[Strawbale] Insulated concrete vs wood cross post

[Shody Ryon]

My interest in SB construction includes an interest in
a high performance insulation envelope, which
surprisingly includes the roof and floor. I wonder if
the whole basement and slab on grade theory (that they
are desirable) sucks (energy).
I wonder if above ground SB houses would be more
energy efficient and much better for the environment
cheaper faster easier and use less trades to build.
Some areas allow some percentage of fly ash, my area
only allows 25% in the foundation. I heard a rumor
that every heavy kilo, there for small volume of
concrete, or perhaps portland cement, yields 2 light,
therefor very large kilos of carbon dioxide that warms
the earth.  
The debate about which system sucks less is lost in
the lesser of 2 evils, unless it is acknowledged as
such, when I wish were proponents of doing things
better.
I wish some one would explain what I am failing to
see, but perhaps my point is so off base that time is
better spent doing something else.
Tada, I give you “the cross post”:
p.s. I cross posted this before, I pray it wasn't
here, if so, my apologies for the repeat, sort of.

In insulation
> Raising the entire structure off the ground high
enough
> to park undeneath is also an option.

In the north, it may provide a cold storage, in
winter,
or even in summer, with insulation and good ground
coupling...also a good place to keep a snowmobile,
bicycle, etc....out of the weather....a little
carport,
like on my little demo house.

> Depending on how this is done it doesn't necessarily
> raise the cost as much as one might think.

In the north, it is not much more than having longer
posts.
It is just a tall crawlspace, above ground.

> It gives great views and makes it easier to cool
passively.

It also gets the house higher for more winter
sunlight,
over the treetops, which was my initial reason to do
it.
Though I have acres of land, on which to build, my
only good clear (not really all that good) was close
to the southern property line, and not very wide.
I will not get early morning and late afternoon
sunlight. In late December, when I need sunlight
the most, it will be partially blocked by trees.

A far as cost, raising the floor up gives me a covered
storage work area, for less cost than any other way.
Concrete and XPS Foam insulation have gotten so
expensive lately, that it is more economical to build
a wood frame floor, and fill it with cellulose. For
example, in Maine, in January, when outdoor air
gets the coldest, and averages about 15°F, the deep
ground temp may be around 42°F, but you have to
deal with the ground temp near the surface, so it is
more like the average, which would be around 28°.
If we assume a floor temperature of about 65°, we
can look at a 1000ft² R20 concrete floor heat loss,
in January of about (65-28) x24x31x1000/20 =
1,376,000BTU. With 2x12s and cellulose, we will
have about (65-15) x24x31x1000/35.4 =
1,051,000BTU. (about 24% less). The XPS foam
insulation will cost about $2000, and is not very
"green". The cellulose will cost about $300, and
is very "green". The wood floor or concrete will
cost about the same in materials. Maybe the wood
might run an additional $500, since it needs to be
closed in underneath. Again............wood "green"
concrete...."not green" So the savings is in a range
around $1000, and you get a floor that is insulated
a third better, when you need it the most. The
foundation will cost about the same. In milder
months of the heating season, the slab will suck
even more heat (relatively) from the house. Even
an insulated slab is a heat loss. That can be a good
thing where cooling is the priority, but in the north,
where heating is a greater concern, a slab is a big
additional heating load.

-Laren Corie-
Natural Solar Building Designs, Since 1975 


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