It gets tiring after a while- roof framing

[rktect 1]

No matter how many notes, wall sections and details I can get the architect to place on the drawings, it never fails that when a contractor tries to align the new stick built roof to a truss roof, they do this.

View attachment 1798

View attachment 1798

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[Glenn]

The widespread use of engineered trusses is destroying the passage of conventional wood frame construction knowledge from generation to generation.

I feel your pain, as I too deal with this regularly.

 

[fatboy]

Yup, have seen it done dozens of times, just shake my head and walk away, telling them to get me an engineer's analysis.......

 

[Yankee]

What is the issue? It isn't obvious to me.

 

[Mac]

The now 'flat bottomed' rafters have only about half thier strength left. Prescriptive framing wants the rafter ends fastened to the ceiling joists.

 

[rktect 1]

There are at least two issues.

1. The ceiling joists should be nailed to the rafter ends.

2. The rafter heel should be resting on the top plates, not the toe.

 

[SCBO1]

The fix?

Also check the CJ connection at the bearing center wall if the CJ break on a room bearing wall. Is there a space between the CJ's as well or do the reach the other exterior wall with no break?

pc1

 

[rktect 1]

The ceiling joists were lapped and nailed correctly over an interior wall. Just not connected to the roof rafters.

 

[Yikes]

@ Yankee - it's what mac said.

The ability for a beam (or rafter or horizontal framing member) to resist gravity loads is exponentially proportional to the depth of the beam, as it is supported from it's bottom, typically be resting on a plate or on a hanger.

When they cut of the bottom of those 2x8 rafters right near the bearing point, they made it structurally equivalent to a 2x4 rafter that has some useless extra wood tacked on underneath it.

In reality, I may be exaggerating slightly at the present... but the day will come when the wood rafter will want to slowly split apart lengthwise, where the cut was made. Meanwhile, if you asked an engineer to justify the loading, it would require some really complex caculus for a "statically indeterminate strucutre". It would be much easier to simply do destructive testing to establish the rafter beam's structural value.

Steve

 

[GBrackins]

I'm always amazed at how the hurricane ties are usually on the interior side of the wall, yet the continuous uplift load path is on the exterior side of the wall. the connector and load path have to be on the same side of the wall not opposite sides, at least according to Simpson. I don't see any stud plate connectors on the interior side.

 

[ICE]

I'm always amazed at how the hurricane ties are usually on the interior side of the wall, yet the continuous uplift load path is on the exterior side of the wall. the connector and load path have to be on the same side of the wall not opposite sides, at least according to Simpson. I don't see any stud plate connectors on the interior side.

I haven't been exposed to that before. Could you post a link to Simpson's literature that deals with this?

Thanks

 

[GBrackins]

shirely for you .....

http://www.strongtie.com/ftp/catalogs/c-2013/C-2013-p181-183.pdf page 182, note #6. it states that installation on the inside of walls is acceptable. For uplift Load Path, connections in the same area must be located on the same side of the wall.

it was explained to me in a workshop by one of their senior engineers that having sheathing attached to the exterior side of the wall creates the uplift load path on that side. he stated that with the sheathing attached on the exterior and tie on the interior that in a high wind event uplift would cause the nailed side to act as a hinge with the rafter/truss pulling upward separating the top plate from the wall. if the tie is on the interior side (ones that only connect to the top plates) a stud plate connector must also be installed on the interior side to connect the top plates to the stud.

this is the reason Simpson developed the H2A connector as it connects the rafter/truss to the top plates and stud in OVE construction.

 

[GBrackins]

when I was in Florida I had a roof that came off in a storm event (like Florida ever gets those) that pulled the top plates off the walls and laid the entire roof upside down in the back yard. every truss was attached with H2.5 connectors installed on the interior side of the walls to the top plates. the roof was still intact, just upside down.

 

[ICE]

Gary,

There's so much for us to know and so little time to do it in. The Simpson footnotes can be as big as some of the tables that they are attached to.

This latest lesson is an important one and I had no clue. That's why I am here.

I learned from Chris and Glenn a few days ago so it's been worth the entrance fee this month.

Come to think of it, I learned from North Star too and probably a few others.

If it ever gets out what a great resource this forum is, we'll be swamped with members.

You should be careful with some of these guys here.....like Dennis for example.....if I use what I learn from him, people think I know more than I do.

Fatboy and Mark Handler will affect your waistline.

Jeff has a vivid imagination.

 

[GBrackins]

I hear ya, that's why I'm a member. as much as I read and attend I learn more on this site than anywhere else.

 

[rleibowitz]

Just to add a code section to your picture 2009 IRC R802.7.1 Sawn Lumber...Notches at the end of the member shall not exceed one-fourth the depth of the member . The tension side of members 4 inches or greater in nominal thickness shall not be notched except at the end of the member.

 

[Yankee]

@ Yankee - it's what mac said.The ability for a beam (or rafter or horizontal framing member) to resist gravity loads is exponentially proportional to the depth of the beam, as it is supported from it's bottom, typically be resting on a plate or on a hanger.

When they cut of the bottom of those 2x8 rafters right near the bearing point, they made it structurally equivalent to a 2x4 rafter that has some useless extra wood tacked on underneath it.

In reality, I may be exaggerating slightly at the present... but the day will come when the wood rafter will want to slowly split apart lengthwise, where the cut was made. Meanwhile, if you asked an engineer to justify the loading, it would require some really complex caculus for a "statically indeterminate strucutre". It would be much easier to simply do destructive testing to establish the rafter beam's structural value.

Steve

I hadn't seen that before but it makes sense as it is the same issue as having full bearing of the rafter cuts up on a ridge board. ThanksAs to the other issue, there is not enough info in the picture to determine whether the ceiling joists and the rafters must be connected. there may be an alternate way of providing against the rafter thrust. Such as a structural ridge.