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Re: GSBN:Fwd: CASBA_ Pea Gravel
Hello all -
I've been silent for some time, largely due to my recent 5 weeks in
Pakistan, which I will brief you on in a future e-mail. But about this
subject of pea gravel / capillary break / drainage plane.
For my input I start with the language from my proposed SB Appendix to the
California Building Code (status of which is the subject of another
L104.6 Bale/Concrete Separation. There shall be a moisture barrier and a
capillary break between bales and supporting concrete. The moisture barrier
may be any durable sheet or liquid applied membrane that is impervious to
water. The capillary break may be gravel or other material that prevents
the wicking of moisture across that material and into the bale. Where bales
abut a concrete or masonry wall that retains earth, there shall be a
moisture barrier between that wall and the bales.
It boils down to the following goals/concepts:
1) prevent migration of water vapor from relatively wet concrete (in
contact with relatively wet earth) to relatively dry straw. (movement
mechanism: wet to dry diffusion)
2) provide a capillary break that prevents the migration of any liquid
water at the base of the wall into the straw. (movement mechanism: capillary
3) provide a drainage plane that keeps any liquid water at the base of the
wall from direct contact with the straw (movement mechanisms: direct
contact, capillary action)
Sources of water:
a) ground water
b) intrusion of rainwater
d) interior spill (plumbing fixture, water appliance, your olympic-sized
swimming pool overflowing)
In my proposed code language I require a "moisture barrier" and a "capillary
break". In principle I think a drainage plane is needed, but I don't
require it by name, because I think if you provide a capillary break you
also have a drainage plane. (However, for purposes of describing intent,
maybe the term should be included)
I also address the condition of bales abutting concrete that retains earth.
A moisture barrier is required, but no capillary break or drainage plane. I
have thought that this is sufficient for this condition, but as I think
about it now, maybe there should be a capillary break/drainage plane here
also, in case of condensation or a failure in the moisture barrier.
It's interesting to look back and try to understand my own logic in this
code section. If the logic or language is deficient, I'm open to
improvements (as always).
I agree with most of what everyone has said about the subject in the
thorough and entertaining dialogue, but will expand on or challenge a few
Re: the subject of performance vs. prescriptive code language - I believe
that depending on the issue, performance and/or prescriptive language should
be used. If I had to pick one I would say performance, but I sometimes
favor the use of both. By using both you're essentially saying "Here's how
(whatever) needs to perform, and here's an example of something that
provides that performance." Is there anything wrong with satisfying both?
Re: intent included in code language - To varying degrees, performance
language at least implies intent, and in some cases is identical. I think
conveying intent in the language is a good idea. If it becomes too
unwieldy, there could be (and often is) a commentary that accompanies and
supports the code.
Re: the drainage plane becoming a "moisture collection basin" (J.S.) - With
normal detailing at the bottom plates, this won't happen. Well before it
could fill up and reach straw, it would weep to the inside (good for
detection) and/or outside (good for release and/or detection). And I do
think the concept of a drainage plane is legitimate here. Yes water could
come from above and you'd have bigger problems. But it could also come from
outside, near the exterior surface or at the bottom of the wall, or a flood
source from inside. Even from condensation on the top surface of the
supporting concrete (slab/foundation). (As an aside, I've been running
water supply pipes laterally in this space between the bottom plates, and if
they leak there in a drainage plane, they would presumably do little harm.)
In all these cases a drainage plane keeps the bales away from liquid water.
That said, in Pakistan Darcey Donovan and I are now using gravel bag
foundations with no drainage plane between the top layer of bags and the
bottom of the first course of bales. We are painting a moisture barrier on
the top course of gravel bags (which are capillary breaks themselves, albeit
below the moisture barrier) and are dipping the bottom of the first course
of bales in clay slip as insurance in case moisture occurs at that interface
short term. In Pakistan we are well outside the jurisdiction of the
California code and must answer only to our sense of good practice, and
occasionally the Taliban. (I'm trying to keep both my sense of humor and my
drainage planes dry.)
I like many of the ideas shared by everyone for this small but important
space between bottom plates. Like rock that contains air and is more
insulating, or a small thickness of foam insulation against the inside plate
with gravel in the remainder, or layers of gravel and insulation.
Also, from John Swearingen's first e-mail on this subject, I think his
"Gore-Techs" sign-off is one of his best in a long line of clever and
occasionally brilliant puns.
Glad to be back in the discussion.
Martin (Give me a capillary break!) Hammer