Trusses not over studs?

Hi Evereyone, We are looking a a little investment property which has a small unfinished garage on it. It is just studs on the inside, and we noticed, the studs are not under the trusses! It appears to be framed 16" on center but the trusses are set @24" on center? This way some trusses rest on the double top plate in the middle of the studs?
It is framed 2X6 ,fully sheathed, with great ties to the slab, the trusses are all tied to the top plate, etc .It all pretty much looks great, it has had stucco exterior for 6 years and not to much as a single crack..
I just wanted to know if this is acceptable design? The owner has the original order from the truss company which actually indicated 24" on center over 16"!! They have since closed up however!
So , is this normal and , should I fit in 2X6's under the errant trusses?(Since the walls are still open)
Any help appreciated G
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It is perfectly normal to have 24'' truss spacing with 16'' wall studs.
AustinScoobee wrote:

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This is completely normal, and I framed my house the same way.
The double top plate basically acts like a header to transfer the load of a truss that doesn't land over a stud to the nearest studs.
Works fine... No worries!
Anthony
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2x6 not 2x4 walls?
The load of the roof should be brought down to the footing of the building by lining up studs from the trusses all the way down the walls.
one person said that they put trusses on a double top plate
which means there are two 2x4s at the top of the wall unfortunately two is the standard and to fix a problem like miss aligned studs you need a three layer top plate
Now again this depends on loads like snow and wind
hopefully they did it right and the people that made the trusses would have told them how it should be layed out
For you it means that you cant have an attic full of stuff If you have access up to the attic you cant put heavy loads up there like your AC unit or finnish it into a room.
that is the difference you offset the cost of 20 extra 2x4s or 5 extra trusses to form an attic bonus room durring the framing and endup losing the ability to put a load in that area.
So just use it for a box or 2 of christmas decorations. and dont build a floor and stick your air compressor and a water heater up there.
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My understanding is that you are off by one here: if the studs/trusses are perfectly aligned everywhere, I believe the building code allows a single top plate (with the proper splice detail). Using a double top plate is standard practice precisely because it allows the studs/trusses to be offset.
Cheers, Wayne
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In a previous post Wayne Whitney wrote...

Wayne is correct. Not to mention that once you add solid sheathing on the wall the double top plate is not going to go anywhere without destroying the sheathing.
BTW, there is another reason to use a double top plate: chord forces in the roof or floor diaphragm. It is possible to use a single top plate, but the diaphragm cannot be very large and you must strap across any splices to provide load continuity. The use of a double top plate provides two benefits: studs and roof members don't have to be aligned and chord splices are done by offsetting the ends of the plates.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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Indeed, the double top plate has interlocked endplates, and in addition, since the framing members are all 2X6, this also means the top is 2X6 double plate..pretty strong I would think.. Anyhow, so long as the building inspector sees nothing wrong with the arrangement, I feel pretty comfortable with it now, I even called a local truss company, who confirmed (in thier opinion) that this is done very often, and in fact there were indeed certain instances where even fewer lined up with the studs..(trusses over curved/angled walls)
Once again, thanks very much to the group and you're input! G
Bob Morrison wrote:

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'chord forces, chord splices', I have not heard of these terms. Do they have something to do with pulling apart? Like a collar tie?
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remove one of the @\'s unless you are a spammer.
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This is arcane engineer speak for the forces at the edge of roof and floor diaphragms when the building is subject to wind or seismic forces.
A simple description might be the forces in the top & bottom flanges of the horizontal beam that is the roof or floor diaphragm. These forces can be significant when the building long and narrow.
If you look at the required nailing table in most U.S. building codes you will see a minimum number of nails called for when splicing the double top plates. "Chord forces" is the reason.
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Bob Morrison, PE, SE
R L Morrison Engineering Co
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wrote:

It is also quite reasonable to use single top plates and the studs spaced at 24" O.C., then line up the trusses on the studs and tie everything together with hurricane straps. By using less lumber in the exterior framing you lessen the area of cold spots across the wall face, couple this with using minimal corner framing and you could easily reduce the cold spots by 10% and keep the cost down as well. But then again, you probably want to go to 5/8" drywall instead of 1/2" drywall because of the spacing so the cost savings would go disappear.
It just takes a little more pre-planning to layout the wall framing and roof trusses but it may be worth it for the energy savings. But you have a point with the splices - either they have to be at a stud or you need to strap the slice.
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I believe that with a single top plate, any splice in the top plate requires a metal strap. The prescriptive details are spelled out in the building code. The purpose is to transfer any tension forces in the top plate that develop as part of the lateral force resisting system for wind and seismic loads.
Cheers, Wayne
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wrote:

yeah but, there are many more engineer's who have study this and apparently came to the conclusion that it is totaly exceptable to use single top plate construction, not exculding the chord argument.
IRC 2003
R602.3.2 Top plate. Wood stud walls shall be capped with a double top plate installed to provide overlapping at corners and intersections with bearing partitions. End joints in top plates shall be offset at least 24 inches (610 mm).
Exception: A single top plate may be installed in stud walls, provided the plate is adequately tied at joints, corners and intersecting walls by a minimum 3-inch by 6-inch by a 0.036-inch-thick (76 mm by 152 mm by0.914 mm) galvanized steel plate that is nailed to eachwall or segment of wall by six 8d nails on each side, providedthe rafters or joists are centered over the studs with a tolerance of no more than 1 inch (25 mm). The top plate may be omitted over lintels that are adequately tied to adjacentwall sections with steel plates or equivalent as previously described.
R602.3.3 Bearing studs. Where joists, trusses or rafters are spaced more than 16 inches (406 mm) on center and the bearing studs below are spaced 24 inches (610 mm) on center, such members shall bear within 5 inches (127 mm) of the studs beneath.
Exceptions: 1. The top plates are two 2-inch by 6-inch (38mmby140 mm) or two 3-inch by 4-inch (64 mm by 89mm) members.
2. A third top plate is installed.
3. Solid blocking equal in size to the studs is installed to reinforce the double top plate.
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In a previous post snipped-for-privacy@butme.com wrote...

I'm well aware of these regulations. Most framers that I have seen don't want to take the time and effort to lay out the studs exactly and don't want to stop and add metal straps. BTW, the straps can make it harder to install sheathing or drywall if installed on the face of the framing. And, have you ever tried to put (6) 8d nails in a 3x3 space at the end of a framing member? There won't be much solid wood left, especially if it's hem-fir.
This is one of those, "It's nice in theory, but in practice it isn't often done because it takes too much time and effort."
I'm not fond of using this type of framing. Why? Half the time I can't the framers to use the correct nail size and spacing when installing the wall sheathing. Why would I give them something more complex to have to think about when they can't even get the simplest thing done correctly?
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Bob Morrison, PE, SE
R L Morrison Engineering Co
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2x6 is very common to allow the space for R19/R21 insulation. Of course, it also makes for a stronger wall.

Ideally, yes, but what about window openings, door openings, etc.?
The headers above these openings support the loads above, and carry them down to the foundation below.
The double top plate works in much the same way, when trusses are spaced 24" on a wall that is 16" OC. For every two trusses, one lands over a stud, the other sits between two studs. Half the load carried by that truss is shared by the nearest stud on either side. Shouldn't be more than a 14.5" span between the two studs.

Unless you're talking some serious roof loads, I don't know why you would need three top plates? A double 2x4 header is usually adequate for a 3-4 foot window opening. Granted, the header would put the 2x4's on edge instead of flat, but the double top plate has less than half the span.

I'm just guessing, but I would think the lower chords of the roof truss would be a bigger issue for carrying loads than lining up the trusses with the studs. Unless they are specifically designed for the purpose, I don't believe most trusses are intended to carry significant weight on their bottom chords?
Anthony
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