Florida Residentail CMU 1

[Raspo]

So... can anyone give me some insight into why production home builders in Florida do not use horizontal reinforcement(ie durowall, etc.)?

Why do engineers feel comfortable in not requiring it in their designs?

Would you consider it to be standard practice?

Thanks,

Raspo

 

[DaveAtkins]

If the CMU spans vertically, and has enough control joints to control cracking, then horizontal reinforcing really is not necessary.

DaveAtkins

 

[Lion06]

Most homes aren't engineered anyway, are they?

 

[IceNine]

Ha, control joints in a residential cmu wall. That's a good one!

 

[Raspo]

Thanks for the quick response Dave.

I forgot to mention that control joints are just as evil in their eyes. So no control joints and no horizontal reinforcement outside the #5 bars in the bond beam.

Surprisingly, in the past 2.5 years that I have been dealing with designing residential CMU in Florida there have been few issues with cracking until recently. One of the houses we are dealing with has an 80' long wall with a crack that is occurring about 2' back from where the 8' garage transitions to 10' main wall height. You would think the crack would occur right at the re-entrant corner but it is not. There are no high point loads and the slab/footer are fine. No cracking on the interior drywall either.

According to calcs, the shrinkage expected is 5/16" in that long wall. I am wondering if there might be some slippage occurring in the bond beam between the 2'L bar that ties the horizontal steal to the vertical steel at the step as the step itself is rather well reinforced.

Ultimately, the lack of horizontal reinforcement has always been a thorn in my side but there have been few instances where I was able to say... "I told you so."

 

[JedClampett]

I thought in FL they liked to use horizontal joint reinforcing in lieu of bars.
Don't they even have that?

 

[swivel63]

i always spec'ed horizontal when i was working in florida.

 

[structuresguy]

The quick answer is Florida Building Code - Residential doesn't require horizontal joint reinforcing in masonry walls with the block laid in running bond. It is only required by the code if using stack bond.

Heck, the code doesn't even require you to engineer and sign drawings for masonry houses, if using the empirical design portion of the code. That may be fine for 1000SF single story homes. But what about all the 3000SF+ multi story homes going up. There are many new homes along some of the golf courses I regularly play that I am sure would not meet the strength requirements of the code.

Here is a better question: Why can they build a 2000SF house without engineered walls when they can't build a 2000SF office without it being fully engineered, signed and sealed? Are the loads on the house less than on the commercial building of the same size? Which one is more likely to result in injury or death during a hurricane or tornado, the home where people are sleeping or the office that was closed at the first signs of the storm?

 

[Raspo]

Jed,

Much to my chagrin, no, they do not even have horizontal joint reinforcement. When an engineer does spec it... it often ends up on the ground and not in the wall.

The bizarre thing about this issue is that one of the communities that DOES have horizontal joint reinforcement every other course in the exact same house plan is seeing the crack develop in the exact same location.

It might come down to requiring CMU control joints which they are going to be oh so happy to hear I am sure...

 

[asixth]

We don't tend to put horizontal reinforcement for 6" CMU but we do with 8".

 

[JedClampett]

My experience with FL design is strictly industrial. The codes are pretty rigorous with tie beams, columns, etc.
But I thought that due to all the hurricane damage in the 90's, that FL had polished up its act for residential also. Don't the insurance companies have a major stake in residential home quality? The contractors just want to get out with their money, but there are other entities with lobbyists involved.

 

[Raspo]

I guess it would come down to whether or not you believe joint reinforcement rises to the level of "structural" when it mainly combats shrinkage and/or stair-step cracking. I think they see it as a service/warranty issue. I am repeatedly informed that they see very little of this cracking occuring and none of the other engineers that they work with are requiring it.

In the end it ties my hands in a way because rejecting ALL horizontal reinforcement outside of the bond beams in CMU forces me to take the step to a form & poured concrete solution which will cost more and bring about the "over-engineered" montra.

I guess what I am trying to get at is if there is a perceived/established "industry standard" in the Florida residential market in which joint reinforcement is considered optional?

Just trying to be wise in picking my battles on this one.

 

[hokie66]

Not in Florida, but my opinion is that wire reinforcing in CMU is useless and can lead to corrosion staining. Certainly a cast in place concrete wall is more expensive and probably overkill. A reinforced and fully grouted CMU wall, with control joints appropriately located, is the standard where I am. I've never really understood leaving block walls unfilled, as it is such a brittle material.

 

[structuresguy]

hokie66: While I agree with you about wanting for fully grout walls, even here in FLorida unreinforced and ungrouted CMU walls was very common until only a decade or two ago, even in commercial construction. I get involved in lots of reno work, and see ungrouted masonry all the time.

On example is the local hospital, which has been built in stages since the 50's, has ungrouted unreinforced masonry walls that date to the mid-80's. During a hurricane evaluation of the facility, we found that the unrefincored block walls from the 80's were weaker than the double wythe unreinforced brick walls from the orignial building done in the 50's.

The bottom line for residential is that the Florida Residential code does NOT require horizontal joint reinforcing in running bond block walls. So as long as that is the case, the contractors will not install it in the walls. The engineer can jump up and down all he wants, but unless he is out there monitoring the construction, it won't happen. The city inspectors are not looking for it, so they wont notice. Even if the engineer went to the building official, he may still fall back on not required by code.

 

[hokie66]

If these are engineered structures we are talking about, the engineer should be able to dictate what goes into them. Codes are only minimum standards, not necessarily a prescription for quality construction.

 

[SLTA]

I actually had a building department tell me that the deck beam sizes on sealed drawings we submitted didn't match their "calcs" (ie non-engineers using a computer program they didn't understand with wrong loads, materials, sizes, etc) and so we were required to change our design.

in other words, code officials can do whatever they want, even trump an engineer's sealed plans.

 

[hokie66]

That's a very active building department. Where I am, the local authority wants nothing to do with any responsibility for structural decisions.

 

[jeffandmike]

The current residential code in Florida is the 2007 Florida Building Code - Residential (

http://www2.iccsafe.org/states/florida_codes/).

Section R606 (page 6.47) of this code governs masonry wall construction. For the purposes of design and construction, this section takes you to the referenced standard (ACI 530) and/or to the provisions of the 2007 FBC-R. Lower construction costs will typically result from prescriptive provisions. So, being the businessmen they are, contractors will do their best to provide structures that utilize the prescriptive provisions.

Section R606.7 of the 2007 FBC-R only requires horizontal joint reinforcement for "stack bond construction", not "running bond". One-story structures utilizing running bond construction that is, for the most part, ungrouted and unreinforced is typical.

The above statements should answer all three of your questions.

However, just because the code allows it, just because it is standard practice, just because we are not seeing widespread collapses of residential structures, does not mean it is a good idea.

Given the combination of loose, sandy surficial soils, the widespread lack of gutters on roof eaves and/or code-required downspouts discharging water away from the foundation, the widespread lack of code-compliant site grading, the widespread lack of control joints and ungrouted/unreinforced masonry construction, stairstep cracking distress (due to slight differential settlement of the supporting soils) is very common in the walls of residential structures. When a homeowner that lives in Florida observes this type of distress, and particularly after they have seen billboards sponsored by sinkhole attorneys (and/or they have learned about sinkholes from their neighbors), they file a claim with their homeowner's insurance company.

Many times, the insurance company-sponsored subsidence investigation "cannot rule out sinkhole activity" (very loosely defined), and expensive remediation of the subsurface is required (many times exceeding the replacement value of the structure). This drives up insurance premiums for everyone in the state.

Shoddy construction practices, in part driven by weak building codes, lack of thorough plan check procedures and building inspections (by the jurisdiction) don't just cost the individual homeowners, but also everyone else who pays for homeowner's insurance in the state.

 

[boo1]

Florida Residential Permit Placement:
1. Building permit shall be placed six (6) inches from road way. Permit location shall providing drive up access.
2. Permit shall be place with the signature block 48 inches from road way or at window height of F100 truck.
3. Donation envelope shall be located...

 

[BAretired]

In a cold climate such as we have in Alberta, wire reinforcement is customarily used in alternate courses of stack bond and every third course in common bond. Masonry contractors would not consider omitting it here. In addition, the bond beam at the top is minimally reinforced with 2 - 15M (2 - #5) bars.

In Florida, the temperatures are not so extreme, so perhaps it is acceptable to omit the horizontal wire reinforcement there. For a masonry wall eighty feet long however, control joints at about twenty foot centers would seem prudent.

BA