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structural issues/ideas for vaulting a ceiling?

chadzajdel's picture

Does anyone have any experience with removing a second floor bedroom to create a first floor vaulted ceiling? The home is a cape cod style where the rafters land on the first floor walls and the 2nd floor bedroom that we are removing has the knee walls on each side. The rafters are currently 2x6 at 16"oc. with a 2x8 ridge beam. The 2x6 rafters are long. I'm guessing approx. 20 feet in length and I'm thinking that the kneewalls are really helping to keep the 2x6's from bowing. Also I'm thinking that the floor system for this 2nd floor bedroom is keeping the walls from bowing outward from the pressure from the rafters. Has anyone out there done this? I'm sure it can be done, but would love some input from an experienced remodeler. My thinking is to almost create a different interior ceiling pitch so I can get more insulation up there, as well as using 2x10's etc. May be I need to add a new ridge beam under the current one as well? Just thought I would throw it out there to see if anyone has any input.  Thanks for anything you have!!

Hire an engineer. (post #207130, reply #1 of 7)

Hire an engineer.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

It seems I end up doing (post #207130, reply #2 of 7)

It seems I end up doing something like this once a year on a remodel.  You can vault most any existing structure, but it requires much more work than would appear on the surface.

If you add a load bearing ridge beam (not a 2x8) there is a lot of work to get an old sagging roof to follow a heavy straight beam, not to mention many roof ridges aren't all that perfect from the day they were first framed.

If you don't add a weight bearing ridge beam there is a limit to how high you can go with your rafter ties (ceiling joist placed above the normal location at the top of the walls) and you'll have a fairly sizeable flat rather than a fully vault.   Without a load bearing ridge beam (essentially keeping the 2x8 you already have at the ridge) there is a dramatic reduction in load bearing capacity for the rafters the farther you push the rafter tie up closer to the ridge.  A code book with load tables will list the allowable span for various rafters and in the fine print you'll see the reduction in span for using rafter ties. 

I recently vaulted a room with 2x6 rafters and it required adding two 2x8's for every existing 2x6.  The connection between the rafters and rafter ties is very important and code is specific about the size and number of nails. 

If a room is gutted and all the nails penetrating the roof sheathing are clipped off, it will still take an experienced remodeler the better part of two days to add the extra framing if everything goes perfect and the new lumber doesn't have much of a crown.  Rarely does that happen and on average you may spend the better part of a week.   If you are inexperienced the time can quadruple easily.

In cases where the existing rafters are sagging a great deal you'll have to go with new rafters above what's indicated in the load tables since you're having to bend what's existing into submission.  In the worst situations I've had to sister 2x12's onto existing 2x4's and use a hyrdrolic hand-pumped ram to force the new rafters into position a little at a time. 

Nothing about your project is rocket science, but none of it will be easy and you have to do it right or your house will have structrual issues that are much harder to fix down the road.

I think it's a good idea to hire an engineer to go through things with you and show you what's involved.  Don't skimp on anything and expect to have a steap learing curve.


If I could edit my location it would say I'm now in Reno :-)

Hope all engineers are not the same..... (post #207130, reply #3 of 7)

I really appreciate your input on my vaulted ceiling project. I spoke with a man that does timber framing today and he was talking about putting a 10x10 beam under my current 2x8 ridge beam and putting posts in at each end of the beam to carry the load to the foundation.  it sounds nice but I'm sure it's very expensive. I love the idea of seeing some large beams in the house, but unsure how that translates to helping those 2x6 rafters not sag. He probably has plans to put in some rough cut collar ties or something in the way of timberframing. The rafters are in pretty good shape and a stringline tells me they are actually in very good alignment!

 I had a terrible experience with an engineer who drew me plans for an addition last year. So I'm a little on the fence with hiring another. I will however look into the load bearing capacities that you mentioned. I'm in no rush and will do it right no matter the cost.

The ridge beam won't keep (post #207130, reply #4 of 7)

The ridge beam won't keep your rafters from sagging. It will keep your roof from pushing out the wall. If your rafters are to small for that span, then you will need another beam to lessen the span, or bigger rafters.

The ridge beam won't keep (post #207130, reply #5 of 7)

The ridge beam won't keep your rafters from sagging.

It will keep the ridge from sagging.  But if the knee walls are currently supporting the rafters mid-span (which sounds like it must be the case, unless the rafters are made of something better than standard lumber) he'd need either heavier rafters or purlin plates.  Pulin plates might be simpler and more in keeping with the timber frame theme.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

What you really need is a (post #207130, reply #6 of 7)

What you really need is a good architect. One who is experienced in working on home remodels. If you can find one with good hands-on building experience, so much the better. Architects can usually size the new support members themselves and fit those dimensions into the overall design appearance. An engineer may have to be hired to confirm the architect's structural design depending on the complexity and your local code enforcement department. Engineers, in general not always, are unimaginative when it comes to aesthetics and tend to have a bit of tunnel vision. 

Some great ideas here!! Thank you! (post #207130, reply #7 of 7)

My cousin is a contractor and he was planning on not putting in a new ridge beam but mentioned using plywood and changing the interior pitch coupled with 2x? to almost make a new truss under these 2x6 rafters. I personally like the idea of putting in a new ridge under the current 2x8 one. I do think this helps with the outward force on the 19' of wall. I talked to a salesman at a lumber company and he said he thinks that I may end up going with a triple 19'  14"LVL ridge beam and 2x12 rafters. (not sure what his plan is to help those 2x6 rafters from sagging, may be attach them to the 2x12's?) But he is going to talk to a truss company engineer to check out loads etc to see if this would work.   All in all I still like the idea of timberframe but I have lesser contacts for that type of construction.