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  1. #27
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,160
    The homes I have seen this install in are mostly several years old.
    No problems from the install, while I have not measured with a flow hood to
    determine the air flow per room, no complaints in these well used homes.
    Several new homes seek to incorperate this install, but it has to be incorperated
    in the design phase. Very few homes not designed with a central to all rooms
    area can make this work.
    There have been 2 new homes that incorperated the fur down hallway,
    both were commercial ac company owners. Both did the fur down without
    ductwork, have low utility costs, enhanced hvac performance, and no issues
    of condensation or mold.

    If I didn't make myself clear...foam boards of any kind can not be used in this application. My understanding is that in the heating season that foam will offgas.Use only materials made for hvac..in this case, ductboard & mastic. It just makes sense.

    I do agree that if the ductboard was installed with insulation facing out, that this would
    be the correct install. sealing the foil faced sections of ductboard would be easy, and
    you would not (or I would not) worry with the issue of particles of ductboard insulation entering the home.

    Transfer grills can be offset with in the same wall cavity..one side 6" lower than the other to lessen sounds from passing thru the grill. Sound moves in straight lines, if you
    can make it turn, it lessens the sound. (I'm sure there is a more professional way to phrase this!)

    There are lots of ways to build the semi conditioned attic. Foam insulation being the easiest. I won't get into the issues I have with foam insulation, but lets keep talking about alternate routes to achieve the same result.

    After hurricane Katrina I was in New Orleans to 'oversee' a slate roof replacement.
    Ended up working the install also due to lack of skilled workers and the language barrier..
    what we did was to remove the old slate..and an interesting thing was that the rear of the roof was not slate, but asbestos siding sections..
    removed old slate, cleaned & stacked for re-install on rear/back section of roof
    installed roofing membrane,
    installed 1" polysyrene foil sheating boards, foil facing up
    on top of foil boards 1" furring strips
    layer of plywood
    and then slates.
    the edges of the roof were sealed air tight.
    This install is called 'ice house roof'
    It performed as a radiant barrier with the air space
    unvented roof because of the sealing of the edges.
    In this cottage attic space was turned into a guest suite and the
    peak was not acessable to add additional insulation.
    the eaves of this guest suite was storage and we spent
    an addtional day caulking and sealing storage areas.

    The complaint for the guest suite was that in august sept that it
    was unberably hot. Now it stays an even temp year round.

    Lots of ways to achive the same result.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  2. #28
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,160
    Adrian..the hall is 7' the rooms adjacent to the hall are at least 8'
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  3. #29
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by shophound View Post
    Curious...perhaps I'm visualizing it incorrectly, but running an unbroken plane of ceiling drywall from exterior wall to exterior wall...are there no load bearing interior walls? You could essentially frame up all the exterior walls, build the ceiling joists and rafters, drywall the joists, and then have one large cavernous space before erecting interior walls?
    Here in this part of Florida, the exterior walls of most houses are actually concrete block with stucco finish on a monolithic concrete slab. After the block goes up the trusses are set. In smaller homes it is rare to have any load bearing walls inside so you end up with a large open space after framing the trusses. Then 3/4" thick R-Matt 4 X 8' sheets of insulation are tacked onto the inside of the block wall all around the parameter. Then 1X2 or 1X4 furring strips are nailed on top of the insulation at 16 or 24" centers. Then the rest of the interior partitions are set. Yes, the only wall insulation the vast vast majority of houses in Florida have is that 3/4" of insulation board with the 3/4 air cavity that exists between the furring strips. I think the board is rated at R-5.4 and you get some additional credit for the air cavity between the furring strips. The concrete block is rarely foam filled although that is becomming slightly more popular as of late. code requires downpours of concrete in the block every 6 feet and on each side of each window and door and each corner and for the tie beam course on the very top.

    Quote Originally Posted by shophound View Post
    More thoughts on this...say you're the electrician up in the attic searching for where to drill through the top plate to send down Romex. He might say, "Hmm...can't see the top plates up here. All I see is drywall. I wonder where that bathroom wall is."
    He would do his drilling from down below and only have to be in the attic to pull the wires. Again, we would leave full sheets off in the middle of the rooms to make their job easier. No question that it would involve some coordination and the electrician would certainly curse when he saw what he had to do. My guess is that it wouldn't be too bad, once they got into it and the benefit is a lifetime of positive separation between living area and attic.


    Quote Originally Posted by shophound View Post

    Concluding thoughts...frame the house as usual. Then, wherever drywall meets an interior or exterior top plate, caulk the joint. If you wanna go crazy, run a bead of caulk along the top plate before slapping up a sheet of drywall. The ceiling is always rocked first, and there's no solid backing behind where the ceiling rock meets the wall top plate (unless you decide to go super crazy and block it), so caulking the ceiling to wall juncture is a good idea, anyway. Before even reaching that point, any penetration through top plates are to be sealed.
    We tried exactly what you say here, doing the work ourselves (gluing the wall board to the top plate with drywall adhesive and sealing all top plate penetrations. The ceiling board is always resting on trusses or dead wood backing). Of the two houses we did a blower door test on using this method you describe, we were told that they were the tightest houses the rater had ever tested. So yes, that method does work well. We determined that it would happen with someone else doing the work, as long as someone was there watching the job every moment. These drywallers get on a roll and they don't want to stop and do as you suggest. There is no way to see their level of compliance after to rock is up.

    We are trying to come up with a more fool proof method of sealing the separation between attic and living area that is not too onerous. Yes, anything beyond the traditional method involves more work or they would already be doing it that way. We are trying to avoid cutting corners on an issue that exists for the life of the house and that is oh so much harder to deal with later.


    Quote Originally Posted by shophound View Post
    The entire roof deck had been foamed. It was over 95 degrees outside. The attic had several visitors plus a docent explaining the HVAC. The attic was not hot or uncomfortable. It was completely sealed to the exterior. This was my first experience in a residential attic with a spray foamed roof deck. It's wonderful.
    This is the way most people are dealing with the issue of having a conditioned space for the ductwork, when they decide to do something about it. Icynene is the name that most people are familiar with to the point that the company name is used generically to describe this insulation system.

    I have the following issues with it.

    First, it is expensive. I think it costs about $2/square foot around here, although that number might be a little bit high. R-30 blown insulation is about 1/4 that. For that $2/foot you get R-21 and it is about 3 1/2" thick. Thus is pretty much fills the cavity between the top chord of the trusses. They claim that the R-21 is equal to R-30 or better in a traditional attic with blown insulation. I imagine that they are taking duct work benefits into account when they say that, but I am not sure. Well, if is is just equal to R-30, then what am I gaining, and it is costing me 4 times the money. Remember that R-value is supposed to be an apples to apples number. I agree that a leaky ceiling plane with traditional blown insulation is not good and very inefficient but I'm dealing with a sealed ceiling plane so all I need is a nice big blanket up there to maintain the separation between hot and cold.

    The other issue is this with their claim of R-21. A 2X4 truss top chord has an R-value of about 4. Since their insulation is only between the trusses, and deeply blown insulation covers the trusses and creates a true blanket, we must factor that into the net R-value of foam. (OK, I just did the math on this and it look like the penalty hit here is not to severe.)

    Finally, when you insulate the top truss chord instead of the bottom chord, you are increasing the hot/cold separation area substantially. In other words there is a great increase in surface area, depending on the roof slope, that must be insulated when you insulate the top chord. This can't help but reduce your efficiency. In addition to that, and again depending on roof slope, you are also increasing the cubic feet air volume that must be cooled. That attic air is not moving around much, but the cooler living area air is having to permeate through the sheetrock and vice versa or those attics would not be so comfortable.

    The government website http://www1.eere.energy.gov/consumer...nsulation.html recommends R-38 minimum in the attic and I think it is cost effective to go well above that with blown insulation. To get to that true R-value with Icynene style methods gets very expensive and thus, I have never seen it applied that thick.

    Bottom line is that it seems like, if you deal with sealing the drywall plane and if you can get the A/C in conditioned space, putting traditional insulation down on the flat plane, at a very thick level, is hard to beat. There is no question that the Icynene method is easier, but I don't think it can be near as good. As I am also a solar contractor I try to look at making these as close to zero energy as possible without solar so that, if we add solar, we don't have to add as much to wipe away the electric bill.

    Did I convince anyone? If not, perhaps you can at least see where I am coming from.

    Thanks.

    DavidJ

  4. #30
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Quote Originally Posted by energy_rater_La View Post
    Adrian..the hall is 7' the rooms adjacent to the hall are at least 8'
    If the entire hall is unducted supply how will he be able to return over the doors? 8' or 20' ceiling in the bedroom he will need to make provisions for the returns because there will be no room over the door for the return back into the unducted supply only ceiling.

    I apologize for the confusion.

    We have done a few older homes that did not have a/c this way; only we ducted the supply.

  5. #31
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by dash View Post
    1. Ductboard has it's moisture/air barrior on the outside,insulation on the interior.You'll your intended moisture/air barrier on the inside(drywall),insulation on the outside,so moist/warm air in a ventilated attic,can reach the drywal,which is not a moisture barrier.

    The vapor barrier on batt insulation ,isn't suffiecent,in my opinion.

    Flex or metal duct has air barrier on the inside,then insulation,then moisture barrier on the outside,leakage of the moisture barrier,will cause the insulation to become wet and useless.
    OK, Now I understand that the vapor barrier is the issue and I see where you are coming from.

    Quote Originally Posted by dash View Post

    2. Yes, duct systems have resistance,properly designed ,no more then the fan can handle.Too little resistance,and fans won't perform properly,could be an issue if the cavity is large enough to cause one.In a large cavity you'll have low velocity,then closing registers will increase velocity,this uses up the static ability of the fan,static is what moves the air,could be an issue.

    3.Registers are not designed to be the sole source of balancing.May not be able to get the correct air flow,or may become noisey when closed enough to get the correct airflow.POlus using the cavity likely means less then ideal register location,so the air pattern from the register is more critical,to have even comfort throughout the room.
    I see where you are coming from here as well.

    Quote Originally Posted by dash View Post

    4. You could use a two ton,two stage ,in low about a ton.Not sure what the inverter based units drop down to.Florida code regulates oversizing,though seldom ,if ever enforced,but leaves the contractor liable,even though it passes inspection.


    Using 1" ductboard eliminates all the possible issues,return thru the bottom is fine,only suggested the cavity so uninsulated ducts could be used with no issues.
    Do you have any experience with super efficient homes here in Florida? I see you are from Crystal River. If so, what is the highest number of square feet per ton that you have seen successfully implemented?

  6. #32
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    David

    What is being considered when they are talking about the R value of foam verses typical batt or blown insulation is the absence of thermal bypass. The commitment and discipline it would take to get the insulation integrity of batts (or foam board in the attic)to equal that of spray in place foam would be labor intensive and thus a fairer cost comparison. Your doing great though just getting the ducts below the thermal and pressure barrier.

  7. #33
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by dash View Post
    1. Ductboard has it's moisture/air barrior on the outside,insulation on the interior.You'll have your intended moisture/air barrier on the inside(drywall),insulation on the outside,so moist/warm air in a ventilated attic,can reach the drywal,which is not a moisture barrier.

    The vapor barrier on batt insulation ,isn't suffiecent,in my opinion.

    Flex or metal duct has air barrier on the inside,then insulation,then moisture barrier on the outside,leakage of the moisture barrier,will cause the insulation to become wet and useless.

    2. Yes, duct systems have resistance,properly designed ,no more then the fan can handle.Too little resistance,and fans won't perform properly,could be an issue if the cavity is large enough to cause one.In a large cavity you'll have low velocity,then closing registers will increase velocity,this uses up the static ability of the fan,static is what moves the air,could be an issue.

    3.Registers are not designed to be the sole source of balancing.May not be able to get the correct air flow,or may become noisey when closed enough to get the correct airflow.POlus using the cavity likely means less then ideal register location,so the air pattern from the register is more critical,to have even comfort throughout the room.


    4. You could use a two ton,two stage ,in low about a ton.Not sure what the inverter based units drop down to.Florida code regulates oversizing,though seldom ,if ever enforced,but leaves the contractor liable,even though it passes inspection.


    Using 1" ductboard eliminates all the possible issues,return thru the bottom is fine,only suggested the cavity so uninsulated ducts could be used with no issues.
    Maybe you could use the same foam as the block walls,on the trusses first,then drywall,and interior walls,I'd feel safer that way.

  8. #34
    Join Date
    Apr 2002
    Posts
    11,808
    Quote Originally Posted by DavidJ View Post
    Here in this part of Florida, the exterior walls of most houses are actually concrete block with stucco finish on a monolithic concrete slab. After the block goes up the trusses are set. In smaller homes it is rare to have any load bearing walls inside so you end up with a large open space after framing the trusses. Then 3/4" thick R-Matt 4 X 8' sheets of insulation are tacked onto the inside of the block wall all around the parameter. Then 1X2 or 1X4 furring strips are nailed on top of the insulation at 16 or 24" centers. Then the rest of the interior partitions are set. Yes, the only wall insulation the vast vast majority of houses in Florida have is that 3/4" of insulation board with the 3/4 air cavity that exists between the furring strips. I think the board is rated at R-5.4 and you get some additional credit for the air cavity between the furring strips. The concrete block is rarely foam filled although that is becomming slightly more popular as of late. code requires downpours of concrete in the block every 6 feet and on each side of each window and door and each corner and for the tie beam course on the very top.



    He would do his drilling from down below and only have to be in the attic to pull the wires. Again, we would leave full sheets off in the middle of the rooms to make their job easier. No question that it would involve some coordination and the electrician would certainly curse when he saw what he had to do. My guess is that it wouldn't be too bad, once they got into it and the benefit is a lifetime of positive separation between living area and attic.




    We tried exactly what you say here, doing the work ourselves (gluing the wall board to the top plate with drywall adhesive and sealing all top plate penetrations. The ceiling board is always resting on trusses or dead wood backing). Of the two houses we did a blower door test on using this method you describe, we were told that they were the tightest houses the rater had ever tested. So yes, that method does work well. We determined that it would happen with someone else doing the work, as long as someone was there watching the job every moment. These drywallers get on a roll and they don't want to stop and do as you suggest. There is no way to see their level of compliance after to rock is up.

    We are trying to come up with a more fool proof method of sealing the separation between attic and living area that is not too onerous. Yes, anything beyond the traditional method involves more work or they would already be doing it that way. We are trying to avoid cutting corners on an issue that exists for the life of the house and that is oh so much harder to deal with later.




    This is the way most people are dealing with the issue of having a conditioned space for the ductwork, when they decide to do something about it. Icynene is the name that most people are familiar with to the point that the company name is used generically to describe this insulation system.

    I have the following issues with it.

    First, it is expensive. I think it costs about $2/square foot around here, although that number might be a little bit high. R-30 blown insulation is about 1/4 that. For that $2/foot you get R-21 and it is about 3 1/2" thick. Thus is pretty much fills the cavity between the top chord of the trusses. They claim that the R-21 is equal to R-30 or better in a traditional attic with blown insulation. I imagine that they are taking duct work benefits into account when they say that, but I am not sure. Well, if is is just equal to R-30, then what am I gaining, and it is costing me 4 times the money. Remember that R-value is supposed to be an apples to apples number. I agree that a leaky ceiling plane with traditional blown insulation is not good and very inefficient but I'm dealing with a sealed ceiling plane so all I need is a nice big blanket up there to maintain the separation between hot and cold.

    The other issue is this with their claim of R-21. A 2X4 truss top chord has an R-value of about 4. Since their insulation is only between the trusses, and deeply blown insulation covers the trusses and creates a true blanket, we must factor that into the net R-value of foam. (OK, I just did the math on this and it look like the penalty hit here is not to severe.)

    Finally, when you insulate the top truss chord instead of the bottom chord, you are increasing the hot/cold separation area substantially. In other words there is a great increase in surface area, depending on the roof slope, that must be insulated when you insulate the top chord. This can't help but reduce your efficiency. In addition to that, and again depending on roof slope, you are also increasing the cubic feet air volume that must be cooled. That attic air is not moving around much, but the cooler living area air is having to permeate through the sheetrock and vice versa or those attics would not be so comfortable.

    The government website http://www1.eere.energy.gov/consumer...nsulation.html recommends R-38 minimum in the attic and I think it is cost effective to go well above that with blown insulation. To get to that true R-value with Icynene style methods gets very expensive and thus, I have never seen it applied that thick.

    Bottom line is that it seems like, if you deal with sealing the drywall plane and if you can get the A/C in conditioned space, putting traditional insulation down on the flat plane, at a very thick level, is hard to beat. There is no question that the Icynene method is easier, but I don't think it can be near as good. As I am also a solar contractor I try to look at making these as close to zero energy as possible without solar so that, if we add solar, we don't have to add as much to wipe away the electric bill.

    Did I convince anyone? If not, perhaps you can at least see where I am coming from.

    Thanks.

    DavidJ
    You must have a belt beam poured around the top of the wall to strap the roof down to.

    Should have bit the bullet and bought 2 more rows of blocks.

    Blocks with stucco are pretty air tight. The sealed attic and you would not of had to worry about infiltration at all.

  9. #35
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Quote Originally Posted by Carnak View Post
    You must have a belt beam poured around the top of the wall to strap the roof down to.

    Should have bit the bullet and bought 2 more rows of blocks.

    Blocks with stucco are pretty air tight. The sealed attic and you would not of had to worry about infiltration at all.
    Excellent idea and no code issues regarding ceiling height or return pathways.

  10. #36
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    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??

  11. #37
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    Apr 2002
    Posts
    11,808
    Quote Originally Posted by adrianf View Post
    Excellent idea and no code issues regarding ceiling height or return pathways.
    The house itself has more of an impact on comfort, energy efficiency and humidity control than any HVAC system installed.

  12. #38
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    [QUOTE=Carnak;1940833]The house itself has more of an impact on comfort, energy efficiency and humidity control than any HVAC system installed.[/QUOTE

    True but the real infiltration doesn't start until you turn on the air conditioner.

  13. #39
    Join Date
    Jul 2008
    Posts
    86
    Quote Originally Posted by adrianf View Post
    David

    What is being considered when they are talking about the R value of foam verses typical batt or blown insulation is the absence of thermal bypass. The commitment and discipline it would take to get the insulation integrity of batts (or foam board in the attic)to equal that of spray in place foam would be labor intensive and thus a fairer cost comparison. Your doing great though just getting the ducts below the thermal and pressure barrier.
    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.

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