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  1. #40
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Quote Originally Posted by DavidJ View Post
    I completely agree that that is what they are doing but I am trying to take care of the thermal bypass by having an airtight ceiling plane by installing sheetrock on the ceiling first, before interior partitions, as I talked about in my original post. At that point, it seems that all you need from your insulation is lots of R-value. Stated differently, you pay a huge premium for the thermal bypass qualities of sprayed foam. If you use other methods to deal with the thermal bypass issues, then you can get much more R-value for your money with blown fiberglass, in addition to the other advantages of insulating the bottom plane, as I mention in my secondary posts.
    The drywall will be a pressure barrier with little insulation value. But did you look at the link from the FSEC? Page 16 in particular.

  2. #41
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by dash View Post
    We have done a number of home with the foam/concete walls,some with spray foam roofs,but I'd have to check the files to see what size the system was ,to the sq. ft..

    Do you have a load calc.,on this home yet??
    No I don't. The A/C contractors around here don't seem to do load calcs - they just assume the same parameters as any other house so they can fill out the required energy form and then they apply their outdated 500 SF per ton rule and do what they want. I know that there must be some that do better than that around here, but that appears to be what prevails.

    We have used the services of Calcs Plus http://www.calcs-plus.com/ before to verify the results we were calculating ourselves. We were coming up with load calcs using Energy Gauge software from the Florida Solar Energy Center. In case someone is not familiar with the software, it is the software that shows a builder how efficient a house is relative to a standard home for purposes of determining eligibility of certain builder tax credits. Every imaginable parameter is keyed in to determine building efficiency and resulting BTU needs. It then simulates the weather conditions based on your local weather and gyrates through a simulation to come up with its numbers. I think that Manual J is incorporated into its calculations. On the home that we also checked with Calcs Plus, their tonnage number requirements came up slightly higher than ours but I think they were being a little more conservative. Based on observed performance, I think that our calculations, which were a 1/2 ton lower or so, would have also met the cooling needs of the house.

    I need to take the time to key this unit into Energy Gauge to see what it comes up with. Have you had any opportunity to compare your results with anyone using Energy Gauge? How close do you stick to the Manual J numbers. Do you always round up from Manual J to an actual system size or do you sometimes round down? From your observations and real world experience, have you found that the numbers always cover you?

  3. #42
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by adrianf View Post
    The drywall will be a pressure barrier with little insulation value. But did you look at the link from the FSEC? Page 16 in particular.
    I realize that drywall would offer very little insulative value but I would have R-50 above it in the attic.

    Yes, I remember seeing this or similar document some time ago. I think that some of our ideas came from here. This is the principal of what we are talking about, but this is showing ductwork in the cavity which we were trying to see if we could avoid. Clearly, most people on this thread feel that we are asking for problems if we don't use ductwork in the cavity to distribute the air.

  4. #43
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by dash View Post
    We have done a number of home with the foam/concete walls,some with spray foam roofs,but I'd have to check the files to see what size the system was ,to the sq. ft..
    I'm very curious to see what the "feet per ton" numbers are on the ICF walls with foam roofs that you've done.

  5. #44
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    The two most popular Man J programs have an export to EnergyGauge feature that companies that do room by room heatloads use.

  6. #45
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    Quote Originally Posted by DavidJ View Post
    I'm very curious to see what the "feet per ton" numbers are on the ICF walls with foam roofs that you've done.
    I think that ICF's make more sense in the north.
    Foam roofs are one answer, but not the only one.

    North Central Texas - Fort Worth
    4,000 sq. ft. frame construction.
    R49 cellulose in the attic.
    2 ton heat pump.

  7. #46
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,160
    Simpson strong tie makes ties to strengthen walls and connect walls to roof rafters
    and carry the load path to the sole plate.
    fortified building, a company that reviews plans and
    defines what ties are needed and where they are attached.
    Keeping the roof on in hurricane areas is a must and this is an alternative
    to foam.
    If I had a bit more time I'd find the website, but think that google could do it also.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #47
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    I didn't know Energy Gauge did calcs,so inquiring with our estimators ,they said it shows btus,but says on the screen they are btus per "X" sq ,feet,always higher then the Man. J calc.



    Around 1100 sq ft per ton,however it just barely required the next half ton size,soo if it had been a little smaller or less windows,it would have been more sq ft per ton.



    All the ones we have done have been custom homes,with quite a bit of glass.


    For simplicity ,lets say a ton ton is 24,000 btus,if the load is 24,500,you get a 2.5 ton.If you added insulation or a better window,etc., you could get that home to two tons,which would increase the sq ft per ton.

    Calcs Plus is well known to do a great job.

  9. #48
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,315
    Quote Originally Posted by paul42 View Post
    I think that ICF's make more sense in the north.
    Foam roofs are one answer, but not the only one.

    North Central Texas - Fort Worth
    4,000 sq. ft. frame construction.
    R49 cellulose in the attic.
    2 ton heat pump.
    How did your place perform yesterday, Paul, when we hit 105? I started a separate post on my basic attempts to measure my attic temps and a/c system performance. Was an eye opener to see how warm an attic with spray-on RB still can get. Several factors involved, I realize, such as volume and height of attic...would think a squatty attic like mine allows the heat to get closer to the insulation, where the sensor is, vs. an attic with a high peak.

  10. #49
    Join Date
    Apr 2002
    Posts
    11,808
    ICF is diminishing returns when compared to a cold climate.

    ICF is stronger than concrete block, more hurricane resistant, and you do not need to fur your walls to make a place for insects to live

  11. #50
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    Quote Originally Posted by shophound View Post
    How did your place perform yesterday, Paul, when we hit 105? I started a separate post on my basic attempts to measure my attic temps and a/c system performance. Was an eye opener to see how warm an attic with spray-on RB still can get. Several factors involved, I realize, such as volume and height of attic...would think a squatty attic like mine allows the heat to get closer to the insulation, where the sensor is, vs. an attic with a high peak.
    The house did fairly well.

    It was no where near a typical weekend for us. We had 4 house guests for the weekend, plus about 20 people that showed up for a party that started about 2pm on Saturday and ended about 3am Sunday morning. The oven, microwave, cooktop, hood exhaust, bathroom exhaust, and laundry were all running for hours at a time. The highest indoor temperature we saw was 75 degrees but the humidity was down to about 38% at that point, so nobody was suffering.

    Sunday, I still had the thermostat set at 73 degrees, and I had to turn it back to 74, the humidity was still quite low and it was on the cool side.

    Because we had so many guests, we also had the mini-split in the master bedroom running all weekend, and it stayed 70 degrees in there.

    I was watching the CO2 as well. Any time the kitchen hood exhaust was running, the CO2 level plummeted to about 700. Late in the evening after all the cooking was done, and everybody was sitting around talking, it hit about 2,700.

  12. #51
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by energy_rater_La View Post
    Simpson strong tie makes ties to strengthen walls and connect walls to roof rafters
    and carry the load path to the sole plate.
    fortified building, a company that reviews plans and
    defines what ties are needed and where they are attached.
    Keeping the roof on in hurricane areas is a must and this is an alternative
    to foam.
    If I had a bit more time I'd find the website, but think that google could do it also.
    Actually the way we secure trusses in Florida, they ain't goin' anywhere. We put the Simpson strong ties into the wet concrete when pouring parameter tie beam on the top course of block. The framer lays out the trusses on the block before pouring the concrete so that the concrete pumpers know exactly where to place the ties.

    It works no different with ICF (insulated concrete forms) construction. After all the foam blocks are up and before pouring the center core, the framer lays out the trusses on the sides of the foam wall and then the ties are placed at the top by the concrete pumping guys.

  13. #52
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by paul42 View Post
    I think that ICF's make more sense in the north.
    Foam roofs are one answer, but not the only one.

    North Central Texas - Fort Worth
    4,000 sq. ft. frame construction.
    R49 cellulose in the attic.
    2 ton heat pump.
    Yes, walls are not our area of greatest concern in Central Florida. However, once you've dealt with everything else, then they start constituting a larger piece of the total pie.

    2,000 square feet per ton! Very impressive, especially reading your later post about all the company you had this weekend. So what's in your secret sauce to achieve that besides R-49 , or has that already been discussed on another thread on this site?

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