Truss Connections ?

[Joe_Carrick]

What do you specify for connecting trusses to the exterior walls and interior shear walls?

I am assuming some sort of Simpson object but which one?

[Chopsaw]

Usually the truss company will specify all necessary connectors.  Depends on the uplift potential.  USP RT3A on one of my recent builds.

[Ridge_Runner]

1 minute ago, Chopsaw said:

Usually the truss company will specify all necessary connectors.

That's the way we work here also. The truss guys spec the Simpson clips, in our case, based on the uplift.

[HumbleChief]

Only ever use this one for interior non-bearing walls. Never have had to spec an exterior bearing wall truss connection. I assume that's within the truss calcs/specs. Also haven't come across an interior shear wall truss connection in forever but do not know how that shear would be transferred to the roof diaphragm.

 

https://www.strongtie.com/trussclips_platedtrussconnectors/tc_roofclips/p/stc.stct.dtc

[javatom]

I use H2.5. for exterior walls.  Interior walls are not attached to the truss.  This can compromise the structural integrity of the bottom chord.  The item Larry linked to is almost the only simple way to do it.

[HumbleChief]

24 minutes ago, javatom said:

I use H2.5. for exterior walls.  Interior walls are not attached to the truss.  This can compromise the structural integrity of the bottom chord.  The item Larry linked to is almost the only simple way to do it.

That STC bracket is actually required by (some?) plan checkers in my city/county of San Diego. Oh yeah and also requires a gap between top plate and bottom chord.

[GeneDavis]

We like the Simpson screws, SWDC.

[Joe_Carrick]

2 hours ago, javatom said:

I use H2.5. for exterior walls.  Interior walls are not attached to the truss.  This can compromise the structural integrity of the bottom chord.  The item Larry linked to is almost the only simple way to do it.

In some cases trusses must be designed to bear on interior walls.  In that case, particularly if the wall is a required shear wall, they are definitely attached to the trusses.  The house I'm working on currently is 100'x43' and the code requires braced walls no more than 25' apart.  Consequently there are interior bearing walls and the trusses are designed to be structurally supported at approximately mid length.

[javatom]

Brace walls are for keeping the walls from moving.  They don't have to be a bearing point for the trusses.  We span those distances all the time without a third bearing point.  The truss designers have their own set of instructions for keeping their roof system from moving.  Their "brace walls" are usually a kicker 2x from the top of the gable ends to the bottom chord at about a 45 degree angle.  They also usually call out for lateral bracing in the form of 2x "rat runs" nailed at certain points along the webbing.  The only time I have seen the two world mingle is in the case of a really high energy heel.  Some building departments want blocking between the trusses at the exterior wall with the sheathing running up almost to the top of the top chord.  The brace wall requirements are for wall support not truss support.

[RL-inc]

9 hours ago, Joe_Carrick said:

In some cases trusses must be designed to bear on interior walls.  In that case, particularly if the wall is a required shear wall, they are definitely attached to the trusses.  The house I'm working on currently is 100'x43' and the code requires braced walls no more than 25' apart.  Consequently there are interior bearing walls and the trusses are designed to be structurally supported at approximately mid length.

Joe 

Are you certain that you are not referring to the code section that requires braced wall panels to be a max of 25' apart in a wall line for lateral shear in a prescriptive path condition?

 

While it is quite possible that the trusses are designed to have midspan support every 25' that seems like overkill.

 

[RL-inc]

Regarding the truss to wall connections it is my experience that they were generally required at he exterior wall lines and along ibt weereior shear walls. The main reason is to resist uplift.

 

As mentioned h2.5 clips or h1 are pretty standard but there is a new toe screw detail that allows for an @ 4-6" timber-lok screw to be run up through the top plate into he truss on an angle. Much faster installation.

[HumbleChief]

9 hours ago, Joe_Carrick said:

In some cases trusses must be designed to bear on interior walls.  In that case, particularly if the wall is a required shear wall, they are definitely attached to the trusses.  The house I'm working on currently is 100'x43' and the code requires braced walls no more than 25' apart.  Consequently there are interior bearing walls and the trusses are designed to be structurally supported at approximately mid length.

Doesn't the truss company provide all needed details and connectors for any condition specified?

[Joe_Carrick]

10 minutes ago, RL-inc said:

Joe 

Are you certain that you are not referring to the code section that requires braced wall panels to be a max of 25' apart in a wall line for lateral shear in a prescriptive path condition?

 

While it is quite possible that the trusses are designed to have midspan support every 25' that seems like overkill.

 

1.  That code section CRC R602.10 requires the "Braced Wall Lines" to be not more than 25'.  Then there are minimum lengths of "Braced Panels" within each "Braced Wall Line", depending on the lengths of the "Braced Wall Lines". 

2.  Actually, the mid span support for long trusses is less costly.  It basically just requires a "KingPost" at the bearing point up to the peak.  This will typically reduce the number and/or length of additional web members.

[Joe_Carrick]

17 minutes ago, HumbleChief said:

Doesn't the truss company provide all needed details and connectors for any condition specified?

Sometimes yes, but in many cases their details are sketchy.  I'm looking at one that only specifies (2) 16d Toenails in a generic detail.  For large overhangs (potential wind uplift) this may not be sufficient and as the responsible professional I'm not comfortable with that.

[rlackore]

I like to use the Simpson H3 - it can be used on either side of the wall and works well with both rafters and trusses. But I've also used the SDWC screws and other connectors, depending on the situation. I've found that H3s at every truss connection are usually sufficient to tie the roof diaphragm to the exterior wall plates - then I'm free to design the remaining uplift load paths independent of the roof structure.

[HumbleChief]

16 minutes ago, Joe_Carrick said:

Sometimes yes, but in many cases their details are sketchy.  I'm looking at one that only specifies (2) 16d Toenails in a generic detail.  For large overhangs (potential wind uplift) this may not be sufficient and as the responsible professional I'm not comfortable with that.

(2) 16d Toenails doesn't seem sketchy at all. It seems to be very specific and might be exactly what that connection requires but of course on the other hand you don't have to be comfortable with that detail. For any uplift condition I would imagine Simpson's hurricane connectors  https://www.strongtie.com/hurricanetiesforplatedtruss_trusstiedowns/h-tsp_productgroup_wcc/p/h.tsp to be just what the doctor ordered. This one seems especially robust  https://www.strongtie.com/resources/product-installers-guide/h10a-rafter-condition 

 

It's such an inexpensive item it seems there's no reason not to specify the strongest connector for the condition.

 

Curious as to what you ultimately choose.

[RL-inc]

18 minutes ago, Joe_Carrick said:

1.  That code section CRC R602.10 requires the "Braced Wall Lines" to be not more than 25'.  Then there are minimum lengths of "Braced Panels" within each "Braced Wall Line", depending on the lengths of the "Braced Wall Lines". 

2.  Actually, the mid span support for long trusses is less costly.  It basically just requires a "KingPost" at the bearing point up to the peak.  This will typically reduce the number and/or length of additional web members.

Again- i think the code section you are referring to is discussing lateral stability along a given wall line. Not across the section of a building.

 

The king post option to reduce the truss span is generally used to reduce reactions at the endpoints.

[Joe_Carrick]

18 minutes ago, RL-inc said:

The king post option to reduce the truss span is generally used to reduce reactions at the endpoints.

It only does that if the king post is located at an internal bearing point.  Note that the king post doesn't have to be perfectly vertical.  It just needs to be relatively close.  (My case is about 85 degrees from the bearing wall to the peak of the truss.)

[rlackore]

41 minutes ago, HumbleChief said:

(2) 16d Toenails doesn't seem sketchy at all. It seems to be very specific and might be exactly what that connection requires

 

That connection gets about 114 lbs of uplift resistance, assuming G=0.50 (doug fir or better) and no adjustment factors. No way to tell if that's enough unless you run the calcs on the roof projected area and the vertical pressure zones. 

[HumbleChief]

53 minutes ago, rlackore said:

 

That connection gets about 114 lbs of uplift resistance, assuming G=0.50 (doug fir or better) and no adjustment factors. No way to tell if that's enough unless you run the calcs on the roof projected area and the vertical pressure zones. 

Kinda my point - it might be exactly what that connection requires -  or not  - but it certainly isn't inherently sketchy unless one deems it so.

 

I don't do my own structural or truss calcs so I depend on those disciplines to get it right and "run the calcs on the roof projected area and the vertical pressure zones" as needed to determine the appropriate connection spec and detail. Puts me at a slight disadvantage but these days all my engineer's are so conservative in their spec's and calcs I tend not to concern myself about those things. NOT for everyone, especially those licensed for such things but I don't have much choice, not being licensed in any given discipline, other than, again, to depend on those specific disciplines. 

 

Curious Joe, Did you make a decision on the connector?

[HumbleChief]

Here's a note provided by the truss manufacturer in my area. Should be easy to spec, or exceed that uplift load I would think but certainly won't cover every condition, especially those one is not comfortable with but has been good for many years in my business.

 

"Provide mechanical connection (by others) of truss to bearing plate capable of withstanding 100 lb uplift at joint(s) 10, 2, 11, 12, 13, 14,
15"
 

[Joe_Carrick]

10 minutes ago, HumbleChief said:

Curious Joe, Did you make a decision on the connector?

Not yet, but I will probably go with the Simpson H1's.  My eave overhangs are 3' and the site is on the high point of a relatively steep hill with about a mile clear of any obstructions.  With the design wind speeds of 110 mph the uplift potential isn't insignificant. 

 

In addition I have a conventionally framed roof (2x14's) with a overhang of 6' and that I know is a problem without the H1's.

[HumbleChief]

1 minute ago, Joe_Carrick said:

Not yet, but I will probably go with the Simpson H1's.  My eave overhangs are 3' and the site is on the high point of a relatively steep hill with about a mile clear of any obstructions.  With the design wind speeds of 110 mph the uplift potential isn't insignificant. 

 

In addition I have a conventionally framed roof (2x14's) with a overhang of 6' and that I know is a problem without the H1's.

Cool Joe appreciate the info and logic. Thanks

[rlackore]

6 minutes ago, Joe_Carrick said:

Not yet, but I will probably go with the Simpson H1's.  My eave overhangs are 3' and the site is on the high point of a relatively steep hill with about a mile clear of any obstructions.  With the design wind speeds of 110 mph the uplift potential isn't insignificant. 

 

In addition I have a conventionally framed roof (2x14's) with a overhang of 6' and that I know is a problem without the H1's.

 

That slope is going to add a significant topographic adjustment factor, and you're already in Exposure Category C. If you find the H1s don't give you what you need, I've used two TSP connectors, one on each side of the wall, to increase the uplift capacity for specific areas, like on either side of a large punched opening. The other part to the equation is tying the roof to the foundation - it sounds like your particular situation will need careful design of the uplift load paths.

[Joe_Carrick]

3 hours ago, rlackore said:

The other part to the equation is tying the roof to the foundation - it sounds like your particular situation will need careful design of the uplift load paths.

That won't be much of a problem since here in earthquake country we will need Simpson HD2's in key locations anyway.