Tall walls at gable end query (NBC 2015)

[Inspector Gadget]

Mornin' folks. Our shop is about to have a discussion on how to deal with stud height limits on non load-bearing walls that may exceed stud heights.

Let me explain using this thumbnail as somewhat illustrative. This isn't my pic, but for giggles and grins, assume a 2x4 wall to start the discussion.



Table 9.23.10.1 says that 2x4s on exterior walls are limited to 2.4m (8') height without lateral support.

So presuming 2x4 wall construction, the gable truss is not permitted.

My interpretation is that as long as there's a double top plate for the non loadbearing wall - and in this case, there is - and the top plate is tied into the adjacent walls properly, there should be no issue.

Next extrapolation: let's assume the same sort of scenario, but now the builder wants 2x6 studs to run to the underside of a cathedral roof deck: no top plate involved.

9.23.10.1 says 2x6 studs @16" OC on non-lb walls are capped at 3.0 m (10' or close enough). If a couple of 2x6 studs run 12', that's also technically a violation.

The question here is would you permit it? Why or why not?

 

[steveray]

The Americanos have this...

 

[tmurray]

First, you need to confirm via the truss drawings that the scissor truss actually bears only on the ends, not it's whole length. I have seen both.

If the builder wants to run the wall to the underside of the cathedral roof deck (not to the underside of a structural member, but to the deck itself), wouldn't that make it load-bearing by default? If so, top plates are always required in load-bearing walls (9.23.11.3)

We permitted 2x6 @ 16" spacing up to 3.6m per the table.

Apart from that, making sure the studs are continuous (9.23.10.4) is the other major factor in these walls to eliminate the hinge point issue.

 

[Plumb-bob]

First, you need to confirm via the truss drawings that the scissor truss actually bears only on the ends, not it's whole length. I have seen both.

If the builder wants to run the wall to the underside of the cathedral roof deck (not to the underside of a structural member, but to the deck itself), wouldn't that make it load-bearing by default? If so, top plates are always required in load-bearing walls (9.23.11.3)

We permitted 2x6 @ 16" spacing up to 3.6m per the table.

Apart from that, making sure the studs are continuous (9.23.10.4) is the other major factor in these walls to eliminate the hinge point issue.

I also see gable trusses designed both ways: as clear span or bearing on the wall below.

For a vaulted roof I would want the gable wall to have top plates tied into the load bearing walls, and gable studs installed above that, so allowable stud lengths are not exceeded.

 

[Inspector Gadget]

First, you need to confirm via the truss drawings that the scissor truss actually bears only on the ends, not it's whole length. I have seen both.

If the builder wants to run the wall to the underside of the cathedral roof deck (not to the underside of a structural member, but to the deck itself), wouldn't that make it load-bearing by default? If so, top plates are always required in load-bearing walls (9.23.11.3)

We permitted 2x6 @ 16" spacing up to 3.6m per the table.

Apart from that, making sure the studs are continuous (9.23.10.4) is the other major factor in these walls to eliminate the hinge point issue.

a) Noted on the scissor truss. I actually had to tackle this in my own place, fwiw.
b) Let's assume "underside of cathedral truss, but in a non-loadbearing kind of way."
c) Valid observation on the hinge-point issue.

 

[Inspector Gadget]

*ahem* Excuse me, sir, but you're in the Canadian forum, eh?

 

[tmurray]

a) Noted on the scissor truss. I actually had to tackle this in my own place, fwiw.
b) Let's assume "underside of cathedral truss, but in a non-loadbearing kind of way."
c) Valid observation on the hinge-point issue.

We always looked at the load-bearing as a worst case scenario, so based on that premise, non-loadbearing meeting the same requirements as load-bearing, would obviously be complaint.

I always question if there is such a thing as non-loadbearing for exterior assemblies. Ultimately, they do need to withstand lateral loads from wind and loads from pressure differentials between inside and outside spaces.

 

[ICE]

*ahem* Excuse me, sir, but you're in the Canadian forum, eh?

My bad… I’ll delete it.

 

[Inspector Gadget]

I always question if there is such a thing as non-loadbearing for exterior assemblies. Ultimately, they do need to withstand lateral loads from wind and loads from pressure differentials between inside and outside spaces.

Valid point. "Loadbearing" isn't defined, and while intuitively used to mean an assembly that transfers loads from the top of the wall to the bottom, doesn't exclude dynamic horizontal loads - or for horizontal seismic stresses if applicable.

Your view is supported by the fact the table doesn't have a non-loadbearing exterior wall. So I think the discussion is largely settled.

 

[Plumb-bob]

We always looked at the load-bearing as a worst case scenario, so based on that premise, non-loadbearing meeting the same requirements as load-bearing, would obviously be complaint.

I always question if there is such a thing as non-loadbearing for exterior assemblies. Ultimately, they do need to withstand lateral loads from wind and loads from pressure differentials between inside and outside spaces.

I had an old and wise architect tell me that all exterior walls are load bearing, for the reasons stated above. I took it to heart.