Roof Framers - Need some help

[scootermcrad]

Hey folks! I need some help with project I have. I know there's a ton of framers around here, so I thought maybe someone can give me some help.

I have a ceiling that is much too low and I want to open it up a bit to utilize some of the space above with the tall pitch I have.

Details:
- 10 foot ceiling joist span
- 12 foot roof length
- 14-12 pitch
- 2x6 rafters
- 2x6 ridge board
- roof structure is essentially trapped/supported between two bearing walls
- Shingles over plank

I attached a sketch that simplifies the current roof structure.

Goal:
- Raise ceiling by removing ceiling joists

Questions:
- Can I build scissor trusses IN PLACE with the top chord being the existing rafters and retaining the ridge board?
- Anyone have a good link to scissor truss guidelines so I can start designing and planning it out? Need some rules/guidelines.

Any help would really be appreciated!!!! I've gotta get crackin' on this thing before is starts getting cold. I know it's slightly OT, but I thought it would still apply to general framing practices for garage roof structures since everyone is always looking for to open up their garage ceilings.

Thanks!
Scott

 

[scootermcrad]

This probably best describes (visually) what I would like to build IN-PLACE.

 

[scootermcrad]

Bump for the afternoon crowd...

 

[Falcon67]

Just a guess, but response may be weak on this one. Can it be done - bet so. Will anyone here do napkin engineering, supply a materials list and assume liability for the design - not likely. This is a real engineering thing and you'll likely have to take all the pertinent info to a PE and get something back from them.

 

[willymakeit]

It can be done as mentioned by Falcon. Get a engineer to design it, which is what you will need in a permited situation.
Roof trusses need the dead load, live load, wind and snow loads to be taken in to account. It is worth paying a engineer since the repairs for a bad design are not cheap.
Your insurance company may require something should a probelm ever develop.

 

[Daniel Dudley]

That is pretty small. Put a couple of 2x10s under the ridge to keep it from sagging. Header off any openings under whatever you post it with on the gable ends. Put in three if you are the nervous type.

I worked on a twenty foot long addition once that was 30 feet wide, with 2x12 rafters on a 3 pitch. A single 2x12 ridge 20 feet long, and no collar ties. After 20 years of snow loads, that ridge cracked near the center. No doubt there was some sag in that roof, so we jacked it up and put 5 or 6 2x12s under the ridge. Posted them down to the foundation, and that was it. If you calculated the load, you would probably find you needed more in that application. In reality, you don't.

You could also put in a couple of cables at four and eight feet to act as collar ties. This is a small shed with a steep pitch, so you aren't going to have any snow load. Or put two 2x4 a third of the way up at 4 and 8 feet. Use 5 16 penny nails on each side into the rafters.

Oh yeah. You need to get an engineer.

http://www.youtube.com/watch?feature=endscreen&NR=1&v=OEJh2FFUUoU

 

[ThePress]

Havingbeen a contractor and construction worker for many years, I can tell you your design for a scissor truss is strong enough, but you will need to add gussets at all the joints (pressed steelor plywood) to ensure the shear strength of all the joints is good.

 

[bczygan]

You can open it up even more than a scissor truss would allow. First, what is the purpose of this? If it is just to give a more expansive feel to a living space, then maybe a couple of cross beams in the space wouldn't be objectionable. If you need the space completely clear then there are a variety of things you can do. Scissors trusses is one. A combination approach can also work. You have walls at both ends according to the sketch. A ridge beam will cut the load on rafters if you can transfer the load from the ends of the beam, down through these walls. It will reduce the outward load on the side walls of the space. Collar ties will also help. Another thing is to add deeper rafters or engineered members between the existing rafters. If removing all the ceiling joists, one solution to resist the outward thrust of the rafters at the top of the wall is to create a horizontal beam at the top of the wall. Install an additional top plate of a material and size that will resist that load. Imagine a 2x13 or an LVL placed flat on the top of the wall. That is the idea. A wall built out of 2x6's with a 2x6 top plate or double 2x6 top plate (Or bigger) does this kind of thing too. Of course you have to calculate material sizes and materials to know what kind of deflection there will be in all the members based on the loads, vertical or horizontal. Of course, as usual, the connections between members need to be adequate. I like metal straps or nailing plates.

 

[scootermcrad]

Hey guys! This is great info! THIS is exactly the kind of feedback I was looking for.

By trade I'm a mechanical engineer, but my discipline covers very little truss and structural work. I know how to calculate everything. Not worried about that part. Something I've learned along the way, is, you can know "everything" the books tell you and I can do the calculations till I'm blue in the face, but EXPERIENCE will often get you to a solution faster. There are lots of great and new and traditional techniques for framing roofs. Which is why I'm reaching out to you folks.

You could consider this a construction/framing example comparable to a decent sized shed. In actuality, this is an entry room to the rear portion of our house. The reason for vaulting/raising it is purely aesthetic (the house is worth it). We normally chat about garage stuff around here, so I tried to keep the discussion vague so the topic at hand is focused on. And I appreciate all the input I'm getting.

I found some horrifying things last night when I got up in the ceiling. I also got some better measurements. I'll post up some sketches in a bit. Had some new ideas.

I'm really trying to keep this focused on the framing/structural techniques, so things stay on topic. Hopefully it will help someone with a unique shed and/or garage project.

Thanks guys!

 

[scootermcrad]

Okay, I did some quick sketches, showing what my directional thinking is...

One shows the CURRENT configuration, with the ceiling joists as the lower chord and sitting directly on top of the top plates. The other two are a lower 1/3 collar tie raised ceiling and a built in-place scissor truss.

I'm leaning HEAVILY towards the more simple lower 1/3 collar tie method. It's easy, less material, etc.

The one thing I discovered last night is the lower chords/ceiling joists on the current configuration, go all the way to the outer fascia boards and the rafters sit right on TOP of them. VERY strange, and I'm guessing not a proper construction. So, I will sister and/or gusset those pieces together, as well as add the hurricane ties. I'm also going to block between each cut location.

 

[bczygan]

Before you decide on structural solutions you need to look at the design considerations.Some questions.
Do you intend to have a lot of light in the space from openings in the wall? How about light from above as in skylights . Do you want a decorative ceiling of some kind such as T&G boards or exposed beams of some kind?
How much insulation value do you want to maintain in the roof structure?
What will the walls between this space and the adjoining spaces be like? Will there be just doors or will there be major openings making this space open to the adjoining ones. Will any of the adjoining spaces have tray or open ceilings or higher ceilings that can link with this one to create visual flow?

Photos?

Bill