Supporting Elevated House 1

[BR_PE]

Has anyone elevated a house on Masonry blocks greater than 6 feet on piers/pedestal placed on a grid with steel beams to support the load bearing walls? If so what code did you follow?

A friend has ask me to be the EOR for raising his house, after reading thru TMS 402, i think the piers should be design as a column with 4 vertical bars and ties at 10" spacing (#5 vertical bars). My friend's contractor is saying that I have over engineered the supports since they have done this 400 times in wind area with wind speeds greater than 140 mph and when the house height is less than 10 feet above grade they have only used 12"x16" blocks with two vertical bars and ties at 36".

When I review the IRC (which I have never used), I get more question than answers. In section 606.6 it states the grouted piers can be 10 times CMU thickness, and in section 404.1.9.2 it states the max height for an exterior pier supporting a floor girder shall be 4 feet.

 

[nmerr]

Ive only done elevated house designs in coastal flood zones so the idea of lightly reinforced masonry sounds totally inadequate. It does really matter how big the house is and what the column spacing is. Last one I did was a relatively large 2 story home with 9 columns total to allow cars to park underneath, the columns were relatively heavily reinforced cast concrete.

 

[IRstuff]

Seems to me that if the purpose of raising the house is because of flooding, it's not just a matter of being above water, but also surviving debris flows. While debris impact forces might not be an issue, per se, any debris trapped by a pier will transfer flowing water pressure to that pier. The owner isn't going to be happy if the house collapses because trapped debris toppled its piers

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[phamENG]

nmerr - most of the ones I've done were federally funded, so there was little thought given to frills like parking unless the homeowner was willing to shell out extra cash. That mean plenty of masonry. Are you referring to elevated houses as in a new house that's elevated, or lifting an old house? I'm talking about the latter, and that's how I read the OP's question. Cast in place concrete is nice, but a bit of a challenge when the house is hovering over your head on cribbing and has to be let down somehow.

IRstuff - very good point. Debris impacts are an issue and are covered in the codes (typically designing for 1000# at the point below design flood elevation that provides worst effects if no other data is available to better quantify the debris). Preventing debris accumulation is more of a qualitative consideration and is discussed in several of FEMA's publications.

 

[r13]

The owner will be too obsessed with insurance and government assistance after a major flood, but the insurance company may want to know more.

 

[nmerr]

phamENG - I've only done new construction on piers. I totally agree with you its super hard to give OP an answer because there are so many variables, 1 story small ranch with piers every 4' masonry sounds easy to make work.

That was my whole point, on initial read the reinforcing sounds super light to be because I used project my experience to fill in the gaps. OP didn't fully describe the project and everyone is guessing at the details to answer which is a dangerous game to play in our industry.

 

[SteelPE]

I have worked on a few of these in the past. Most of our work in this area has involved lifting existing houses. I absolutely hate them..... although, after reading through the comments it seems like we all do take the same approach (which makes me feel a little better).

In our instance, we use poured in place concrete either 16" square or 20" square columns. We have never used masonry. I don't want to give my clients any ideas.