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jonathanwilkins (Civil/Environmental) (OP)
1 Oct 09 14:11
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 (Structural)
1 Oct 09 15:24
tell the client something has to give. if it doesn't work, it doesn't work.
Teguci (Structural)
1 Oct 09 16:51
scissor trusses?
msquared48 (Structural)
2 Oct 09 2:22
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 (Structural)
2 Oct 09 3:42
Mike

I don't think that the 2nd floor extends over the living room.
msquared48 (Structural)
2 Oct 09 3:50
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 (Structural)
2 Oct 09 4:33
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 (Civil/Environmental) (OP)
5 Oct 09 11:58
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 (Structural)
5 Oct 09 13:17
sketch here would be great
Stillerz (Structural)
5 Oct 09 13:33
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 (Structural)
6 Oct 09 11:32
I agree with Stillerz.  A sketch would be helpful.

BA

paddingtongreen (Structural)
6 Oct 09 14:10
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 (Structural)
6 Oct 09 20:57
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 (Structural)
6 Oct 09 21:21
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 (Structural)
6 Oct 09 21:31
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 (Structural)
6 Oct 09 22:06
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 (Structural)
6 Oct 09 22:21
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 (Structural)
6 Oct 09 23:50
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 (Structural)
7 Oct 09 0:28
You might also check out this link...

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

Mike McCann
MMC Engineering

apsix (Structural)
7 Oct 09 2:34
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.
 
Stillerz (Structural)
7 Oct 09 10:34
Man, someone had a bad meeting with an Architect recently!!! (by the way, at our office we call them "A's"..can't even say the full word).
I've never seen someone get so pissy about a little misnomer.
Do you also get pissed when someone says "footer" instead of "footing"?  
msquared48 (Structural)
7 Oct 09 13:28
If this is common and accepted terminology in AU, the UK or other countriues, my appologies.

My point was not made in anger.  If you construed that, you're wrong.  I am a stickler though on using proper English as well as proper technical terminology for what I perceive is my profession.  It was merely meant to educate.  Take it as you will.  No worries, and no offense intended.

Mike McCann
MMC Engineering

paddingtongreen (Structural)
7 Oct 09 13:50
Not an accepted term in the UK, or not before I came here.

Apsix, I must have been stuck in Mid-Atlantic, I intended to write, "Sheeting Rails".

I thought we were just passing time, waiting for a sketch of the problem, especially with all of this ambiguous terminology floating around.

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

BAretired (Structural)
7 Oct 09 14:08
Quoting a portion of the definition from the glossary of building terms which Mike introduced,

Quote:

One of a series of structural members of a roof designed to support roof loads. The rafters of a flat roof are sometimes called roof joists.
Personally I would not call a roof joist on a flat roof a rafter.  I would call it a joist, but if it can be called a rafter, then maybe floor joists can be called floor rafters.

Just kidding!  I really don't find the term "roof rafter" to be all than offensive.

BA

jonathanwilkins (Civil/Environmental) (OP)
21 Oct 09 21:04
Sorry I haven't posted a sketch, the roof is a hip roof...there is no gable end to post a ridge beam.  That would be too easy.  The main ridge terminates at a point over the vault...no where to post down.

I wound up not doing anything.  The contractor is in an area where engineers aren't required & he "can make it work."  Just thought an engineer could help him.  I'm interested to see if I hear back from him.

Thanks for all the replies.   
BAretired (Structural)
21 Oct 09 22:20
Post a sketch!  We are not mind readers!  You are not fulfilling your obligation, namely to clarify the problem so that we have a clear understanding of it.  We need your input in order to provide intelligent responses.  Otherwise, this whole thread will have been a waste of time.  Move it!!!!!

BA

apsix (Structural)
21 Oct 09 22:42
Use a steel cranked ridge beam.
And, post a sketch.

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