Second floor addition over first floor with cathedral ceilings?

[bodvar]

I have a rancher style house with cathedral ceilings and I want to add a second floor addition over them (keeping the cathedral ceilings as they are.) Any thoughts? Can I build a small section of framing onto the existing framing of the exterior walls high enough to get level with the top of the existing roof and then add floor joists and framing for the second floor above that (this is assuming that I can shore up the support beams in the existing ceiling well enough to support the second floor joists)?

Any thoughts on this would be greatly appreciated.


Bodvar

 

[hokie66]

Don't even think about supporting the new floor on the existing sloped roof framing. The floor joists would have to clear span the house. This could get complex, so best to retain the services of a structural engineer.

 

[JAE]

You need to get an engineer to look at the specific conditions, framing etc. This site would not be well suited to give you a definitive answer.

 

[msquared48]

I third the opinion.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MiketheEngineer]

Fourth

 

[bodvar]

Thanks for the opinions guys. fwiw I have an engineer to check things with and always do before I finalize any plans. But what I'm after here are just some opinions or maybe comments from someone who has done something similar with regards to the concept. This is a very low pitched roof (maybe 3/12 in pitch) and has a ridge beam (roughly 12 x 4's over an 18 ft. span) that carries the upper end of the rafters (roughly 4 x 4's over an 8 ft. span) on top of it - hence the Cathedral ceiling. Obviously there is no ridge board here - this is much more robust to begin with. It was built in the 50's and is made out of wood (vertical grain fir with cedar behind) that I don't want to disturb as it is quite beautiful and there is lots of it.

Perhaps I should be asking only for comments from anyone who's ever been involved in a similar scenario - what did you do? But I don't want to limit my question that way. I'd like to hear from anyone that has an innovative idea.

Anyway, enough said - looking forward to hearing what you guys might come up with (hopefully a little more creative than being directed to consult with an engineer.) If not - that's fine too.

 

[MiketheEngineer]

Balloon frame your new walls from first floor to new roof.
Install ledgers
Install clear span floor joists - might be LVLs or TJIs
Install SOB or other approved sheathing.
Don't touch exsting celing.
Before you begin, check that footins can carry additional load.

That is the basics....

 

[msquared48]

OK:

A thought here... The loading for floor is 40 live plus 10 to 20 psf dead, depending on whether or not you have gypcrete on your floors. Probably not. So figure a normal 50 psf loading for your new floor.

The dead load of the existing roof structure is probably 12 to 15 psf (unless you have a tile roof, with a live load of 20 psf. You ccan get extra capacity of 3 to 5 psf in the existging roof structure by removing your existing roofing material. If you are in a region that has snow load too, if that design roof snotw load is equal to or greater than 40 psf, you MIGHT be able to post down to the existing roof scissors trusses, but that would be the call of the structural engineer you ARE going to consult.

The design would still be subject to the other limitations mentioned above.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[dicksewerrat]

I think you should make a drawing of what the outside of the house will look like before you do anything. The house may not look as good as you think it will.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[hokie66]

Mike,
He said he has a ridge beam and rafters, not scissor trusses.

 

[msquared48]

Sorry. Brain f&*(.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[bodvar]

Thanks guys, I really appreciate your input. I think MiketheEngineers' idea is bang on. Everyone around here does everything via platform framing and hence my frame of reference to frame up from the existing walls. But I can see how balloon framing from the first floor up would be a great way to do this. The look of the additional beams that I could use would probably complement the existing woodwork very nicely too.

Intuitively seems to me that taking the existing roofing material off of the parts of the roof that get covered is a good idea too - wood likes to breath. And as you say it will probably save some weight as well (~2.0 psf for asphalt dead load probably makes up for the second level sub-flooring in those areas.)

 

[hokie66]

Sounds like a plan, but where do the long studs go? Outside or inside the existing wall to miss the existing plate?