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Rafters & Ridge Board (again)


Terence McCann
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Originally posted by MMustola

If they are not supported properly they may crack over time.

FWIW, I see that configuration commoly in older houses in my area and don't believe I've ever seen a rafter spliting (at least obvioulsy) because of it.

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Hi,

I see it on older homes a lot too. Around here, it's common to find a piece of 1 by 4 tongue-and-groove planking used for the ridge board with the heels off the board. Most of those old houses have 2 by 4 rafters spanning more than 16 ft. that are overloaded with several layers of roofing and sagging more than my gut in the center.

I've found maybe, if memory serves, 3 rafters that have split out at the end because of this.

Doesn't make it OK, I know, but I wouldn't expect to see a roof collapse because of it......ever. Could be wrong, have been many times, still....

ONE TEAM - ONE FIGHT!!!

Mike

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I believe the intent of the code is to give full support to the butt end of the rafter. I agree that is is not common to see cracks. Also, it's not a fair comparsion to judge want may happen with today's wood by looking at old houses with old growth wood.

If you have to tell a client why the ridge board needs to be repaired I think explaining that the rafter may crack if not properly supported is an accruate statement.

Do you disaggree?

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Originally posted by MMustola

Also, it's not a fair comparsion to judge want may happen with today's wood by looking at old houses with old growth wood.

Do you disaggree?

Yeah, I do. Prof. Paul Fisette, my predecessor on the Building Science forum over on the Journal of Light Construction, runs the Wood Technology Department and is the Director of Building Materials Technology and Management at the University of Massachusetts, Amherst. He once told me - on JLC, I believe it was - that the idea that old growth wood is somehow stronger and more durable than new timber is a myth. He said that research has not substantiated any provable improvement in strength/durability of old growth timber over new timbers.

Now, I'm not an educated guy. Hell, I barely made it through 1st year math in high school. So, when Paul Fisette tells me something about wood, I tend to take it to the bank and make a deposit.

ONE TEAM - ONE FIGHT!!!

Mike

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Originally posted by MMustola

I believe the intent of the code is to give full support to the butt end of the rafter. I agree that is is not common to see cracks. Also, it's not a fair comparsion to judge want may happen with today's wood by looking at old houses with old growth wood.

If you have to tell a client why the ridge board needs to be repaired I think explaining that the rafter may crack if not properly supported is an accruate statement.

Do you disaggree?

I not only point out issues, I give my clients my best judgement of how likely I believe the potential problems might arise. (I've already prepared them in my inital talk to understand that uch in the home isnepction biz is subjectiove and involves judgement calls)

So, in tha case at hand, I'd point out the deficiency, tell them the reason for the concern, tell them one possible fix (also mentioning different contractors might take different approaches - SOP disclosure, again) and tell them that I believe the likelihood of any rafter splitting is low. I'd recommend they monitor the situation and repair if needed. [something with a more difficult/expensive fix woulkd be handled differently]

If they were exhibiting signs of being awake and aware and reasonable, I might also add: "Unless some splitting actually starts, I'd have to really bored before I got around to this one"

FWIW, I use code to inform my analyses: but I've seen far to many problems where code was followed, and far too many code shortfalls where there were no problems, to assume that code is any sort of reliable predicter of performance.

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Hi all,

I'll throw in this idea. It is hard to tell, but lets say that the ridge board is a 2x6 or 2x8. For the support of the roof perhaps only a 2x6 is necessary. The extra unsupported part is merely for the increased space for insulation.

Obviously the heel should still be supported----just an observation as to how it got to be this way.

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Originally posted by charlie

. For the support of the roof perhaps only a 2x6 is necessary. The extra unsupported part is merely for the increased space for insulation.

Obviously the heel should still be supported----just an observation as to how it got to be this way.

I don't think the ridge board is needed to support the roof - lots of old houses don't have any ridge board - the rafters just butt together.

I think the ridge board (as opposed to a structural ridge beam) is mainly intended as an aid to erection - (remember, we didn't have viagra until just a few years ago) [:-bigeyes

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It's hard to see without enlarging and altering the contrast

That's the best I can do with the Firefox browser. I can't do the link thingie to a larger image.

...is that a mortise and tennon connection at the ridge? If so, that's a new one on me.

Kind of - it's a fork & tenon joint. The one in the center of the image failed.

This is what I have found in my region:

2007110142646_rafterdates.JPG%20

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OK,

Thanks Bill, I understand now.

Gary, if that that's a tenon (what most non-woodworkers will refer to as a tongue) on the end of that rafter, and it extends up into a square slot (mortise) cut in the end of the beam that houses it on 3 sides, the correct term, and the one most woodworkers will use, is an open-mortise-and-tenon joint, although a tongue-and-fork joint or fork-and-tongue has been used by non-woodworkers to describe these joints as well.

I'd have expected to see a mortise-and-tenon joint used in a timber-frame structure. In his book, The Timber-Frame Home, Tedd Benson, desribes their use for rafter joints at the ridge. I've just never seen one used in a house - at least not in a "modern" house. Of course, Bill works with very old buildings, so he probably sees them all the time. I've been in what is believed to be the oldest surviving building in Washington state - a log cabin up on Whidbey Island owned by some friends of mine - but it only dates to 1855. That would be considered a kid compared to some of the buildings Bill looks at.

ONE TEAM - ONE FIGHT!!!

Mike

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Mike & Bill:

One of the coolest things about this forum is how people express their feelings with respect. You two exemplify that.

Since I come from an engineering bent, I may well have a different terminology. The following link is an example of where I come from:

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JSENDH000125000001000003000001&idtype=cvips&gifs=yes

Thanks

Originally posted by inspecthistoric

Strictly speaking, I believe that's called 'Fork and Tongue'

That's what I used to call it until I was scolded by folks that have access to, and study, primary documents pertaining to old buildings. Only recent generations refer to a tenon as a "tongue".

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Ah, so Grasshoppa. I understand now.

I would have loved to have been an engineer. I just couldn't get past the math. My brain refuses to comprehend it. Just trying to understand the numbers in the service charges on a bank statement makes my head hurt.

When I went through the SF Engineers Q Course, they provided us with a self-study workbook that teaches one mathematics. It is designed to teach you math even if you've never done it in your life. It takes you from 1 + 1 = 2 up through basic calculus and one can work one's way through it in about 2 days. My math comprehension is so bad that I have to break it out every year or so and force myself to work my way through it all over again. Then, for a few months, I'll remain somewhat competent at math until it's lost again, and I repeat the cycle. It's very frustrating.

I cudda been a cointenda!

OT - OF!!!

M.

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  • 2 years later...

When I got out of HS I was going to be a ski racer. Not. Then, a couple of years later, got suckered into going to college to become a doggie doctor. Not. But, I had to start out taking bonehead math at college cause I forgot it all. I busted my ass and got a lot of A's, only to forget it all 3 weeks later into the next semesters teachings. Inappropriate hang glider landing got me into an insurance claims investigation job for 25 years that resulted in downsizing me out. Went to take a test for getting on with CalTrans that had a ton of 9th grade level algebra in it. I ate it big time and got a speeding ticket on the way home. It's turned out that it has all been the Lords way of telling me I am supposed to be a starving home inspector.

And the tradition continues. My son only got one B the entire time he was in HS and that was in woodshop. Oh well. He will graduate from Davis with one of the worthless degrees in mechanical engineering. Ah, the rest of his HS grades were all A's. Poor guy.

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