Replies

1. 
   Mongo | Dec 05, 2014 01:25pm | #1

   thermal bridging plus cost

   Why are 2x10s a bad idea? Because the solid 2x10 will offer a bit of thermal bridging through the entire wall. Because every individual stud cavity offers an opportunity to for the insulation installation to be compromised. Not to mention 2x10s just not being cost effective.

   I'd actually recommend you looking at framing with 2x4s, add 1/2" ply sheathing over the studs, then covering the outside shell of the house with two layers of 2" XPS insulation, with the seams offset. The idea, in and of itself, it more efficient and more cost effective and more labor efficient than double walls or single thick walls.

   Over the XPS you screw 3/4" thick and 2" to 3" wide vertical furring strips through the foam and into the wall studs. Essentially, the furring strips over the foam will mirror the wall framing behind the foam. There are drainage plane issues to be considered, and there are insect screening issues for the vertical furring cavities, but you'll see more about those when you further your research. 

   Then run your siding fastened to the furring strips.

   Your windows can be "innies" or "outies".

   You can go with more foam. Or less. XPS is about R5 per inch, so that's a very effective R20 completely wrapping the outside of your shell. Polyiso is R6 or so, but there can be issues with the effective R value of polyiso beign lowered in cold temperatures.

   Lemme find some reading for you. These came up with a quick search:

   Polyiso versus XPS: http://www.greenbuildingadvisor.com/blogs/dept/musings/cold-climates-r-5-foam-beats-r-6

   Minimum thickness of exterior foam: http://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing

   Exterior foam in general: http://www.greenbuildingadvisor.com/video-superinsulating-home-rigid-foam

   And...you've probably been to the Building Science website. If not, look at their exterior foam and "chainsaw retrofit" articles.

1. 
   MYBuilder | Dec 05, 2014 10:03pm | #2

   Bad. Think of cup, twist and warp with the difference in temperature and moisture across that well assembly.

1. 
   Mongo | Dec 06, 2014 02:27pm | #4

   ??

   MYBuilder wrote:

   Bad. Think of cup, twist and warp with the difference in temperature and moisture across that well assembly.

   Be more explicit. You replied to me, and my post is recommending exterior foam, so are you saying exterior foam is bad?

1. 
   MYBuilder | Dec 06, 2014 08:07pm | #5

   100111100. That's" sorry

   100111100. That's" sorry Mongo" in binary. When I reply via my phone my fingers are too big. You are correct, to me, in your wall assembly. I meant bad 2x10 idea. 0001101010.

2. 
   Elisa1 | Dec 15, 2014 09:32am | #6

   2" x 10" Exterior walls & Low-e reflective Ins. part 2

   Thank you all for your well expressed comments in regards to the original post & it gave me a lot more research to do, but in the end the one 2" x 10" stud wall is now up with exterior OSB attached.  I'll update this post as things evolve-both good & bad.  Seeking any one with expereince with Low-E reflective insulation [www.low-e-ne.com].  Goal: To have one consistant floor level throughout the house, & instead of poly foam sheets or spray foam for underneath the raised floor joist system, we are considering ESP Low-E insulation with air space below the floor sheathing (e.g. "Floor Joist Application".  Upper, conditioned subfloor system/air space will house water & sewer runs.  No fiberglass batting under/inside the raised floor system.  (Currently the 2,200 sq. ft. addition floor is 100% non-insulated concrete & has 4 different levels!)  No known history of moisture issues & not in a flood zone-very dry.  House will be wrapped using their wrap product unless I hear negative feedback on either of these options.  Thank you all again & I look forward to hearing your thoughts on Low-E vs. other options. 

1. 
   Mongo | Dec 15, 2014 12:33pm | #7

   Low-E

   I can't advise using any foil-faced bubble product if you are using their "publicized" R-values to get a code-required R-value in your thermal envelope.  There is a difference between

   The foil can work as a radiant barrier if kept clean and if installed with an appropriate air space.  Radiant barriers are more effective where you have a high Delta-T. Arizona? Las Vegas? You'll see a greater benefit their then you will in Vermont.

   If properly detailed, it can work as an air-infiltration barrier, a vapor barrier, eyc. They can be useful in construction.  But getting back to R-values...

   When integrating them into your structure, you need to be very careful regarding the R-values of these products. The actual product itself may only have an R-value of R1 or so. But they sometimes publicize their R-values are as part of a building system, and that has duped many a consumer into thinking they are getting R6 or R8 or R-whatever our of a 1/8" thick product. They're not. Look at their literature. See if the R-values have asterisks with the "real details" in fine print.

   So...be careful. Know why you are using this product. If you are installing this for it's R-value to achive a certain structural R-value, then call the company and ask them what the actual R-value of the just the product is. The product alone, not when it's installed in a "system" with air gaps, etc. Be prepared for hemming and hawing. That's the R-value you'll need when calculating your envelope requirements.

   As you continue your research, you might find less expensive alternatives to do what this product actually does.

   Good luck!

2. 
   Mongo | Dec 15, 2014 12:38pm | #8

   heck...read this...

   Did a quick search. Read this:

   http://www.greenbuildingadvisor.com/blogs/dept/musings/stay-away-foil-faced-bubble-wrap

   Did you come across that article while doing your resarch? I searched for "r-value of radiant film barriers" and that was the first hit.

   So again...know what you are using the product for.

2. 
   mark122 | Dec 06, 2014 09:21am | #3

   continue double studded systems

   Elisa1 wrote:

    passionate about sustainable, green building techniques & lowering energy usage, but not in a fanatical way!  

   would not consider 2x10 framing to be sustainable, green or energy saving. as suggested, there are multiple ways to achive energy efficiency, and "green" techniques but the suggested 2x10 construction would not be one of those.

3. 
   Elisa1 | Dec 16, 2014 06:17am | #9

   Low-E ESP reflective Insulation

   Thank you, great site!  Here is the link to the product we are considering for beneath the subfloor & above the concrete pad.  Good news, it's not bubble wrap, but poly filled, aluminium faced.  http://www.low-e.com/media/Low-E_Insulation.pdf .  Still seeking pro/con input from a real time installed system, but I'm always open to other concepts.

1. 
   john7g | Dec 16, 2014 06:35am | #10

   Something to consider in your research,,,, have any of the various miracle film insualtions lived up to their claims?  My exp with them goes back only 20years and if just 1 would've wroked so well to meet it's claims I think we'd see it everyehre.  

2. 
   catmandeux | Dec 16, 2014 06:48pm | #11

   foam is just a bunch of small bubbles.

   The Low-E stuff is still bubble wrap with foil on it, just smaller bubbles than most. 

    

3. 
   Mongo | Dec 16, 2014 08:49pm | #12

   It's still...

   It's R-value is probably around R-1, maybe R-1.5 or so.

   Radiant barriers are good where you have a high Delta-T, or under a metal roof, for example. Other than that?