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re: frugal homes
14 jun 1997
roger p williams   wrote:

>wayne l  wrote:

>: how do you build a home for $50.00?
 
>others have posted where to get mike oehler's delightful book, but i
>thought it would be a good idea to post a quick summary for the more
>distantly curious.

thanks for the summary... 

>oehler's homes are underground homes.  he calls his technique "post
>shoring polyethylene," or psp.  basically you dig a hole, sink posts along
>the walls, put up shoring behind the posts, build a shed roof, and 
>surround it with polyethylene to provide a moisture barrier.  cover with
>dirt, and there you are.

sounds simple, especially if you have a backhoe or 2 dozen people with shovels.
these $50 houses might be expensive with paid labor. polyethylene film is
wonderful stuff. i wonder how well it works for the roof, vs epdm rubber,
which is much tougher and only comes in 20' wide rolls. people get very fussy
about installing it under dirt. maybe 2 layers of poly would help...

what does oehler do about insulation? earth is very poor insulation, something
like r2 per foot of thickness, vs r40 per foot for fiberglass, altho soil can
be a  little  better when dryer. the poly vapor barrier would tend to trap
moisture inside the house, if there were insulation inside it. 

the roof has to be very strong to hold up the dirt as well as snow. perhaps
it should be covered with leaves instead of dirt. the walls need to be fairly
strong too, once the earth starts pushing in. i have a friend in pennsylvania
who built a solar underground house that has an annual electric resistance
backup heating bill of $58. his house was fairly expensive, with thick slabs
of reinforced concrete and styrofoam up to a foot thick, outside the concrete.

>oehler also recommends carpet over polyethylene over bare earth for the
>floor as being both easy and healthy for your feet,

sounds nice to me. our solar cabin has astroturf over gravel over poly in the
sunspace, and astroturf over foamboard over poly inside the cabin. i'm not
sure we needed the gravel, after we added some perimeter trenches filled with
gravel... it's on flat ground with very poor drainage, giant flat puddles on 
the ground for a day or two after it rains... 

>perhaps the oddest part of oehler's design is the "uphill patio."
 
>imagine the stereotypical underground home on a slope with the big picture
>window facing downhill.  oehler calls this the "first thought" design
>because it is terrible for drainage -- water going down the roof backward
>meets the water coming down the hill, and it sits there until it finds a
>way through your moisture barrier.  oehler knows that polyethylene can be
>breached, so his  houses are designed to get the water away from them
>naturally.  to this end, he digs a patio on the uphill side of the house. the
>big windows look up to this landscaped area, and the patio routes water past
>the house through french drains instead of backing it up against the roof.

sounds reasonable.

>...all in all his houses are exquisitely simple in construction but beautiful
>and well-matched to the landscape.  i think i'd quite prefer living in one of
>oehler's psp houses to the square box i have, but as i posted before the
>landscape makes it impossible here.

i wonder if there's a way to do this on flat ground with very poor drainage.
drainage would be less of a problem if the house were above ground. i keep
thinking of starting with a plastic film greenhouse... the materials cost
about $1/ft^2, and it takes 3 people 1 day to put up a 30x100' greenhouse,
from scratch, in a field, starting with no foundation. but that has little
insulation, and the plastic needs recycling every 5 years or so (which takes 
a couple of hours, at a material cost of about 5 cents per square foot), and
some say it looks ugly, and the structure itself (vs the plastic) is not very
strong, so it may collapse in a heavy snowstorm. people say the curved
galvanized pipe bows may collapse if it snows more than 3" per hour, if the
greenhouse is heated inside. and it isn't burglarproof. 

one might cover the film with newspaper or burlap soaked in a cement slurry,
but that may rot, and it seems messy and permanent and difficult to take apart
or fix if something happens to the plastic underneath... 

if we tried to build one of these psp houses on flat ground, it sounds like
the first problem might be trying to pile up earth against vertical walls...
how about sloping the walls inward and upward at something like 45 degrees,
vs what dan beard called "white man's walls"? i can sort of see the dirt
sliding down the poly walls. maybe some sort of terraced arrangement that
looks like this from the side...

                                                                        ---
                          |         dirt         |
                       |  |   ----------------   |  |
                    |  |  |  |                |  |  |  |
                 |  |  |  |  |                |  |  |  |  |
              |  |  |  |  |  |                |  |  |  |  |  |           9'
           |  |  |  |  |  |  |                |  |  |  |  |  |  |
        |  |  |  |  |  |  |  |                |  |  |  |  |  |  |  | 
     |  |  |  |  |  |  |  |  |                |  |  |  |  |  |  |  |  |
  |  |  |  |  |  |  |  |  |  |                |  |  |  |  |  |  |  |  |  |
 ---------------------------------------------------------------------------

make the "planters" out of old tires, tied together with cheap strong synthetic
rope, in some sort of horizontal array, filled/heaped (not rammed) with earth? 
this is beginning to look like fun. let's see... an 8' wall with a foot of dirt
on the roof might have 18 6" thick x 2' diameter tires stacked next to it,
17 more 2' away, 16 more 2' further out, etc. n(n+1)/2 = 171 tires stacked up
alongside every 2' of wall perimeter, extending outwards 36 feet from the wall.
seems like a pretty good approximation to a cave, or some sort of earthship 
that can stand up by itself, without excavation, with a reasonably large and
maybe desirable thermal conductance to the ground below, without much inward
force on the walls, and nice deep windowsills... a 30x30 house would use up
about 20,000 tires, not counting the corners...

can we use fewer tires and dirt, and make the walls slope at something closer
to 45 degrees? surround the house with an 10' tire perimeter, about 5 tires
deep, tied together in a horizontal array on the ground, pile about 2 feet of
dirt on top, with some rope sticking up from the lower tires, tie on another
layer of tires 4 deep, add another 2' of dirt, another 3-tire skirt, another
2' of dirt, a 2-tire skirt, 2 more feet of dirt, or maybe something fluffier,
a final 1 tire skirt and another 2' of dirt, 15 tires and about 100 cubic feet
of earth (2 hours of labor, shoveled at 1 cubic foot per minute?) for every
2' of building perimeter, not counting the corners. a 16x16' cabin might look
like this: 
                     pumpkins growing 
		   out of black plastic?
                   . . . . . . . . . .              ---
                 .       leaves        . 
                .  t horizontal rope t  .
               .     ---------------    .
              .  t t|               |t t  .
             .      |               |      .        10'
            .  t t t|               |t t t  .
           .  dirt  |               |        .
          .  t t t t|               |t t t t  .
         .          |               |          .
        .  t t t t t|               |t t t t t  .
  ----------------------------------------------------------------


           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t
	   t t t t t                 t t t t t     4(8x15+25+16+9+4+1)
	   t t t t t                 t t t t t
	   t t t t t                 t t t t t     = 700 tires...
	   t t t t t                 t t t t t
	   t t t t t                 t t t t t
	   t t t t t                 t t t t t
	   t t t t t                 t t t t t
	   t t t t t                 t t t t t
           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t
           t t t t t t t t t t t t t t t t t t

i guess all the dirt might be dug out of perimeter trenches to make a small 
plastic-lined moat connected to a large reflecting pond on the south side...

my mechanic charges $3 each for disposing of old tires, when he sells new ones.
he says that's what he has to pay to have them hauled away. he might pay me
$2,100 to build a cabin like this, or $6,300 to build a 30x30' (i.d.) house...

how can we solar heat this thing? make the center part of the south wall
vertical, using concrete blocks and 2x4s and fiberglass insulation, and
add a curved quarter-cylinder sunspace 16' wide x 10' deep x 8' tall, to
gather about 100k btu/day of heat in the winter? this structure has about
1500 ft^2 of exterior surface. without a good thermal connection to the
ground, keeping it warm on an average day in december requires about
24(70-30)1500/r = 100k, ie the walls need an r-value of about 14... 

what do we do about insulation, which would ideally be outside the thermal
mass of the dirt? peat moss? piles of leaves? some sort of fluffy mulch above
the dirt in the terraced planters? how do we keep it dryish on the outside?

how far should the poly film vapor barrier on the ground extend out under the
dirt wall, to keep moisture from coming up out of the ground? that's the main 
mechanism for upward heatflow in soil--evaporation of water in layers below
and condensation in layers above...

below ground, we can count on soil having an r-value of about 10 and a more
or less constant temperature of about 55 f, but not above, unless it has a
better thermal connection to the earth below than the air above...

nick


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