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Building envelope – insulation

demoss | Posted in Energy, Heating & Insulation on March 12, 2009 09:02am

I’m in a quandry as to what to do for insulation in a new house I am currently in the process of building. The house is located in the San Juan Islands of Washington State ie. fairly temperate maritime climate. I’d like to get R-30 walls and R-50 in the attic. First floor walls are 2 by 6’s on 16″ centers on concrete slab. Exterior walls are board and batten w. a rain screen underneath ie. firring strips and 15lb tarpaper underneath the board and batten.

Here is what I would like to do: Utilize 2″ of BSF closed cell foam in 2 by 6 walls then fill in the rest of with ecobatt insulation. Next, to eliminate thermal bridging I wanted to put (on the inside of the house – as opposed to the exterior walls) a product called p-2000 (3/8″) which is a rigid foil backed foam and then put sheet rock over the rigid foam. (The electricians have already set the electrical boxes out to accommodate for sheet rock and p-2000 thicknesses.

My concerns – one – I am not sure my local building department is going to allow me to use the foam and the batts together. Right now they are saying I can’t “mix and match.” ie use two different insulative properties. If they do allow this combination I am wondering if I am going to have any issues with moisture buildup in the studs.

Secondly, if the building department nixes the combination described above what would be a good (or better?) insulative envelope. Something like spray in BIB fiberglass and then the p-2000 as well as making sure to calk and seal all plumbing/electrical intrusions, etc.?

Any feedback would be appreciated. Thanks in advance.

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Replies

  1. DaveRicheson | Mar 12, 2009 01:25pm | #1

    First, welcome to Breaktime

    If you use the search function on this site you may get a lot of information that will help you decide what to use. A good place to start is a search on the "Mooney  Wall." I think it may be in the current active crop of topics and is quiet extensive in the number of post.

    You may also want to look at http://www.buildingscience.com  for insulation packages/techniques that are suiteable to you area of the country.

    I'l be the first one, but not the last, to tell you, you do not need foil faced rigid foam inside. The foil serves no usefull function, other than a vp on the inside of a wall assembly. Sprayed foam insidethe 2x6 wall will likely achieve your objective without the m8ixing of material that your ahj is grousing about. It will also be a one step procedure, thus reducing the labor and assorted material cost of you multi layer approach. You will also get the air sealing of the various penetration as part of the spray installation.

    Others will be along shortly to really fill out your topic.

  2. DickRussell | Mar 12, 2009 03:31pm | #2

    I'm inclined to agree with Dave on the foil foam. With so much moisture out there, the foil (a totally impervious vapor barrier) won't allow any drying to the inside. You could be inviting trouble. You might think of a layer without the foil to take up the space already allowed by the electrical boxes. You also should be very careful to seal the cavity against air leaking into it from inside the house.

    I don't follow why the building dept would say mixing insulation types is a bad idea. It's all about movement of heat and water vapor in either direction. Mixing insulation types doesn't affect heat movement, other than via different R values contributing to the total. Different insulation types do have different water vapor permeabilities. Thus you have to be careful to eliminate convective transport of bulk water vapor into the cavity (via air leaks), and you need to consider dew point issues.

    The foam outside will seal against air leaks from outside as well as really limit diffusion past the outer sheathing, which itself is somewhat low perm. A layer of some low-perm foam on the inside (but not ultra low), or even just vapor retarding primer on the drywall, will really limit movement of moisture from inside the house into the cavity during those times when the air outside is dry (hah - when is that in your area?), while allowing drying to the inside.

    If you can show them the numbers you should be able to convince them that the assembly will work very well. But then the inspector may just be a stinker who won't learn anything new.

  3. Piffin | Mar 12, 2009 07:38pm | #3

    If you want better, just simplify things and spray the cavities full of foam and eliminate all those layers.

    3/8" will do little to stop thermal bridging and your climate is not a candidate for worrying about that.

    My concern would be having two layers of foam capturing a layer of FG. You are not highly likely to get moisture in there, but if you eve do, it will never dry out, but will support molds and rot.

    The hybrid of sprayed and FG is gaining recognition, but the double ply of VB with capture space is bad.

    Another option is one I often use - to pack cavities with batts, blown FG or cells, and then 1" of foil faced foam on the inside of the studs, followed by furring and then wall board

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

    1. demoss | Mar 13, 2009 12:20am | #5

      I'm a little concerned about the costs associated with spraying the cavities with foam - thus the hybrid approach - ie. either batts or fiberglass in conjuction with the foasm Thanks for the heads-up regarding the concern about capturing moisture between two VB's. That said, if I put in two inches of foam initially in the interior of the stud walls wouldn't that effectively seal off moisture to begin with - thus eliminating moisture between the two VB's? At any rate in reading the posts everybody is saying that I should be simplifying.What about the idea of ditching the foam and just going with sprayed in fiberglass or cellulose along with the p-2000? In terms of thermal bridging it is something I read about all the time but are you saying in the NW that it is not something I need to be especially concerned about? My intent with this new building is to try and make it a super insulated house that is as airtight as possible...Could you elaborate a bit more on your last option? You are saying pack the studs w. whatever insulation you are using then is that rigid foil faced foam? What would be the difference between that and using the p-2000 ie. a foil backed foam? Thanks again for your input.

      1. Piffin | Mar 13, 2009 01:34am | #6

        Thermax is the brand name of one of the rigid foam boards that I use. R-7 per inch.i am not familiar with the p2000, but keep in mind that to benefit at all from a radiant barrier you need a wall system that leaves an inch of air space in front of the foil. So a thin material such as that is relying very much on radiant properties rather than actual thermal resistance to make up claims of high insulative properties. And only 3/8" of foam will do almost nothing to benefit you in preventing thermal bridging. Where I have seen signs of that being a problem is in climates and temperatures well below zero. onto the moisture issue. You seem to be thinking the moisture would only get into the wall from outside when you make the comment about the spray foam keeping it out. But most of the moisture in a wall cavity comes form interior humidity that is present anytime people live in a house. You give off a couple quarts a day just breathing and sweating. Then there are showers, cooking, house plants, etc....That airborne moisture can find its way into wall via any penetrations such as recepticles, screws in the sheetrock, picture hangers, and other minor gaps or penetrations.So the general principle is to not use two barriers on the sides of a wall. one side only 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      2. Piffin | Mar 13, 2009 01:51am | #7

        Forgot to mention - yes sprayed in foam is expensive, but a system of multiple layering takes a lot of labour you need to account for in comparisons too. 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      3. davidmeiland | Mar 13, 2009 03:08am | #8

        Greetings from a fellow islander. IMO you are better off building thicker walls and using blown-in cellulose insulation alone. Adding 2x2 or 2x3 horizontal strapping across the inside of the studs will give you close to R-30. The foam creates a lot of hassle with attaching siding (if the foam is outside) or drywall (if the foam is inside), although if you are furring the exterior of the building with horizontal 1x4 to create the rainscreen you may be able to tame the foam that way. Cellulose (or blown FG) will perform very well, along with 15# or 30# felt on the exterior of the sheathing. Some folks would prefer Tyvek or similar, because it can be taped and possibly forms a better air barrier, but I pick felt every time.

        Claims associated with P-2000 are absurd, IMO. I had an architect tell me he could get R-27 in a half-inch, or something like that. Although it may have some useful reflective properties if installed with an air space in front of it, my bet is that if you install it as you described you will get approx. R-2.

        I would also suggest you read up on air-tight drywall and think about incorporating it as much as you can. Limiting air movement thru the walls is a big deal. Check out Resource Conservation Technology for useful air sealing products. Things like the wall caps you use for vent fans and dryer ducting make a big difference. I recently started using Seiho vent caps and they perform very well.

  4. User avater
    xxPaulCPxx | Mar 12, 2009 10:15pm | #4

    BTW, that P-2000 came up here before.  I believe the consensus was that their claims were a big load of hooey.

    Tu stultus es
    Rebuilding my home in Cypress, CA
    Also a CRX fanatic!

    Look, just send me to my drawer.  This whole talking-to-you thing is like double punishment.

  5. Clewless1 | Mar 17, 2009 06:20am | #9

    RUN, don't walk, in the opposite direction of P2000! Snake oil, scam, BS. Simple as that. Their formerly outrageous claims border on fraud.

    As for mixing and matching ... shouldn't be an issue. Generally, I think the BO is wrong ... but hey, I've been know to be wrong, too. My only question is the issue that you are placing the foam (and vapor retarder) on the outside of the batt insulation; maybe that is the issue? You should be able to mix and match in general. And I don't think codes restrict this type of combo. 

    How do you plan on getting your R-30? If you are relying on the P2000, forget it. 2 inches polystyrene = R10 leaving 3 1/2 inches left ... R-13, maybe R-15 ... you are running R-23 to R-25. You can get R-21 or R-23 w/ straight fiberglass batts ... not sure about the eco batt in higher densities.

    It is not unusual to place a rigid board on either side of framing to gain the thermal break and boost insulation levels. A friend of mine routinely did e.g. 1/2" thermax on the outside in lieu of OSB sheathing. Very effective.

    Sorry to come on so strong, but P2000 ... in my humble opinion ... is junk. I've been in the energy business for 29 years, now ... I remember when this product came out about 12+ years ago ... claiming R-40 or R-50 per inch!! Give me a break. In your case, the reflective surface will boost performance negligibly. For a reflective surface to work, it must face a dead air space AND remain REFLECTIVE (which few materials do in typical residential construction).

    1. MartinHolladay | Mar 17, 2009 03:12pm | #11

      Clewless,

      Anyone interested in more information on exaggerated claims by marketers of P2000 should check out

      http://www.greenbuildingadvisor.com/blogs/dept/musings/beware-r-value-crooks

      Martin Holladay, senior editor

      http://www.greenbuildingadvisor.com

       

      1. frammer52 | Mar 17, 2009 09:57pm | #14

        Martin, do you read the threads at contractor talk.com?

        We were having a discussions about the p2000, when a representative of the company came on.

        Edited 3/17/2009 2:57 pm ET by frammer52

  6. Clewless1 | Mar 17, 2009 06:27am | #10

    Also ... cutting rigid foam to fit in stud cavities may likely be a HUGE labor effort. Even meticulous framing will see large variations (relatively speaking) in stud width. While you can cut the foam very cleanly and accurately ... framing isn't that clean, uniform, or accurate. While there is a time and place for everything ... think twice before you decide to slice rigid for all of your framed cavities. Make sure you are willing to commit.

    1. Billy | Mar 18, 2009 04:14am | #20

      Also ... cutting rigid foam to fit in stud cavities may likely be a HUGE labor effort. Even meticulous framing will see large variations (relatively speaking) in stud width. While you can cut the foam very cleanly and accurately ... framing isn't that clean, uniform, or accurate. While there is a time and place for everything ... think twice before you decide to slice rigid for all of your framed cavities.

      Actually, you don't have to -- and don't want to -- cut the foam to tightly fit between the studs.

      Leave a gap between the foam panel and studs that you can fill with spray foam for a good solid seal and tight fit.

      Billy

      1. Clewless1 | Mar 18, 2009 04:25pm | #24

        good point. Messy and expensive, though. But yeah; more than one way to look at or apply a material. Still a lot of cutting. Many cavities aren't 'standard stud bays'.

  7. PedroTheMule | Mar 17, 2009 05:45pm | #12

    Hi demoss,

    Properly installed radiant barriers do make significant differences and in my opinion are a must in any climate....generally a lot of bang for the buck but once again....properly installed....I have a double radiant barrier in my home but didn't leave sufficient air space for it to have maximum effect. According to my latest research I'm getting about 30% from one and 20% from the other. I put in twice the effort and cost to get 1/2 of a single layer. I don't regret for a moment putting it together but I could have done a better job......next house!

    In researching the p-2000 web site it does momentarily mention using the product inside but it appears that all of their most effective data relates to using it on the outside of the envelope which makes sense. Use it to control thermal bridging and moisture "before" it enters the envelope. I consider anything inside the finished siding material to be a part of the envelope since it affects everything beyond that point. Any moisture within the envelope can then be controled through various ventilation and humidity controls.

    Take out the marketing fluff of P-2000 and it should perform equally to entry level insulated barriers....now compare the costs to get the best value.

    Under no circumstances though, would I intentionally seal both sides of the wall unless I were using metal studs and sprayed everything with antimicrobial chemicals. Simply too much potential for mold otherwise.

    Pedro the Mule - Warm, Cozy & no bad fur days when it's humid

    1. DickRussell | Mar 17, 2009 09:24pm | #13

      "Properly installed radiant barriers do make significant differences and in my opinion are a must in any climate..."I have to disagree with that statement. A radiant barrier invariably means a foil of some sort, and that means a completely water-impervious layer. Such a layer has the potential to cause more damage from preventing diffusion of water vapor than is warranted by whatever thermal gain it provides in a wall assembly. Building a thermally efficient wall is fairly easy to do without having to incorporate radiant barriers.

      1. PedroTheMule | Mar 17, 2009 10:16pm | #15

        ......whatever thermal gain......

        Good Afternoon DickRussell,

        Do you find thermal value in Low-E for windows? Radiant Barriers & Metal Roofs provide similar results. Inexpensive addition with a noticeable return in my area.

        My experience is the moisture this keeps outside (fairly high humidity issues in Central NC) is worth what it may trap in. What is trapped in can be handled with proper ventilation and/or mechanical removal. Radiant barriers add so much comfort reducing loads that afford the moisture control expense. It all has to work as a package. Simply throwing on a radiant barrier will rarely provide any value if everything else is left as an old construction technique.

        Our radiant barrier, although not maximized as well as it could have been, was factored into the overall home load. It allowed the HVAC to be significantly reduced in size....2.92 ton for 4600 sq. ft....other techniques I've come across since then would have reduced that even further but that's the next house.

        As far as humidity experiences are concerned, 2 houses back was a home someone else built. While performing some maintenance/upgrades, I found they had used a  foil covered foam board and super sealed it - unusual for a 30 yr. old home. There was absolutely "0" mold or moisture signs. We lived there 14+ yrs.

        If the radiant barrier is not fully sealed, then outside moisture still comes through and then has added difficulty drying back out as you have apparently experienced. Again this process is a package deal, not a simple add on.

        No expert here, simply experience from several directions over many years.

        Pedro the Mule - Lovin' the comfort of radiant fur

        1. DickRussell | Mar 17, 2009 10:59pm | #16

          "Do you find thermal value in Low-E for windows?"A window and a wall assembly are two very different things, in two ways. Other than in the frame, the window has no insulating material besides the thin layer air or argon trapped between the panes of glass. Without a low-E coating, the gas layer provides very limited insulation. Thus the coating does reduce substantially the heat passed by the window. An energy star window is only about R3, and a top line window is about R5.Further, the construction of the IG window must be very tight, to absolutely eliminate migration of gases to and from the cavity, including water vapor. For the most part, the construction is successful, or the window would fog early in its life. Finally, when moisture does get in by seal failure, it can't rot the glass and seal material.The wall of course is built up from parts, typically on site. OK, the SIP proponents will argue that factory assembly of panels lets those be far more tightly built, but those panels have joints at all four edges, and the OSB has to be kept dry by housewrap, flashings, etc.There is no easy way to make a wall assembly to the tightness of a window IG unit. It has insulating material within it in abundance, with overall R value far better than that of even a good window. But the materials (wood and any non-plastic/glass insulation) can rot or degrade if too much moisture collects within the wall.One of the Building Science arguements against vapor barriers (not retarders) in all but the coldest climates is that the design should do a good job of keeping moisture out of the wall cavity, but it should allow for its removal (drying) reliably when it does get in. The argument is that you can't build the perfect wall, so you have to make it tolerant of upsets.My prior post argues that a foil layer doesn't offer anything in the way of a thermal barrier in a wall that can't be provided by insulation. It does block diffusion of water vapor out of the cavity in at least one direction, leaving only the other. There are some climates where it is desirable to have drying potential in either direction at times.Putting a foil layer on the outside in a humid, cooling-dominated climate or on the inside in a drier, heating-dominated climate may work well and present no problems most of the time. It evidently has worked well for you in your location. Still, I would argue that if the same thermal goal can be attained without a nearly zero-perm layer such as foil (it can), then inclusion of foil seems like an unnecessary risk.

          Edited 3/17/2009 4:37 pm ET by DickRussell

          1. PedroTheMule | Mar 18, 2009 02:43am | #19

            Good Evening DickRussell,

            .......if the same thermal goal can be attained without a nearly zero-perm layer such as foil.....

            Thanks for your detail time......so how would you recommend constructing to obtain the same effect with similar payback of materials......in my case you can even recommend something that will take extra labor as I do all of my own personal construction now......for others that may read, labor may have to be included.....

            My view and positive experience is that radiant barriers are very cost effective and work as regulatorially advertised when it pertains to energy savings.....please recommend your practice to obtain the same effect.

            Pedro the Mule - Looking forward to staying the same temparature

          2. DickRussell | Mar 18, 2009 03:05pm | #21

            ".....so how would you recommend constructing to obtain the same effect with similar payback of materials......"I won't recommend any particular construction. What is appropriate for any situation depends on location/climate and what level of thermal performance is desired. In your area, you may be most concerned with water vapor diffusing inward. In mine, the reverse is the case for a good part of the year and not a particular worry during summer. What we call oppressive humidity is your "nice day outside."For thermal efficiency, some will argue that R20-24 that actually performs at that level is just fine. Compared to what the BI may pass as R20 (FG, poorly installed), that may indeed be just fine. For a heating-dominated climate, some (myself included) argue that R40 is a better target with comfort and future cost of fuel in mind.There are proponents of ICF, SIP, double walls, modified Larson trusses (a form of double wall), and all sorts of variations on standard framing with foam layers and cross-mounted strapping of 2x.For any thermal target, there are multiple ways to achieve it, each with its proponents. So I won't recommend any particular construction, but I will point out potential problems with a zero-perm layer such as foil. I don't think I'm alone on that.What are your goals in terms of thermal performance? I would think you'd want to start there and consider different ways to achieve it without incurring moisture problems, rather than start with a general type of construction and see how efficient it can be made.

          3. PedroTheMule | Mar 18, 2009 08:25pm | #27

            Hi DickRussell,

            What are your goals in terms of thermal performance? I would think you'd want to start there and consider different ways to achieve it without incurring moisture problems, rather than start with a general type of construction and see how efficient it can be made.

            1. Labor is not a concern....I will construct all myself.....I find great personal satisfaction from making something from nothing regardless of the labor involved....it's my hobby....a far cry difference than the way I run business. Business is all about timely performance to get the client back up and running....high material quick secure labor.

            2. Planning for what will hopefully be my "final" resting grounds....SouthWest Virginia close to Kentucky. I'm young enough and motivated enough to put in incredible amounts of work to make my end days 50 yrs. from now a real leisure time. In other words do it right now and do practically nothing later.

            3. Between the streams on my property, ridge lines and clear southern views with deciduous trees surrounding the homesite, I should be able to self sustain through hydro, wind & solar power sources. An externally operated wood fired boiler with on demand backup propane water heater and backup generator....hope to never use the backup equipment.

            4. For the missus - appearancewise I want to build a traditional 1 1/2 story home with full basement...garage in rear at the main level for ease of access. Considering a passive solar porch south facing with closets and storage surrounding the other walls. The porch, storage and garage will buffer the main inner shelled primary living quarters. Both layers to be super insulated.

            5. For ambience I will build a high mass chambered fireplace near the center of the house with fresh air intake. Potentially burn a good hot hardwood fire a couple of hours of the evening and let the fireplace mass reradiate the heat through the night.

            6. Potentially earth cool through buried pipes and convection vent through a walkup roof top mounted cupola.

            7. Although I will have multiple sources of heat, I want to minimize the use by maximizing the insulating and passive shell characteristics. This will minimize the amount of equipment to wearout and minimize the amount of electricity I'll have to produce and cut way back on battery storage.

            8. So maximizing comfort performance up front and spending some $ and lots of labor will save significant $ in the other areas of support. Although my numbers have not been researched for accuracy as of yet, I expect for every $ I spend on efficient design will be a $ less spent on equipment up front, not to mention less maintenance long term. Win/Win

            So how's that for a start?

            Pedro the Mule - Workin' hard now before this old pack mule gives out

    2. Clewless1 | Mar 18, 2009 04:32pm | #25

      I must disagree to some extent. Radiant barriers are difficult to install "properly" in my opinion. Any radiant barrier will end up dirty ... which tends to significantly decrease its performance. In the lab ... the radiant barrier works great ... but houses don't exist in the lab.

      I installed a solar tube skylight ... nice shiny mylar tube. Installed it very carefully. It's sealed top to bottom. I removed the lens the other day only to find a film of dirt on the bottom side of it. It wasn't significant, but it did illustrate that even under the best circumstances a radiant barrier will get dirty. In walls and attics, it is inevitable. While the performance shortly after install may be good, it can't last long.

      If it is low/no cost to install (e.g. using Thermax), then by all means do it, but to go out of your way, IMO, is a bit much.

      My opinion - you simply can't install it "properly" to get the potential performance. At least not practically in the normal construction industry.

      1. Piffin | Mar 18, 2009 06:37pm | #26

        Another point about how these surfaces end up getting dusty no matter how well they are sealed...That dust does not just magically appear. it is fine particles that are carried about and laid into place by air currents, even within a wall cavy - convection loops at work example. 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

      2. PedroTheMule | Mar 18, 2009 08:31pm | #28

        Hi Clewless1,

        I must disagree to some extent. Radiant barriers are difficult to install "properly" in my opinion. Any radiant barrier will end up dirty ... which tends to significantly decrease its performance. In the lab ... the radiant barrier works great ... but houses don't exist in the lab.

        Ok so what am I missing then? My metal roof still works as good at reflecting the suns heat today as it did when I installed it?

        I agree that a lab clean product will perform measurably better but in the case of a radiant barrier I still find a purpose in it.

        My question is....if not a radiant barrier....what better alternative for the long term money would you suggest?.....my last post to DickRussell has more detail of what I want to achieve.

        Pedro the Mule - No sweat under my radiant barrier and ain't froze yet either

        1. MikeSmith | Mar 18, 2009 08:58pm | #29

          radiant  barriers  in a  wall system  are  a joke

          you're  better  off  spending  that  money  and  labor  on  more  insulation...

          the   3/4 "  space  for  radiant  is  better off  with  insulation in  itMike Hussein Smith Rhode Island : Design / Build / Repair / Restore

          1. PedroTheMule | Mar 18, 2009 09:17pm | #30

            Hi MikeSmith,

            radiant  barriers  in a  wall system  are  a joke

            you're  better  off  spending  that  money  and  labor  on  more  insulation...

            the   3/4 "  space  for  radiant  is  better off  with  insulation in  it

            So in your opinion where does it work?.....I'll fight you for my metal roof.....has been the best heat defense money I've ever spent.....

            Would you recommend aluminum siding?

            Pedro the Mule - Luvin' that cool shade in summer

        2. User avater
          CapnMac | Mar 18, 2009 09:25pm | #31

          what am I missing then? My metal roof still works as good at reflecting the suns heat today as it did when I installed it?

          That's reflectivity.  The 'radiant' effect in walls is from emissivity.  Which is perverse in a way.  Put foil on a cookie sheet, make some nachos on the foil.  Pull the cookie sheet out of a hot oven, and you need a mitt to grab the sheet, but you can grab the foil with your fingers.  The foil has low emissivity, the cookie sheet (and, more importantly, the nachos thereupon) are higher.  All while both the cookie sheet and foil can have similar reflectivities.

          So a radiant barrier "works" by not emitting heat by radiation, which is why it has to have an air space on its conditioned side.  And, that ideal is compromised by any material that falls/adheres to the surface.  For the radiant roof decking, there effectiveness is directly reduced by the rafter contact surface--same way if you put your finger on the nacho foil nad press on the hot cookie sheet.  That's where the snake oil starts in.

          The trikiest part of all this is that there is no one ideal solution, even on the same street.  You could have a house with twice the window area of its neighbor, but with shading and glass selection be just as efficient.  Or the window areas can be the same, but with different approaches to the wall mass assembly.  Or they can be equally inefficient, too.Occupational hazard of my occupation not being around (sorry Bubba)

          1. PedroTheMule | Mar 18, 2009 10:17pm | #32

            Hi CapnMac,

            That's reflectivity.  The 'radiant' effect in walls is from emissivity.

            Ok, you're doing a good job of gettin' through my muley head but my mental use of a radiant barrier has been on the premise of "Reflectivity"......reflecting the outdoor heat during summer and the indoor heat during the winter.

            Maybe I'm misusing terms to describe what I'm thinking....not uncommon for me....I had the priviledge of seeing snakeoil in action in a lab a few years back. It had to do with side by side comparison of identical windows, standard & Low-E versions and how that reduced heat loss. Although it was nearly impossible to "see" any difference in the windows transparency....the coating made significant differences in heat transfer. It was explained to me by the lab techs that it worked by reflecting the heat back into the room, thus I'm looking at using that principle to reduce IR heat loss....by super insulating behind the radiant barrier, it will reduce the time to transfer of the 15% loss.

            a room at 70 °F radiates energy in the far IR (maximum radiation occurs at around 10 micrometer wavelength)........85% of the radiant heat is reflected back towards the room

            The above is some of the testing spec sheet info given at that time.

            So where from here?.....I'm looking to utilize multiple properties.....airtight, foam insulation, thermal mass, reflectivity etc. - If it were just me, I'd build an earth home but the missus wants something that looks traditional and it'll be easier for me to get over the hurdle of super building than it will changing her mind....she's worth it!

            Pedro the Mule - Keepin' the best little burro happy!

          2. User avater
            CapnMac | Mar 18, 2009 10:29pm | #33

            my mental use of a radiant barrier has been on the premise of "Reflectivity"......reflecting

            Took me a while, too.  The use of "radiant" keying into reflectivity seems to be very common.  may be because we humans intuit conduction and convection so much better, that radiant emissivity is not often thought of.

            Here in primary-cooling land, it's the mass that gets'ya, not the emission.  That, and the detail for executing very-needed overhangs gets very complicated when using the radiant roof decking.

             Occupational hazard of my occupation not being around (sorry Bubba)

          3. Piffin | Mar 18, 2009 11:02pm | #34

            Two good options - no, three...Build 2x4/sheathg/1" Thermax/furring/Hardi with urethane spray foam in teh stud spaces
            = R30Build 2x6 filled cellulose or chpped FG/ sheathing/1" Thermax /furring/Hardi siding
            = R 28Build 2x6 / sheathing / 1" Thermax / furring/ Hardi
            For stud spaces spray flash foam 1.5" then stuff with FG bats
            = R 32None of these estimates takes radiant of the foil face into account. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          4. PedroTheMule | Mar 18, 2009 11:37pm | #35

            Hi Piffin,

            I sure do appreciate all of your ideas and time.

            Build 2x4/sheathg/1" Thermax/furring/Hardi with urethane spray foam in teh stud spaces= R30

            Build 2x6 filled cellulose or chpped FG/ sheathing/1" Thermax /furring/Hardi siding= R 28

            Build 2x6 / sheathing / 1" Thermax / furring/ HardiFor stud spaces spray flash foam 1.5" then stuff with FG bats= R 32

            None of these estimates takes radiant of the foil face into account.

            Confound it! That's "almost" identical to what I did with the current house...mine is on the lower end but similar design...it's great but I'm trying to make sure I do it the best on the next house.....I ended up with R 19.5 not incl/half functional rad. coating in the walls.......R 25.5 on the north wall.....R 31.5 in the basement walls and R 31 in the roof....dang cathedral ceilings.....taped, glued, caulked outside, caulked "entirely" inside and foamed all boxes and entrys and then filled bays with fiberglass.

            You know, I think I'll reflect inside heat with mirrors and knock holes in them to let the moisture through.........

            Pedro the Mule - Replowing the same furrow

  8. RKReges | Mar 17, 2009 11:08pm | #17

    I'm just a handy home owner, not a professional, but I've been building and remodeling in Alaska for years so I know alot about insulation.  If allowed to mix batts and extruded foams, I'd put up a heavy mil plastic vapor barrier on the studs.  Tape all joints and around electrical boxes.  Any moisture that drives itself through your outermost layers won't hit your batts.  I also try to use some unsealed wood within the rooms to absorb and release excess moisture.

    I've tried every type of insulation on the market and by far the best is icynene spray-in foam.  Not toxic.  Fills all cavities.  Sound deadener.  By far the best solution if you can afford it and if you have a nearby pro' who sprays it in.

    Robert R.

    1. Piffin | Mar 18, 2009 03:53pm | #22

      "by far the best is icynene spray-in foam."The urethene foams provide nearly twice the R-value and are closed cell and will not retain moisture as the icy will 

       

      Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  9. fingersandtoes | Mar 18, 2009 12:38am | #18

    A small point, but one of the main reasons board and batten has all but disappeared around here is that since the code mandated the use of rainscreen techniques few people have wanted to go to the trouble of installing the double layer of strapping necessary to maintain a ventilation and drainage plane. A single horizontal layer of strapping may in fact be worse than no strapping at all.

  10. frenchy | Mar 18, 2009 04:04pm | #23

    that's the real weakness of studs..   they rot and cause other problems.. SIP's or ICF's are a proven solution to those problems and already meet all building codes..

      I built using both and if I ever were to build again I'd build using ICF's  right up to the roof which I cover with SIP's ..

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