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Old 09-25-2013, 08:17 PM   #1
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double top plate question


Hi,

When building exterior walls is it necessary to run the sheathing up to the top of the double top plate? Reason I ask is because I am using rafter ties and part of it covers most of the sides of the top plate so the sheathing wouldn't sit flush.

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Old 09-25-2013, 08:44 PM   #2
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double top plate question


yes, sheathing should run to the top member of the double top plate. hurricane ties are normally attached after the sheathing. sheathing is used as braced wall panels and to provide a load path from the roof to the sill plate.

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Old 09-25-2013, 10:38 PM   #3
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yes, sheathing should run to the top member of the double top plate. hurricane ties are normally attached after the sheathing. sheathing is used as braced wall panels and to provide a load path from the roof to the sill plate.
Ok, so I take it when your figuring your rafters lengths you add the sheathing thickness as well?
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Old 09-25-2013, 10:48 PM   #4
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double top plate question


did this change your overhang? if not rafter length is still the same.

you'll have to account for the sheathing for your bird's mouth notch on your rafters.
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Old 09-25-2013, 11:34 PM   #5
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did this change your overhang? if not rafter length is still the same.

you'll have to account for the sheathing for your bird's mouth notch on your rafters.
when cutting rafters for ridge construction or trusses do you need to add the sheathing thickness to the rafter lengths? Im using a truss roof and I did not add the sheathing thickness to the bottom chord length so that is why I asked about not sheathing the top plate.
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Old 09-26-2013, 07:29 AM   #6
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double top plate question


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Originally Posted by detroittigerfan View Post
when cutting rafters for ridge construction or trusses do you need to add the sheathing thickness to the rafter lengths? Im using a truss roof and I did not add the sheathing thickness to the bottom chord length so that is why I asked about not sheathing the top plate.
I'm not sure you're asking the right questions, but here goes...

In a stick built roof (traditional rafter design), if you're using math to compute rafter length, then whether sheathing needs to be taken into account depends on which way you compute the lengths. There isn't a single way. In the end, it's all about triangles. If your triangle involves the inside edge of the wall top-plate, then no--sheathing does not come into play (other than affecting the birds mouth cut, as GBrackins pointed out). If your formula uses the outside edge of the wall, then, yes...sheathing has to be considered in order for the rafters to fit properly when installed and to have exactly the desired pitch. BTW, John Carrolls' "Measuring, Marking & Layout" book explains rafter calculation brilliantly.

If you have prefab trusses, and you're worried you didn't include the sheathing thickness in the numbers you gave the truss company, then the only impact is on the amount of overhang you'll have. Assuming your roof design provides eaves (and thus has overhang), a 1/2" reduction in overhang will mostly go unnoticed. However, if there are no eaves and the rafter was designed to end right at the outer edge of the building, then the miscalculation is more serious. However, I doubt that's the case.
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Old 09-26-2013, 08:27 AM   #7
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double top plate question


Dang, just how thick IS this siding, that you are so concerned about it?
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Old 09-26-2013, 10:03 AM   #8
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[QUOTE=cortell;1246656]I'm not sure you're asking the right questions, but here goes...

In a stick built roof (traditional rafter design), if you're using math to compute rafter length, then whether sheathing needs to be taken into account depends on which way you compute the lengths. There isn't a single way. In the end, it's all about triangles. If your triangle involves the inside edge of the wall top-plate, then no--sheathing does not come into play (other than affecting the birds mouth cut, as GBrackins pointed out). If your formula uses the outside edge of the wall, then, yes...sheathing has to be considered in order for the rafters to fit properly when installed and to have exactly the desired pitch. BTW, John Carrolls' "Measuring, Marking & Layout" book explains rafter calculation brilliantly.

If you have prefab trusses, and you're worried you didn't include the sheathing thickness in the numbers you gave the truss company, then the only impact is on the amount of overhang you'll have. Assuming your roof design provides eaves (and thus has overhang), a 1/2" reduction in overhang will mostly go unnoticed. However, if there are no eaves and the rafter was designed to end right at the outer edge of the building, then the miscalculation is more serious. However, I doubt that's the case.[/QUOTE

The bottom chord of the truss has to including sheathing thickness.
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Old 09-26-2013, 10:28 AM   #9
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double top plate question


Just don't cut any part of "trusses"!
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Old 09-26-2013, 10:31 AM   #10
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Originally Posted by cortell View Post
I'm not sure you're asking the right questions, but here goes...

In a stick built roof (traditional rafter design), if you're using math to compute rafter length, then whether sheathing needs to be taken into account depends on which way you compute the lengths. There isn't a single way. In the end, it's all about triangles. If your triangle involves the inside edge of the wall top-plate, then no--sheathing does not come into play (other than affecting the birds mouth cut, as GBrackins pointed out). If your formula uses the outside edge of the wall, then, yes...sheathing has to be considered in order for the rafters to fit properly when installed and to have exactly the desired pitch. BTW, John Carrolls' "Measuring, Marking & Layout" book explains rafter calculation brilliantly.

If you have prefab trusses, and you're worried you didn't include the sheathing thickness in the numbers you gave the truss company, then the only impact is on the amount of overhang you'll have. Assuming your roof design provides eaves (and thus has overhang), a 1/2" reduction in overhang will mostly go unnoticed. However, if there are no eaves and the rafter was designed to end right at the outer edge of the building, then the miscalculation is more serious. However, I doubt that's the case.
What do you mean not asking the right questions?
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Old 09-26-2013, 10:47 AM   #11
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double top plate question


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The bottom chord of the truss has to including sheathing thickness.
Sorry. Indeed it does. I did not carefully think through the truss's bearing point detail. That "arm pit" (where the top chord intersects the bottom one) is meant to be snug against the outside edge of the wall.

The workaround seems simple enough, though. You just need to make a small notch in the sheathing. 1.5" wide by maybe 1/2" long. No doubt a pain, since you need a notch for every truss, but not a tremendous amount of work either.
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Old 09-26-2013, 10:58 AM   #12
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What do you mean not asking the right questions?
I just meant your latest question was confusing to me. You start by talking about cutting rafters, then mention you're dealing with trusses. Are you stick framing a traditional roof, are you fabricating your own trusses, are you using pre-fab trusses? No offense intended. Just was having a difficult time understanding exactly what you were asking.
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Old 09-26-2013, 11:13 AM   #13
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The bottom chord of the truss has to including sheathing thickness.
it depends on the type of truss. typically yes you have to account for the sheathing thickness. that's why when building trusses you always give some extra wiggle room (inch or so extra) so that if walls are not perfectly parallel the truss will still work.

if this is a cantilever truss where the bottom chord extends out to the facia then no sheathing thickness does not come into play.

got a sketch of your truss?
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Old 09-26-2013, 11:46 AM   #14
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Sorry. Indeed it does. I did not carefully think through the truss's bearing point detail. That "arm pit" (where the top chord intersects the bottom one) is meant to be snug against the outside edge of the wall.

The workaround seems simple enough, though. You just need to make a small notch in the sheathing. 1.5" wide by maybe 1/2" long. No doubt a pain, since you need a notch for every truss, but not a tremendous amount of work either.
This is for a small shed roof so if I just keep the top of the double plate not sheathed that shouldn't be a big deal.
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Old 09-26-2013, 12:09 PM   #15
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double top plate question


do you have to pass any inspections?

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