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Double stud wall construction-anybody seen it/done it?

Post in 'The Green Room' started by Badfish740, Oct 7, 2010.

  1. vvvv

    vvvv New Member

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    Buildingscience.com specified r-10 minimum for exterior foamboards so to avoid condensation from interior air penetration into wall cavity. alaska may be more due to colder weather?

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  2. GaryGary

    GaryGary Feeling the Heat

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    Hi -- thanks for the kind words!

    I'm always looking for good projects to add to the collection, so if you (or anyone) has one, please send it in.
    You live in a great place for solar.

    Gary
  3. vvvv

    vvvv New Member

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    i posted a window foam panel, elastic scheme on your site but could only manage to post it as a response to another project. its ugly foam but the concept is very easy to use. here's the blog i did if u wanna grab it or comment..........great site u have.
    http://czarcar-foamwindowinsulation.blogspot.com/
  4. Wallyworld

    Wallyworld Member

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    Here is what I did on my new shop, 2 inches of closed cell over the studs, plywood over the foam. R19 fiberglass inside the 2 by 6 studs

    [​IMG]
  5. btuser

    btuser Minister of Fire

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    I like the PT plywood on the bottom.
  6. jotul8e2

    jotul8e2 Feeling the Heat

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    Re: 10% loss through walls. I've heard that a lot and I am ... skeptical. Yes, I know heat rises. I would like to see some actual data on this - can anyone point me to some? In any event, the elephant in the room is always windows and (to a lesser extent) doors. The very best windows on the market have insulating values of r 2 or so, and very few have coatings to reflect ir back into the house, so even more heat is lost to direct radiation through the glass. I think the heat losses through conventional windows and doors are far higher than most people suspect - again, I'd like to see some data if anyone knows of any.

    I built my house (southern Missouri) with 2X6 walls on 24" centers, r19 batts, with standard chipboard sheeting and an overlay of 1" foam panels. I estimated the extra cost of the 2 X 6 walls to be something less than $400 - more expensive studs, but fewer of them. Keep in mind you only use them on the outside walls. With the drywall, insulation, sheeting, foam, and exterior siding, I must have just a bit less than r 30 at the cavities. I also chose smaller and fewer windows. We can see out, but I have no 16' atrium windows or anything silly like that. The attic is r 60 - 70.

    We have 2600 sq. ft. over a full walkout (but unfinished) basement, are all electric, and on a well so I pay to pump my water. I also have a 2200 sq. ft. shop which I air condition (humidity control). My total consumption last year was just under 13000 kw. By far most of that was in the summer months as I heat with wood all but 8 weeks or so in the winter and spring.

    Back to windows: I have just recently got to work on doing something about the widows. I have put up single cell thermal blinds in all but two windows. We shall see. For a more significant effect I may add insulating, close fitting drapes.

    We could do better, but as pointed out in some other posts the return on investment gets pretty poor pretty quick.
  7. Seasoned Oak

    Seasoned Oak Minister of Fire

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    =====================
    I googled this and got percentages all over the map. THe wall loss was in the range of 25 to as much as 50%. Some sites had more being lost through walls than the roof,perhaps cuz there may be more wall area than roof. After reading all this id say insulate them both well and dont worry about the %
  8. midwestcoast

    midwestcoast Minister of Fire

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    You won't get a good rule of thumb on what %age of heat is lost through walls, windows, doors.... There are just way too many variables:
    Tightness of envelope
    Design & shape of the house (2-story has nearly 2X the wall area as a ranch, large square house has much lower wall area to floorspace ratio than a small rectangular one...)
    Amount, type & install quality of wall & attic insulation
    #, size & quality of windows & doors
    Foundation insulation
    It goes on & on, but here's the way I look at it; The better insulated your attic & the higher quality windows & doors, the more heat (%age wise) you'll loose through the walls and vice versa. You won't have a highly efficient envelope unless all parts are tight & well insulated. I really don't see 4" of fiberglass batts as a well insulated wall for modern construction, especially with the poor instalation practises that are nearly universal.
    Doors & windows (if they seal properly) don't loose as much heat as many think since they're typically a very small %age of wall area. The payback on window replacement is often very long (aesthetics & functionality notwithstanding) & I've never seen it calculated-out by a window company as a way to entice customers.
    Oh, and I just gotta say it: Heat doesn't rise, hot air rises
  9. ihookem

    ihookem Minister of Fire

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    I built 2 exact houses and lived in the first for 4 years. The second house I spent just one winter in. Both were 2x6 walls. The first was blown in cellulose ,the second is 4-41/2 " of closed cell foam. The foam was 1500 more than cellulose. The first house with cellulose walls didn't let any airflow through that I could tell by putting my hand over all the outlets on the outside walls, I could not feel any cold air coming in through the outlets even at 40 mph winds. This was a "true" r-18 wall plus r-6 for 1" foam plus r-2 for the brick to equal a "true" r 26 wall. Batts of r 19 is not a real r 19 if the wall has air leaks. My new house has with 4-4 1/2" of closed cell foam. This makes r 28 plus r 1 for the osb sheathing plus r 2 for the brick, equalling an r 31 wall. I don't think I can tell the difference in heat loss but my first winter with foam was an easy winter. If I did it again I think I would spray 1" closed cell and fill the rest with cellulose to save about 1,000 dollars. Also, weather you get foamed walls or not make sure you foam the floor trusses in the basement and between the roof trusses and make sure they spray up the bottom of the roof sheathing a few feet. This stops the chance of draft going into the attic and stops ice back damming.
  10. Seasoned Oak

    Seasoned Oak Minister of Fire

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    I would think the best combination is Standard levels of Insulation combined with Solar and Wood heat. Once you go over a certain amount in the walls and roof you will just lose it all through the windows and doors.
  11. GaryGary

    GaryGary Feeling the Heat

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    If you are in a cold climate, I'd respectfully disagree a bit.

    I'm a pretty dyed in the wool solar heating fan and get a good fraction of my heat from solar collectors, and I've consulted with a lot of people who have put solar heating in. My conclusion is that if you have the luxury of building a new house that putting your money first into a very good thermal envelope, and then into solar is the way to go. I think that the standard level of insulation, infiltration sealing, windows ... is not good enough, and you can see codes changing around the country now to require higher levels. A home with a good thermal envelope can be heated effectively with solar and without an excessively large collector array. I think the Passive House Institute is pretty close to the right ball park on their homes - maybe just a bit over the top.

    For retrofits, its harder. Our house is insulated to the code of Montana in 1995 -- R19 walls, R38 ceilings, double glazed low-e windows. We have worked fairly hard at improving this with more attic insulation, more sealing, crawl space insulation, inside insulating window treatments. This has all made a significant difference, but even with the thermal envelope improvements we have made, the 240 sqft of solar collector we have only provides about 30% of our space heating. Our total heating bill with envelope improvements and solar is down to a bit less than half what it was when we move in. If I were able to start from scratch on the house, I could cut the heat loss in half, and then the 240 sqft of solar would provide 60% of our space heating.

    It would be interesting to hear what other peoples experiences have been.

    Gary
  12. Seasoned Oak

    Seasoned Oak Minister of Fire

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    The author of this thread did not address windows and doors.My point is if your going to go to extreme lengths on the walls and ceilings without doing the same with windows and doors your heat will indeed escape there.
    Yes a super insulated home can be heated with very little heat,but at what cost. At some point you will never recover your initial investment. Windows with performance to match 12" walls are not cheap and probably its not practical to even try it with a retrofit.
  13. precaud

    precaud Minister of Fire

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    More accurately, your heat loss through the windows and doors will be the same whether the walls are treated or not.

    Actually, at some point you WILL recover your cost - when you sell the home. And it will be accelerated by the cost of heating fuel increasing. The chances of both of these things happening is very good...
  14. Seasoned Oak

    Seasoned Oak Minister of Fire

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    Precaud wrote
    Actually, at some point you WILL recover your cost - when you sell the home. And it will be accelerated by the cost of heating fuel increasing. The chances of both of these things happening is very good...[/quote]
    ================
    With a huge % of the countries homes UNDER WATER people are lucky to recover the cost of a regular home. My heating cost is $750 for the year for a 3000SF home in central PA,and 400 SF of my wall area in a 100 year old home has no insulation at all. Yes i will probably get around to it soon but what will i save $50 a year? hardly worth taking a day off work to do it. Im a big believer in insulation but there is a cost benefit to consider.
  15. precaud

    precaud Minister of Fire

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    Gary,

    Absolutely no question, retrofits are harder to make efficient. And that's unfortunately what most of us have to deal with. I think we can get them pretty efficient, but with larger day-to-night temperature swings than a properly-designed thermal envelope would have.

    I'm going into this winter with 160 sq ft of solar (plus two sets of another 32 or so sq ft of windows that give 1/2 day of direct gain each) - that's a bit more than double what I had last year - heating 1150-1200 sq ft with 9 ft ceilings, R48 average in the ceiling, uninsulated but massive walls, full basement under heated on weekdays only, but never at night. The 6.3 ratio of floor area to glazing area is on the low side, but I felt it would be necessary for the solar to carry the entire daytime heat load during the coldest part of the year. Last year I used a tad over 1.5 cords of wood to supplement the solar upstairs; I'm interested to see how much less is needed this year. Comfort levels are WAY up already - by 4pm it's 79F in the house, diminishing to 67 at 5am. This is with no wood heat and lows in the upper teens/low 20's. We'll see how it fares in January, when we see the season's coldest temps.
  16. precaud

    precaud Minister of Fire

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    I think you're confusing the issue by generalizing it so much. Under-water homeowners aren't going to put any money into efficiency, so there's no reason to even bring them into the picture.

    I can only think of maybe $30-$40 that I've spent on insulation that has not added to definitely reducing heat loss and raising comfort levels. They were experiments that didn't make any difference. Unfortunately I'm at a place now where the next step that will make a significant difference (insulating the walls on the exterior), if I am to take it, will cost a bunch. Unless a windfall of unexpected proportions comes my way, it probably won't happen.

    [Sigh.]
  17. benjamin

    benjamin Minister of Fire

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    The homes that are underwater aren't because they spent too much money on insulation. Insulation is a tiny fraction of the cost of even a modest new home, and in most cases the extra insulation in a new home has a payback in a few years on energy costs, plus there is a comfort factor. There are still new homes built with no insulation under or around the foundation, even with finished basements. Really? most people aren't storing their cider barrel and potatoes down there anymore.

    Obviously if you're heating an existing home with coal, free wood, or sawdust (thanks Kenny!) then it's not going to pay to get extreme triple glazed windows or do superinsulation. On the other hand if you start looking at what people pay for wood boiler systems, heat pumps or even standard HVAC then the insulation starts to look like a bargain.

    I see lots of old homes with little or no insulation because "it won't pay off", but when gas or oil hits a certain price they will pay to do it, and they will pay a lot more than if they had done it thirty years ago, not to mention the heat wasted and comfort missed in the meantime.

    Then again... since in a few years we'll all be living in vacuum canister apartments with Gary's incredible solar collectors, maybe we shouldn't sweat the small stuff?!?
  18. precaud

    precaud Minister of Fire

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    My major point is: it's a mistake to view "payoff" only in money-out-of-pocket terms. Increased comfort level, less work expended on preparing firewood, increased value to a future purchaser of the home; these (and other things) are all real, tangible payoffs.
  19. midwestcoast

    midwestcoast Minister of Fire

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    Sounds like you have a very efficient home there. nice job! There are many examples of indoor removable storm windows on the builditsolar.com site. Should get you another R-1 all day long, not just night.
  20. Seasoned Oak

    Seasoned Oak Minister of Fire

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    I do agree with every word. I rehab old houses for a living and i insulate as thorough as possible. The last house i did was done so well it never went below 50 in winter even with the heat turned off. That said,there are still other factors at play.When doing my house the biggest savings by far were had through changing from a liquid fuel to a solid fuel heat. I saved the entire cost of the furnace the very first year. I also save about 20% annually by enclosing a south facing porch making a passive solar collector out of it for very lo -cost. Finally i will add insulation to the mixture which has the lowest payback per $ spent in my case. Obviously if you want to keep your electric or oil or other expensive heating sources than insulation may be your highest payback upgrade,for your particular situation. Each case is different. Dont get me wrong,im not discounting the value of insulation. I know from experience in the absence of a changeout of heating fuel sources insulation can make all the difference. In my case though the cost of 12" walls and triple pane windows would be way more than i will pay for heating fuel for the rest of my life.
  21. precaud

    precaud Minister of Fire

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    Well it's clear you understand the game, trump. The key is to identify the highest payoff vs cost scenarios and execute them. And each house has to be evaluated and optimized carefully.
  22. jimbom

    jimbom Combustion Analyzer

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    Hi, I built 12" double stud walls when we built our retirement home in 1990. We have a 50 x 40 foot home with ample glass east/south and minimal glass west/north. In the Ozarks, heat and coolth cost about the same so insulation saves money in both seasons.

    I had the lumber yard rip my 2 x 6 studs into 2 x 3 studs. They did it at no cost. The framers had to erect one extra exterior stud wall, which they did in a flash. From that point forward, labor costs were the same as conventional construction. The walls are 12inch. It is fiberglass batt construction with Tyvex house wrap. I paid very careful attention to airtight features. The cost difference between 12" and 6" batts in 1990 was minimal. Double stud made the electrical wiring go very quickly, but since I did the electrical, no dollar savings were realized.

    The ceiling has two foot of fiber glass blown in. The trusses are 2' deep at the bearing point. Deep trusses were less expensive for my application because it permitted more 2 x 4 chords where 2 x 6 would have been required. I was the general contractor on the house and did much of the mechanical and electrical work myself. Before the ceiling insulation, I carefully and completely foamed up all the potential air leaks. All places where wires and pipes penetrated top plates were foamed closed. The access hatch to the attic is in the front porch ceiling so no air leaks around that penetration. Air vents were foamed carefully. The house is truly air tight. Because of this, I have outside air intake for the basement mechanical, the dryer and the fireplace. Make up air for the stove exhaust and bathrooms comes from the basement under a generous gap in the basement stairs door.

    At the time I built, energy prices were relatively low, and people questioned the wisdom of my actions. No building code would have recommended this level of insulation for our climate at that time. They still don't. I am conversant with diminishing returns with regard to insulation. I am a registered professional engineer with degrees in mechanical and civil engineering. I worked in horizontal and vertical construction for 20 years before retiring. So I was able to quantify the returns versus investment increments. I my house, the most expensive part of 12 inch walls was the loss of 90 square foot of interior floor space at $50/square foot. I included this in my investment cost. The Law of Diminishing Returns should really be the Suggestion of Diminishing Returns. Because each situation has unique aspects that should be considered. It is not a simple 'insulation around the pipe' problem.

    At the time of construction, I anticipated solar heat in the future so I designed and installed a simple warm water radiant floor. It uses conventional pea gravel concrete, ASTM D3309 polybutylene pipe, and inexpensive site built copper pipe manifolds. We heat the house with one 35,000 BTU/hour gas 40 gallon hot water heater which also provides our domestic hot water. It is air conditioned with one 18,000BTU/hour central air conditioning unit. Savings from having no furnace and a 1.5 ton air conditioner were not included in my calculations, but would reduce the original investment. We raised two boys here and had few hot water problems. We have replaced the hot water heater twice or three times, but are still on the original AC unit. The polybutylene pipe has been no problem and will likely last fifty more years at the temperatures I need.

    Because my energy costs over the years were so low, solar heat was never high on the to do list. Then I saw Gary Reysa's BuildItSolar site and was inspired to complete the original solar concept. Gary is an exceptional man and probably has given more freely of himself to make our country energy independent than anyone in the USA. I have never met the man but he has my respect.

    Since my annual costs are so low, I cannot justify many dollars for solar. So, I have been picking up components off the internet and Craiglist postings for the last two years. If you wait long enough, everything you need will come up for sale cheap. For example, I bought 500 square foot of tempered glass for a dollar a square foot. I bought 500 square foot of used freezer panels for $100. Right there, I have the back, insulation and cover for my water panel. My panel will not have tubing, rather the water will just run down the freezer panel surface similar to a Thompson system. I have also obtained a 1000 gallon steel water tank for $200 and an unbelievable amount of cheap structural steel for the panel structure. My panel will be site built 40 x 12 foot. This will require a well made structure to accommodate wind loads. I have all the major components for very little money. Another $1000 or so will see it to completion.

    This has been way to much information. However, my madness has a point. You just cannot isolate a twelve inch double stud wall from the rest of the variables. The climate, energy costs, all investment costs, all energy savings, and all the other elements of the structure should be considered if you want an accurate guess of the utility of a tight house envelope.

    Sorry for the long post, but thanks for having this site. I am learning a lot from the posts on here and hope to be able to contribute a little on the wood side when I become more knowledgeable about my wood stove and my wood lot. Thanks, Jim
  23. nate379

    nate379 Guest

    The problem I see with that though is you loose most of the shear strength the plywood provides.

  24. Wallyworld

    Wallyworld Member

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    The inside walls are screwed OSB so doubt thats a factor. I should have screwed the outside plywood also. It was done with a nailer, 3 1/2 nails and way more nails than normal but I see your point and thought of that. I think if if was screwed and maybe even construction adhesive so you had a sandwiched wall it would be no issue. I'll tell you as far being comfortable inside it rules, I use solar and a wood stove to heat the space. Haven't had a fire in 2 weeks and the temps inside are still in the 50s.It was 2f yesterday morning.
  25. btuser

    btuser Minister of Fire

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    JimboM:

    How do you heat the house and get hot water from the same water heater?

    I'm in the same boat when it comes to solar. I just scrounged a brand new controller, but I've been looking for a tank for a long time.

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