CMU Pier code question

[lattimer]

I'm a steel and concrete guy, and looking at a problem regarding piers for a residence I found something that doesn't quite jive with my "common-sense-o-meter".

The residence in question is a 1900s era post and beam house, founded on highly questionable rubble piers. Frost is 48". Girders are roughly 3' above grade. State/city have adopted IRC.

2015 IRC R404.1.9.2 States that "piers supporting girders for exterior bearing walls shall have a minimum nominal dimension of 12 inches and a maximum height of 4 feet from the top of footing to the bottom of sill plate or girder."

Has anyone seen any clarifications on this? Are CMU piers effectively banned in certain areas now, since we certainly would not want timber girders sitting at grade.

 

[dik]

Is there provision for grandfathering?

Dik

 

[MotorCity]

CMU piers are not banned, in fact in certain areas they are quite prevalent. You mentioned there are piers, but quoted a part of the code that deals with exterior bearing walls. In any case, the IRC was probably not around in the early 1900's. Sounds to me like it is simply old construction that has stood the test of time. What makes the piers "highly questionable"?

 

[lattimer]

Well, it is old construction, but it hasn’t withstood the test of time too well. It’s approx 20’ wide and about 6” out of level. The beam is over stressed, and there are numerous types of piers of various quality and states of disrepair.

By my view as well as the owners preference, existing piers will not be saved. All new. CMU is the preferred material, but for the exterior piers the above excerpt took me by surprise. I had planned on a row of cmu piers spaced as dictated by loading and the beam section and properties.

If I’m reading this correctly, it throws a wrench in those plans.

 

[MotorCity]

If you replace the interior piers w/ new cmu piers, you can easily make them at least 12"x12", right? And they are not supporting an exterior wall, so no problem there. As for supporting the exterior, can you provide a continuous cmu wall instead of individual piers? If not, a quick chat w/ the building official may allow you to use piers if you convince him/her that it is an engineered design. CMU piers taller than 4' are used all the time. I don't have a copy of the IRC in front of me, but there may also be language in there that lists exceptions to the rule you cited.

 

[lattimer]

Thanks MC, you’re echoing my thoughts and I believe a call to the code official will be required.

I’m hoping that I’m missing something in the code and that there is an exception somewhere, but I haven’t seen it. It is certainly a common practice, especially in areas further south of me (I’m in NY where full basements are the norm).

 

[JAE]

The IRC is simply a prescriptive code - you can always just design the piers as an engineer and sign/seal the design.

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