[jklingel]

At EXTERIOR walls, is truss uplift a concern, like it is at interior, non-load bearing walls?

Ignorant as a puppy, I never worried about it on my house 32 yrs ago, (which has an interior load bearing wall), but now that I am aware of truss uplift I have a question about it on exterior walls.

I have a shop that is 20' wide, clear span, and the trusses span the 20' width. My plan was to stop screwing the lid sheet rock to the trusses about 16" from the exterior wall and then put a few screws through the lid sheet rock into a 2x8 block that is nailed to the top plate of the wall.

Make sense? A 2x8x22" block, laid horizontally and nailed to the top plate of the wall, sticking into the room 2", for a screwing surface. This should allow the truss to lift a little bit and not affect the sheet rock.... I think. I'd also stop screwing the wall sheet rock to the walls about 8" below the ceiling. Is truss uplift at the exterior a huge deal?

Is the 2x8 necessary or even helpful for holding the lid sheet rock in place? Thoughts? I should add that this is climate zone 8, so there will be significant temperature differential between the top and bottom chords of the trusses, thus a potentially large truss uplift.Thanks.

 

[joecaption]

Just install these and it will not lift.
http://www.strongtie.com/products/categories/seismic_hurricane.html

 

[mae-ling]

For us we do not screw/glue at edges of drywall sheet, keep the last screw 12" in.
Truss uplift seems to only happen at the middle walls not the outside, the bottom chord of the truss arc's creating a gap on interior walls.
If attaching at interior walls, use blocking connected to the top of the walls and not to the trusses.

 

[jklingel]

Just install these and it will not lift.
http://www.strongtie.com/products/categories/seismic_hurricane.html

Joe: Yes, those are for wind uplift. I am talking about uplift in the middle (more so) due to temperature differential between the bottom and top chords of the truss. You can not prevent that.

 

[jklingel]

For us we do not screw/glue at edges of drywall sheet, keep the last screw 12" in.
Truss uplift seems to only happen at the middle walls not the outside, the bottom chord of the truss arc's creating a gap on interior walls.
If attaching at interior walls, use blocking connected to the top of the walls and not to the trusses.

OK. That is what I was referring to. Thanks for the confirmation.

 

[Gary in WA]

http://www.buildingscience.com/documents/insights/bsi-023-wood-is-good-but-strange/

Gary

 

[jklingel]

Gary: Thanks. I had read that a while ago. One thing not mentioned there, and I still puzzle over, is what, exactly, to do w/ a truss that is parallel to a wall (in my case, an exterior wall) and only 8" away. I don't think it would be wise to let the sheetrock float for 24 + 8 = 32" by only screwing it to the next truss over. Nor do I think it would be wise to screw it to the last truss and let it float for only 8". Would it be advisable to install blocking between the last and second last truss and screw the sheetrock to the blocking, 16" from the outer wall? (Maybe closer on the ends; 12") What do sheetrockers normally do in a situation like this?

 

[Gary in WA]

I figure 7" away is OK- (what I have done); http://bestdrywall.com/files/ReduceCallbacks.pdf

Gary

 

[jklingel]

Gary: OK. I assume then you are saying that the truss that is parallel to the wall and 8" away is ok. In the article you referenced, when he says "On ceilings, place the first screw 7 to 12 inches from the corner along the perimeter of the ceiling" I assume "corner" refers to the intersection of the wall and the ceiling. Yes? Thus, since my truss is 8" from the "corner", I can screw the 'rock into it and not fiddle w/ the blocking between the first (it) and second trusses. Yes? I actually read that article a while ago, but was confused about the "corner" thing; wasn't sure he was not referring to a corner where two walls meet the ceiling. I think I have it now, if the "yes" questions I asked are in fact yesses. On the walls that are perpendicular to the trusses, ie the trusses rest on them, should I put a couple of screws through the ceiling 'rock into the blocking on the top wall, or let the 'rock float between the trusses there? There should be precious little truss uplift there. On the wall, I'll do as per the article. Maybe I should draw this out and post a pic? Thanks again.

 

[jklingel]

Here is a quick sketch of what I am talking about. Leonardo DaVinci would be proud.... The blocking sticks into the shop 2". I could screw into it or just jamb the wall 'rock up against the ceiling rock to hold it. Which? The wall is an exterior wall, and supports the trusses. Thanks.

 

[Gary in WA]

If you are describing the wall/rake ceiling joint, you don't need the flat horizontal backing on top the wall. The top edge of the (wall) drywall doesn't require fastening into the top plates unless it is a diaphragm shear wall against lateral movement; Fig. 3: http://www.lafarge-na.com/GA-216-07_English.pdf

4.9.1---- 4.9.3 on pp.7, and 4.8.2 on no fasteners (at bottom/top plates) in partition walls.

Gary

 

[jklingel]

The blocking is for a couple of screws for the lid 'rock. I will stop screwing the wall 'rock several inches below the top plates of the wall. The blocking is 2x8 atop a 2x6 top plate, so it sticks horizontally into the shop 2", to catch the ends of the lid 'rock. My question was whether or not to bother screwing the lid 'rock into the blocking, or just let the wall 'rock support the lid 'rock there by squeezing the lid against the blocking. Sorry for the confusion, and thanks again for your help.

 

[mae-ling]

Don't screw the ceiling (lid) right to the edge.

 

[jklingel]

Don't screw the ceiling (lid) right to the edge.

OK. I will stop the screws in the trusses about 12" to 1' from the wall, and then NOT put any screws into the blocking that is between the trusses and above the top plate of the wall. Thanks.:thumbup: