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TahoeSkier
Registered Users
Posts:4
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| 02/18/2008 7:37 AM |
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My wife and I are going to build a house in South Lake Tahoe. The last house on the lot burned during the Angora Fire and the rest of the trees in the area will be dead this spring/summer. So we have a perfect south face with no shade. We are going to calc out the glass for the south side of the building, put thermal mass in and go passive solar. The passive solar part of the house will double as a green house for us, we grow sugar pine seedlings for our non-profit, www.sugarpinefoundation.org.
So I get the thermal mass in the floors and green house area. That makes sense to me. But in a cold climate, I don't understand the thermal mass in the walls. If there is equal insulation both interior and exterior, it seems like the concrete in the walls is of no benefit. My wife grew up in a concrete apartment in Sophia Bulgaria, and it was really cold. In a cold climate, it seems like I would always be fighting against the cold concrete, and I have to get heat into the concrete. It seems to make a lot more sense for the couple months during the summer when it gets hot.
It seems to me like the issue is getting thermal energy into the concrete through foam, and the concrete then conducting that energy to the exterior of the home. Wouldn't I be just as well off building 2x6 with foam insulation, gaskets etc.
I am not worried about the fire thing, I can easily build a stick home that won't ignite. That has more to do with details like attic vents, roof type and defensible space. |
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Alton
Registered Users
Posts:314
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| 02/18/2008 8:56 AM |
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TahoeSkier,
I just sent you an e-mail. Let us see if the e-mail feature is working.
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Alton C. Keown
Residential Designer and Construction Technology Consultant
Auburn, Alabama
334 329-0957 AT&T Cellular |
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renangle
Registered Users
Posts:91
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| 02/18/2008 2:39 PM |
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Tahoeskier,
Best of luck with your house in the Tahoe area, I am a bit fan of that area having been there twice. You are right when you say you and your wife lived in a concrete apartment that felt "cold", as concrete itself has very little "R" value. ICF technology creates a "thermal mass" because the concrete is insulated on the outside and inside, so when the temperature changes outside, very little happens on the inside. Compared to 2x6, ICF will beat is all day long. My friend lives in an ICF house (we are a distributor) and our city recently lost power. In one day, he said that his house lost maybe 3 degrees in 30 degree weather.
Also, we recently built an ICF house for Habitat for Humanity. The house is about 1200 sq.ft. and right next to another Habitat House that is energy star certified and the same size. The ICF average bill has been around $40 per month, the energy star is about $80...again no comparison. We are in Virginia and December/January was cold here.
Just my humble opinion. Best of luck in your build. |
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TahoeSkier
Registered Users
Posts:4
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| 02/18/2008 3:18 PM |
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Alton, I didn't get an email you can try me at FireSafeChapters (AT) Yahoo (Dot) Com.
Thanks
John |
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dmaceld
Registered Users
Posts:494
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| 02/18/2008 4:51 PM |
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Posted By Alton on 02/18/2008 8:56 AM
TahoeSkier,
I just sent you an e-mail. Let us see if the e-mail feature is working.
Did you use the Message button on the left? That seems to be the only method of PM that works.
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Building house - what a way to spend retirement! |
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Alton
Registered Users
Posts:314
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| 02/18/2008 6:42 PM |
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I used the e-mail and not the PM method to send the e-mail. Now I will have to remember what I wrote that got lost.
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Alton C. Keown
Residential Designer and Construction Technology Consultant
Auburn, Alabama
334 329-0957 AT&T Cellular |
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Jelly
Registered Users
Posts:274
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| 02/19/2008 4:24 AM |
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TahoeSkier, there is a lot of research that has been done about this, and you can find it out there if you search enough. The hard part is wading though all the opinion and misinformation to get to an objective explanation of thermal mass. But you're right, to truly take advantage of concrete's thermal mass you would want the insulation only on the exterior.
That concrete apartment in Sophia was probably not insulated at all. But right now in central Europe there are a lot of "zero-energy" structures being built of concrete with rigid foam only on the exterior. Passive solar energy gets into the structure through orientation and glazing and gets stored in the concrete. There is supplemental heating sometimes, but it only uses a few kilowatts. |
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toddm
Registered Users
Posts:14
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| 02/20/2008 9:39 PM |
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| If you haven't tried it, you should download UCLA's HEED energy efficiency software (free) and sort out the variables for yourself. For the passive solar house I'm building in central Pa, 9" ICF is marginally more efficient than a 5" solid masonry wall with 2" of foam on the exterior, while an uninsulated 8" masonry wall is expensive beyond belief. These results are only as good as the assumptions built into the software, of course, but it makes sense for my design. ICF's thicker insulation saves money in the winter. But the masonry wall saves money in summer, when you want exposed mass cooling the home during the day and giving up heat at night. An ICF wall isn't going to respond that quickly. Your results will vary. HEED asks you build a 3d model of your home and place it in its proper orientation, putting the glass and the doors where you want them. You load in the closest weather profile, which in my case was decidedly unsunny Harrisburg, Pa. You should get a much larger passive solar gain in Nevada, and you might benefit from exposed wall mass carrying the heat into the evening. Copy and paste this link for free solar design tools, including HEED: http://www.builditsolar.com/Tools/tools.htm |
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clydesdad
Registered Users
Posts:4
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| 02/24/2008 5:38 PM |
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Hi there, Tahoeskier, this is my first post on this site...I'm actually looking for info about heat recovery ventilators for the ICF house I'm building right here in the South Tahoe burn area....We got rebuilding quickly this past Fall hoping to organize a "green" ICF house project and hoping to get sort of a good faith/cooperative effort from various local builders, designers, subs and material suppliers. It all seemed pretty good until we got hooked up with the "engineer from Hell" recommended by the ICF supplier. Now, as it snows and snows, we're in the middle of building a simple but very labor intensive roof system. Our dream of good weather in the Fall and getting enclosed by December 1 failed as the engineer couldn't/wouldn't finish the plan (First floor ICF walls sat ready to pour all of that glorious dry November--the
"Foundation Only" permit option allowed us to get that far.) Anyways, despite all this, we're still pleased with our plan and we're incorporating plenty of passive solar with exposed interior masonry walls and concrete floors for our thermal mass. We don't consider the concrete in the ICF walls, being surrounded by 2.5" of polystyrene inside and out as thermal mass at all but just as the structural part of our well insulated wall system. Perhaps this isn't technically correct but it seems reasonable to me. Our situation might be a bit different from yours in that trees and buildings directly south of us survived the fire so we will still have a short "dead of winter" period with very little solar gain. In the early days after the fire when we were considering various building systems we were drawn to the ICFs partially because of various personal connections with the suppliers and an ICF contractor but also because my wife's uncle had built with them before. Our architect is currently designing another ICF house in the burn area but also two houses using 3-D panels (reinforced concreted surrounding polystyrene insulation). Those systems might be better if your goal is to maximize thermal mass. To sum up...please feel free to contact me or visit our building site, and good luck with your rebuild and recovering from the fire generally. I'm VERY glad to hear that other people are thinking of taking advantage of the solar opportunities in the burn area.
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clydesdad
Registered Users
Posts:4
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| 02/24/2008 5:48 PM |
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I just looked at the link to your sugarpinefoundation.org site....we always loved the sugar-pines in that piece of Forest Service land between Tahoe Mountain Road and the High School. I've walked around a bit in there since the fire but I wonder how those various trees are doing. If you're not familiar with those particular trees I could show them to you some time. Steve/Clydesdad
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TahoeSkier
Registered Users
Posts:4
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| 02/25/2008 8:21 AM |
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Are you building off of Tahoe Mtn? I was just talking with a friend who is rebuilding off of Boulder Mtn and we were talking about your house. I thought we were going to have a bust year after the dry November and December. Jeff has been struggling to keep building on his lot. He has been through a lot of sheer pins on his snow blower from hitting stuff when he cleans his foundation.
I think we are going to go with 2x6 construction and then use spray insulation, radiant heating and a super high efficient wood stove. The Forest Service lots next to us are toast, the trees will die this spring when the bark beetles show up. So I have a lot of firewood. We are taking full advantage of the south view off of Mt. Ranier.
Those sugar pines you mentioned are doing great. We did a bark beetle survey up there this year and the only tree that died was right by our trap, so we probably killed it with the attractant we use. The beetle population is very healthy though, so you may get more south sun than you have now. We are expecting a huge round of mortality this year.
If you are going to replant let me know, I have sugar pine seedlings growing now. The TRCD is going to buy some from me and give them away to burn victims, so I could probably get you hooked up for free.
John |
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