Replies

1. 
   Piffin | Dec 04, 2004 08:38pm | #1

   Is this an exterior wall or an interior like in a Cape?

   with an exterior wall, your concern is with outthrust forces of the roof loads as adressed in your ridge beam Q posting here. With an interior kneewall, the concern is that for this kneewall to be load bearing, the joists supporting it must be designed to handle not only the loads of that second floor, but transfered loads fromt he roof as well.

   These two separate posts point out that you are somehow trying to plan or build a roof system. How about giving us the overall goal and situation and see if it is easier to answer except in generalities.

   Specific enginweering answers are harder to come by because of the potential liabilities and danger inherent.

    

    

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1. 
   rees | Dec 05, 2004 07:59pm | #6

   Ok, heres a little more info. I have always beleived that once you have a design, and then you start building, you don't stray from that plan. Well the story goes that we have a very straight forward design, 20x32 2story simple mellow pitch roof. Well we start framing in early fall, begining of the rainy season here in Northren California. We have an open floor plan on the first floor with a timberframed floor system all exsposed. So nothing can get wet. The first rains come about a month early. We erect a hoop house over the entire building, were fine and dry. Our best effort yet at staying out of the elements. Well it was way to much stress for the owner. He now wants to scrap the full up stairs and make the house a cape with a dormer. Now first off it is a small house to begin with. Second we have large exposed beams with handcut joinery designed for certain situations like the stairs. Thats where the problem is, the stairs don't work and there ain't no moving them. Our options are simple in my mind, stick to the original plan, but they are not so clear for the owner. This is where the kneewall comes in. I would have balloon framed this wall from the start. In regards to the ridgebeam they want the exposed beam look. On the original plan with the full 2nd story walls we had collar ties halfway down the rafter span. But the design change kind of throws that all into the air. I like my first option the best, but I want to see what other options there are if any.Thanks for your time.

1. 
   Piffin | Dec 05, 2004 08:40pm | #7

   A house that small does not allow for to much change. You would be right in sticking to the original plan, despite the nervous colon on the ground 'helping' you with advice.But if you have to change, the only solutuion i see here is a ridge beam, sized to carry that load which will make it fairly large, unless you can shorten the span, such as by placing a center post to carry load to foundation. If you try to use kneewalls in center, that will add to load on those exposed ceiling timbers down below and make them sag. As narrow as the building is, you need kneewall at exterior to get any usable ceiling room at all above, so the ridge beam is the answer. Unless you switched to some sort of scissor truss that is. Owner would have to be willing to accept that sort of system, but it could be a faster way to get closed in. 

    

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2. 
   mike_guertin | Dec 04, 2004 09:29pm | #2

   There are only two ways to resist thrust problems on knee walls (actually 3 ways but you don't want joists at hip level)

   Balloon frame the walls is the way I prefer. First floor walls extend all the way up to knee wall height of second floor. Let-in ledger supports the floor joists. Joists resist thrust. Roof needs no structural ridge or rafter ties (other than the metal connector ones)

   My house is done this way (see FHB 123 pg 111 - The only ties you see are those keeping the dormer walls from blowing out). It's fast, no extra framing or dealing with oversized ridges. And it works.

   OTHER way is structural ridge. LVL or solid or steel. Piffin described issues there.

   MG

1. 
   Piffin | Dec 04, 2004 09:41pm | #3

   Mike, I agree on the balloon frame, but wanted to hear more from Rees about the nature and extent of this project. There is always more to it than first preseteed, which is why engineering solutions are hard to answer online, in the blind 

    

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1. 
   mike_guertin | Dec 04, 2004 09:50pm | #4

   Blind engineering! I think you are on to something.You're right. Blind engineering is not a good idea. I'm just impatient I guess. MG

1. 
   Piffin | Dec 04, 2004 10:13pm | #5

   LOL, You lay Braille shingles in the rain too? 

    

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