Replies

1. 
   BossHog | Mar 05, 2012 06:37am | #1

   Are you talking about building a full 2nd story vs. a 1.5 story with attic trusses? 

   I don't understand where the sloping flat trusses would come into play.

1. 
   Bigtuna3 | Mar 05, 2012 08:49am | #2

   I was told I could use the Sloping Flat trusses to build the roof (coming down to the floor) as an alternative to the room-in-attic trusses. Then I wouldn't lose the space. Not a good option?

1. 
   calvin | Mar 05, 2012 08:59am | #3

   big

   Boss worked a long time as a truss designer, you should be able to gain some insight into your project from him.

   Why not provide the usual dimensions you have to give some idea of what you have.   Perhaps the frame of the first floor details as well.

   You do not plan on adding walls to gain height?  Realize that many jurisdictions only allow livable floor space to the 5' kneewall height.

1. 
   Bigtuna3 | Mar 05, 2012 10:59am | #4

   I'm looking at 32x24 but would also consider going down to  30x24 or 28x24 if it means big cost savings.

   My first floor will be completely open besides the set of stairs to the upstairs.

1. 
   calvin | Mar 05, 2012 06:54pm | #5

   And when Boss comes back.............

   is the gable end the short side?

2. 
   BossHog | Mar 05, 2012 07:23pm | #6

   I think the confusion came from the terminology you used. But the terms vary  by region, so what you used may be perfectly normal in your area.

   To me, a "sloping flat" truss would have a flat (horizontal) BC, and the TC would slope at something like 1/4" per foot. Typically used for a flat (rubber) roof.

   I think you're talking about a "parallel chord truss", where both the TC and BC would have the same pitch. They are for all practical purposes a rafter.

   One big drawback to using them is that you would have to use a ridge beam. With a clear span up around 30' or so, it would be one heck of a beam.

   If you use a ridge beam you could use 2x lumber or I-joists about as easily.  (And they would probably be less expensive)

   A floor system that spans 24' will be fairly deep. You're probably looking at 16" deep wood webbed floor trusses or I-joists.

   I do a lot of 24' attic trusses at 12/12 with a 12' wide room.  If you want a wider room you could look at a couple of options. One would be to raise the heels of the trusses.  Another would be to do a gambrel roof. But you're limited to a room about 16' wide with a 2x12 BC.

   Some manufacturers use LSL BC material and can do wider attic rooms. But they're few and far between. All you can do is ask around.

   I don't mind tossing around some more ideas if you want to hear them.

1. 
   DanH | Mar 05, 2012 10:32pm | #9

   I do see that this form of overgrown scissor truss is refered to as a "double sloping flat truss".

   Presumably it could be manufactured in a more vertical form, but doubtful that it would ever be tall enough for a "room".

   
2. 
   semar | Mar 26, 2012 07:16pm | #12

   parallel cord/flat truss

   I am working on a plan with exactly the same layout in the attic

   I choose  I joist with 16" depth because i could get R40 just in the I beam, then strap the bottom with 1 1/2" rigid insulation

   I use a ridge board rather than a ridge beam.

   Check   trusjoist.com for span tables. My design with 36' width at the gable end comes up with 23' span from outside wall to the ridge under heaviest load condition. 2x6 LVL collarties at 8' ceiling height and 5' vertical wall for comfortable living space.

   I insulate the rafters right to the outsidewalls rather than bothering with insulating the attic floor and vertical walls.

   that way you could use the attic "void" for storage

   If you have skylights in the roof area you must strap the i-joist with 2x  on top to achieve ventilation around the skylights

   PS when I say ridgeboard I mean the ijoists resting against the ridge not on top of it. Size to be determined by engineer

1. 
   BossHog | Mar 28, 2012 06:45am | #13

   I have never heard of an I-joist supplier approving a design with I-joists as rafters leaning against a ridge board.

2. 
   Bigtuna3 | Mar 05, 2012 10:05pm | #7

   A few more ideas would be great... and of course, how would you do it if it were you? :)

   All we really need on the second floor is a small bedroom, bathroom and an open space which will be a small living room / office. The kitchenette will be on the first floor.

1. 
   BossHog | Mar 06, 2012 07:43pm | #10

   Additional ideas

   I figured I'd run a couple of framing ideas by you and see what you think.

   If you use attic trusses, keep in mind you can add dormers to gain room. You have to double up or triple up the members around the dormer. But dormers can be up to 10' wide, which gives you a lot of added space.

   If you start the dormers on spacing you can even do it without adding extra trusses.  i.e. if the trusses are 2' O.C., start the dormer 8' in from the end and make it an even number of feet wide. The dormers that would have fallen within the dormer area can be moved out to make up the double or triple truss.

   With a 24' wide attic truss you could use something like a 2' overall heel at the end of the truss and get a wider room in the truss.

   If you're really hung up on having room all the way out to the exterior you could probably go with a floor truss and rafter system. Use clear span floor trusses, and put a 2x top plate on top of the end of the trusses. Put rafters on that in the form of I-joists or 2x lumber and run them up to a ridge beam. (It can't just be a ridge board.  If you don't know the difference let us know and we'll get that taken care of)

   Be sure to design in a hole for the stairs. Don't let anyone tell you that you can cut things out later as needed to form the stair hole. With engineered components things just don't work that way.

   That's all I can come up with at the moment.

3. 
   DanH | Mar 05, 2012 10:25pm | #8

   They occasionally build homes with parallel chord trusses up here, the idea being that the trusses allow a better depth of insulation than more conventional rafters.  But unless you need that insulation space the option seems to be both expensive and a space hog.  (Where do you live?)

4. 
   Bigtuna3 | Mar 15, 2012 10:36am | #11

   In the end we scrapped the idea of a second floor. One story, scissor trusses, dividing wall in the middle to separate living space and garage garage.