[poolecw]

See below for a layout of my deck piers. I have read through the Prescriptive Residential wood Deck Construction Guide and have tried to base my designs off its codes. I am not required to follow codes in my area, however.

Note: Frost line is 12" in my area.

I have couple of questions that I hope you guys can help me out with.

1. If I read through correctly, my pier footings are to be 24" x 24" x 11" and the piers would be 8" diameter. This seems like overkill to me. Does this seem right to you?

2. Overall deck height will be 2' so I will plan on not using 6" x 6" posts between pier and beam. Instead, I will rest the wooden beams directly on the concrete pier. Any concerns there?

3. What fastener would you recommend to connect the 2x10 beams to the concrete pier? I would like something adjustable in case I'm slightly off in my X direction or height.

4. I will have close to $900 in just material for the footings and piers. This is not counting digging equipment rental. Are there alternatives such as the Titan Deck Foot anchor that would work just as well?

Thanks and I appreciate any comments you can throw my way.

 

[de-nagorg]

I noticed 1 thing that needs rethought.

Wood should never rest on concrete, it will rot the wood too fast.

And depending on the size of your beams, 8 inch piers sound right to me.

ED

 

[poolecw]

I noticed 1 thing that needs rethought.

Wood should never rest on concrete, it will rot the wood too fast.

And depending on the size of your beams, 8 inch piers sound right to me.

ED

Correct, I wouldn't rest the beam directly on the concrete pier. I am looking for some time of connector with a standoff.

I'm really not questioning the 8" dia piers but rather the 24 x 24 x 11 footing that the pier would rest on.

 

[de-nagorg]

Simpson makes good standoffs, look their website up, and see them.

The 24X24X11 does seem a lot too much for a deck, you could just use the 8 inch piers if you went down past your frost line.


ED

 

[Daniel Holzman]

The Guide is not code, it is simply a guidance document. Some jurisdictions (mine included) have adopted the Guide as the local code, but apparently you have no code in your area, so the Guide is just that.

As for pier size, you can size piers based on the soil bearing capacity, which requires you to understand what type of soil you have. Bearing capacity for soil varies a lot, from something like 500 pounds per square foot for weak soils like soft clay or loose silt to up to 10,000 pounds per square foot for dense glacial till. Your local building inspector may know the bearing capacity of typical soils in your area.

Assuming you can figure out the soil bearing capacity, you then need to know the load on each pier. Since you have no code, you can probably use 50 pounds per square foot deck load including live and dead load. Figure out how many square feet contribute to each pier, multiply by 50, and you will have the total load on the pier. Double the load as a factor of safety to get design load.

The calculate the area of the pier resting on the soil. An 8 inch pier has an area of 0.35 square feet. So if your design calls for say 25 square feet on a given pier, the design load would be 25 * 50 * 2 = 2500 pounds. 2500/0.35 = 7160 lbs per square foot, which would be on the upper end of soil bearing capacity. Now you can see why the Guide recommended a larger area, since it is unlikely your soil has such a high capacity.

If you used the value you indicated you got from the Guide, namely 4 square feet, then for the same design load of 2500 lbs, you would only need about 600 pounds per square foot soil bearing capacity, which is on the low end of soils, and likely your soils would work.

Conclusion: You need to understand your pier loading, which depends on the geometry of your deck. The load on each pier needs to be individually computed, and you might as well design each pier for the highest loading. You also need to know how strong your soil is, which depends on soil type and groundwater level, but for most soils 600 psf is OK.

 

[ront02769]

Look somewhere else on this site and you will find someone in deep doo doo with the locals for a n eight inch pier.....wanted twelve inch! Ron

 

[de-nagorg]

Look somewhere else on this site and you will find someone in deep doo doo with the locals for a n eight inch pier.....wanted twelve inch! Ron

In OP first paragraph, they are not required to follow codes for their area.


ED

 

[carpdad]

Your pier locations: the joint between small and big squares - you don't need separate piers. One set of piers there and may be one more hole because the load is greater, but two sets there can make the joint become two different heights later if the piers settle differently.
I'm in NJ and the usual footing is 12" diameter when 8' o.c. That is on beige looking soil, hard compact when 3-4' under the surface. I dig down and then hand dig again with a small shovel until I can feel undisturbed soil. That's always passed the inspection - some towns want hole inspection and some did not. Ask your town. They can tell you a general condition and general footing size requirements. Ask for the soil inspection. Have handy clam hole digger and 6' spike - they make small adjustments easier.
Using posts make the work easier and maybe later repairs. Posts are separate and smaller pieces then one whole beam.