Thread: Rafter Alignment

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Jeff,

It's a requirement in the IBC: " 2308.10.4 Ceiling joist and rafter framing. Rafters shall be framed directly opposite each other at the ridge. There shall be a ridge board at least 1-inch (25 mm) nominal thickness at 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."

... but not in the IRC.

Go figure.

The code is what should be followed, no doubt.... however, I talked over the staggered rafters at length with an engineer once and he was convinced it isn't a problem.... I see older houses like this all the time and don't call it.

I don't think I've seen it on a house newer than 1940.... it's one of those things that makes me wonder.... even if it was okay, why? Was the framer just bored?

It is good practice to have the rafters aligned on both sides of the ridge. That way the horizontal loads are transferred from the end of one rafter to the opposing rafter directly through the ridge member so the ridge member is simply being pinched between the opposing rafters.

If the rafters are not aligned the ridge member is placed into bending and shear between the rafters. In this case the ridge member must be designed to resist the bending and shear stresses. Where a 1X ridge member may be perfectly fine with the rafters aligned on both sides it may be woefully inadequate when the rafters are offset by 8". (That's the midpoint of the typical 16" spacing.) If the ridge member has a large knot located where the bending or shear stresses are high it has a greater chance of failure.

Very often the bottom ends of rafters are nailed to the ceiling joists so the ceiling joists will prevent rafter spread. To be able to nail the rafter to the joist the opposing rafters cannot have more than a minimum offset.

Jeff,
Were you able to walk the roof? Did you notice anything unusual at the ridge (e.g. wavy, sagging, etc.)?

Didn't anyone notice the painted lines on the decking in the photo???????

The manufacturer has a stamp on each panel stating that the opposite (smooth) side should be down. I don't lnow why anyone would instal it with the smooth (slicker) side up as it would make it unsafe for the roofing installer. The manufacturer coats one side with a vapor barrier coating and installing with the wrong side out could allow for internal rot of the OSB itself.

Regardless of the reason, the manufacturer DOES tell you which side to place to the up.



Also, is that a rafter repair to the right of the incorrectly installed OSB?

Originally Posted by Jon Randolph

Didn't anyone notice the painted lines on the decking in the photo???????

Didn't you notice the stamp?

The stamp goes down. And it is.

Jerry,

Look at the first photo. There is no stamp and the painted marking lines are usually on the side opposite of the stamp.

Originally Posted by Jon Randolph

Jerry,

Look at the first photo. There is no stamp and the painted marking lines are usually on the side opposite of the stamp.

Jon,

Look at the second photo, there is a stamp ... with the chalk lines.

Jeff:

I started out in the business in the mid-70's as a framer's helper. After framing about 100 houses I and another helper were allowed to frame a gable roof on a big two-storey house. We didn't install the rafters opposing one another, though we had been taught to do just that.

The foreman, a gruff old German named Art Koenig, saw what we had done, climbed up the ladder with his rig axe, and proceeded to knock the whole damned thing down to the ground. He then sent us home for the rest of the day to think about it. On that next payday we found the cost of the materials for that roof deducted from our checks.

After that we always opposed all rafters whether at ridges, hips or valleys. To do otherwise would have meant our jobs.

OK, so it's not in the written code. It is in the unwritten code for real carpenters. And yes, there are still a few of them above ground.

Aaron

Jerry,

No disrespect as you have been doing this much longer and undoubtedly have more experience and knowledge than I.

Is it possible that the blue line in the 2nd photo is either the manufacturer painted edge or a chalk line snapped by the person who installed the decking. And typically (like I said) the painted marking lines and stamp are usually on opposite sides.

If you actually blow up that photo, I believe that I can see the H-Clip along the blue line leading me to believe that it is the painted edge.

Originally Posted by Jon Randolph

Is it possible that the blue line in the 2nd photo is either the manufacturer painted edge ...

If you actually blow up that photo, I believe that I can see the H-Clip along the blue line leading me to believe that it is the painted edge.

Yep, I see that H clip now too.

aaron,
it is written in the code that rafters be opposing each other and i call it when they don't. i framed for 25+ years and had a similar experience to yours. a little 12 ounce therapy will make the scars go away.

Originally Posted by brian schmitt

aaron,
it is written in the code that rafters be opposing each other and i call it when they don't. i framed for 25+ years and had a similar experience to yours. a little 12 ounce therapy will make the scars go away.

Brian:

Wouldn't it be nice if they trained tradesmen that way these days? Well, on second thought, we might be out of a job . . .

Aaron