Super insulating a new house?

Discussion in 'Alternative Energy' started by Randy Rooster, Oct 19, 2006.

  1. Randy Rooster

    Randy Rooster Well-Known Member Supporter

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    I am getting ready to build a new place- dont know exactly yet whether I am going to use 2x6 stick built walls or an insulated concrete form, but wondering if I go with the 2x wall some suggesstions for having a place that is extremely well insulated. Im going to heat and cool with a heat pump, but electric is still expensive in my area so I want to get that bill down as far as possible. I think I would use blown cellulose in the walls. Would it pay to then put some of that sheet styrofoam over the studs on the inside or outside? What about under the floor joists and in the attic? I have heard that sprayed foam directly over the inside of the roof sheathing is the best for the attic. Just wondering if anyone else has done any of these and how it has worked out.
     
  2. joken

    joken Well-Known Member

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    I have never heard of insulating the roof sheathing except for open beam ceilings. Do you not vent the attic then? Seems like you would just be heating unoccupied space. Bat insulation in the walls has a higher R-value than blown in. I think? you can get R-23 bats for a 6" wall. If your house is too tight your exhaust fans won't work and you will have humidity issues. Maybe introduce some outside air on the return side of the heat pump. Put a damper in it so you can adjust it to the minimum required. I am a heating guy and have seen insulated crawl spaces with a rat slab. Last house I built was on slab with the ductwork ran thru a soffit between up and downstairs. This eliminated all duct heat loss/gain and made it easy to heat both floors.Good luck, Ken
     

  3. MartyPalange

    MartyPalange Member

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    When we built our home 20 years ago we used double wall construction. Exterior 2x4 wall that is load bearing, 1" space, then interior 2x4 wall. The wall studs need to be offset since the weak point in the wall insulation barrier is the wood stud. We used tyvek (wind barrier) on the outside and sheet plastic (vapor barrier) on the inside under the drywall. We heat with a woodstove @3 cords in CT. No air conditioning. This may be more than you need in North Carolina. At the time we wanted to avoid rigid insulation. Most people today use 2x6 walls with rigid insulation on the exterior to achieve the same R value. As a side note, if you super insulate your home, you may need an air to air exchanger. Here in CT, the utility company is a good source of information.
     
  4. GREENCOUNTYPETE

    GREENCOUNTYPETE Moderator Staff Member

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    I know a fammily from church that built thier home in the late 80's and super insilated it here in south central wisconsin.
    they did a 2x4 outer wall and a 2x4 inner wall the outside to inside measure was 16 inches they filled this with fiberglass insulation and double wrapped with 3 mill plastic inside and out also they put all the outlets in the floor and lights on the second floor were all wall sconces on interior walls basicaly they never punctured the walls or second floor ceiling the outside of the house was a stained cedar siding and all windows were the best thermal pains they could reasonably get it is built into a hill about 5 feet up the north side and large windows on to the south they say they never go over 35 dollars a month heating or cooling heat is a simple forced air natural gas system air is furnace mounted central air and they have a small wood stove that they run ocationaly but they say that unless it is very cold the stove raises the house temp to 80 in a hurry
    and it is a fairly large 4 bed house 2200 to 2400 square feet would be my guess

    i heard somplace r35 in the walls r40 in the attic is the point at wich more insulation has little effect

    hope this helps
     
  5. SolarGary

    SolarGary Well-Known Member

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    Hi,

    For the 2X6 stud walls (on 24 inch centers -- not 16), the insulated sheathing goes on the outside to reduce the thermal bridging through the studs. Some don't like the insulated sheathing in that it does not have the strength of plywood or OSB sheathing, and this might be a consideration if you live in a high wind or earthquake area. Having something like the insulated sheathing (or the techniques listed below) to break the thermal brdiging by the studs is very important. Here is a calculator that will show you how much the thermal bridging hurts on otherwise well insulated walls:
    http://www.builditsolar.com/References/energysimsrs.htm#Walls

    A coupe other wall thoughts:
    Some of the builders around here are using 2X6 studs, then spraying an about 2 inch thick layer of the polyurethane foam, and then using bat insullation to fill the rest of the cavity. The foam gives bombproof air infiltration protection, and only using 2 inches keeps the cost down.

    I think that the wall construction used by Gimmie Shelter (and the similar Mooney wall) offer really good insulation and low thermal bridging at a good cost.
    http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#Stick
    These guys have worked out a whole wall construction that is high R, low thermal bridging, and low infiltration -- its worth a careful read.
    http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm

    SIPS
    SIPS are good of you have a builder who is familar with them -- good insulation and tight.

    ICFs
    If you go the ICF route, there is an advantage to using the type that has the insulation on the outside and the concrete on the inside. This keeps the thermal mass inside the insulation where it can do some good.
    Like the Dow T Mass and some of the other here:
    http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#ICF

    Strawbales are good to -- lots of insulation, tight, built in thermal mass, and easy on the planet.

    ---
    If the house is well insulated, then air infiltration becomes the big heat loss, so this is worth really paying attention to. Some types of construction (like SIPS and ICF) are naturally pretty tight, while others can be, but it requires really careful attention to detail throughout the construction.
    http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#Best

    On the inulsulated roof deck. This is a somewhat new development in which the attic becomes part of the conditioned space, and is not vented to the outside. I know there is a house on my site that uses this, but I can't seem to find it now -- I think if you Google around for it you will find something. I think it may be a good idea if excuted well.

    --
    heat pumps:
    I know people are very up on heat pumps, and you can feel free to ignore my negative thoughts on them :)
    I don't care that much for heat pumps in that while they use electricity very efficiently, most of that electricity is generated at very inefficient coal fired power plants. These power plants generate 4 times as much greenhouse gas per BTU of energy produced as a modern gas furnace. A heat pump with a COP of 3 or so still leaves you generating more greenhouse gas than a good gas furnace would. If it were me, I'd spend the money on very good insulation and infiltration control, and try to use passive solar and maybe active solar -- these technolgies have no greenhouse gas penelty.

    On the cooling front, in addition to the good insulation and low infiltration, you want to really control unwanted solar gain with overhangs or the right kind of glass.

    Good Luck!

    Gary
     
  6. gccrook

    gccrook Well-Known Member

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    We used standard 2X construction, but with scissor trusses for a cathedral ceiling. We had the Icynene sprayed on foam, and they sprayed it on the roof decking. If I did not have cathedral ceilings, I would not have sprayed it on the roof decking. It is only 3.5 inches thick, which gives an R value of around 13, but it feels much better than that, because it eliminates all air infiltration where it is sprayed. It is also very quiet in there now.
     
  7. Jackpine Savage

    Jackpine Savage Well-Known Member

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    This site has some good information on insulation and vapor barrier strategies for different parts of the country: http://www.buildingscience.com/

    Make sure you include an air exchanger in your plans.
     
  8. Randy Rooster

    Randy Rooster Well-Known Member Supporter

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    Thanks to every one for the help. If I use the additional 1/2 or 1" foam sheathing over my plywood sheething it adds about 2 and 4 r values. I am curious if anyone knows how to figure what that extra r value means in heating/cooling costs reduction - how long would it take to pa back the extra cost?
     
  9. SolarGary

    SolarGary Well-Known Member

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    Hi,

    On figuring the value of adding the outside foam:

    If you go to the "whole wall" calculator mentioned above
    http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/NS/SimCalc.htm
    It gives a real (whole wall) R value of 14.1 for 2X6 24 OC with no foam on the outside. With 1 inch foam it gives R18.35

    If you take these to my Insulation Upgrade calculator:
    http://www.builditsolar.com/References/Calculators/InsulUpgrd/InsulUpgrade.htm
    And put in an area of 32 sqft (one sheet), 8000 deg-day climate, and Propane fuel at $2 per gallon, it gives:

    First year saving = $2.74 per sheet of foam board.
    10 year saving with 10% fuel price inflation per year = $43.71 per sheet.

    I guess that one sheet of 1 inch thick foam in builder quantities might be $12 per sheet?

    So, not counting install labor, it pays back a (2.74/12) = 22% return, with a simple payback period of about (12/2.74) = 4.3 years -- less if fuel goes up.
    One way to look at it is that you can borrow the mortgage money to do it, and save more money each year than the interest on the extra mortgage money.

    It probably also gives you a little bit tighter a house.

    It also reduces green house gas emissions by 18 lbs per year for each sheet of foam board.

    Looks like a deal to me :) Remember, this house is going to be burning fuel and making greenhouse gases a hundred years from now.

    Note that if you live in a less than 8000 deg-day climate, or use cheaper fuel, it takes longer.

    Gary

    Gary
     
  10. CatsPaw

    CatsPaw Who...me?

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    Meaning no offense to any of the responders here, I have yet to see an explaination on insulation yet that I believe. I say this because I've seen yeas and nays from trades and homeowners. There is always some factor that is not taken into account. And really I think it would take an accountant and some hard pricing to figure it out.

    Also, I will state that I don't know the answer! These are some of the things that make me wonder (or...Things that make you go...hhmmmm.)

    Somewhere, I read from an insulation industry source, based on some 20 year study, that 2 x 6 walls were not cost effective, based on savings, increased cost of materials and such. Fuel prices were alot cheaper then too.

    Next The last time I priced spray foam insulation about 6 months ago, for an 1800 sq.ft. house would be about $9000 compared to $1200 for standard, in a 2 x 4 framed house.

    Also borrowing for the increased cost of the super insulation is probably a real bad idea if you're looking at return on your investment. This is based on what I perceive as a major extra expense (as in, extra framing, extra insulation or spray foam all running maybe an extra $10K-$20K depending on the size of the house.) Mortgages are amortized. Meaning a straight return on cost doesn't work since the increase in monthly payment is almost all interest, like 95%-99% in the early years. You can at least deduct it, but that means you're only shelling out 70% or 75% instead of 100% of the extra cost from borrowed money. Pay out 70%-75% vs. 22% return = 48%-53% on the negative. I think most people don't realize what they actually pay for their house over the life of the loan. Check your mortgage out. There will be a figure that is the sum total of all the payments. Compare it to the purchase price. (One lender trick is to say "Hey, it'll only increase your monthly payment by $20... which adds up to a huge amount over the life of the loan.)

    As far as the environment, think of the v.o.c.'s from that spray foam and where the chemicals come from in the first place (petroleum), the extra trees for the extra framing. Probably though less over the life of the product compared to what is burned in fuel. (there is a campaign stop stop logging around here, but, I'm not a tree hugger....being a carpenter and all.)

    Air handlers, the last I heard, could run an extra $2000-$4000 (I think this was on a fairly large house....maybe 3000 sq.ft.) You will HAVE to have one if you make the house really tight. Between various unseen molds and v.o.c.s and cooking fumes and other things, indoor pollution is becoming a real topic.

    Any way just some thoughts. Maybe some day I'll actually know the answer.
     
  11. Randy Rooster

    Randy Rooster Well-Known Member Supporter

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    CP- thank you for your questions- it is always good to hear other perspectives, but most of the items you brought up dont apply to my situation. They may be more meaningful to othewrs readingthis thread and contemplating doing this type of insulating.

    The primary reason I am choosing to use 2x6 construction is the strength of the materials. Not only will yellow pine 2x6 make for much stronger walls, but yellow pine is stronger than spruce/pine fir lumber of an equal dimension. The extra insulation value of 5 1/2 inch cavity over a 3 1/2 inch one is a bonus. In my area yellow pine is much cheaper than spf. So much so that a 2x6 of stud length is cheaper than a 2x4 of the same length that is spf. I may have to pick through the yellow pine a bit more, but it is still cheaper than 2x4. Yellow pine is also local grown, and sawn. It doesnt need to be shipped 1000 miles from canada like the spf lumber. I am not planning on using spray foams- I will use blown cellulose and probably rigid foam insulation sheets on the outside of the walls. In my area air conditioning is a must for 3-4 months of the year. Electricity to run that a/c is very expensive.

    I will also be paying for my materials as I go. No mortgage for me. I was lucky enough to have sold my home when the real estate market in my area hit its peak and I made a bundle of money- more than enough to purchase the materials for me to build my new place.
     
  12. Randy Rooster

    Randy Rooster Well-Known Member Supporter

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    Gary-

    I used your calculator and found that I would save $196 a year from heating savings alone, by adding an r-4 insulation. In my area cooling is just as important if not more so than heating for 3-4 months a year, so I am guessing conservatively to be able to save $400 a year by adding the rigid insulation. I think it will be well worth it. Thank you.

    Do you have any plans to upgrade you caluculator to take cooling into account?
     
  13. SolarGary

    SolarGary Well-Known Member

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    Hi Randy,

    One caution about my Insulation Calculator is that tends to overestimate the heating bill savings in warmer climates. This is because it does not account for the heat that comes from internal sources (like bodies and appliances), and these contribute a greater percentage of the heat in a warmer climate. I have not done anything about this yet, because, as you say, the insulation helps on cooling as well as heating. This is a long way of saying I think that $400 may be a little on the high side. But, even if its only $300 -- thats pretty darn good!

    I would like to upgrade the calculator to take into account both cooling savings and internal loads. But, I think its going to have to be after Christmas.

    Gary
     
  14. fantasymaker

    fantasymaker Well-Known Member

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  15. Randy Rooster

    Randy Rooster Well-Known Member Supporter

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    FM-

    For some reason it is next to impossible to get syp 2x 4's round here.
     
  16. agmantoo

    agmantoo agmantoo Supporter

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    Randy, I too live in NC. I have 2x6 studs with the external sheet insulation. Two things that give me a good return are the windows and the geothermal heatpump that I have. I have Hurd windows designed for the south, there is a plastic film between the two panes of glass. The film reflects to almost eliminates the solar gain to reduce cooling expenses. The geothermal heat pump is the key to low utility bills. In the summer it just loafs since the water coming to the unit is around 56 degrees and the house thermostat is around 76 degrees. In the winter the heatpump has to work a bit harder to extract from the 56 degree water enough heat to bring the house to 70 degrees. No backup (strip) heat is required since the heatpump works as if the exterior temp is 56 year around. The efficiency holds regardless of the weather.
     
  17. Burbsteader

    Burbsteader Well-Known Member

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    I can't tell you specific savings and I do not have first hand experience with blown insulation.
    What I can tell you is that we have bat insulation in the walls, up in the attic and shortly after moving in, under the floor joists.
    A lot of people overlook the floor and I think it is a big mistake. (I also recommend using foundation vent covers and quilted window treatments in the winter)

    When we did ours, we noticed an immediate temperature difference. DH put in about half of the living room floor, then came in to the living room and took temperature readings.
    There was an immediate 5 degree difference between the insulated and non insulated floor. If I remember correctly, it climbed closer to 10 degrees or so difference as the day went by.

    Can't give specific savings, as we live in the PNW. But I can tell you that we do not have the heat running yet and it is comfortable. When the outside temps dropped into the 30s it was a little chilly in the morning, but not cold.
     
  18. ET1 SS

    ET1 SS zone 5 - riverfrontage Supporter

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    Today, I just finished spraying our new house with foam.

    I still have a bit left in the tanks so tomorrow I will spray on a second layer on one wall, but the entire house [walls and roof] have a 2 inch coating of hard styrofoam epoxy on, as of now.

    It cost us $4950.

    Using Dow's Froth-paks, well okay actually I found a cheaper competitor that market's the same thing as 'touch-n-seal' but if you want to google it, try the froth-pak, as that is what everyone calls it.

    Our house is 2400 square foot with 14 foot cathedral ceilings. 60 foot long by 40 foot wide, with 12 foot eaves and a 14 foot peak. I sprayed the entire ceiling [roof] and walls [except for the doors and windows].

    Our house is a steel building. Much cheaper than stick, and no thermal-bridging.

    I did not really learn the 'tricks' of doing it right and getting the foam to work the best until I was on the last couple of tanks though.

    LOL

    Good luck.
     
  19. ET1 SS

    ET1 SS zone 5 - riverfrontage Supporter

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    A really tight house?

    Have you ever seen a foamed house? The walls are totally sealed, no air drafts anywhere.

    V.O.C.s Do you mean like from back in the 1960s and 1970's? Wow, I don't think that you can even buy that old stuff anymore.

    This stuff is compressed in nitrogen. It does outgass, it outgasses nitrogen.

    The two chemicals mix in the nozzle and form an epoxy, they heat to over 200 degrees, and spray out onto the wall or ceiling. and it sticks. It expands to a few inches thick, and within 2 minutes it is hard.

    V.O.Cs??? No.
     
  20. Cabin Fever

    Cabin Fever Life NRA Member since 1976 Supporter

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    As homes become more insulated, and superinsulated….and as homes become more tight due to better windows and being essentially wrapped in plastic…the need for fresh air circulation becomes imperative. This is an issue you’ve probably already considered, so I’m not going to dwell on it. Indoor air pollution, due to greater indoor humidity, can and often results in the increased growth of molds and mildew. Likewise, modern building materials contain glues, plastics, and other man-made chemicals that off gas into new homes. Because of these and other indoor air pollution problems (eg, smoke, carbon monoxide, etc), many building codes require the installation of air exchangers in the home. I believe this is what CatsPaw was referring to. An air exchanger allows fresh air to be brought into the home and at the same time exhausts stale, humid and “polutted” indoor air. The air exchanger has an internal heat exchanger which transfers the heat from the outgoing indoor air to the incoming outdoor air such that the use of the air exchanger doesn’t rob the home of heat. If you’re serious about superinsulating a home…or even building a “tight” home…you really have to install an air exchanger.