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Old 01-10-2011, 08:12 PM   #1
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Wall insulation techniques - 2x6 vs double 2x4 vs foamboard sheathing


This home building process really taxes the ol' noggin, so many different options!!

I'm building a very small scale home (120sq ft) and would like it to be well insulated with no thermal bridging. I'm aware of several options that would insulate the walls well: so called "advanced framing" with 2x6s on 24" centers, two 2x4 walls with a space in between, 2x4 staggered studs on a 2x6 plate or a 2x4 wall with foam board attached to the outside

I had initially decided on staggered stud but am now second guessing and wondering if I shouldn't just do 1" foam board (plus cellulose insulated stud bays)

Pros of the foam board approach: Very good insulation, less lumber than other approaches, no need for housewrap (saves some money)


My only concerns with the foam board are attaching windows and doors; the thicker sheathing seems like it would require special windows/finagling.
I would have 1/2" plywood, 1" foam then mesh and stucco




Any help in this decision making process would be immensely appreciated

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Old 01-10-2011, 08:54 PM   #2
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Wall insulation techniques - 2x6 vs double 2x4 vs foamboard sheathing


For small home like that, the problem is the thermal short circuiting from the triple stud corners and the studs and jack studs that eat up energy at every opening. The only way to minimize that is to use rigid extruded foam (XPS) to cut the heat loss. Fill the areas between the studs with cellulose. A normal 2x4 or 2x6 stud wall with proper insulation should suffice unless there are other reasons and that would be on a question of diminishing returns.

Then your biggest problem will be the windows that are always really holes in the wall and provide little insulation no matter what kind if gas is used and what films are used because it is hard to get any insulation into a window. - Window salesmen do not like hear that.

Based on your location, why go extremes for insulation in a temperate climate?

Dick

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Old 01-10-2011, 09:22 PM   #3
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Wall insulation techniques - 2x6 vs double 2x4 vs foamboard sheathing


Pardon the slightly off-topic question, but why does one build a house of only 120 sq. ft. ??
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Old 01-10-2011, 09:35 PM   #4
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Wall insulation techniques - 2x6 vs double 2x4 vs foamboard sheathing


Staggered stud, double 2x4 wall and foam board all prevent the thermal bridging of studs to the outside, including the corners
I'll be minimizing the number of windows and when used, they'll be high efficiency and south facing.
Its not the most extreme of conditions but its cold enough that Id like to insulate well. The house Im in now is freezing cold and we try not to use the heater because of how fast the heat goes away.


I like the idea of a tiny house; very simple living with few possessions or excesses. This is also being built in the backyard on a lot shared by a 1500sq ft home so space is at a premium. Also, its a good small project for someone like me who needs to take their time with the construction process
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Old 01-10-2011, 09:50 PM   #5
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Wall insulation techniques - 2x6 vs double 2x4 vs foamboard sheathing


California does not get that cold, even in Oakland. Yes, tonight at 39, daytime at the highest, mid to high 50's. I would not worry about going to the extreme on insulating the home, since your main concern would be making it safe from an Earthquake first and foremost. As for proper building techniques, buildingscience.com has all the info you need.
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Old 01-12-2011, 05:11 PM   #6
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Wall insulation techniques - 2x6 vs double 2x4 vs foamboard sheathing


You're right, its not very cold but we do still enjoy a house 65F and would like to do whatever we can to retain as much heat as possible.

I've decided to do 1" foam on a standard 16"oc 2x4 wall with cotton batts
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Old 01-12-2011, 09:58 PM   #7
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Wall insulation techniques - 2x6 vs double 2x4 vs foamboard sheathing


i'm sure you mean 1200 sqft

10x12 is a shed

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