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Need advice for increasing exterior wall

taiter | Posted in Construction Techniques on May 30, 2008 05:56am

Hi guys,

I’m the new girl around here and I need a little bit of advice regarding a green renovation project. We have stripped the exterior of a 1910 home down to the 2×4 (full dimension) fir studs. I am attempting to increase the wall cavity by furring out these studs. Keeping in mind that ALL of the interior walls have and WILL remain in tact (as part of the conservation effort), what is the best way to fur out the studs?

I would prefer to use at least a 1.5″ strip. My main concern is to ensure the sheathing is securely fastened to the stud system and I am not sure how this kind of “extension” would affect shear strength of the wall (though in my area, there are no crazy requirements due to storm or seismic activity).

Here is my theory: I would like to nail the furring strips with 8d nails to the fir studs at 12 o.c. Then, I would like to nail the sheathing THROUGH the furring strip and into the stud (with the intention to penetrate both members). I would use 10d deformed nails for this, which would give me full penetration through the furring strip and a little over 1 1/4″ penetration into the stud. Obviously the sheathing would be nailed 12 o.c. offset to the nailing schedule of the furring strips (and 6″ o.c. on the edges of the sheathing. Aditioally, I was thinking that some strapping might be an added benefit to attaching the furring strip to the stud.

Any thoughts?

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Replies

  1. User avater
    Sphere | May 30, 2008 06:09am | #1

    If the search function here worked wortha flip..

    Try Mooney wall..I did, it wasted my time.

    Heres your bump so someone else can direct you.

    Hang on.

    BTW? why you have my cat's name..(G)

    Spheramid Enterprises Architectural Woodworks

    Repairs, Remodeling, Restorations

    "We strive for conversion,we get lost in conversation, and wallow in consternation. "
    Me.

    1. taiter | May 30, 2008 09:39pm | #6

      Shpere,Thanks for the Mooney wall recommendation. I was interested in trying to make that concept for me, but since I am working from the exterior and the interior walls are remaining completely in tact.The issue with the Mooney wall was that I could not properly attach the sheathing to the studs.

      1. Billy | May 30, 2008 10:17pm | #7

        Are you sure the Mooney wall approach won't work for you with horizontal strapping on the exterior?  Your structural engineer should be able to tell you if it's OK with, for example, 2x3 strapping and sheathing glued to the 2x3s?  It sure would lower the conduction loss through the studs. 

        Remember, an R-40 foam SIP is different from spraying an R-40 thickness in stud bays.  The SIP makes a roughly R-40 wall assembly but the R-40 foam in stud bays does not make an R-40 wall assembly.  R-40 foam sprayed in a Mooney wall might get you closer.

        Billy

        Edited 5/30/2008 3:18 pm ET by Billy

  2. JohnCujie | May 30, 2008 06:10am | #2

    My first thought is that the firring strips will splinter apart from all that nailing. Where are you?

    John

  3. Billy | May 30, 2008 06:30am | #3

    Reading between the lines I assume you want to increase the depth of the stud cavity so you add more insulation for your green project?  If that's the case, I wonder if you are better off filling the cavity with closed cell foam (you could use soy foam) and then sheathing over that?  This may give you the R value you need, and although the foam is expensive it would save you the expense of replacing all of the exterior window and door trim and adding exterior jamb extensions (yech) to deal with the furred wall.

    If you want to add the furring you could use 2x3 instead of 2x2 to reduce splitting.

    Billy

  4. Clewless1 | May 30, 2008 05:14pm | #4

    Billy has some good thoughts.

    Are you furring out by attaching the 2x2 furring to the LENGTH of each stud (i.e. Not across horizontally)?

    Properly attached furring, you should be able to attach sheathing conventionally ... My first reaction was 8d was too little to attach furring. I would nail gun 16d ... but I'm not an expert ... just occasional builder type. Or maybe even 3" screws (for a measure of overkill). And then std 8d sheating shot into the furring. Nail gun important to minimize damage to existing interior/finishes from over pounding.

    If the furring is attached well/properly, my sense is that you will have good shear strength with standard sheathing. No issues, no worries ... except the ext. details per Billy's comments.

    1. taiter | May 30, 2008 09:07pm | #5

      Thanks to all these great responses.I didn't think of the splintering - it's a VERY good point. My worst fear would be to split my studs and they would be hidden from view and we wouldn't find out until the house falls down :-/My structural engineer had mentioned pre-drilling even for nails. This is not a problem for me. I guess my question is do I securely fasten the furring to the stud and not worry about the fasters for the sheathing penetrating the studs? Or do I need to securely fasten the furring strips AND make sure the sheathing nails penetrate the studs?The studs are hard as a rock. I'm open to all suggestions as I've had a MILLION ideas run through my head.NOW - Reason I am doing this (sorry I didn't mention before). I AM using a closed cell urethane foam - the stupid expensive stuff ;-) I still want to increase the stud bay to get an r-40 thickness. I am placing a second storey addition on our single storey home. The second storey will be comprised of SIP walls and a stick roof. The second storey will have R-40 walls and R-60 roof. I am essentially trying to mimic a SIP on the first floor. Don't worry, I understand the difference - I've actually had training for building with SIPS. In any case, I will be diligently foaming EVERY nook and cranny and developing a nice tight envelop for the main floor.We will be putting in air exchangers, etc., etc. It's a veritable green home check list - but it's by no means a new home. The structure is SOLID and I'm confident I'll find my answers to keeping it that way. Thanks guys!! I appreciate any more direction you can give me.

  5. segundo | May 31, 2008 02:01am | #8

    two thoughts, posting after reading everybody elses.

    1. a mooney wall from the exterior should work, especially if you use the spray foam in two applications, ask the foamer and see if he can do it this way. spray in the first layer of foam in the vertical bays thin so as not to fill all the way out.

    then install horizontal firring stripps with a nailgun (thats been my experience what works best with old hard studs) and another application of foam sprayed horizontally this time to be finished flush with the outside.

    then install sheathing. i would glue and nail. there are adhhesives that will work with the foam, i forget the company that makes one i read about, but you can spray that on the whole thing, firring strips and foam, then install plywood and nail, good to go.

    the spray foam should act to tie everything all together, and the shear should transfer through the firring. i think the shear strength of one 16 penny nail is about 2000 lbs so if you have the firring nailed at every stud, even with 8 penny nails @ 1000 lb shear per nail adding the 1000 for each one.... again all in the details, you could back gouge foam and add strips of ply flush to outside of firring for vertical seams of ply to be screwed etc. plus everything all being glued by the foam, plenty strong.

    2. apply the foam and sheath the walls and then fir the walls with sheets of closed cell foam. this may be easier and a superior insulator as it will have even fewer thermal bridges than mooney wall. i believe there was a fine homebuilding issue describing in detail exactly how to do this in Jan-Feb 2007?

    ps. i am curious to know what geographical area you are in? where is your 1910 house, how long have you had it, is it a new to you? good luck!  

    1. taiter | May 31, 2008 07:13am | #9

      I know the article - thumbed through it several times. I am MOST interested in the mooney wall. I had just assumed my structural engineer would say no way. Personally I was concerned about the shear structure of the sheathing being transferred through these horizontal strips.The house has been mine for about 7 years. I'm the first and ONLY person within SEVERAL "prestigious" downtown locations to PRESERVE MY HOUSE :-) The materials are AMAZING and I can't build new as big as it was originally built. Why in the world would I pay to rip it down?? I guess the simple answer is to avoid these little design headaches. I find them fascinating.I am going to explore the mooney wall possibility. With my background in engineering, I fell for the idea when I first saw it a while back. I just assumed it wouldn't "hold up". And I asked my foamer (ME) if I could spray in two passes - and I said yes ;-)I had already planned on glue to the strips, so that just affirms my original intention. I am very excited to get this feedback. Thanks a lot guys!!

      1. Billy | Jun 01, 2008 12:23am | #10

        The shear will be where the horizontal strips meet the studs.  You could insert small Simpson angles on the studs below the strips for support, but I think that's overkill.  The horizontal strips will be bonded to the plywood over a large surface area so there shouldn't be a shear problem there.

        What material are you using for siding?

        Billy

        1. taiter | Jun 01, 2008 01:05pm | #11

          Hardee Plank. It's light - I THINK. I only inspected a sample. I know when fiber cement first came out, it was DARN heavy. But I have been told it has change a lot.Do you think it's strong enough? I want to add strength to the structure, not force it to bare more. Horizontal - IN THEORY - should be stronger and wit glue and cavities that will be foamed solid, it SEEMS more than adequate.I'm still waiting to talk to my structural engineer. But he seems too eager to go along with anything I ask, so I am getting good feedback here.

          1. Billy | Jun 01, 2008 03:41pm | #12

            I think your structure will be plenty strong, but you're right to speak with a structural engineer.  You need to get the permitting folks to sign off too.

            Hardi won't add any strength.

            I'll let others chime in on the "best" ways to attach the hardi -- furring strips, rain screens, etc.

            Billy

          2. taiter | Jun 01, 2008 09:23pm | #13

            My late night reply was a bit confusing. I know Hardee won't add strength. I just wanted to ensure my proposed structure was strong enough to hold it.Thanks for the info - much appreciated.

  6. DanH | Jun 01, 2008 09:28pm | #14

    Taiter, where do you live? Insulation advice needs to be tailored to your climate.

    It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
  7. Piffin | Jun 01, 2008 10:35pm | #15

    I should probably read the rest of the thread first, but I have a Q

    It sounds like you are stripped down to the studs on the exterior side where you are talking about adding dimension out. Is that right?

    Also, what sort of insulation do you plan? That has an effect on all this.

    And - I would not be nailing 1=1/2" materials to the studs with only a 8d nail. Those are 2-1/4" so you would only have 3/4" hooking you into the stud. use tens if inside and twelves if outside

     

     

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

    1. taiter | Jun 02, 2008 02:04am | #16

      I am right down to the studs right now on the exterior. You are correct in that.I am using urethane, a closed cell fire rated insulation that sprays on at 1" thickness at a time. It cures, the the insulation is layered until you reach the desired thickness.The nails I have are 3 1/2 ring shank Paslode nails. That is what I would want to nail down the furring strips with.I would assume that I need to nail the 2x3 like this: || ||
      __||__________||__
      /_________________/|
      | ||
      |_________________|/as opposed to this: || ||
      __||__________||__
      / /|
      /_________________/ /
      |_________________|/This is exaggerated a bit. I'm not afraid to go with bigger nails. Though the regs have changed from 1 1/2" min. penetration to 1", I'm perfectly fine with assuring the extra penetration to assure secure fastening.You sound like you have an idea - does this info help illustrate my intention?Thanks again!!

      1. Piffin | Jun 02, 2008 01:56pm | #17

        I stayed out of the discussion 'till hearing back from you because as is common with Breaktime, it got a lot of divergent ideas thrown in.I think you are on the right track ( though I don't understand your schematic here) and the polyurethane foam is the best insulation. I question the need for going that thick with it, but given the upper level addition and the quest for super insulation and the fact that you have a finished interior already, you have my blessings, LOL.The caution I would add is to have somebody watching on the interior as you proceed. The nail gun could shake plaster loose whereas a screw for the furring would have less impact. using glue with 3" nails lets you do this at 18-22" oc, IMO. No need to predrill.Also watch interior when spraying the foam and do that in two passes. 6" is a lot to control and it expands so much that it could try to push the interior plaster or SR off the studs or make it bulge. 

         

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

        1. taiter | Jun 03, 2008 01:06pm | #18

          Thanks for your blessing ;-)i am using a slow rise formula for the foam. I can only spray it 1" thick at a time so if i am patient, I should be able to control the conditions and I am open cavity which allows me to watch th whole process. I am limited to doing at least 6 passes for 6 inches :-) I agree with you on Urethane - it's the best around right now. I am very excited to be using it.The plaster: One of the cool and exciting things about my project is that the gentleman that bought my home and remodeled it in ~1940 was a master plasterer. He hand plastered all the walls and the ornate drop ceilings. The walls are about 2.5" thick with plaster - it is AMAZING. Fully decked out with horsehair and walls that consistently bow out in their centers, it is a nice little piece of history that I am going well out of my way to preserve :-)If the demolition didn't wreck it, nothing will.Thanks to everyone for the input, I will post pictures very soon. I will also let evryone know what worked. I HATE hanging threads ;-)

          1. Piffin | Jun 03, 2008 01:36pm | #19

            Interesting!All that plaster will give you some nice thermal mass to help the insulation! 

             

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

  8. frenchy | Jun 03, 2008 05:42pm | #20

    taitor.

      You want to fir out the wall to have some additional room for insulation, correct?  Hopefully others have explained how this will wind up costing you big time plus add a lot of complexity. 

      Why not go for a better insulation?   Spray in foam will strengthen the wall, seal all air leaks and can  have a much high R value. Then you can repalce all the old trim etc.. and not lose interior space..

      Firring out won't gain massively because you will still have a thermal bridge every place there is a stud and if you use fiberglas you have the issue of poor actual performance  (even though it labratory tests at near the same number)

    1. taiter | Jun 03, 2008 07:29pm | #21

      I'm actually furring out AND using Urethane :-)And the thermal bridge should be significantly reduced to only the cross sections, where the furring meets the studs: http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htmThanks for the concern, though. You are right - this is not a good solution for fiberglass as far as R value and strength vs cost.

  9. BlueBottle | Jun 04, 2008 01:31am | #22

    Here's a different approach:

    1. fill the cavity you have with spray-in as planned.
    2. apply plywood or osb sheathing
    3. apply a layer of rigid insulation, sealing joints with tape or foam; creating your moisture/vapor barrier
    4. drainage plane: either battens nailed through to sheathing or a vented mesh/corrugated house wrap
    5. siding

    The actual wall assembly may need tweaking due to region, but what I am getting at here is a layer of rigid on the outside of the stud bays instead of extending the stud bays.

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