I Need A Good Framing Idea

[frozen_bohemian]

Just started the design stage of the garage "blowout" and I need some help with a framing detail.
I need to raise the ceiling height in part of the addition to my garage and house. I plan on connecting the existing garage to the existing house with a wood framed addition. I need to have approx. 12 ft. ceiling height in the shop area, but 9ft. ceilings in the house area.
The roof framing will be stick built 2 x 10 12/12 pitch.
I would like to maintain the same sidewall heights thruout, so I wondered if it was possible to raise the lower chord (ceiling rafters) above the header plate.
I have seen timber framing done like this and some prefab trusses like that.
Not sure if this is a common stick built framing detail or if there are issues with this method.
The other obvious solution would be to use drop trusses in the house space to lower the ceiling, not my preferred method.
Any other ideas are welcome.

 

[little d]

Frozen,
ceiling rafters not only give you something to cover for a ceiling but, keep the walls from pushing out with the roof load. You can use rafter ties for your ceiling joists to raise your ceiling hight but ya gotta be carefull on how ya build them. I'd susgest, if your going to build it yourself, do your research...Get ya a book on general carpentry and read up on what does what and why....

 

[scarpozzi]

I'm building my garage addition next to the house and building a 2 ft block stem wall....then using 8ft lumber to make my ceiling height 10 feet. I suppose you could do the same thing with yours but use 10ft lumber. As for connecting to the house, I'm doing a gabled roof and connecting it into the existing roofline with a lower connector gable that will house a staircase to get to the upstairs of the garage from the house....so I can use it as livable space later. (code dictates that you can't have egress from livable space into a garage due to fumes, etc)

 

[astroracer]

Raising the chord is common practice for vaulted or cathedral ceilings. My house is full of them. You should talk to a builder or rafter supply shop to get the correct building standards. Do it right the first time so you don't have to tear it of per a cranky inspector...
Here is what we are talking about.

 

[kbs2244]

When you do this the rafters become “collar ties.”
Depending on the snow load in your building code they can be from 1/3 to 2/3 of the height from the wall header to the peak.

Yahoo has a lot of good PICs

 

[KELLHAMMER]

Be careful. There are limitations for how high a ceiling joist can go up. Some think the 2/3 - 1/3 rule is ok. But , that only works in certian cases. Nowadays, in addtion to the ceiling joist, we frame a 2x just to the underside of the ridge to hold the opposing rafters tight to ridge. This is partly to counteract the effect high winds can create with high pressure/ suction on opposite sides.
If you rafters are maxed out for their span and you raised the ceiling framing a couple of feet you could weaken the structure or cause the roof to behave badly due to the tenison member (ceiling joist) being placed closer to the rafter midspan. Raising the ceiling joist most likely will require either installing a structural ridge or beefing up the rafters. Things to be aware of are: Snow & snow drifting loads, wind loads , current dead load etc. etc.

 

[frozen_bohemian]

Be careful. There are limitations for how high a ceiling joist can go up. Some think the 2/3 - 1/3 rule is ok. But , that only works in certian cases. Nowadays, in addtion to the ceiling joist, we frame a 2x just to the underside of the ridge to hold the opposing rafters tight to ridge. This is partly to counteract the effect high winds can create with high pressure/ suction on opposite sides.
If you rafters are maxed out for their span and you raised the ceiling framing a couple of feet you could weaken the structure or cause the roof to behave badly due to the tenison member (ceiling joist) being placed closer to the rafter midspan. Raising the ceiling joist most likely will require either installing a structural ridge or beefing up the rafters. Things to be aware of are: Snow & snow drifting loads, wind loads , current dead load etc. etc.

I would definety run this by an engineer to be sure.
One thing I should have mentioned is that I wanted to use the space above as an attic for storage.
I was hoping to be able to stick build this, would it make a difference if this was a factory built truss? Raising up the lower chord no more than one third was always my plan, thanks for confirming that.

 

[KELLHAMMER]

There are several paths you can take. An pre- engineered truss is good and can be a economical way to do it. Depending on the whether the requirements of disassembling / reassembling the exisitng is minimal. Or you can stick frame it either by beefing up whats there or totally rebuilding it. A structural engineer is always money well spent. I rely on mine in my work, and he has made difficult structural conditions much easier to deal with.