Provo/Orem Energy Source

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Thursday, November 02, 2006

Passive Solar House in Provo

Last night my family went to visit with Russell Sias and his wife about their home. They live in a passive solar house here in Provo. I met Russell through a yahoo group for Republican Utah State Delagates. In discussing an article on design I asked if any one knew any one who lived in a passive solar house. Russell emailed me back saying that he lived in such a house and would be happy to show the house and discuss it. It took a few weeks to find a time that would work for both of us.

Basics of the design:

  • 1380 sq ft
  • Floor is a 4 inch concrete slab poured over 3 inch styrofoam, sitting on top of compacted gravel (can't remember exactly how much)
  • Exterior walls are 6 inch thick concrete with 3 inch styrofoam on the outside finished on the outside with stucco and the inside with a drywall mud texture.
  • Roof, has a 3 foot overhang which is enough to shade the south facing windows starting about April 1 every year. The roof is insulated to about R-40 with fiberglass batt insulation and blown in fiber insulation. Finished off with tar paper then clay tile.
  • Sheathing for the roof was reused plywood from the cement wall forms.
  • Not many windows on the north face, two large picture windows on the south, doubled paned, but nothing more. Also have a heavy screen door with glass panes they open in the afternoon to bring in more heat.
  • Earthbanked to just below the level of the windows with xeroscaping. (mostly rock that matches the color of the tile on the roof well)
  • Heating with a flueless gas stove, small in central location - if do again would do radiant heating in the slab.
  • Extra cooling in the summer provided by a one room A/C unit ran about 4 hours during the hottest days of the year.
  • The hip roof ended up being a real head ache as the people they contracted with couldn't get the trusses right.

My Observations:
The designed relied heavily upon the thermal mass of the walls to moderate the temperature changes, (6" x 8 ft x aprox 150 ft parameter ended up being 5 cement trucks (aprox 65 cubic yards) of cement - current price at Geneva rock about $7,000 delivered). The earth banking added extra insulative value and made wonderful planting beds. My guess is that the earth banks would also help with drainage. The earth banks also blended the building into the landscaping very nicely. The low light put out from what appeared to be solar landscaping lights made an inviting walk to the front door. There really wasn't that much glazing on the south face, maybe 36 sqft (2 aprox 3 ft x 6 ft windows). This to me seems the tricky part of the design, how much glazing do I need to get the warmth I need but no more. I think I would prefer going with more. As long as windows can open, the tempurature could be regulated that way on warmer days, or drapes could be utilized as well. They didn't use thermal shutters to cover the windows at night, but I always hoped that would be unnecessary as I didn't like the look of those I had seen in books. I think the glass technology has probably progressed enough to eliminate them. Russell corrected me in that they do use insulated drapes, but I just didn't see them, (they obviously were not the ugly things I was looking for). - 11/3/2006

R-40 roof insulation seemed like lots when I saw the attic, but I seem to remember higher values being recommended for passive solar houses. I have seen criticsm of fiber insulation for this purpose and a much lower R-value will suffice if foam is used, (spray-in). (The idea being that much of the insulative value of fiber insulation is lost when small air currents form from the temp differences in the top of the insulation and the bottom, spray in foam would have no currents. See R-Value Myth) This is an area I'm not very familiar with. With the design of the roof came the unexpected bonus of additional storage space in the attic which is always welcome.

The passive solar designs I've seen in books have focused more on thermal mass in the floors and used the relatively stable ground temperature (aprox 55 degrees F around here) to cool in the summer instead of insulating the pad with styrofoam below the slab. I suppose the trade off of connecting the thermal mass to the ground is helpful during the summer, but a detriment during the winter. Russell loved the warm floor, and I think that I would feel the same way regardless of losing the cooling value in the summer a warm floor in the winter is worth the trade off. Possibly a 6" slab over the styrofoam would increase the thermal mass enough to lighten the walls some. I should note that the walls were warm to the touch, very different from the masonry walls in my house right now (begin of Nov).

The cement walls were difficult to hang cabinets on, and once the home was arranged it became very difficult to change any of it. Drilling holes in cement to hang pictures is much harder than a nail or plastic anchor through drywall.

The rooms seemed overly large to me, but then my family of three lives in about 850 sqft. I think I would have carved up the 1380 sqft into more rooms, this was a 1 bedroom 1 bath home. I would think closer to 3 bed 1 1/2 bath would fit nicely and still feel roomy if laid out to my taste, (I prefer small bedrooms and a combined living room kitchen design which saves lots of space). Of course with that said, my wife doesn't necessarily agree with that. :)

See: for more info insulating the outside of the thermal mass instead of the inside.

I would love to visit other passive solar houses in the Provo/Orem area if anyone reading out there knows of any.

The following was added as comments from Russell on 11/3/2006. As a preface, the house I visited was built next to another home that was built much earlier following the same methods:

Actually there are insulative drapes, and we do close them at just didn't see them! They are insulative. A bit pricy, but well worth it, in my opinion. Not opening them during the day causes a significant heat loss from the sun entering, and will require much more time for the stove to run (in the winter time).

We didn't need or want more bedrooms,one was enough for our purposes. The other place, does have 3 bedrooms, it is also a few feet smaller in square footage, not much, but a bit. I really didn't care that it was oversized rooms, or bathroom, for I knew about what the cost was going to be, and figured, what the heck....


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