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  1. #1
    Join Date
    Dec 2006
    Location
    Roswell, GA. a little north of Atlanta.
    Posts
    93

    Default Knee wall to support rafters.

    I have an attic remodel. My carpenter says that we can do a knee wall to support the roof rafters. There are strong boards (2x4) that are being used to brace the rafters that sit on top of the top plate in the middle of the room. Can we install a 2x6 strong back along the floor joists and make a knee wall like my carpenter suggest? I thought all bracing needs to be above a supporting wall?

    David
    Of course I don't look busy, I did it RIGHT the first time!

    Nari member. CKBR, CLC

    www.attentiontodetailatl.com

  2. #2
    Join Date
    Nov 2006
    Location
    Swansboro, NC
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    1,550

    Default Re: Knee wall to support rafters.

    David,
    I would say no without knowing the full details about the joists span and size, the span of the rafters and there size. There are a lot of details that you would need to fill in the blanks on to know if you could do this. But my guess is that without seeing it is no. And judging from prior posts on here from people in Ga, I feel you might already be dealing with under sized rafters and joists.
    Rob
    O'Brien and Sons Construction
    Swansboro NC

  3. #3
    Join Date
    May 2005
    Location
    Truckee, CA
    Posts
    396

    Default Re: Knee wall to support rafters.

    Is your carpenter a licensed engineer?

  4. #4
    Join Date
    Jul 2004
    Location
    Desloge, MO
    Posts
    1,035

    Default Re: Knee wall to support rafters.

    I'm fairly sure that a knee wall can't work as a support because it is not anywhere near perpendicular to the roof plane.
    -----------------------------
    Dustin Wyatt
    -----------------------------

    The first principle is that you must not fool yourself—and you are the easiest person to fool. - Richard Feynman

  5. #5
    Join Date
    Dec 2006
    Location
    Roswell, GA. a little north of Atlanta.
    Posts
    93

    Default Re: Knee wall to support rafters.

    Quote Originally Posted by O'BrienConstruction View Post
    David,
    I would say no without knowing the full details about the joists span and size, the span of the rafters and there size. There are a lot of details that you would need to fill in the blanks on to know if you could do this. But my guess is that without seeing it is no. And judging from prior posts on here from people in Ga, I feel you might already be dealing with under sized rafters and joists.
    Thank you for your response. Why would builders in GA be undersizing there rafters and joists? I'm sure that we have to follow the same IRC guide lines as the other states.


    David
    Of course I don't look busy, I did it RIGHT the first time!

    Nari member. CKBR, CLC

    www.attentiontodetailatl.com

  6. #6
    Join Date
    Nov 2006
    Location
    Swansboro, NC
    Posts
    1,550

    Default Re: Knee wall to support rafters.

    David,
    I was assuming when I posted that, becuase there has been prior posts on here from remodelers in Ga dealing with joists that are way under the spans listed in the IRC codebook. I don't know how GA does there permitting and inspections. But, again, from prior posts about 2 year old homes, span charts were clearly not being followed. There is no reason to do this, the money saved by using a 2X8 instead of a 2X10 or 2X12 is really minimal when your talking about 20 or 30 floor joists for a large room. I wouldn't do it, and I would hope that an inspector would catch it if someone else did.

    I will say that a buddy of mine is moving to GA near Albany, and he has been looking at new homes there. The prices per sqft were extremely low compared to what I'm used too, so maybe that is why. They are trying to cut every cost possible to make housing affordable to the market there.
    Rob
    O'Brien and Sons Construction
    Swansboro NC

  7. #7
    Join Date
    Nov 2005
    Location
    Georgia
    Posts
    105

    Default Re: Knee wall to support rafters.

    O'brienConstruction:

    Georgia is the largest state east of the Mississippi and has 159 counties. That means you are generalizing about 159 different jurisdictions, each of which makes their own rules regarding permitting, code enforcement, etc.

    Some counties are very rural and behind the times. Some counties are experiencing rapid growth and they haven't changed their backwards ways. Some bad houses are being built. But that is not true for most of Georgia.

    If you want to discuss someone else's bad practice, feel free to, but have first-hand knowledge of it. You know what they say about assuming.

    Gabel

  8. #8
    Join Date
    Nov 2006
    Location
    Swansboro, NC
    Posts
    1,550

    Default Re: Knee wall to support rafters.

    Gabel,
    I was in no way pointing a finger at GA. And I think I clearly stated it was an assumption and not to be taken as gospel about the entire state. I was citing a prior experience and testimony from a friend of his experience. Chill out. Ga is like every other state in our United States regardless of how big or how many counties it has. I've lived in 6 different states for more than a year each from the Northeast, the southeast all the way out to Cali, and I love them all, and many more that I have only vacationed in.
    Rob
    O'Brien and Sons Construction
    Swansboro NC

  9. #9
    Join Date
    Nov 2006
    Location
    Atlanta
    Posts
    152

    Default Re: Knee wall to support rafters.

    I believe that O'brienConstruction may be referring to a post I put up a couple of weeks ago about a new construction home, fairly large for that matter (approx. 3200 sq. ft.) that has 2x8's for floor joists on the main floor. I'm finishing the basement and the room in the basement in question has a room larger than 18'x18' with no support under the 2x8's whatsoever. I need to tray the ceiling in this room and the 2x8's were the issue.

    The rest of the story is that this is the first newly constructed home I've come across without I joist being used as floor joists. 2x material is very common in older homes around here but in the newer ones I joists are the norm.

    I would say that gatimberframer is correct in his assessment that this house is in an area that has grown so fast that inspectors are being hired to fill spots quickly and the building dept in this county hasn't been able to keep up with the growth.

    I may have generalized Ga.'s inspection process and quality of building in my post and for that I apologize, but I'm from GA. I primarily focus on rennovation and remodeling but I build a few new homes per year and it is very difficult to compete with the so called "custom homes" that are being thrown up with little regard to craftsmanship when you're trying to build a real quality home. Being that you are an exposed timber framer (a sign of quality) here in Georgia I'm sure you would agree that 8.00 and hour illegal labor off of some street corner is an indicator of a "Bigger Picture" mindset. You would also have to agree that there is definitely a group of builders here in Ga. that just wants to turn a piece of property for a buck and move on to the next location where there is a population explosion and can take advantage of the situation by building cheap disposable housing, which by the way, believe it or not, around here can still very easily run in the mid one million range. These exorbitant figures can be easily explained by Georgia also having one of the highest rates of builders involved in mortgage fraud. A fact that can easily be verified.

    Facts are facts and like it or not, quality construction, and I mean true quality construction can only be found in about 15-20% of new construction. The rest are built with transient population in mind, even and sometimes especially the larger homes.

    I also apologize to those innocent bystanders that may be reading this and may very well build a quality home here in Georgia, if you do then this is not towards you. Quality is on the rise here in Georgia and it will get better eventually. It will just take a concentrated effort on the part of the smaller builders and help from the larger builders that do have a solid reputation to make it happen.

    The man said you needed first hand experience, well here you go my friend. I've sat on my share of construction notes for extended periods in this crazy Georgia, primarily Atlanta market. I guess in some folks minds I'm the guy that has it backwards, I was the businessman that ran subs and now I hold a hammer with my men.
    Last edited by ownerslashjanitor; 01-21-2007 at 05:09 PM.
    Just riding down the road throwing chicken bones out.

  10. #10
    Join Date
    Nov 2006
    Location
    Atlanta
    Posts
    152

    Default Re: Knee wall to support rafters.

    As for the original question from davidshammer, are you saying you want to get rid of the supports that run from the ceiling joists up to the rafters and replace them with knee walls further out to allow you to open up the space?
    Just riding down the road throwing chicken bones out.

  11. #11
    Join Date
    Nov 2006
    Location
    Swansboro, NC
    Posts
    1,550

    Default Re: Knee wall to support rafters.

    Janitor,
    Thanks for your post. I was citing you partially in my post. The problems that you see aren't centralized to your state alone. We have a pretty thorough inspection process here, but things still slip by. Part of the problem I have started to see, is that with the slow in house sales. Some builders are trying to maintain there income levels from the explosive years, by cutting corners anyway they can to milk all profit out of each home they do sell. Not everyone does this, and I could be wrong on why it is happening. I'm assuming again, but I have noticed as a framer and builder myself, that as sales slowed. The "just get it done" attitude was quickly replaced with a "how much is that, what can I delete to cut costs".

    One simple thing for instance, gable roof trusses. I framed a ranch house where trusses started out spanning 38' at one end. As you came down the house the trusses stepped out to 50' to cover front and rear porches. Then back to 38' at the far end. Where they stepped from 38' to 50' we normally have enough trusses to nail a 38' along side the 50'. This home the builder decided to skip the last 38' trusses and instead we nailed blocking to the sides of the 50' trusses in plane with where the 38' would have been. Not a significant savings in material costs, and I'm not an engineer, so this might not have made any structural difference. But to me it seamed like a crappy place to cut costs.
    Rob
    O'Brien and Sons Construction
    Swansboro NC

  12. #12
    Join Date
    Jan 2007
    Location
    TN
    Posts
    11

    Default Re: Knee wall to support rafters.

    David,

    Your description leads me to believe the joists are ceiling joists and not floor joists in the attic. That's problem 1. You can't load a roof load down through a knee wall onto any joists not designed to carry the applied roof loading. Then you must be sure the rafters are properly sized for the new span.

    It's not and inspection problem during construction as much as it is a modification to a once properly code compliant roof framing. If you modify it, you MUST make it code compliant.

    Example, I had a framer install dbl 2x8 header per plan in a 9' opening, carrying a 16' floor span. Then he built a knee wall and birdsmouthed his rafters down to the floor(not per plan). Now the once properly sized header carrying floor is carrying a concentrated load of 1395# at the middle 1/3 of the header span. He ended up with a dbl LVL to replace the header.

    You are essentially attempting the same thing...doubling or more the max load the joists would be designed to carry

  13. #13
    Join Date
    Dec 2005
    Location
    Western Massachusetts
    Posts
    8

    Default Re: Knee wall to support rafters.

    Ideal situation for a structural ridge.........kneewalls will add roof load to floor jst & u dont want that in a re-model. The structural ridgebeam will take the rafter thrust out of the picture & will no longer be considered a hinge wall.

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