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Dormer Framing / Truss Design

Dormer Framing / Truss Design

Dormer Framing / Truss Design

(OP)
This is definately a basic question. But does anyone have a truss design of a basic dormer they can post? I just started with truss design and am wondering what is standard.  I am putting in 6' dormers. Do I put a flat girder across the 6' gap for framing weight, if so where do I put it? Sorry to bother with a beginner question...

RE: Dormer Framing / Truss Design

If the dormer is false then you simply layout trusses under the false wall and provide trusses for the dormer framing. The framer then goes in and builds on top of the roof decking with a sloped 2x4 wall and installs the short trusses. Blocks between the last truss and the main roof plane (or uses valley trusses). I would add additional dead load to cover yourself and CLEARLY mark the trusses on the layout. When it gets to the jobsite it can get confusing if you don't properly do this. Mark their dimension from a outside frame dim on the plan (interior wall lines are more likely to be popped incorrectly).

If the dormer is open then I suggest putting two girders along the length of the dormer, and either boxing in the dormer if it is short, or allowing them to field frame the overspan between the girders (you will need to drop the TC to allow them to properly frame this*). You will need to load these girders based on the additional framing material weight.

I find field framing between the girders to be easier than installing tall height box girders to carry stubbed trusses.

This is what we do in Texas in a non-hurricane area. We have near zero snow loads, light wind loads (in my area), and framing labor is cheap. So adjust for your area as needed.

* If you have Mitek Engineering then you will see what I mean when you give the truss a > 2' O/C spacing.

RE: Dormer Framing / Truss Design

Just curious. What is a chemical doing answering a structural question?

RE: Dormer Framing / Truss Design

My roommate is a structural EIT and works for a truss manufacturer.

RE: Dormer Framing / Truss Design

There are a few way to do dormers. If it is false you can do it as already described here. You also can space the trusses to align with the dormers and build a flat top chd that matches the profile as shown in the architectural plans. You then can add some small roof trusses that span the flat top chds. This is how it is usually done in wind zones as balloon framed walls on top chds are a lot of trouble to build and connect. The same concept is used on functional dormers. You add a floor and roof girder or beam that spans the dormer

RE: Dormer Framing / Truss Design

We like to hold trusses apart to the outside of dormer walls. Then flat girder under the front wall (loaded to carry wall, roof, window, usually ran at L/960 deflection), and floor trusses under the floor area of the dormer. Dormer walls are then built on top of the 3/4 floor decking.

RE: Dormer Framing / Truss Design

Trussme68,
Did you mean L/360?

RE: Dormer Framing / Truss Design

A truss carrying a wall, stucco, SGD or window, and roof. L/960 is what we prefer to avoid future problems.

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