catheral cielings ridge beam

[mark handler]

 

[Glenn]

Have you read the rafter tables?The prescriptive sizes of rafters are based on ties and ceiling joists being used.

What do you do then ties and ceiling joists are not used?

Disagree.

R802.3.1

"...Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice."

There is nothing special required of the rafter..."these rafters"...as in...the same prescriptive rafters discussed earlier in the section detailing rafter ties. Nothing special about the rafters when "ceiling joists or rafter ties are not provided". The "wall or girder" however, must be designed using accepted engineering practice. A plf load table from an engineered beam mfgr (LVL, LSL, Glu-lam) is not too hard to use.

Nothing fancy, unless you make it fancy. We approve these prescriptively on small residential projects, otherwise wind drives engineering.

 

[mark handler]

No. you agree go back and read the posts.

what I have been saying all along is "designed in accordance with accepted engineering practice."

 

[fatboy]

"designed in accordance with accepted engineering practice."

And I for one, do not think that requires a stamp necessarily. If I can calculate a beam using section modulus and F/b, uniform loads, that is accepted engineering practice. It is a mathematical equation, not engineering.

 

[Glenn]

No. you agree go back and read the posts. what I have been saying all along is "designed in accordance with accepted engineering practice."

I disagree that the rafters need special design. The rafter spans are still valid even without the collar tie/rafter tie. In fact, there is less stress on the rafters under a ridge beam situation. With rafter ties, you can raise them up to one third the height of the rafters. When they are raised, the thrust force is resisted within the span of the rafter. This puts additional bending stress on the rafters, beyond just the live load supported. This phenomenon does not occur when they are not installed and a ridge beam is in place. Therefore I would argue the rafters are under less stress (potentially) than when constructed with rafter ties that could be raised.

Only the beam must be designed.

I also disagree with this statement:

"you cannot use prescriptive and non prescriptive on the same assembly."

R301.1.3 engineered design

"When a building of otherwise conventional construction contains structural elements exceeding the limits of section R301 or otherwise not conforming to this code, these elements shall be designed in accordance with accepted engineering practice. The extent of such design need only demonstrate compliance of non conventional elements with other applicable provisions and shall be compatible with the performance of the conventional framed system.

I consider the beam to be an element of the roof assembly. Performance is the goal...regardless of the mix of prescriptive, engineered or tested validation.

 

[mark handler]

Glenn how do you justify, codewise, not putting in rafter or ceiling ties without engineering something?.oras some say "mathematics"? Of one or more elements?

 

[Glenn]

Glenn how do you justify, codewise, not putting in rafter or ceiling ties without engineering something?.oras some say "mathematics"? Of one or more elements?

???

Please note:

Only the beam must be designed.

 

[mark handler]

???Please note:

Ties required by code.

What happens is ties are not installed?

 

[jwilly3879]

The designed ridge beam basically creates 2 shed roofs, there is no outward force on the walls, just vertical. In my area the rafters usually sit on top of the ridge beam, not hung from it and they are strapped over the peak.

 

[Mr. Inspector]

"...Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice."

So even if a simple 2x4 framed wall that is supporting the ridge needs to be engineered? But a wall supporting the top of a shed roof doesn't?

 

[fatboy]

"girder designed in accordance with accepted engineering practice."

Again......... if you can do the math, it is accepted engineering practice, but not practicing engineering. Does not, will not need a stamp in my jurisdiction. It's a cathedral ceiling, not unlike the many tens of thousands, that have stood for centuries, all lacking an engineers approval......

 

[mark handler]

tens of thousands, that have stood for centuries......

Tens of thousands of buildings stand today that would not meet the current building codes, are you saying we need to scrap the codes because these examples still stand?

and by the way, there are laws about practicing Engineering without a license...

 

[fatboy]

I'm not practicing......

Have you noticed you are the lone ranger on this issue?

And I'm done.

 

[Glenn]

It's called empirical evidence. Mark...if everything had to be drawn up in an office by an engineer the world would never have been civilized. I am out of this thread, as I don't feel you are completely reading the posts before you respond. I feel you aren't taking this conversation seriously. Enjoy your battle, but know that many are using the span tables provided by beam manufacturer's and the only "engineering" being done is figuring out PLF. Sorry...not something worth defending your license over, but you are welcome to your opinion.

 

[mark handler]

Sorry...not something worth defending your license over, but you are welcome to your opinion.

Are you implying my license is at risk over this?

I don't think you are reading the posts, you never did answer what you do to mitigate omitting the code required ties....

 

[mark handler]

I'm not practicing......Have you noticed you are the lone ranger on this issue?

And I'm done.

I thought the pig enjoyed demud

I guess that's only when you're sure your right

 

[mark handler]

It's called empirical evidence. Mark...if everything had to be drawn up in an office by an engineer the world would never have been civilized. I am out of this thread, as I don't feel you are completely reading the posts before you respond. I feel you aren't taking this conversation seriously. Enjoy your battle, but know that many are using the span tables provided by beam manufacturer's and the only "engineering" being done is figuring out PLF. Sorry...not something worth defending your license over, but you are welcome to your opinion.

Empirical clause, is that the I've been building it this way for forty years, ,clause?

 

[Yankee]

Are you implying my license is at risk over this?I don't think you are reading the posts, you never did answer what you do to mitigate omitting the code required ties....

I still am reading it this way,"R802.3.1

"...Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice."

So, , nuff said, we aren't making any headway and I shall agree to disagree.

 

[mark handler]

I still am reading it this way,

accepted engineering practice..

Not the non-existent Empirical clause

 

[tmurray]

I still am reading it this way,"R802.3.1

"...Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice."

So, , nuff said, we aren't making any headway and I shall agree to disagree.

So, are talking about picking an engineered product out of a table, or allowing a layperson to attempt engineering calculations?

 

[jar546]

Am reading this entire thread for the first time and see that it got a little testy but yet no resolution. When I read some of the comments I think I am seeing where the intent of the post and the perception does not agree, even though in general, everyone seems to agree for the most part.

I would like to continue this great thread by posting what I am getting from this and this is also my opinion. I will use numbers to make it easier to respond to and by the way, I am really loving the great information and opinions being shared.

1) If you use a ridge board and not a properly sized ridge beam, you must have rafter ties in place to resist thrust. I think we all agree on this. Correct me if I am wrong.

2) If you choose to use a ridge beam and support the weight of the roof between the ridge and vertical exterior walls, no rafter ties are needed because there is no outward thrust under normal conditions.

3) There is the element of wind that creates outward pressure on the leeward side that creates an issue for designs with ridge beams and no rafter ties that needs to be addressed.

4) If the design for the ridge is to support it prescriptively with a 2x wall that transfers the load to the foundation, that would not need to be engineered because the wall and any headers can be designed prescriptively.

Please let me know where we stand on my opinions and I will be happy to clarify any of them.

 

[globe trekker]

I wonder if "Rick18071" ever got a satisfactory answer to his OP & Post # 3?

The OP seems to have turned in to another "Stairway to an Attic" topic.

We ARE trying to help answer questions on here aren't we? ...and we wonder

why no one wants to become a Sawhorse, or to engage in to topical discussions.

Let's play nice folks!

.

 

[GBrackins]

jar

#1 agree

#2 agree

#3 agree, see Table 3.6 & Table 3.6A of the Wood Frame Construction Manual for connection requirements

#4 agree, See Table 3.29 (A-D) for prescriptive ridge beams based upon ground snow load

 

[Yankee]

So, are talking about picking an engineered product out of a table, or allowing a layperson to attempt engineering calculations?

I am talking about picking an engineered product out of a table after having determined the loading. I personally would not have my office document the use their(our) own calculations for the approval file as I think that would be a practice that might invite liability.