Wide Air Gap Between Brick Veneer and Backing 1

[Mike Mike]

Architect wants a 5" air gap between typical brick veneer and typical exterior wood stud wall. Non-seismic. Low wind. BIA recommends 4 1/2" max unless "rationally designed" (tech notes 28 and 44B). My specifications say ties must be "capable of withstanding a 100 lb load... without deforming... 0.05 inches", along with ASTM standards, permissible products, and other non-structural requirements. But as the SEOR, I don't specify tie spacings. If air gaps are beyond prescriptive limits, who specifies spacing? Do I have to tell the architect I can't handle a 5" air gap?

 

[RWW0002]

But as the SEOR, I don't specify tie spacings

Why not? If it is something that you are concerned about, why not just specify the spacing and type of tie you recommend? Joint Reinforcement and veneer tie requirements come up on high seismic work fairly often, and is often covered on the structural drawings.

That being said, a 5" air gap is pretty large. Do they need alot of rigid insulation in the gap or something? Watch out for any large openings that typical loose lintels have a hard time spanning. Supporting brick off the structure with these large air spaces can be challenging.

 

[dik]

Is there a reason for the large air gap. Depending on the venting, it can be a detriment to the building envelope. Using adjustable ties, it can be an interesting detail.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[MotorCity]

I would say that "rationally designed" beckons the services of a structural engineer (i.e. you). I would start by checking the ties as "mini columns" with an axial compression load due to seismic and/or wind. I'd be curious why the wants an air gap that large unless it is to align the brick veneer with some other cladding feature. Maybe just grout the gap solid as a collar joint.

 

[dik]

I thought the gap was in addition to any insulation, else I would use 'gap'.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[AvengerMolly]

I had an architect request a certain out-to-out of the brick veneer and based on CMU backing size, it didn't make sense to cut block. We ended up with about 3". Typically, we see about 2" of air gap. NCMA specifies 4.5" max. Can your wood wall not extend further out to reduce that gap size? I would discuss with architect and see if you could reduce that at least in half. Otherwise, the cost of both materials and labor for the veneer would be higher than average. Most owners don't want that.

 

[WARose]

About the only thing that crosses my mind (aside from finding a tie that will match) is: will it be ok as far as fire rating goes? (If needed.) If you have a UL catalog, maybe check and see what it says before asking the architect about it.

 

[masonrygeek]

The answer to this one will depend on what code you are using. If you are using the 2015 IBC then you are using the 2013 TMS 402/602 (i.e. ACI 530). If you are using the 2013 masonry code, then the prescriptive maximum cavity size is 4 5/8". If you are using the 2018 IBC then you are using the 2016 masonry code. In the 2016 TMS 402 the prescriptive maximum cavity is 6 5/8", although there are some qualifications to that (and corrugated ties are limited to a 1" cavity). If you exceed these prescriptive requirements, then you move into an engineered design and the EOR should analyze the veneer ties to make sure they have sufficient capacity. In some cases a veneer tie manufacturer will do the analysis, but there may be a charge for that.

We are seeing a lot of designers using 4" and 5" of insulation to meet or exceed the energy codes and I don't see that slowing down. I don't see any issues with going to a larger cavity as the veneer tie as they generally have the capacity and their spacing is usually less than the maximum requirements. The issue of larger veneer lintels is a valid statement and to a certain extent that is the result of increasing the insulation levels.

There is a short article on some of the changes to the 2016 TMS 402/602 that also includes a discussion about veneers:

https://www.structuremag.org/?p=13142.

One of the comments mentioned fire issues. With any wall assembly that contains plastic insulation (i.e rigid board) then the wall system may have to meet NFPA 285. If that is the case, there may be some special detailing at window heads such as placing mineral wool insulation to stop the spread of a fire coming out of an opening and propagating into the cavity. But that's an architect's responsibility, right?

 

[Mike Mike]

Thanks everyone, several asked why it has to be 5". The short answer is this is not a typical building. We are salvaging existing limestone veneer, using various veneer thicknesses, and aligning exterior faces of veneers. Arch wants a lot of rigid insulation and a wide air gap.

Loose lintels are not an issue.

masonrygeek: 2015 IBC, 2013 TMS

Motorcity: This product is permitted by my architect's spec:

https://heckmannbuildingprods.com/products/triangular-wire-tie-316

Are you suggesting I do a calc on a 3/16" diameter x 5" tall skewed rod? Would this be overextending in terms of my scope and responsibilities as SEOR? Seems like Heckmann should provide capacities, but I don't see any capacities on the website. I've done hundreds of these buildings and have never gotten this involved.

Typically spec 042113 - Brick Masonry - is written by the architect. Do I need to edit this spec on every project to make sure there are no scope gaps? What do masons do if projects are outside of prescriptive ranges?