Need some know-how here. I know the basic specs for concrete block piers - two 8X16X8 concrete blocks on top of a 16X16X4 pad. However - What I don't know is how to solidify the foundation enough that they won't move/sink over time.

I know sometimes people pour a base a certain depth below grade to reach more stable ground. What suggestions might some of you have for good pier construction?

My initial thought was to put a 10" or 12" sonotube down about 2 feet below grade to get to soil that is unlikely to saturate and pour a pier, then install the pad and blocks above that.

If you're going to dig and set a sonotube, why not just go ahead and pour a concrete pier?

I thought about that, but I need it square/rectangular above grade, and blocks allow adjustments when setting the foundation beams if they aren't permanently attached to the poured piers. One issue with pouring piers is that it requires a much larger hole for the spread base. Because I have to place piers in close proximity to existing piers on the main structure, I have significant concerns about excessive excavation around them - I don't want to cause the house to shift.

Of course, maybe I'm just being stupid.

Ok. As for compaction, I've only done pier and beam on a relatively light out building. In that case we just tamped our footings as hard as we could with the top of a heavy sledgehammer. Little bit redneck though for a home.

What is the foundation for RTT?

I'm planning to rebuild my enclosed porch as an actual part of the house that contains a pantry, utility/laundry room and entry foyer/study.

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One issue with pouring piers is that it requires a much larger hole for the spread base.

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But do you need an underreamed pier or will a straight shaft work? Considering you are attaching this to your house and it will be living areas (versus storage or the original patio), I'd seriously consider spending a few hundred bucks to have a geotech and/or structural engineer take a look-see. I'm not suggesting you have them set up a drilling rig in your backyard and go to town, but see if you can determine the depth you need to reach, things like PI and PVR that will provide an indication of what type of movement to expect and allow for, etc. Do you know what type of soil your place sits on? It isn't just a matter of sinking, in some areas it will heave as well.

Underoos' post is where I was leading the conversation.

If this is going to be a part of your home, you need to involve an engineer. Not only because it would/should be required by code (don't you work in the code department in htown?), but because if you don't get the foundation right, you're opening a gigantic can of ****.

I feel like you know that, so if you're interested just for the sake of being interested, I'll dig out some of my foundation books tonight and see what I can come up with. Whatever it is will vary greatly depending on your soil conditions.

Agree with both of the 2 previous posts. You really need to get and engineer out and have them design it. Then you know it is right and will last.

FWIW, the piers on the rest of the house have really shallow footers and haven't moved all that much in 76 years.

True, but there is now the potential for your new addition to move, or more specifically move differently than the existing part of the house. It hasn't had the luxury of 76 years to perfect it's ass dent on the recliner, so to speak.

I'd still suggest getting a train driver involved. In theory, you could match the existing pier construction, but at the very least there is still the matter of the connection between new and existing. Maybe it really is as easy as embedding dowels with pooky, ne epoxy, but I'd sleep a whole lot better knowing somebody figured out how many and where.

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two 8X16X8 concrete blocks on top of a 16X16X4 pad.

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Solid blocks or CMU? Fully grouted? Size rebar? Reinforcing in the pad? Connection between the two? If those are the details you're needing, see the train driver comment above.

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Need some know-how here. I know the basic specs for concrete block piers - two 8X16X8 concrete blocks on top of a 16X16X4 pad

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Over here at least, a 4 inch deep pad is nowhere near the norm. I think the footing depth is typically half the width or more. The ones I'm building are 24x24x12, reinforced with rebar and Simpson straps (PA51). In Houston does code require you to have hurricane straps? I'd seriously consider them even if it's not mandatory.

I'd consult an engineer and a code book at a minimum here.

My house is not permanently affixed to its piers.

Here are the approved standard details:



This is a detail of my existing piers, as built:

Have you looked up what your house is sitting on using the web soil survey from the USDA? It's not super accurate but it would give you a rough idea of what's under you, geotechnically speaking. Post the PI's and LL's.

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As—Aris-Urban land complex
Map Unit Setting
Elevation: 0 to 4,000 feet
Mean annual precipitation: 8 to 60 inches
Mean annual air temperature: 54 to 73 degrees F
Frost-free period: 180 to 335 days
Map Unit Composition
Aris and similar soils: 55 percent
Urban land: 35 percent
Minor components: 10 percent
Description of Aris
Setting
Landform: Flats
Landform position (three-dimensional): Talf
Down-slope shape: Linear
Across-slope shape: Linear
Parent material: Loamy fluviomarine deposits of late pleistocene age
Properties and qualities
Slope: 0 to 1 percent
Depth to restrictive feature: More than 80 inches
Drainage class: Poorly drained
Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately
low (0.00 to 0.06 in/hr)
Depth to water table: About 18 to 30 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum content: 3 percent
Gypsum, maximum content: 3 percent
Sodium adsorption ratio, maximum: 4.0
Available water capacity: Moderate (about 8.6 inches)
Interpretive groups
Land capability classification (irrigated): 3w
Land capability (nonirrigated): 3w
Ecological site: Loamy Prairie 44-56" PZ (R150AY741TX)
Typical profile
0 to 21 inches: Fine sandy loam
21 to 28 inches: Sandy clay loam
28 to 60 inches: Clay
60 to 78 inches: Clay loam

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0 to 21 inches: Fine sandy loam LL:0-25 PI:NP-7
21 to 28 inches: Sandy clay loam LL:39-48 PI:18-25
28 to 60 inches: Clay LL:42-62 PI:21-36
60 to 78 inches: Clay loam LL:41-60 PI:20-35

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Lots of plastic clay as expected. My vote is for hiring a geotechnical and structural engineer.

Kudos to whomever did your as-built and spent the time to draw all of the "earth" marks.

I find it really hard to believe that a 16x16x4 pier would pass muster for anything but a fancy deck, unless the spacing was 16 oc.

Thank you for the compliment. I can put stuff like that on paper faster than I can put it up in a fancy digital image.

I'm one of the few people I know that still enjoys "manual" drafting. I like drafting with sketch up and autocad for work, but when I'm at home on my time and need a drawing, I break out a scale, t-square, my eraser guard and get to work.

Are you interested in making some money? I'm looking for someone to draft me a set of construction plans for City review. A professional can do it much faster than I can, and I really need some good drawing in case I decide to do the full build myself.

Drafting and cad work are not my business, they just help facilitate construction when I don't have a complete design or need help expressing concerns. One of the BIM guys that I work with is an AIA and very proficient in CAD and may be interested, I can check with him if you'd like.

Sure. I can email a floor plan and elevation as well, if necessary. I have two primary concerns:
1.) getting the foundation right; and 2.) getting the water heater right (i.e. ventilation).

Meant to point it out sooner, but kudos on your hatching. Started playing in this sandbox right after the seeming official death of Monday morning pen shaking and pounce fights. You can often tell CAD folks who started out on a board and understand penweights, arrangment, poche, etc.

If Taco's dude can't help, I can probably have the plumbing done for you.

Well here is my dilemma on the water heater - the utility room is too small for the water heater to be free-standing in the room. It will be a gas water heater. I am leaning toward an electric dryer as well, but I could do gas if I balance the ventilation properly.

What my understanding is (and I could be wrong) is that the WH has to be isolated in it's own closet if the room is too small for free-standing. Upper and lower vents have to be run from the WH closet to the attic for fresh air supply.

I'm not sure how having a gas dryer would or would not affect it.

Can you shoot me a floor plan?

[This message has been edited by UnderoosAg (edited 6/25/2012 6:14p).]

He's gone for the day, so I'll ask in the morning. Guess he's still got a bit of the architect left in him...

Sent.

Block piers were a staple of south-central Texas for construction for many years, fifty years' ago.

This often used off-the-shelf parts solid-cast in a factory, and assembled on site. Friction was usually the only thing holding things together until the weight of the house came in on the piers.

Now--there is some bad news. That detail, the one from CoH? That's for a continuous CMU wall, not block piers. That detail is also missing the anchor details to bolt the mudsill to the block wall, and the straps needed to fasten joints and then framing to the mudsills (otherwise those "hurricane straps" are rather pointless).

So, you need a train-driver.

Does not mean that the train-driver would say no to using an mini-excavator to dig 18" into undisturbed soil, say, using a 34" wide bucket. Then putting a 6" slab with a couple #5 in there. A person with a DIY bent could place CMU block on that footer. I'd be inclined to solid-fill the cells as I went--and not merely the cells with vertical #5 bar.

But, a train driver, one significantly closer than 4 hours' drive, will have a better opinion.

I've decided that, at the very least, I'm going to hire out the foundation work. I'm also strongly considering hiring out the frame shell. I am going to solicit bids for both a shell and full build-out.

Capn - I'm fairly sure that detail isn't for a block wall, not that I would use it for piers anyway.

RTT - shoot me your e-mail address and some basic info on what you want drawn so I can forward it to my coworker. He's interested.



[This message has been edited by Aggietaco (edited 6/26/2012 9:24a).]

[This message has been edited by Ryan the Temp (edited 6/26/2012 9:43a).]

Got your e-mail if you want to remove it.

'Taco,
I concur, but, I'been around what the CoH BI people have to cope with.

Like buubbas who freak at what a solid 8168 runs versus the lightweight "cinder" block down to the big box store.

And, to be in full disclosure, that is the second-to-last foundation I'd recommend anywhere in Harris, Bolivar, Ft Bend, or Waller Counties.

if your going to 24" w sonotube, you'd probably be into using an auger, so if you've got the first cost of an auger covered, go to 5'. deeper the better. if you can get past that first layer of clay and into the sandy clay, you'll be much better off.