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Building the Off-Grid Home Like an Alaskan (PART 3)
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In my last post, I talked about ways to super insulate the off-grid home like an Alaskan.  This past winter, Texas had one of the coldest and longest cold-snaps in recorded history.  Our Texas style home is well insulated for a home having four-inch walls, but it was a struggle to keep the temperature in the upper 60's/lower 70's.  Our two heaters ran continuously plus we had gas logs to supplement the heaters.  Something that would have helped was to have had the house sealed a lot better during construction.  There are two trains of thought about using heavy thickness plastic to wrap the walls and ceilings of a house to stop drafts and unwanted air intrusion.  Typically in an area of high humidity like we are, the old-timers built the attics open to the outside with a lot of vents to avoid the build-up of moisture, and the walls and ceilings were not sealed with a plastic layer.  That does a good job of keeping moisture from collecting in the insulation or on interior surfaces, but that also allows the wind to funnel through your attic and through even the smallest openings in your walls and into your home.  It also allows dust to accumulate in the attic on and in the insulation. 

    Since moisture is the real problem, we first of all, need to understand how condensation occurs.  You'll get moisture where warm moist air contacts a cooler surface (we see this on our glasses when we are on our porches in the summertime drinking iced tea).  If you wrap the inside walls and ceilings with an impervious layer (like plastic sheeting), in the winter, the cooler air will be outside the envelope and the insulation.  If the insulation is thick enough, the cooler air from from outside the envelope will be unable to migrate inward to reach the barrier.  However, if the insulation is too thin, you will get moisture on the heated side of the barrier.  If you see the interior walls "sweating" in the winter, that is the reason.  In the summer time (if you use air conditioning), the warmer moist air is on the outside and the cooler surface is on the inside.  In this case, the moisture can build up inside the walls---unless the attic is well ventilated to move the moist air out. But then we are back to where we started with drafts.

     So what's the answer?  I am open for discussion on this point, but it appears the best approach (although more expensive) is to wrap both sides of your walls and attic, sandwiching a generous thickness of insulation between the impervious layers. For the attic, you still need ventilation but the problem we ran into was the gable vents on the north and south ends of the attic.  Whenever the wind blew, it was like a wind tunnel in our attic---cold drafts in the winter and hot ones in the summer.  To better control the unwanted air flow without impairing the need to keep moisture from building up, we are planning to install commercially available gable louvers that can be opened and closed.  There are some that will operate remotely--this is what I am considering.  An added feature, although it uses electricity---is to put an exhaust fan on the attic side of the louver that you can also operate remotely.  This will not only reduce moisture in the attic, but will also cool the attic---and consequently, the rest of the house.  One other thing that is vitally important---you must have a way of getting fresh air into the envelope.  You may need to occasionally open a window or two.

     If you are building your home, you have an even better option.  Using the offset stud-wall method mentioned in Part 2, wrap the walls on both sides since there should be a generous thickness of insulation.  But do you really need an attic?  Why not design your roof with clearstory windows facing south and the roof higher on the north side to accommodate the clearstory windows.  Then, have your finished ceiling installed directly to the underneath side of your rafters (see diagram).  Again, with ample insulation (or even using the spray foam insulation) and the impervious layers if you don't foam, you totally eliminate the need for air flow through an attic space.  Add to that a positive air flow system that allows cool air in the summer to enter from below and hot air to escape through the clearstory windows, and you've got a house that breathes by itself.  In the next Part, I'll give you some ideas on the next step, and that's adding natural cooling and heating to compliment the clearstory roof.


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