Top Beams + Waterproof Or Not?

[M J Epko]

        At 07:05 AM 10/3/96 -0400, Pat Newberry, whose updates to the SB
list on his progress I appreciate even though I get sorta jealous reading
them, wrote:

>The bond beam, I heard one person mentioning a cement bond beam.
>regardless of cement or wood....is this the same thing as a top plate in
>straw bale????

        Did I miss this? (Probably. Maybe I even said it myself. Been
working on an update for the SB links site & it's eating up all of what tiny
bit of spare time and functioning brain cells I have... I'm taking a break
before I get too much more exasperated.)

        It's a good question, one I hadn't considered. Maybe it's in
Shannon's long post from last week. Maybe I should go read that right now.

*

        Okay, I did, and it's not. (I've also been delinquent in ordering
the booklet from Cob Cottage, so maybe my answer is in there. But I've got
you all here now - so...)

        What about attaching the roof? Here in deep-snow country, a fair
pitch is generally desirable; we need to attach the rafters somehow. Would a
wood beam (perhaps nothing more than 2-by dimension lumber, say 2x10 or
2x12?) be attached to the top of the wall using the porcupine method? That
would seem insufficient to withstand uplift, especially if generous
overhangs are part of the plan. Perhaps foundation-type anchor bolts are
built into the top layers of the wall & the beam/plate is simply bolted on?

        Same concern for concrete. And what, besides being easier to level
than cob, would be the advantage of a concrete running bond beam? Couldn't a
person use an easier-to-handle-than-concrete wood beam and just stuff cob
under it into any unlevel parts once it's bolted down? Am I missing
something obvious again?

        How about using peeled poles viga-style (protecting the exposed ends
from the copious precipitation with the pitched roof), which would be
incorporated *into* the wall & to which a wood top beam (perhaps flattened
logs) could be bolted. Since wood's R-value is roughly comparable to cob, it
wouldn't be much of a thermal break. Perhaps horizontal holes could be bored
through these vigas where they cross the center of the wall and rebar could
be threaded through for additional uplift resistance. Oh, I'm just swimmin'
with unusual and unneccesary ideas.

>I have heard that straw is NOT a necessary ingredients. Any comments????

        Personally, I'd guess that it's not *vital*, but I'd also guess that
it does add significantly to the monolithic strength of the wall. Like those
fiberglass-strand additives for concrete... they're just weenie little
things, much littler and certainly no stronger than any self-respecting
shaft of straw, but they DO increase the strength of the concrete substantially.

*

        Our building plans are changing. I'd grossly and embarrassingly
underestimated the passive solar potential of our building site (s'what
happens when yer site's 6 hours away & ya've never been able to just *sit*
on it for even a day) - so we're going for mongo exterior insulation.

        Here's what we're thinking, and I welcome all comments and
suggestions: phase one will be a somewhat spiral-like (like a top view of a
snail shell) cob structure on a shallow (non-frost-protected) rubble trench,
about 12' inner-diameter minimum at the small part. This will be the bigass
bathroom (our current one has 3-1/2'x4' of open floor space not occupied by
permanent fixtures, and we're fed up with that), and will vent directly
outside through the roof. It will be fully enclosed by a circular or
octangular strawbale structure 10 to 12 feet larger all around than the cob
part. The cob wall will be the bearing system for the interior of the radial
joists. The chimney for the wood-heat system will also be incorporated into
this wall, and it will provide more-than-adequate thermal mass
fully-protected from exterior temperature swings.

        The question: should the bathroom side of the cob wall be
waterproofed, or do we suspect that the direct ventilation will suffice? The
source of my wedded bliss wants a sauna in there - this changes the picture
some, eh?

        The other question: will this work? Will it be far more difficult
than I'm anticipating?



       M J Epko    duckchow at ix.netcom.com
        http://www.netcom.com/~duckchow/