Residential Deck - Wood Post

[slickdeals]

I don't have experience in residential construction and might come across as a rookie question

What is the preferred foundation detail for a wood post that supports a balcony deck. Recommendations are for bottom of footing be 42" below the existing grade for frost protection.

I was thinking of using a 12" diameter sonotube, 4 foot tall (no flare at bottom). The top of sonotube would be at grade level so that slab on grade at the entry can go around the wood post. Or should I do a 16x16x8" footing and have a 10" sonotube set on top of it.

 

[CANPRO]

These bigfoot forms work well.

http://www.bigfootsystems.com/

 

[CELinOttawa]

Often it is simply a posthole... Depends on the geotech, and often longer is used to avoid the footing. Actually getting the footing down without silly amounts of excavation is the trick.

Those big foots are great, but necessitate a great deal of excavation. I don't favour them at all.

 

[JAE]

slickdeals - what I've done in design and for my own deck:

Excavate a 12" to 16" dia. hole x 4 ft deep (or whatever you need to get below frost).
Set a single anchor bolt in center to work with a post base product like this:

http://www.strongtie.com/ftp/catalogs/c-2013/C-2013-p055.pdf

I had four 6x6 posts that were set like this:

 

[rittz]

The sonotube on a footing is ok if you are not in soil that is soil subject to frost heave. We often set such a post on cast in place concrete piles dia 10 to 12" and depth 10 to 12 ft. They are economical if you have access to a drill.

 

[CELinOttawa]

Rittz: While there is a great deal of frost action on the side of the sonotubes, they can successfully be used in soils that freeze. We have a frostline below five feet and most every deck I know of around Ottawa has simple sonotube foundations. The bottom of the drilled sonotube shaft is typically specified to be belled out, but this is often either minimal or not possible at all below 4 feet of excavation.

I agree that it is best to have a real footing in frost, but you can design around the restriction.

 

[rittz]

Hi Celinotawa
I was thinking more of decks which are covered with a rof which is attached to the house (walls and often roof). I have seen a deck built to be just that (a deck) later become what amounts to an addition which damaged the main roof due to heave or more often settlement.

 

[CELinOttawa]

rittz: Absolutely; I've seen those as well! It is shocking that the Cities don't just plain old fashioned force people to correct or tear down. Sometimes I think our industry has become almost too "customer oriented" without remembering that it is the next, and after the next (etc, etc) which we are meant to be protecting.

 

[madmantrapper]

I'm in Maryland, most counties here require 16 to 20 inch diameter 8 inch thick footer below frost line 30 inch in most areas.

 

[rittz]

Maryland
I love your frost line !! Try 66" .... -25C here today! !

 

[Splitrings]

If you truly have a soil that is frost susceptible, (not just a soil that freezes) you are going to want a bell or footing below the frost depth. I have seen and personally experienced a frost susceptible soil pull 6 and 8” construction tube concrete columns out of the ground like toothpicks. This then jambs the deck and or porch rails into the side of the structure it is attached to.

 

[slickdeals]

I am going ahead with a 16" x 16" x 10" footing or giving the contractor the option to use a 24" diameter "bigfoot".

Some of these posts are also supporting a roof over the deck and I would rather be a little conservative in this case.

 

[CELinOttawa]

Absolutely agreed: Bell bottoms are best!

 

[XR250]

I guess you could also use helical piers and extend the pipe up to the framing

 

[a2mfk]

Remember that roof could have some high uplift forces if it is connected to the main structure and acts as a overhang... If you use a sonotube, this may not give you much in terms of frictional forces but you may want to neglect those anyway and just use the dead load of the concrete.