Offset Rafters at Ridge Board

[Bob Hunt]

I had a home inspection with a site framed roof. House was built in 2006. At theridge board some of the rafters were not set opposing each other at the ridgeboard. Several were offset from eachother; some by a few inches. Ridge board did not appear to be wavy; roof line appeared to be straight. I do not find any statement inthe code requiring that the rafters be set opposite each other at a ridgeboard, only that they be framed to a ridge board. Is there a section or requirement that I am not seeing?

[Eric Barker]

Skirting around any code requirements, and based upon my 19 years in this business, as long as the ridge board was a 2X I probably wouldn't have much concern for the offset, particularly with a higher slope.

[Wayne Carlisle]

The requirement for rafters to be opposing each other has been in the I-Codes since they first came out in 2000 but removed that text in the 2009 IRC. However in the 2009 IRC the code refers to an illustration which shows the rafters opposing each other. The intent is there but not the wording.

[Bob Hunt]

Wayne: I do not see any such illustration on chapter 8 (Roof -Ceiling Consruction) of either the 2003 or the 2009 IRC. Neither do I see any wording stating that it is required in the 2003 book. Is it in another chapter?

[Wayne Carlisle]

I have the commentary version so that might be the difference. I''ll look it up on previous versions and try to post.

[Wayne Carlisle]

Okay...I was wrong on the years...it was the UBC that had it and the IRC ommitted the lanquage....Here is an interpretation from the ICC that a friend emiled me.
I will attach the pictures if needed.......

RE: 2009 International Residential Code(IRC)

Section R802.3

Dear Mr. XXXXXXXXX :

In response to your question, per your e-mail of August 29, 2011, we offer the following opinion of the meaning and intent of the code on this subject. It is my understanding that your e-mail poses the following question:

Q:I am really embarrassed to have to admit this but I have been teaching a section of code all wrong. What I need you for is to verify my wrong. I have always taught that rafters shall be directly opposing one another at the ridge. I have looked in 2000 to 2009 IRC and that language is gone. Here is a very old carriage house that if you look closely on not one rafter matches up with the other. Does the IRC require rafters to be directly opposing one another when framed to the ridge board?

A: Yes. Section R802.3 requires the rafters to be framed to each other (directly opposing) with a gusset plate or framed to a ridge board.See Figures R802.3(2) and R802.3(1).


Although when framed to the ridge board, the code does not specifically state “The rafters shall be placed directly opposite each other”.

When using a ridge board if the rafters are not directly opposite each other it is no longer a ridge board but a ridge beam. A ridge beam requires a design in accordance with Section R301.1.3.

This opinion is based on the information which you have provided. We have made no independent effort to verify the accuracy of this information nor have we conducted a review beyond the scope of your question. As this opinion is only advisory, the final decision is the responsibility of the designated authority charged with the administration and enforcement of this code.



Sincerely,
LarryD. Franks, PE, CBO
SeniorStaff Engineer
Codesand Standards Development
InternationalCode Council, Inc.
BirminghamDistrict Office
900Montclair Road
Birmingham,AL 35213
888-ICC-SAFE(422-7233) x5279 phone
205-592-7001facsimile

[Jerry Peck]

House was built in 2006.


The requirement for rafters to be opposing each other has been in the I-Codes since they first came out in 2000 but removed that text in the 2009 IRC.

The 2009 is not applicable to the 2006 constructed home. Nonetheless, though, the intent of the 2009 is to have the rafters framed to each, not sure why they would remove something as clear as that.

[Wayne Carlisle]

The 2009 is not applicable to the 2006 constructed home. Nonetheless, though, the intent of the 2009 is to have the rafters framed to each, not sure why they would remove something as clear as that.

Didn't say it was...but you guys...(home inspectors) always make reference by usually stating something like...not up to current standards. And as far as we know the house could have been built using the UBC regulations... depends on what code the AHJ was under at the time of construction.

Just was making a comment that I thought the text was removed in 2009 because he was asking about the opposing rafters. Came back later and admitted I was wrong and it was UBC that the text was the last code book it was in rather than IRC.

And I agree..they should have never taken the verbage out!

[Bob Hunt]

Wayne: As I read Mr Frank's letter, he states that the IRC definitely requires that the rafters be set opposite each other at a ridge board. This is based on illustratioins that are not part of the IRC, and the IRC does not contain the words requiring it, and it is only his opinion-others may have a differing opinion.

To me this seems to be very convoluted way of stating that the code intended to have the requirement but does not. If the illustrations in the study guide are needed to clarify, then they should be incorporated into the IRC, as well as adding the words. This seems like such a simple solution.

In the meantime it appears to me that the IRC does not require that the rafters be set opposite each other at a ridge board since no words or illustrations are incorported in the document. I have been told by several building code officials, in various words, "If the code does not require it, it is not required. If the code does not prohibit it, it is not prohibited".

I do hope that the ICC incorporates an appropriate change in a future version so that this portion can be as clear and detailed as other sections.

[Jeff Zehnder]

Anyway…

Just to add some fuel to this fire…

The code says what the code says… but I can state from years of field experience this practice was common and accepted in “olden” days (prior to the 70s) in the North and Northeastern areas of the USA. While the code appears to be confusing (from the posts) on this issue if all of the other framing was first rate, I would simply note the condition existed in the general comments of my report and add a comment that this style or method of framing was generally no longer used but I would not likely call it out as deficient. If other area of framing where a mess then I would lump it into the entire category and call for repairs.

[Wayne Carlisle]

Bob, I totally agree with you. I was the one that pointed it out to the instructor that the code does not say that the rafters must be opposing each other. That is the reason for my friends letter to the ICC.I also agree that this is one mans opinion and there may be a 100 more that don't see it that way.

If the rafters are not opposing each other in the field I cannot write that provision up because it is not there. Now if they are so far offset and cannot install collar ties then there my be a problem.

I also agree that this should be spelled out in the IRC like it is in the IBC...



2308.10.4 Ceiling joist and rafter framingRafters shall be framed directly opposite each other at the ridge.
There shall be a ridge board at least 1-inch (25 mm) nominal thicknessat ridges and not less in depth than the cut end of the rafter.
At valleys and hips, there shall be a single valley or hip
rafter not less than 2-inch (51 mm) nominal thickness and
not less in depth than the cut end of the rafter.

[Bob Hunt]

Wayne: The IBC wording certainly leaves no doubt. Since you have some contacts at the ICC, why not suggest to them that they incorporate similar wording? Maybe send them the link to this thread so they can see some of the confusion. Basically it is only a few words additional to the pertinent section.

I presume from the letter in your ealrier post that you are an code instructor in Texas.

[Jerry McCarthy]

From the 2006 IRC Code & Commentary Vol. 1

[Bob Hunt]

Jerry:

The point is that the illustrations are not in the IRC. The one you posted is in a commentary volume, not in the the 2006 IRC book. There are no illustrations in the 2003 or the 2009 books either. I suspect that most states, like WV, adopt the IRC but not the commentaries. If the code council intends for the rafters to be installed opposite each other, it should be stated in the IRC.

[Ray Thornburg]

Without actually being there I would say there is nothing wrong with what you describe. There are many instances where rafters wouldn't directly oppose each other at the ridge.....for instance on Hip ridge with two different pitches...Occasionally it happens at the common ridge usually by an inch and a half from necessity and sometimes someone puts an extra rafter in there that doesn't line up.....not a big problem.....

[Door Guy]

Without actually being there I would say there is nothing wrong with what you describe. There are many instances where rafters wouldn't directly oppose each other at the ridge.....for instance on Hip ridge with two different pitches...Occasionally it happens at the common ridge usually by an inch and a half from necessity and sometimes someone puts an extra rafter in there that doesn't line up.....not a big problem.....

I agree with Ray, can anyone explain how it could be a problem and for what reason? If you have an offset of 1.5" it allows you to face nail both rafters without creating an angle with your nails. I just don't see what the problem would be and have seen this in many pre 1970's construction.

[Matthew Klein]

Are folks overlooking the wording in the ICC fellow's statements? If the rafters are not opposite each other, the ridge structure has to be be a BEAM and not a board. These are two different things. With the rafters being opposite each other, no shear force is being put on the ridge board and the roof load is being supported equally by the rafters. When the rafters are opposite one another, the ridge board, in this case, is acting as a stabilizing and spacing structure. The rafter loads are being transferred only to the walls, with the ridge board bearing relatively little load. If the rafters are not opposite each other, the structure between them is being put in shear and each rafter is bearing the roof load independently. Consequently, each rafter's load is being transferred to the ridge structure AND the walls. Therefore, the ridge structure is a beam and must be designed to carry load. It also needs to be able to take shear forces in addition to bearing forces. As such, the ridge structure (beam) should be beefier than a meer ridge board.

Code or no code, if you do not know for certain that the ridge structure was designed as a beam, you should call it in your reports if the rafters are not aligned. If you happen to know that it was designed as a beam or are credentialled to state that it was designed correctly, you can state that it is not an issue (of course, using the usual wiggle words). BTW, if someone has cut a section our of a ridge BEAM, the issue is more of a concern than if someone cut a section out of a ridge BOARD.

[Jerry McCarthy]

Bob
I was totally aware of what I posted and did so as I thought it interesting that the "IRC Commentary" had that detail in it and yet the IRC Code book did not?
I may well be the oldest framer on this BB and recall as a young apprentice carpenter being instructed that a maximum 1-1/2 inch offset for rafter placement at the ridge was acceptable because gussets could still work in that configuration. As a long time instructor at our community college I found the IRC, adopted from the old CABO One & Two Family Dwelling Codes, to be missing several details only found in the UBC, which to my mind was and still is a far more detailed code book.

[Matthew Klein]

Jerry, your point is a good one about the codes. I recently got into one of those situations where the code stated one time did not include certain language and then in the next round added language for clarification. The issue was about proper flashing of a vertical to horizontal surface, such as decks, balconies and such. Essentially, the two code versions said the same thing except the later version specifically included balconies where they were not included in the earlier version. Both are structurally similar as far as flashing requirements. The builder wanted to argue that it followed the codes of the time, even though the structure was leaking where the flashing should have been installed.

Sometimes, just knowing the codes is not good enough. As an engineer, I believe that knowing the basis for the codes is also important, if for no other reason than to know the limits of the codes. I have also found that knowing the background for codes helps to argue the importance of those codes. A reason usually exists for the varilous code requirements. They are not there simply to make life difficult for the builder, as a number of them seem to think.

[Jerry McCarthy]

You're right Matthew; just knowing the codes is not good enough if you don’t know how, why or when they’re applied. The building codes are a home inspector's road map and show me an inspector, jurisdictional or private sector that doesn't have very good handle on the building codes and I'll show you an inept inspector.

The unspoken secrete in our industry is the big lie about we don't do code inspections! If that's true then just what does a home inspector base their opinion on? Yah, I know, "accepted practices in the construction industry," which is Mongolian speak for building codes. Once you remove the dead-front cover from the home's electrical service panel you're doing a code complying inspection. However, in our industry "code" is a four letter word we have been taught to never udder. Arghhhhh……. :rolleyes:

[Darrel Hood]

Jerry P,
In a post earlier in this thread, you stated that the 2009 requirement does not apply to a 2006 home. This seems inconsistent with your frequent statements in other threads. What do you use as rationale for when to apply a later code and when to not apply a later code?

[Jerry Peck]

Jerry P,
In a post earlier in this thread, you stated that the 2009 requirement does not apply to a 2006 home. This seems inconsistent with your frequent statements in other threads. What do you use as rationale for when to apply a later code and when to not apply a later code?

Darrel,

A 2009 requirement does not apply to a house constructed under a prior code.

That said (and that is true), any newer safety standard recognized by a current code does not make something constructed to a prior code 'safe' or 'more safe' that if it were to be constructed today (I've also said that quite frequently too).

The standard for guard rail openings were 24", then 12", then 9", then 6" and are 4" today (and have been 4" for quite some time now).


The difference is what I said in the above comments is this:
- A house built under a code which allowed a 9" opening in a guard rail cannot have today's code of 4" applied to it (i.e., one cannot make them change the guard rail to meet the 4" opening requirement).
- A house built under a code which allowed a 9" opening in a guard rail ... when the 9" opening was allowed ... is not safe just because the 9" opening was allowed *back then*. *Time* does not make things safer just because a previous standard accepted it *back then*. Today's codes (safety standards) recognize that opening 4" and greater (actually, the wording is 'shall not allow a 4" sphere to pass' means the opening is less than 4", and the load on the guard rail in-fill panel is 50 pounds, so the guard rail needs to be able to not allow that 4" sphere pass with a 50 pound square foot load applied). Because today's code recognize 4" as the minimum standard for safety, then the guard rail built to a code which allowed 9" openings is 'unsafe' because progress has recognized that 9" is 'not safe', in fact, progress recognizes that '4" and greater is not safe'.

The difference is in how you are applying the code. The home inspector is apply the code as a safety standard and anything less safe than what is recognized today is ... well ... 'not safe'.

The home inspector is not applying the code to how the guard rail is to be constructed, the guard rail is already constructed, however, *IF* the guard rail were to be taken down and replaced, the new guard rail would be required to meet the current code of today that the code inspector would be inspecting the guard rail to, and a home inspector who came in later and knew that the guard rail had been replaced recently, the current code would apply anyway.

The home inspector is looking at it from the safety standpoint - the old west guard rails with a 24" spacing 'are not safe' and corrective action should be taken to correct the unsafe guard rail.

When the corrective action is being taken, the code inspector should be checking to make sure it meets current code of less than 4".

See the difference in how and why the different codes are applied?

The home inspector 'is inspecting for code', WC Jerry and I, and others, say that all the time, and if the home inspector knows that the current safety standard ("code") is less than 4", then anything 4" or greater is 'not safe' - and where does the home inspector get that information? From "the code".

[Darrel Hood]

Thanks, Jerry. Now I understand your logic.

[Jerry Peck]

Thanks, Jerry. Now I understand your logic.

Darrel, glad you understand my logic - sometimes I don't even understand my logic. :)

[David Garton]

Except for the occasions mentioned in post #15, most rafters are going to oppose each other anyway, due to the overall layout of the building. If the layout of the ceiling joists are done right then the rafters will oppose each other. A correct layout, in most cases will have rafters opposing each other.

[Garry Sorrells]

Jerry M.,
I like you worked to that spec starting in the 70s, primary reason, as explained to me, was that the collar ties for rafters would work out. Also, general physics of loads and forces. Never had a good reason for layouts that the rafters did not directly lining up. Did what I was told to do the way the boss wanted. I always lined them up when I did a layout, just made sense to me and found it just easier.

[Wayne Carlisle]

Others have stated that the 1 1/2" offset is not a problem.... How are you going to install collar ties? You would have to offset the rafters 3" in order to get the collar ties to install flat against the rafters! OR sister another board onto the tie or rafter to make it be able to attach properly. Now are we starting to have a problem with the way the rafters are offset?

[Garry Sorrells]

Wayne,
The rafter s would be offset 3 inches on center leaving 1 1/2 " between rafters

[Kristi Silber]

Are folks overlooking the wording in the ICC fellow's statements? If the rafters are not opposite each other, the ridge structure has to be be a BEAM and not a board. These are two different things. With the rafters being opposite each other, no shear force is being put on the ridge board and the roof load is being supported equally by the rafters. When the rafters are opposite one another, the ridge board, in this case, is acting as a stabilizing and spacing structure. The rafter loads are being transferred only to the walls, with the ridge board bearing relatively little load. If the rafters are not opposite each other, the structure between them is being put in shear and each rafter is bearing the roof load independently. Consequently, each rafter's load is being transferred to the ridge structure AND the walls. Therefore, the ridge structure is a beam and must be designed to carry load. It also needs to be able to take shear forces in addition to bearing forces. As such, the ridge structure (beam) should be beefier than a meer ridge board.

Code or no code, if you do not know for certain that the ridge structure was designed as a beam, you should call it in your reports if the rafters are not aligned. If you happen to know that it was designed as a beam or are credentialled to state that it was designed correctly, you can state that it is not an issue (of course, using the usual wiggle words). BTW, if someone has cut a section our of a ridge BEAM, the issue is more of a concern than if someone cut a section out of a ridge BOARD.

I've been thinking about this for a while now, and still don't understand it. Whether the rafters are opposite or not, the load (vertical force) ends up on the walls. The horizontal forces on the ridge board are what's different - shear vs. compressive - but either way, the roof load is handled by the rafters the same way. They're like levers, supported on one end by the walls, the weight of the roof pushing down along the rest, causing a horizontal force against the ridge board.

If the ridge board is changed to a beam and supports some of the load on that end of the rafters, there is less horizontal force due to the lever action, so shear isn't so large. It would also make collar ties less necessary. One should be able to tell relatively easily whether something is acting as a board or a beam, I would think.

Does that make any sense?

[Jerry Peck]

One should be able to tell relatively easily whether something is acting as a board or a beam, I would think.

The ridge beam is independently supported by columns, walls, or some other means at the ends of the ridge beam. The ridge beam is also designed as a beam and will be much thicker, possibly a 2x, possibly a doubled or tripled 2x.

The ridge board is sandwiched between the opposing rafters and is supported by the rafter pressing against each other, there is no other support for the ridge board. The ridge board is typically only a 1x as there are no lateral forces trying to bend the board ... that is unless the rafters are not opposing each other, in which case the rafter will bend the ridge board back and forth like a snake (okay, that is an exaggerated visual, but the offset rafters will bend and bow the 1x ridge board).

Yes, one should be able to rather quickly tell whether the there is a ridge beam or a ridge board installed.

Also, with a ridge board, there is an outward force applied to the tops of the walls carrying the other end of the raters, thus collar ties are needed, and rafter ties are needed if the ceiling joists are not parallel with the rafters.

With a ridge beam, which is independently supported, the ridge beam carries the load of the top of the rafters, there is no outward pressure applied to the tops of the walls the other ends of the rafters are bearing on.

[Kristi Silber]

Thank you for elaborating, Jerry. I didn't really explain things, did I?

[Jerry McCarthy]

Now that that subject has been put to bed shall we discuss flying buttresses? :D

[Jerry Peck]

Now that that subject has been put to bed shall we discuss flying buttresses? :D

Once I saw someone really kick someone else's butt big time, and that other butt went flying ... ;) ... but that was only one flying butt. :)

[Garry Sorrells]

Now that that subject has been put to bed shall we discuss flying buttresses? :D

Did you misspell "buttresses" ? Did you mean butt and dresses ?

[Jerry McCarthy]

Medieval rafter ties