in September and I wondered how much good weather I'd have left in between other projects I had to work on besides. It felt like my window of opportunity for that year was already starting to close, but I also allowed the possibility that maybe I'd only get half the job done before winter and then I could at least do insulated wall A vs. exposed wall B comparisons or something. But then that would slow down the whole process of re-determining whole-house heat-loss figures after the job was fully completed. Argh, what to decide?? One morning I decided to just stop being lame and wishy-washy and just *go for it*, and do as much as I could when I could and see how it would go. My adhesion pull-tests had shown that the CIS type board held a slight edge in strength over the IS by being somewhat denser, at a slight disadvantage in R-value. But I figured I needed all the holding power I could get, wood-hardener or not, and decided that the CIS was the most suited for the job. And that's when the sourcing nightmare began. When I eventually contacted the big-box back to price up some quantities, they seemed completely unable to find what product I was talking about. After going around and around with them and Primesource directly it finally emerged that Comfortboard CIS is considered a "commercial" product and thus Primesource not only didn't carry it, they said that they were not *allowed* to carry it -- per corporate policy of Roxul themselves. WTF?? More digging around finally got me in contact with a commercial supplier who could get me CIS, but I'd have to buy an entire pallet which was close to twice what I'd need and came in inconvenient piece sizes. They quoted me for both IS and CIS, which at least gave me a solid fix on the price of two-inch material per square foot, which is a little over a dollar per for either type. But suddenly CIS seemed to be out of reach for my small-quantity needs, because of stupid restrictive channel policies from Roxul Canada [which, incidentally, they deny the existence of]. With some reluctance I finally gave up and decided that IS would probably work just as well, and basically started over. Which led to another nightmare as the disparate computers at Big-Box and Primesource couldn't seem to agree on per-pack pricing for IS, and they fully intended to charge me about *three times* what the stuff is worth. Probably some confusion over units of "pieces" or "bags" but I couldn't convince anybody in the chain that they might have a mistake somewhere. Back to the commercial supplier, then, who said they'd be happy to supply me ten packs of IS at the correct pricing and deliver it right to my driveway for an extra thirty bucks. Done!! And then I fired a major rant into Green Building Advisor about this travesty, to warn other seekers of Roxul product that they might be in for an equivalent amount of, uh, administrative fun in trying to source it. But now I was committed to doing this, and had quite a bit of work ahead even before any goods would hit the doorstep. The supplier told me about a two-week lead time at the outside, and I wanted to prepare efficiently and be ready for delivery. |
Whee! Playing in the dirt again
On the north and east sides of the house where the grade is highest, exposing
three full feet of wall involved a respectable amount of excavation.
And that had to be three feet down from the lowest point of the siding and
flashing metal, not just three feet of block wall height, since the pieces
of insulation would have to be ducked under that outer overhanging stuff
before getting attached.
So basically about five courses of block had to be visible, requiring my
trench to be about 18 inches down along here.
I could almost wish I had the same apparatus that a nicely relevant "excavationless" NREL project had available, but that configuration wouldn't be vapor-open at all. |
I helped the driver unload the stack from his pallet-jack since the
stuff wasn't on a pallet anyway, and with the open trenches and mounds
of dirt visible right along the driveway, he seemed rather interested
in how what he'd just brought me was going to play into the project.
So I finally had my material: ten mostly-undamaged bags of 2" Comfortboard IS. Now the real, uh, fun could begin -- when all those unknowns would start getting resolved. Would this crazy thing actually work?? Had I bitten off way more than I could chew? Didn't matter at the moment; delivery at long last had renewed my vigor, and it was a beautiful day for working on stuff like this, so I tore right into those packs and got started. |
_H* 151030