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Posted by Joe on October 24, 2006, 2:40 am

I'm in the early stages of building a new home.  I am using contractors
so I can be very flexible in the design. At this point, I'm considering
solar arrays, 2x6 framing, and solar water heating. I'm looking for
resources or other pointers regarding energy efficiency of a new home.


Posted by Eeyore on October 24, 2006, 7:56 am

Joe wrote:

How much insulation have you got ?

There is no such thing as too much.


Posted by Anthony Matonak on October 24, 2006, 9:59 am

Eeyore wrote:

There is a point of diminishing returns though. Around these parts it's
common to refer to insulation by R value and, this being a southern and
warm climate, it's not often you see much more than R20 or so in the
walls. I would say that somewhere around R80 would be the point where
adding more insulation becomes impractical for my climate.

Regarding energy efficiency in a new home. I'm no expert but I can
repeat some things I've heard about.

For instance, not all insulation is the same. I'm told that sprayed
foam insulation performs better than similar R valued fiberglass
because it seals up all the cracks.

Also, heat recovery ventilators are a good idea in a tight house.

These days you can go one step further and automate a whole house
fan and motorized windows. Add motorized automatic insulating
shutters and your house can do the entire passive solar song and
dance that a person would normally have to do by hand. What most
folks don't learn until too late is that "passive" solar means
you're always adjusting something.

I'm in favor of active solar thermal air heaters as well. In the
summer you can duct them to your clothes drier to save some energy
or to a food dehydrator or something.

While not energy efficiency related, I'm also in favor of a whole
house vacuum, home run all the electrical, add wiring in every
room (heck, every wall) for network, phone, TV, and security stuff.
It's easy to add all kinds of wiring when the walls are open.
Even if you don't use half of it, wire is cheap. Oh, and take
pictures of everything before they cover it all up.

I suppose, this being homepower, that provisions in the design and
wiring for generators, battery banks, solar PV and all that stuff
isn't a bad idea (assuming it's not already in the plans). Even
if you don't plan for any of it yet, having the space set aside
can help in the future.


Posted by Eeyore on October 24, 2006, 10:17 am

Anthony Matonak wrote:

That R value is more important to the energy efficient builder though. That's
what it's all about. Saving energy in the first place is far more effective
than spending money to replace it !

Does 2x6 framing mean walls fixed on battens 6" wide ? That sounds thin to me
for decent insulation.

Agreed with rest of stuff so snipped for brevity.


Posted by nicksanspam on October 24, 2006, 11:28 am

I wonder where this home will be. SIPs can insulated better than 2x6 walls,
with less air leakage.

Sure, but most US houses already leak way too much air, so HRVs save
little energy... 0.2 ACH is considered "airtight" here, but a 3000 ft^2
house with 0.2 ACH leaks 0.2x3000x8/60 = 80 cfm, way more than ASHRAE's
standard 15 cfm per full-time occupant.

Automatic night ventilation can take the place of AC for all but 2 weeks
per year in Phila. If it senses outdoor humidity, it can also bring in
warm outdoor air to heat a house while avoiding indoor condensation.

People quickly tire of moving insulation twice a day, but motorized
shutters seem expensive, with low R-values compared to a house wall.
We can automatically let air flow up through a vent from a sunspace
to heat ceiling mass, then bring heat down with a slow ceiling fan
and a thermostat and an occupancy sensor. Not purely passive, but
very low power. Motorized insulating shutters.

Sure. Why not cover the whole south wall with transparent siding,
eg clear corrugated Dynaglas polycarbonate greenhouse roofing,
with an air gap and a dark surface behind it?


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