Stone Veneer on Wood
Stone Veneer on Wood
(OP)
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.






RE: Stone Veneer on Wood
Normally, brick veneer usually is limited to 2 stories height between angles, but some codes or architects allow more. It sounds like you have the classic 3" +or- cavity for rigid insulation and an air space for circulation and flashing.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Stone Veneer on Wood
Also another discussion on masonry deflection:
http:/
ACI 530 supporting unreinforced masonry = L/600 and 0.3, reinforced limits do not apply. Section 1.10 commentary
Deflection of walls out of plane held to 0.007. Test by SEAOSC/ACI committe rcommended 0.01h. (See RMHB 6.5.3.I)
I don't think I've really answered your question but maybe this is helpful.
EIT
www.HowToEngineer.com
RE: Stone Veneer on Wood
The treatment would be very similar to any shelf angle but you have a wood connection and the bearing of the backside of the shelf angle on wood backup. A lot of time this may be lag screws into studs (not my favorite). Extra safety factor for fastener bearing creep here may be in order, YMMV. If you can get the joint at the floor deck for some real meat into a extra beefy rim-joist that is maybe a good way to go. Also then the rim will provide some extra stiffness for the headers downstream. Some concern for quality installer here and don't forget those vertical joints too in your flexible tall masonry wall. I usually spec out better masonry ties and spacing too on these tall wall with wood backup especially around the window openings.
MAP
RE: Stone Veneer on Wood
Your title says "Stone veneer", but you then go on to talk about a brick veneer.
RE: Stone Veneer on Wood
The reason is the fact that wood frame shrinks and most clay or stone products do not, so there is a differential in the end that can tear apart flashing and interfere with with window openings. Clay poses a more severe problem because it has a long term EXPANSION that is opposite to the wood shrinkage. Most prescriptive codes are written for categories of materials and stone or clay brick that are lumped together to arrive at the common industry standards. Temperatures also have an effect on the local prescriptive requirements.
The 33' limit fits the typical wood frame/masonry apartment building.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
EIT
www.HowToEngineer.com
RE: Stone Veneer on Wood
He is talking about 42' tall, about a 4 storey building, I imagine.
RE: Stone Veneer on Wood
I saw a 6 story building where the casement windows on the upper floors (no relieving angles obviously)could not be opened because of the differential heights between inner structure and the exterior clay brick that went through the predictable long term expansion. This was one of many problems that created the inclusion of relieving angle spacing in ACI 530.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Stone Veneer on Wood
I also appreciate your concern with the lags not holding over time but In my experience this has not been an issue with good contractors. Why is this any different than a deck ledger on a house? OK, maybe not the best example:) The deck is certainly be a more troubled situation.
One other thought is to install a wood ledger under the shelf angle as a backup fastener in addition to the shelf angle fastening. This may mean more air gap at the veneer but another thought nonetheless. - Similar to when doing a wood beam supporting masonry I put down a steel angle on top of it and then the masonry goes on.
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
In ACI530-02/TMS402-02:
Chapter 6, Veneer
6.2.2.3.1.5 Exterior masonry veneer having an installed weight of 40 psf or less and height of no more than 12 ft are permitted to be supported on wood construction when installed in compliance with the provisions of this Chapter. A vertical movement joint in the masonry veneer shall be used to isolate the veneer supported by wood construction from that supported by the foundation. Masonry shall be designed and constructed so that masonry is not in direct contact with wood. The horizontally spanning element supporting the masonry veneer shall be designed so that deflection due to dead plus live loads does not exceed l/600 nor 0.3 in.
Also note that Table 6.2.2.3.1 gives height limits from foundation for masonry veneer backed by wood of 30 ft at plate and 38 ft at gable.
Hope this helps somebody.
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
The MSJC is a joint committee comprised of The Masonry Society, ACI, and ASCE. They put together the MSJC document which has call numbers for each participant. ACI's is 530.
The combination of these groups is due to the fact that the MSJC has both clay and concrete masonry units included in the code/specification.
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
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.
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
But the limits quoted...30', 33', 38'...don't seem to relate to that logic.
RE: Stone Veneer on Wood
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.
RE: Stone Veneer on Wood
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.
RE: Stone Veneer on Wood
RE: Stone Veneer on Wood
I typically do too.