Thread: Crawl space piers

I was doing a crawl space inspection today and it was pointed out to me by another inspector who had previously inspected the same crawl space that some of the piers were hollow and not filled with concrete and re bar. Sure enough after banging on all of them I did find several that sounded hollow. Is it required to have all piers filled and with re bar? By the way, these were not temporary piers. They were permanent with mortar joints and pad.

Thanks, Jim

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Not all piers are required to be filled, it's based on height. I forget how high.

From the 2006 IRC

R606.6 Piers. The unsupported height of masonry piers shall
not exceed ten times their least dimension. When structural
clay tile or hollow concrete masonry units are used for isolated
piers to support beams and girders, the cellular spaces shall be
filled solidly with concrete or Type M or S mortar, except that
unfilled hollow piers may be used if their unsupported height is
not more than four times their least dimension. Where hollow
masonry units are solidly filled with concrete or Type M, S orN
mortar, the allowable compressive stress shall be permitted to
be increased as provided in Table R606.5.

Hey Dan, Rick is right on the height of piers (32'), however you may want to consult with the local authority having jurisdiction as to their policy. Some areas have wind and seismic factors to be considered. Also a 8x16 block pier should not be spaced more than 8' OC. If this is a modular or manufactured home, most do not want the piers to be over 3 blocks high. If it is it would have to be double blocked (16x16) with a minimum of a 20"x20" pad. All blocks are to be mortared.

Bill

An 8x16 pier would be 32. 4 times 8" = 32". Where 8" is the least dimension.

But lets say the pier is 12x16, now the acceptable height is 48", which is 4 times the least dimension of 12"
16x16 is 64"
24 x24 now the acceptable height is up to 8', 4 times 24"

Rick your math is correct. However, I live out in the boonies and haven/t seen any CMU's that you describe. I assumed that the piers described were 8x16 conventional blocks witha 3/8 mortared joint. As a note, I do not know of any engineer that would approve a block pier without a solid cap block in place as the bearing surface or at least the top block solid motar. All of the FHA inspections that I do, this the requirement that must be met.

Originally Posted by Bill Scott

Rick your math is correct. However, I live out in the boonies and haven/t seen any CMU's that you describe. I assumed that the piers described were 8x16 conventional blocks witha 3/8 mortared joint. As a note, I do not know of any engineer that would approve a block pier without a solid cap block in place as the bearing surface or at least the top block solid motar. All of the FHA inspections that I do, this the requirement that must be met.

8x 16 is the most common size, but there are other sizes also, such as 12x16.
16x16 pier= 2 8x16
16x24 = 3 8x16
a 24x24" pier uses 4 8x16 and 6 bricks (or a 1/2 8x16 block)

When the pier is filled solid, a cap block is not needed.

Hey Rick, I now see my mistake in my orginal comment. A typo of (') instead of ("). My bad. Again you are correct that there are other types of blocks, however they are NOT the most common used in block piers. And you are correct that if the blocks are filled with motar they do not require a cap block, BUT neither is one required when the top block is filled with motar as I stated. I think that all Jim wanted to know is if the darn things were code or not. There were assumptions made on my part in that I was using my 50+ years in the trades that the most common type of pier uses a 8x16 CMU. Hey you don't even have to motar them anymore, you can glue them together. Ain't chemistry great. It is my sincerest intention that the readers of these articles get the benefit of my experience. My study of foundation systems show that many factors have to be considered for the individual site because foundations should be site specific. If we are to get technical in Jims case there are other factors to be considered. For example, what is the dimension of the pad that the blocks sit on? Is the crawl space dry or damp? Is the pier supported to frost depth? Is the first block mortared to the pad or is just sitting on top? What type of bearing surface is the pier supporting? Do wind or seismic conditions apply? I assumed that since Jim lives in a costal state, that frost debth is not a concern in that probably the house has a block or concrete stemwall sitting on a footing that is at frost debth and therefor forms a barrier to frost penetration to the inside piers. I also assumed that Jim was looking at the most common type of pier construction. To Jim, if my descriptions are not what you are seeing, my appologies. I reccomend that you become friends with a structural engineer and pick his/her brain and that might give you a better insight.
I am an old fart of 70 years and helped frame my first house at 12 years of age and have been around the construction trades and doing it since then and will keep doing it until they drive that last nail in my coffin and he damn well better not bend it or I am going to tell him about it. You new guys can keep inspecting the old stuff and I will stick with new construction. I am a red dirt Okie and an opinioniated son of the South, I inspect to code even if I don't agree with it sometimes but I swear if I hear green this or green that one more time I am going to set a couple old tires on fire in my front yard and to hell with them. Yall have a nice day.