roof rafters - no ceiling

[jonathanwilkins]

I'm working on a framing plan for a customer - the house has a very large 12/12 pitch roof and much of the 2nd floor is located inside of it. The living room of the house, on the plans, shows a vault from the exterior walls going flat at the same height as the 2nd floor ceiling. The longest rafter span (to a king rafter) is ~21'. There is also no way to support the ridge as it is over the living room.

End result is I can't use an i-joist rafter because there is no where to support a structural ridge, conventional framing doesn't even come close to working b/c the lack of ceiling makes the rafters way out of span. I thought about designing the top plate as a beam but can't get it connected at the ends.

Any ideas?

 

[vandede427]

tell the client something has to give. if it doesn't work, it doesn't work.

 

[Teguci]

scissor trusses?

 

[msquared48]

If the floor of the 2nd floor is within the rafter space, then why not use the floor joists as collar ties? Just have to have the floor joists and rafters at the same spacing. No need for a conventional ridge beam then.

Mike McCann
MMC Engineering

 

[apsix]

Mike

I don't think that the 2nd floor extends over the living room.

 

[msquared48]

apsix:

The OP said:

"the house has a very large 12/12 pitch roof and much of the 2nd floor is located inside of it. The living room of the house, on the plans, shows a vault from the exterior walls going flat at the same height as the 2nd floor ceiling."

I still see a collar tie situation here, even with a flat vaulted ceiling in the living room, the ceiling of which is the second floor.

Mike McCann
MMC Engineering

 

[msquared48]

Correct me if I am wrong, but I just see an "A" shape collar tie here, with the tips of the "A" supported on the exterior walls of the residence.

Mike McCann
MMC Engineering

 

[jonathanwilkins]

msquared48...you're correct. The (for example) left leg of the "A" is supported on the exterior wall. The right side, though, has ceiling joists at the leg in addition to the rafter. The vault is only on one side.

The collar tie is the ceiling joist for the 2nd floor, the floor joist will be lower and never come in contact with the rafter.

Scissor trusses aren't an option...customer does not want to use them as they'd have to be 2 pieces + lots of overframing as well.

 

[Stillerz]

sketch here would be great

 

[Stillerz]

Can you use some "fake" beams over the vaulted area to tie the load bearing wall back to your second floor diaphram?
I have done this several times in cottage style houses that I have framed.
I'm still not clear as to what you are describing.
I also cannot think of why you cannot use a ridge beam. I have installed ridge beams (LVL 3 or 4 plies, or glulams) that spanned 48'-50' supported by wall framing in the gable ends of the house.

 

[BAretired]

I agree with Stillerz. A sketch would be helpful.

BA

 

[paddingtongreen]

It sounds as though there is a mechanism here, with the rafters kicking the top of the wall outward because of the lack of ceiling joists. If relying on a ridge beam, it would have to be capable of resisting a horizontal kick.

Solution might be to run a horizontal beam along the wall to carry the horizontal loads out to the sidewalls.

Timing has a lot to do with the outcome of a rain dance.

 

[msquared48]

FYI all:

There is no such thing as a "roof rafter" - that's saying the same thing twice, double dipping, repetition for emphnasis, bad termonology, etc. It's a term devised and misused by Architects, and, consequently, misused even by some of us structurally. Don't do it. It also implies that there is such a ridiculous thing as a "floor rafter".

A "rafter" is the proper terminology, and refers to sloping members framing between ridge beams, hips, valley members, and wall top plates.

A "roof joist" would refer to a flat or tapered member framing between the same.

Educate these Architects! Don't let them mislead you! This is a conspiracy!

Mike McCann
MMC Engineering

 

[BAretired]

I am wondering why we have not seen a drawing of the problem at hand. Post a sketch and we will be happy to assist you in any way we can.

BA

 

[apsix]

Slow news day Mike?

Of course there is such a thing as a 'roof rafter'. You might not like it, it may be bad terminology, the 'roof' word may be redundant, but that doesn't mean that it doesn't exist.

 

[BAretired]

I think the problem is self explanatory. Simply provide a glulam beam spanning from point 'A' to point 'B' as shown in the attached sketch and, Bob's your uncle, the problem is resolved.

BA

 

[msquared48]

apsix:

The term may be accepted by some, but that does not mean that it is not a morph of the original accepted nomenclature. Reinventing the rule to your own scruples does not change the rule.

Look at the Architectural Graphics Standards, or the Douglas Fir Use Book.

Mike McCann
MMC Engineering

 

[paddingtongreen]

I'm with Mike. We should be correcting people who use these bastard terms because they obscure communication. If a perfectly adequate term for something exists, and suddenly someone speaks of it under another name ~ total confusion.

So, what other kind of rafter is there? The use of "roof rafter implies that there is.

It was tough enough when I came to the States and had to convert from "siding rails" to "girts", I hope they are not now called "wall girts".

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[msquared48]

You might also check out this link...

http://www.buildeazy.com/glossary/

Mike McCann
MMC Engineering

 

[apsix]

Don't get me wrong, I'm all for using the correct terminology, but eng-tips is not the place to get too pedantic. The national and regional differences means our own preferred term may not apply everywhere.

Seeing the term "There is no such thing as a...." tends to fire me up.

BTW Michael, I'm sure you meant 'side rails', siding is a US term.