Couple Questions On Double Stud Wall

 
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Old 01-05-2012, 04:38 PM   #1
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Couple Questions On Double Stud Wall


How are shear forces addressed with double stud wall construction in the following assembly?

I believe this is referred to as the modified larson truss,

interior load bearing stud wall to catch loads from roof down. built 2x4 16" or 2' OC.

exterior wall balloon framed 2x3 or 2x4, same OC as inside. Ext wall connected to int wall with gussets of 1x, 3x4 ply or 2x, installed ~2' oc on the way up.

I have not seen any shear wall or strapping on the interior walls in my research, is this force only managed by the ext wall?

2nd main question. I am biased against vapor barriers in houses and would like to see my wall assembly without one, is there an argument for installing one in the following wall?

siding, 3/4 strapping rainscreen, typar, sheathing, 10-12" dense pack, air tight drywall

house will include an HRV or ERV system and most likely be built on slab.


I would like to build myself a house in the next 3-5 years and this is the method i'm most fond of. I don't like spray foam or panels when I can choose otherwise and can achieve a very high breathable R with dense pack. Air sealing will be detailed to the highest degree using the rubber gaskets at all plate connections and the best caulking available where required.

I invite all comments on double stud wall construction good or bad.

Thanks
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Old 01-05-2012, 04:59 PM   #2
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Re: Couple Questions On Double Stud Wall


Here's a link to that system:http://www.builditsolar.com/Projects...arsenTruss.htm

Looks expensive !!!!!

Not sure I like the way the load is transferred to the foundation,
Seems the plate cants over foam board?
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Old 01-05-2012, 07:09 PM   #3
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Re: Couple Questions On Double Stud Wall


That's a good point. I'll have to ask an engineer.

Im curious about the cost too but I'm sure I could recoup the added material in less than 5 years. But without the energy modeling I can't say for sure.

I'm talking heat with a hair dryer here...
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Old 01-05-2012, 07:32 PM   #4
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Re: Couple Questions On Double Stud Wall


I read the energy saving projections on that site I posted,
looks promising

I haven't really read over the whole design concept yet,
but noticed a few non-conventional techniques that seem
questionable to me at this point.I guess I really need some
time to look it all over.
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Old 01-05-2012, 07:46 PM   #5
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Re: Couple Questions On Double Stud Wall


I built a double wall house a few years back. My method was to frame a conventional house out of 2 x 4's and then stand up a second interior wall as an interior non-loadbearing partition.

This method takes less labor I think because you can sheathe your exterior walls on the deck and avoid a lot of scaffold work. The disadvantage is that the rim joist (if you have one) presents a challenge, though my insulation contractor used a small spray foam rig to insulate this.

You do have to think through your window detailing. I built boxes out of 1x which extended the full width of the wall.

As far as air barriers, The drywall-as-air-barrier approach is tried and true in some parts of the country. Personally, I feel that if humidity is controlled in a house, the vapor barrier could be omitted in a 12" dense packed wall and it would still be fine, though of course in practice I would include a vapor barrier since it is cheap insurance.
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Old 01-05-2012, 07:58 PM   #6
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Re: Couple Questions On Double Stud Wall


The reason this type of framing has been eliminated is because of fire hazard. If a fire starts or enters a wall cavity of the 1st floor it will spread quickly into a number of void spaces throughout the first floor and open wall cavity of the 2nd floor and into the attic. So if you like this type of construction, consider some kind of a fire blocking, to prevent fire to spread throughout the dwelling inside the wall cavities, this way your house will not become one giant BBQ.
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Old 01-05-2012, 08:15 PM   #7
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Re: Couple Questions On Double Stud Wall


Im curious about the vapor barrier.

This is where I wish I had the know how to calculate this Numerically.

You've heard that factoid how a nail sized hole can let in some crazy number of gallons of moisture in a heating season. My thought is that without it any moisture in the wall can dry to either side.

This is my preliminary, and I'd appreciate any advice how to prove it sound or not
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Old 01-05-2012, 08:20 PM   #8
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Re: Couple Questions On Double Stud Wall


Quote:
Originally Posted by greg24k
The reason this type of framing has been eliminated is because of fire hazard. If a fire starts or enters a wall cavity of the 1st floor it will spread quickly into a number of void spaces throughout the first floor and open wall cavity of the 2nd floor and into the attic. So if you like this type of construction, consider some kind of a fire blocking, to prevent fire to spread throughout the dwelling inside the wall cavities, this way your house will not become one giant BBQ.
I hear that, I think the house in one of the build it solar websites is in vt and here we have hardly any building inspectors to speak of so an issue like this would easily get left out. Fireblocking could be installed at the 2nd story.

I became inspired when I read about a builder that used double stud in a .26 ach @50 house in Maine. That's one of the best I've heard of.
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Old 01-06-2012, 08:12 AM   #9
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Re: Couple Questions On Double Stud Wall


Quote:
Originally Posted by duburban View Post
I hear that, I think the house in one of the build it solar websites is in vt and here we have hardly any building inspectors to speak of so an issue like this would easily get left out. Fireblocking could be installed at the 2nd story.

I became inspired when I read about a builder that used double stud in a .26 ach @50 house in Maine. That's one of the best I've heard of.
Depends on the inspector, but fireblocking isn't necessary in a dense packed wall. How is fire going to chimney through the wall if it packed with cellulose?

Personally I think the dangers of moisture entering a wall through something like a nail hole is overblown. This is especially true with dense pack. The stuff is a far superior barrier to air movement than fiberglass.
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Old 01-06-2012, 09:10 AM   #10
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Re: Couple Questions On Double Stud Wall


Quote:
Originally Posted by Jackpine Savage View Post
Depends on the inspector, but fireblocking isn't necessary in a dense packed wall. How is fire going to chimney through the wall if it packed with cellulose?

Personally I think the dangers of moisture entering a wall through something like a nail hole is overblown. This is especially true with dense pack. The stuff is a far superior barrier to air movement than fiberglass.
It can also wet and dry much easier.

Here's an interesting discussion on wall assemblies.

http://swinburnearchitect.com/wordpress/?p=766
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Old 01-06-2012, 08:46 PM   #11
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Re: Couple Questions On Double Stud Wall


heres where its at:

http://forums.jlconline.com/forums/s...ud+wall&page=3

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