Raising ceiling How high can I go.

Currently remodeling back room and am looking to raise the ceiling from 7'6" to about 8' maybe 9'. I am not sure how high I can go or if I should just leave it alone. Below are the specifics: and thanks in advance. JRE
All Rafters 2x6 span 12' No collar ties. Ceiling Joists are 2x6. Ridge Beam is a 2x10 In New England so snow load is a factor. Ceiling joists span 15'6" across backroom were they tie into wall, from wall another set of ceiling joists span 8'6". Distance from joist to ridge is 2'10".
Here is a link to a diagram I made, Boy was it hell trying to get this online. http://home.comcast.net/~mastermech /
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Mastermech wrote:

It's not clear what you're asking.. Do you mean, can you take out the ceiling joists and add collar beams farther up? or are you willing to re-build the entire roof, or what?
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I am looking to raise the ceiling. Essentially raising the ceiling joists and turning them into joist/collar ties. I only am looking to go up about 1/3rd or 1 foot. and in the larger room only. http://home.comcast.net/~mastermech /
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The only problem I see is that on the left side of your diagram where the ceiling and roofline meet, you can not go any higher without the roof line coming into your room, how much depends on how high you go. What is the reasoning behind wanting to do this, just for curiosity sakes. How tall are you? nataS
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Mastermech wrote:

I don't think it's going to be worth the effort. You're pretty much looking at re-building the roof, no matter what you do. Depending on how everything is put together, it might be easier to just pry the whole roof off intact, lever it up, and stuff 4x4s on to of the existing sills.
If whatever you're trying to accomplish permits it, you could leave tie- beams at the lower level every 6' or so, to resist the thrust of the roof, in which case you wouldn't really need the collar joists at all. (Or you could use cables and turnbuckles)
Alternatively, you could run the joists from the sill (to the left) to the TOP
of the 2x4 posts to the right, making 1/2 a sissor-truss.
I wouldn't want to just raise the joists and attach them in the middle of the span of the rafters, without doubling up the rafters, because even if you only go a few inches, you're converting a compressive load on the rafters to a sheer force.
--Goedjn
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As I read it, you have 24'-0" from wall to wall. That gives a rafter span of 12'-0" which is the limit for #3 Hem-Fir 2x6 at 16" spacing for a snow region, light roof covering, and drywall finish. If all those limits are true, you could add collar ties about a foot down (vertical) from the ridge, then remove the existing ceiling members. The partition that exists parallel to the ridge would have to be supported in some way. If it were my roof, I would be very careful about removing the existing frame members and add collar ties at every rafter. The quality of construction - based on the sketch - leaves me uneasy about the soundness of the structure. It would be good to call in an experienced carpenter / contractor for at least a careful consult before start of demolition.
Tom Baker
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In my experience, adding collar ties to a frame changes a lot of the stresses inherent. Depending on the roof slope, it can add a significant point load to the midspan of a member not designed to handle it. Imagine your roof joists spanning between two supports with a light, uniform load resting on them. Now add a five hundred pound weight at midspan. That's the general effect of the collar ties. I didn't do the the calcs; but somebody nees to. I'd recommend an Professional Engineer. The capacity of the connections at the ends of the collar ties also needs to be looked into.
Also, if you're going to do this, don't remove the exisitng ceiling joists before installing the collar ties. Although they look as though they're not doing anything, the ceiling joists are, in fact, serving as the bottom chord of your roof framing. It's conceivable that your walls would kick out & your roof collapse iff you removes all of them at the same time.
Joe F.
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Thanks for the replies, You make some good points. I plan on having a contractor friend come out to take a look, If only I had known what I got myself into. Ha-ha. So much for a room on a budget. Thanks Again JRE
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