Stone Veneer on Wood

[nhstruct]

I have a wood framed project with 4" brick veneer. The veneer bears on a shelf on the foundation wall and extends 42' tall. Per code we can only go about 33' without needing a releiving angle. Has anyone attached a relieving angle for clay masonry brick to wood framing. Neither me or my boss have a good feeling on attaching the releiving angle to the wood, and it will likely increase our header sizes to maintain an L/600 deflection and the releiving angle. The wall construction is 2x6 at 16" o.c with 1/2" exterior sheathing and 3" cavity between the sheathing and rear face of the veneer.

 

[concretemasonry]

The ACI is not the authority on masonry veneer. The ACI has the staff and publishing contacts to coordinate, print and distribute the documents, which is something that the TMS, BIA and NCMA do not want to get involved with.

When the "masonry code" also known as ACI 530 was written, it was recognized that an engineer could structurally easily support very high (up to 10 stories)veneers, it would not perform well from a practical standpoint.

The problem that creates the established (perhaps arbitrary in some cases) limits is that not all veneers and structural systems have the same properties. Clay brick has long term expansion, concrete masonry has some shrinkage, natural stone is relatively neutral, concrete frames shrink, steel has little creep and wood shrinks a great deal. Because of the various possible combinations an arbitrary (and reasonable) limit a vertical spacing was selected to provide a workable limit and still allow windows to function and opening to be flashed to create a functional structure with some form of compliance with an established standard. Without a reasonable limit a great engineered support system for veneer could be a disaster if the differential movement between the veneer and structure is too great, the entire moisture barrier/flashing could be destroyed and useless and the wall would be considered a failure.

If an engineer wants to micro/over-engineer a specific combination of structural system and a veneer system and sign off on it, it could be acceptable, but costly.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

Well - the limits also had to do with very high continuous veneers not performing well in a seismic event. Six or more stories of veneer loosing their support or stability when only supported at their base is much more catastrophic than individual sections of 12 ft. tall veneer falling.

 

[hokie66]

JAE,
But the limits quoted...30', 33', 38'...don't seem to relate to that logic.

 

[concretemasonry]

There are really two separate situations to consider.

JAE is completely correct that the connection of the veneer to the back-up, is a structural problem compounded by the height and weight of the veneer, hardware used and the supporting system. This is definitely in the field of a structural engineer.

The second is the practicality of the veneer to perform as desired for functionality and not just structurally.

Veneers and back-ups are not always compatible from an expansion/shrinkage/creep standpoint because of the variable materials (natural, fired clay, concrete) when the frame shrinks and the veneer expands/shrinks to where the windows would not open or function. This is why the spacing of relief angles for veneer ended up in ACI 530, which is based on the needs of the MJSC regarding the use of masonry materials.

The ACI 530 document is rightly looked on as the most authoritative masonry structural code, but it also includes many other practical requirements to prevent people from looking only at the structural aspects. When the group (MJSC) was formed, there it was known that a wider view of masonry was needed and reflect the different properties on veneer materials, mortar, grout and possible back-up systems that could reasonably provide some practical standards. Since the members on the committee usually had multiple masonry interests, memberships and activities, the logical place to provide the information was in ACI 530, which in many ways is a consensus standard as evidenced by the MJSC (Masonry Joint Standards Committee).

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

hokie66, what I've always seen in the MSJC is that they limit the foundation-to-top of veneer height to the 30 ft. limit to accommodate 3 story wood framed apartment buildings that are very common in the US.

In a major seismic event, I suppose 30 feet of falling veneer would be a bad thing. But to limit high-rise construction they force the designer to support the veneer at various levels to partition off the sections, allow them to move a bit relative to the supporting structure, and allow only portions of the veneer to fail at one time instead of the whole height.

 

[hokie66]

I'm not arguing for supporting great heights of brickwork without relief. I've never actually done even a three storey building in wood, and don't like the idea of going higher. On concrete buildings with brick veneer, we always support the brick at each floor, or at most, alternate floors. And I certainly recognise the window flashing issues that concretemasonry talked about. The situation I had in mind, and maybe that doesn't correspond to the OP's question, is a brick veneer, without openings, full height. In that situation, and in properly detailed cases with openings, I would rather support a 40' high brick veneer on the concrete footing than on wood bearing walls.

 

[JAE]

On concrete buildings with brick veneer, we always support the brick at each floor, or at most, alternate floors.

I typically do too.