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insulation/studwall construction

drjimeph's picture

I'm new to this forum, but I've been looking for an answer to a question we have about insulation. We're about to build a new home, and while we can't afford all the "pure" green ideas out there, we want to at least make it as well-insulated as possible without breaking the bank.
So here's the question: the plans at the moment call for 6" studwalls, with 2" rigid foam insulation on the exterior, with the joints taped to eliminate thermal breaks. Our contractor, whom we highly respect, says there's significant cost to this, because of the labor costs involved in the multiple trips around the building required to accomplish it (sheathing, wrapping, rigid foam, taping, firring, siding).
Since the principal value of the rigid foam and taping (at least as I understand it) is eliminating the thermal breaks created by the studs, we've come up with an idea that sounds intriguing, but no one can tell us if it would really work. The idea is this: using 2x6 headers and sills, use 2x4 studs 12" on center but alternating sides, so that half the studs would be to the exterior and half to the interior. This would give you 2' on center nailing surfaces both on the interior and the exterior, but eliminate most of the thermal breaks, creating a sort of S-pattern to the insulation if you look at it in horizontal section. It also actually reduces the amount of wood you use (at least in actual volume). It would be a little trickier to frame, but nothing insurmountable, and it eliminates the thermal breaks, which would eliminate (or at least significantly reduce) the need for the rigid foam and several of the the trips around the house.
Is this crazy or innovative? And if it's innovative, why hasn't someone smarter about construction than me thought of it before?

(post #157776, reply #1 of 17)

Greetings and Welcome to Break Time!


Here's a thread on that topic from a couple of months ago.  Good discussion, if I do say so myself. :-)


http://forums.taunton.com/tp-breaktime/messages?msg=122892.1

(post #157776, reply #2 of 17)

I would also research "mooney walls" in the search function as a possible choice for most cost effective way to increasse insulation.


I believe it was in early 2007 that fine homebuilding did an article featuring rigid foam on the exterior, when this system is used by a contractor that is familiar with the step by step procedure that helps to keep the cost down. Also check out the for pros by pros series by taunton book on insulating and weatherizing.


Of the six steps you say your contractor describes as costly multiple steps, three (sheathing, wrapping, siding) are required anyway.


I am curious as to what you are planning to use for insulation in scenario suggested in your post? Fiberglass batts modified to this application would offer no improvement over standard construction IMHO.


There are many things to consider in making a choice of construction method, and if you start mixing and matching you may open all kinds of different cans of worms.


The most important thing about insulation with any of the different systems of insulation is attention to detail and carefull installation. A very well detailed and carefully installed standard 2 x 4 construction fiberglass batt method especially if carefull detail has been given to sealing for air leaks may outperform a sloppy and poorly installed mooney system of dense pak.


Typically one of the advantages of spray foam is that the expanding foam will seal the air leaks, thereby eliminating the need to rely on the care of the installer to some degree, if he misses spots or messes up the mix etc all bets are off.


I have given this subject much thought, and have narrowed it down to two choices for myself. One is ICF's,


 and the other is a modified mooney wall with standard 2 x 4 construction and spray foam first before  electrical and firring and installing dense pak, then I would spec installing 1/2" plywood sheathing on the interior with strips removed for installing dense pak and replaced after dense pak.


this extra layer of sheathing has many benefits (drywalling goes quicker, pictures and widescreen TV's are easy to hang), i think its a good idea for interior walls like bathrooms and closets as well so you can hang whatever you want wherever you want in the future without hoping you hit a stud.


Lots to think about when planning a house.

(post #157776, reply #3 of 17)

Welcome.  You'll find a lot of good info here on every phase of your project.  Many here are generous with their advice and happy to share the wisdom of their experience.


In regards to your idea, I believe there are better, proven methods to improve your envelope, e.g. Canadian double walls, SIPs, or adding a layer of rigid foam to the inside surface of exterior walls. 


I don't agree that the principal value in adding a continuous layer of rigid foam to the exterior is the elimination of thermal bridging. 


The principal value in adding a continuous layer of rigid foam is the added R-value to the wall system, which also happens to minimize the thermal breaks.


What is your builder suggesting?  Energy modeling of the envelope should be strongly considered to make the best use of your financial resources.


Regardless of what system you choose, the important thing is that close attention is paid to air sealing everywhere, window and door installation, and every aspect of the insulation install.


Check out Building Science Corporation's website for a lot of good info for your particular climate zone.


 

(post #157776, reply #4 of 17)

We framed party walls like that 30 yrs. ago, insulated exactly as you describe.  I think there are more efficient ways to accomplish what you're trying to do, but I think you're on the right track. 

(post #157776, reply #6 of 17)

Yeah, that detail is spec'd for sound control a lot.


k

(post #157776, reply #7 of 17)

Double studded exterior walls are nothing new either, but they were usually built on wider plates with the studs aligned so you don't have to weave insulation into them. Insulating with FG is enough of a pain without that. Both sets of studs can be lighter if they are tied together in the middle.


Alternatively, one set could be structural steel and the other light guage.

(post #157776, reply #8 of 17)

yeah, but double studs on a2x10 plate eat up more space, if that's an issue. 


k

(post #157776, reply #9 of 17)

KFC


You are right of course.


I live in an ICF house. Over a lifetime, the extra time I spend passing through my thicker doorway compared to the time my neighbour spends could add up to a leisurely lunch.  


Ron (:>

(post #157776, reply #10 of 17)

Over a lifetime, the extra time I spend passing through my thicker doorway compared to the time my neighbour spends could add up to a leisurely lunch.  


LOL!


I actually like the thick walled look, but I'm in a tight urban area with maximum footprint being a constant issue.  And at $400-$600 per sq ft, those inches add up.   A typical house here might be a 30 x 40 rectangle, so 30 + 30 + 40 + 40 = 140 LF, so two inches difference in plate loses 12 sq ft, or roughly $6000. 


Depends what your constraints are, I guess, don't know what the op's situation is. 


When clients start sketching out remodels, they almost always draw a single line for a wall, and I have to gently remind them those lines on a page actually end up like 5" thick...  It's amazing how often folks forget that. 


k

(post #157776, reply #12 of 17)

"Over a lifetime, the extra time I spend passing through my thicker doorway compared to the time my neighbour spends could add up to a leisurely lunch. "


The easy solution to this is to set your alarm clock several minutes earlier. I get up before my wife to offset her longer life expectancy. 

(post #157776, reply #13 of 17)

fingers etc.


How is she handling the competition?

(post #157776, reply #14 of 17)

She claims it's total lifetime not just the time you are awake that counts. In which case all my rather dubious efforts are in vain.

(post #157776, reply #15 of 17)

fingersandtoes,


Tell her you're going to let her win this one. Then keep on trying anyway.

(post #157776, reply #5 of 17)

"Is this crazy or innovative? And if it's innovative, why hasn't someone smarter about construction than me thought of it before?"

Well, if you read and search in this folder of the forum, you will find that you are trying to re-invent the wheel.

You can search under terms - foam and Mooney wall, etc etc etc.

A factor that is important is your climatic location - need to know that before I get too specific with you

 

 


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(post #157776, reply #11 of 17)

<Our contractor, whom we highly respect, says there's significant cost to this, because of the labor costs involved>

There would be some additional cost, but small compared to a stagger-stud wall system. I did siding on a house recently that was stagger studded w/ 2x4s on 2x8 top and bottom plates. Insulation installers had a tricky time with it (fg batts) but with a bit of patience it could have been some better. Patience costs money, though.

j

(post #157776, reply #16 of 17)

To really get a handle on good solutions for you, we need to know where your house will be located. Good building practice varies considerably among locals.

In other words - Fill In Your Profile!


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.

YAY!  I love WYSISYG editing!  And Spellcheck!

____________________________________________________

(post #157776, reply #17 of 17)

Thanks for the input, everyone. Two things (at least) that I neglected to mention: 1) we'll be using either open-cell icynene (sp?) isulation or blown-in cellulose (the "wet" stuff that doesn't settle) and 2) the house will be in NYS, north of Albany, sort of the foothills of the Adirondacks. The Mooney wall sounds intriguing, and a guy we're consulting with has a truss system that also sounds intriguing, so I'm hoping we'll be able to work out an affordable solution. But the discussion has been helpful. I may be back with more questions soon- you know once we get the building permit and all.