Posted by: "David Neeley" dbneeley@...
> I mentioned the Larsen trusses for those who are building
> in heating climates who may benefit from a super-insulation
The so-called "Larsen trusses" (which many of us had built,
way back in the 1970s-80s, before whoever Larsen is, every did)
are one way to retrofit an existing house, if it also needs new siding
and windows. But, for new construction it is seldom an optimal
cost-effective strategy. Double walls, I beam walls, and several
other approaches (even SIPs) can be more cost-effective.
For the "Northern California" (wherever that means) location,
for such a small structure (interior space at a premium) the idea
of 2x4s with foam sheathing is (IMPO) very good. However, it
should be done in advanced framing, which means to place the
studs and rafters aligned, 24" oc. However, since it is an earth-
-quake prone area, the corners NEED a minimum of OSB or
plywood, under the foam at the corners. Since the building is
so small, it might as well cover the whole walls. It should be
glued, and nailed, 4"oc, around the perimeter, and 8" oc in
the center. Gluing the roof sheathing would also stiffen it up.
Houses, in that region are required to be built with hefty
shear walls at the corners. I would also build at least
one interior wall, that intersects the 12ft exterior walls,
as a shear wall (glued OSB or plywood).
> As I said, though, the design sketch the OP shows has
> a relatively large glass area for Winter heating through
I did not see that. I just saw a drawing of a window that
might have been facing in any direction. How did you
interpret that it was facing South? Did I miss something?
> thus, he may be well advised to consider some sort of
> shade for the glass for the Summer
Even more so, if the window is facing East or West.
South facing windows are quite easy to shade.
(the sun is quite high in the southern sky, in Summer)
> otherwise he could find it uncomfortably warm
> without mechanical air conditioning-
That would depend on the specific climate,
which will vary widely in northern California.
Posted by: "Dennis Otto" queenbeeandthehappydrone@...
> The Idea of useing more rather than less insulation is not only
> to insulate an warm interior from the outside cold, but also
> insulate a cool interior from outside heat.
Typically, in Winter we are looking at temperature
differentials that are 5-10 time greater than in Summer.
So, recommendations, for warmer climates, is not for
thick walls, but instead to focus the insulation in the roof.
This is even more important in very small houses, which
will lose significantly more interior floor area to thick wall.
Shading, particularly of windows, is far more important
than wall insulation. Definitely, the roof appears to be
under-insulated, but 2x4 walls with foam, are a good
system, for that climate, and such a small house. This is
coming from a professional designer, of super high
efficiency houses, with 35 years of experience. In the
northern climates where I do most of my work
(currently in Minnesota, Michigan, Indiana, New
York, Nova Scotia, and Massachusetts), I typically
use foot thick walls, of dense packed cellulose
(R40+). But, for this little house in such a mild
climate 2x4s (advanced framing, 24"oc), fiber-
-glass insulation (use R13 or 15 if you want a
higher Rvalue, and can find it at a good price),
and foam (R5+), is the formula that I feel is ideal.
It was a good choice by the owner-builder.
BTW....I did find the foundation to be very overbuilt,
and wasteful of both materials and labor. It was typical
of amateur designers, who are unsure of where to invest
the resources, and where not to put them. Without
having more details, I would likely have recommended
building it on piers. There seemed to be no reason
for such an elaborate foundation. Those are
very expensive design decisions.
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