As part of a remodeling project we are turning our attached garage into a combination living/dining room and while we could simply keep the ceiling height constant throughout the house, I think it would really make a huge difference if we raised the ceiling over the space (approximately 13'-6" x 23'-6") up to the rafters. I've been told that conversions like these are relatively easy to do, but I don't want to end up with a sagging roof/bowing walls as a result. Here is a rough representation of what I have:

[ATTACH=CONFIG]42595[/ATTACH]

And here is what I'd like to do:

[ATTACH=CONFIG]42596[/ATTACH]

I've gotten conflicting advice on whether or not I would need a true ridge beam in order to accomplish this. Some say yes, some say that upgrading the collar ties to 2 x 8s and bolting them would suffice. Also noted is the need to sister the existing rafters for the purposes of making room for insulation and lighting. Any other pitfalls to watch out for in a project like this?

 

Best bet is to get a structural engineer on-site to evaluate this for you. While it may be do-able, it's not necessarily simple as that 2x6 ceiling joist is keeping everything from spreading out on you.

 

Definitely get an engineer to bless this. You will have an inordinate amount of pressure exerted on the outer walls since they will have no tie, and the collar tie isn't strong enough to offset this pressure.

 

Biggest factor in your area is the snow load.
No way would I personally ever do it the way your suggesting.

 

The engineer will come up with a plan that would make it safe [including handling snow loads] Getting his input is the 1st step and will help you determine if the cost is worth the benefit.

My wife and her 1st husband sold their house to a boy that decided he wanted an open floor plan so he removed the half of load bearing wall that ran down center of the house. No engineer plans or permits, no need to tell you what happened A trailer now sits where that house used to be

 

That's just utterly stupid. If I was going to do something like that I would have done it already. I'm here asking because I'm looking for opinions from those more learned than I. It sounds like an engineer is going to tell me I need a ridge beam, which shouldn't be so bad considering it's only about a 14' span. I wonder if something like this could work?

[ATTACH=CONFIG]42634[/ATTACH]

The APA has tons of information online about the construction of box beams-I just would need an engineer to tell me the specs of what I'd need. The advantage being it could be built onsite cheaply and raised into place very easily.

 

Maybe, but if we knew what the engineer was going to tell you we would tell you.

 

There is no one here that is going to be able to give you the sort of information that you pay a structural engineer for. Having said that, the last time I did something similar, the ceiling joists were moved upward, bolted in pairs and they (along with larger sistered rafters) were left exposed as part of the design. The existing rafters were left as is, as part of a closed, spray foamed roof. Rafter ties were added to ALL rafters at top and bottom. Everything was bolted together after it was nailed up.

http://i231.photobucket.com/albums/e.../noddle001.jpg

Notice that the rafter ties are only about 36" above the top plate. I believe that based on the snow load calculations and the framing size and span, that was the farthest away they were allowed to be in THIS CASE.

For more information, see: rafter ties vs collar ties

You and your structural engineer will need to come up with a plan that is job specific.

 

Understood-I'm sourcing some names of structural engineers who will work with DIY'ers from a friend in the building business now.

 

This may be obvious, but you could remove entire roof and replace with trusses.
I think the engineer would be a cheaper route. It sounds like you can do the work yourself and the engineering costs shouldn't be that great. I would say much cheaper than replacing roof framing with trusses and installing new roofing material.
I've had structural calculations done for me in the past at a surprisingly low cost, and I'm in a high cost area.