Exterior wall studs supporting slate finish 1

[red22]

I am working on the design of cold formed metal framing (light gauge) exterior wall studs supporting a slate shingle finsish. I have spoken with people at the slate company as well as the National Slate Association requesting guidance on the allowable deflection criteria. Neither had any recommendations. Any thoughts?

 

[DaveAtkins]

Slate is brittle--I would use L/600.

DaveAtkins

 

[ishvaaag]

It is rare to see slate pieces in sizes that be very much affected by the deflection of the supporting structure. Otherwise they wouldn't be selling any ... that is, the sizes sold are typically more than enough to take the snow and wind loads they need to deal with at their size. The overall deformation should be easily taken by the gaps at hooks or other fasteners used to keep the pieces in place. Hence those selling the pieces are not particularly concerned with deflection issues, that will be those happening at the supporting structural party.

 

[Lion06]

I agree with Dave, I would use L/600. It's a brittle finish, and absent a recommended criteria from the supplier, that's what I would use.

 

[hokie66]

Use what you want, but ishvaaag is correct. Slate is in small, discrete pieces, and will not be affected by deflection of wall studs. That is why the slate people had no recommendations.

 

[Lion06]

I don't know what you consider small, but I've seen pieces on the order of 2'x2'. I agree they are not spanning or doing any work neither is a brick veneer and we would design that backup for L/600, right?

 

[red22]

Thank you all. At first I also thought that the L/600 criteria was appropriate, however the more I thought about this I came up with the same reasoning as ishvaag and hokie.

 

[PMR06]

I'd go with L/600. If they can afford slate shingles, they can afford the stiffer studs.

 

[Lion06]

Just for my own information, why are you making a distinction between brick veneer (which is also made of smalll pieces mortared together, but not relied on to do any work) and the slate?

 

[red22]

My analogy was that slate shingles are like snake skin. Although each piece is rigid, each shingle is allowed to move independently of the other. This would not be the case for masonry.

 

[Lion06]

I could see that if they are laid over each other like roof shingles and really have that flexibility. The only time I've seen slate used on the exterior of a building (excluding a roof), it was set in mortar similar to brick. It had larger joints, because of the irregular nature of the stone, but was set in mortar nonetheless.

 

[red22]

For the application I am using, the slate shingles are just like roof shingles, except vertically applied. For the application you describe I think the L/600 would be more appropriate.

 

[msquared48]

I agree with l/600, and, actually, considering the application and overall flexibility of the system, might even consider l/360.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[beton1]

This may be a silly question, but I would assume that the 'shingles' are nailed or screwed to a wood (plywood) backer, right? Brick say, on the other hand, bears on something below, and is tied in to the stud wall, (possibly a GP fibreglas drywall backer as well). So now the question is: which "system" is more prone to wind? A brick veneer still seems more rigid, in my mind.
Although the slate shingles have the advantage of 'individual' movement, the stud wall behind may be required to be stiffer as the slate shingles will not contribute to stiffening the wall system. Is this logic flawed? I seem to be saying a smaller deflection, l/600??

 

[hokie66]

You use stiff studs for brick veneer because, unless you go really big with the studs, the veneer is going to be the stiffer element anyway. Not so with shingles applied to sheathing.