Cob Re: Carpet/cement per Pat

[Stephen H. Kapit]

Thanks Don, that was very useful information.

Stephen

Don Stephens wrote:

> On Mon, 29 Jun 1998, Patrick Newberry wrote: You mentioned Earth - not so
> > good sandwiched between the layers of cement/carpet, Yet latter on you
> > mention the wonderful aspects of a living roof (I too have a high
> > opinion of) But then why is a living roof good and earth between two
> > layers not good?  I have thought of putting  living roof on top of this
> > but at this point I'm still leaning toward the sandwich roof.
> > Also on the shed style roof, it will probably not be "flat" like a
> > sheet of plywood. Last time I used this method, the carpet dipped
> > between by 2x4 supports due to the cement carpet drooping between
> > supports. My brain told me (but it's been wrong before) that  hey
> > this is better because it's more like the corregated roof (right
> > word?) anyway I did't fight the wavy-ness by pulling real tight
> > between the support.
> > I'll will go ahead and start making some "test" sandwiches.
> > One test we did ealier here was using peanut shells and a small
> > amount of cement.. Being in Geogia (not too far from Jimmy's place) I
> > have access to as many peanut shells as I want for free. We mixed
> > them with cement and made inch and a half thick squares. I stood
> > gently on it (about 150 lbs) and it  held. My son stood on it and it
> > broke (about 250 lbs) I have thought this might be an interesting
> > middle layer for the roof as the weight of  the squares as much less
> > than  a cement square would be. ...Pat, Mauk GA
> > >
> > > Earth - not so good.  Earth is wonderful stuff and super in cob, rammed
> > > earth, stucco, floors, thermal storage, growing stuff on your roof,
> > > buffering short-term temerature fluctuations, etc., but as INSULATION,
> > > it's heavy and only about R-.2 per inch (dry), eg.: a foot of earth is
> > > less insulating than 1" of straw (~R-3).  Weight of a cubic foot of dry
> > > earth ~ 120# dry - Weight of a square foot of compressed straw 1" deep " ~
> > > 8 ounces!  heavy = more structure = more effort and or expense!
> > > PS:  Are you receptive to the idea of a "living Roof" surface on top?
> > > That's one of the techniques of which I'm particularly fond and one I've
> > > been experimenting with since the 60s.  It's ecofriendly, cheap, gives an
> > > almost eternal life to the waterproofing membrane underneath (no UV, no
> > > freeze and thaw cycle, no dry and wet yoyo, no physical trama from foot
> > > traffic or falling branches), manages run-off better and it's "purty".
>
> The common confusion with earth is between INSULATION and MODERATION.  as
> I indicated above, earth has a very poor ability to insulate - prevent the
> transfer (escape/intrusion) of heat.  On the other hand it has a high mass
> which very effectively moderates temperatures - it takes a lot of heat to
> warm it up, a lot of cold to cool it down.  This means if your day
> temperature is ~ 20 F. but it drops to - 10 F. overnight, the soil surface
> in the morning will have dropped down almost to the - 10, but even just 3"
> down the soil will remain an AVERAGE of all the temperatures of the past
> week - say ~ 15.  So the underlying roof won't "see" those short-term
> overnight drops.  Likewise, in summer, if you have two or three blazing
> days of + 105 F., under even three inches of dirt your roof will never
> "see"  it, instead remaining the several week day/night average of say ~
> 75 F.!
>
> Also the PLANT LIFE on top will reduce windchill and increase air film
> insulation factors in winter and the shading and transpiration cooling it
> provides will help in summer.
>
> So plants/dirt on top shield against short-term weather extremes, but to
> prevent the slow penitration of outdoors summer heat or the slow escape of
> indoors winter warmth, you want INSULATION, and at R-.2/inch, it's just
> too expensive to suport the R-40 (almost 17 feet!) you would theoretically
> need in some northern climates,
>
> I say "theoretically"  because the soil's thermal flywheel effect is such
> that it takes (in dry soil) about a month for heat to travel 18", so in 6
> months (9' of soil)  your winter heat would be escaping but it wouldn't
> matter because you'd enjoy that cooling 'cause it would be summer!  They
> use that principle in Australia (See AUSTRALIAN EARTH-COVERED BUILDING by
> Baggs - Rog, have you seen that one?) to let summer sun arrive in winter
> and winter cool arrive in summer, but it means holding up hellacious
> amounts of dirt with "hell-fer-stout" concrete roofs and walls.  They
> should discover subsurface insulation as a way to hugely deminish those
> loads. (As I've indicated before, I'm into minimizing concrete for
> eco-reasons.)
>
> Bet that's more than you wanted to know about the thermal properties of
> dirt, but because of the chronic insulation/moderation confusion about the
> stuff, I thought maybe it needed to be said.  If irrelevant to you, just
> hit the delete button....Don



--
Stephen H. Kapit
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