Replies

1. 
   r_ignacki | Mar 22, 2002 12:16am | #1

   nowadays, when you stick-build a roof, a ridge board is used, however, maybe if your building some trusses, a gusset made from plywood is used to connect the rafter members together, back to your house, doubling up a 2x4 is probably insufficient to hold dormer walls, maybe if you built them on the attic floor, (more attic floor/cieling framing needed), It could work , who knows what you got there, I bet your 2x4 rafters are bowed,(I like this new site), when you add additional framing to your existing , you will probably have trouble, lining things up with new "crowned" lumber.

     

1. 
   VinceKlimek | Mar 22, 2002 03:05am | #2

   The bottom of the dormer will be resting on the knee wall and the dormer will only be a window width wide, do you still think 2x4s doubled up will be insufitiant to support the dormer walls?

   Vince

2. 
   jimblodgett | Mar 22, 2002 03:06am | #3

   Vince - First off, yes, it is a common practice to frame a roof with no ridgeboard. In most applications the ridge board is not structural and only serves as a convienience for the carpenters as they frame the roof.

   Are you saying you're going to put a gable dormer in? How wide? What pitch roof? When you say "the sides of the dormer" do you mean the walls? How long is the rafter you plan to double span? What pitch? Do you understand what the doubled rafter will carry? What loads do you have to build for in your climate? What type roofing will go on the dormer? What will the new doubling rafter bear on, just the nails where you "sister" it to the original 2x4?

   It sounds like you have a little knowledge, but that can be a dangerous thing. It's important to understand how the weight of the roof is transferred down through the framing to the foundation.

1. 
   VinceKlimek | Mar 22, 2002 10:46pm | #4

   Jim,

   yes I have limited knowledge in this field and that is the very reason I am posting here.

   to answer your questions:

   Yes, I am talking about a gable dormer.

   About 32" wide.

   afairly steep pitch.

   when I said sides, I did mean walls.

   The rafters I plan to double are 22' long.

   Maby you can tell me what the doubled rafters will carry load wise.

   The bottom front of the dormer will sit on the knee wall. will this help carying the load?

   I live in the pacific N.W.

   I will cover the dormer with 25 yr.composit asphalt shingles.

   My original question had to do with how do I give the doubled rafter somthing to bear on in light of the fact that there is no ridgeboard to tie into.

   With this added info, can you give me any suggetions on how to make it work? Thanks in advance, Vince klimek

1. 
   jimblodgett | Mar 23, 2002 09:41pm | #5

   Well, what I'm saying, Vince, is that it's mighty difficult for anyone here online to visualize exactly what your situation is. I gave you a few examples of the variables involved in the design process to illustrate my point.

   I think it's dangerous for you to take advice here on any structural issues unless you have a clear understandiing of how loads are transferred through framing member to the foundation, and based on your question, I'd say you lack that knowledge.

   If you are building a new gable dormer, the rafters usually will bear on the side walls of the dormer, not the gable wall. So the weight of the new roof bears on the walls, which bear on the doubled rafter (sometimes) which bears on the kneewall at one end (in your case) and the opposing rafter on the other end, or maybe a structural ridge beam of some type. So, you see, the pitcch of the new roof will determine how much weight is being transferred, the span will determine required framing members, and on and on.

   Of course, you might run your rafters horizontally from the existing roof to bear on the gable wall, in which case, doubling the existing rafters probably won't give the strength you need.

   The best thing you could do is ask a building professional in your town to take a look. If you want to do the work yourself you might decide to hire that person to give you a design that you could follow that would meet local building codes.

   Thing is, you tinker with your car, and don't get it back together right, it might not run. You tinker with the structural elements of a building and don't get it back together right, someone could get hurt or you could devalue the building.