Wood post sitting on concrete 3

[canwesteng]

I'm doing a deck "design" for an as built deck for an acquaintance, essentially just figuring out what needs to be fixed so I can put a stamp on it to get the city to approve it. The posts sit directly on concrete (pressure treated, still a concern though for rot).
I mostly work in industrial, so rarely deal with wood, and if this came up I would just make the contractor tear it down and install a proper base, or ignore it if it was a temporary install. Probably neither are great options here though. I'm thinking jacking up the deck, and placing some poly or something between the pile and the post. Should I go the whole nine yards and jack it up and put a base plate on to get separation between the two?
The project is in a fairly dry region, but the post base would be damp for some time during spring snow melt.

 

[skeletron]

Strictly speaking in terms of Code, you might want to check (NBCC or equivalent Part 9):

9.17.4.3: Wood column in contact with concrete requirement
9.23.6.2: What is the area of the deck? Is the deck covered? What is the height of the deck?
9.35.3.4: (Kind of like a carport) What is the separation of the top of concrete, u/s of wood to grade

It likely comes down to what the expected performance of the owner and the minimum requirements of the AHJ. I'm not sure you could jack the post and fasten the baseplate (ideal reliability solution) to the concrete without somehow deconstructing the post.

 

[NorthCivil]

>I'm doing a deck "design" for an as built deck for an acquaintance,
>essentially just figuring out what needs to be fixed so I can put a stamp on it to get the city to approve it.
>I mostly work in industrial, so rarely deal with wood

Sounds like great work! a favor for a "friend" outside your scope of practice to design something thats already been built! any design input that requests something additional to what is already there will surely win over their hearts and minds! if not paid, you will surely be appreciated!

Jokes aside, have them put these down.

https://www.strongtie.com/retrofitpostbases_postbases/aba_base/p/aba

thats the standard. keep the wood off the concrete, let it breathe.

 

[NorthCivil]

This ticks all the boxes for the things the engineering associations in Canada tell you to watch out for when agreeing to work on a job! I find this so hilarious, been dealing with my association recently so this gives me a great laugh.

it is just a deck though, but remember, decks often collapse and still need to be done right.

 

[canwesteng]

skeletron -

Good feedback. I'll be designing the deck to the requirements of part 4 (otherwise I wouldn't stamp), but it is good to review the req's of part 9. The AHJ will basically accept anything stamped by an engineer, and the owner is just your regular homeowner, so really I should be dictating the minimum performance here, i.e. a design that protects occupant safety. The thing is, part 9 seems to allow getting poly underneath, I'm concerned with how well that will work if it's exposed to rain/snow, since then moisture gets between the poly and the wood, instead of just migrating through the concrete to the end grain.

Northcivl -

Definitely not rubber stamping this. Oddly enough it's not entirely out of my scope of practice, being basically a braced timber frame, which have some use on industrial sites. Wouldn't be tackling this if it were the standard shear wall/diaphragm construction. I know about the standard post bases from simpson, the problem is I'm only aware of post bases that are screwed vertically into the concrete, so you can't jack up the post and slide it in. The hot tub is also already on the deck, conveniently enough, so they'd need to get a crane back out.

I'm thinking jack it up, then slide in the moisture break, place it down and secure plates like Simpson RPBZ. What if the break was 6 mil poly, a plank, and then the post? Somewhat elevates the post, the end grain doesn't sit on concrete, and hopefully the plank wicks some moisture away.

 

[dik]

Simpson as well as others, I suspect, make a connection using stamped material that elevates the wood above the concrete.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

From an earlier project...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

Use a Simpson CPS4 or CPS6 for retrofit. Does not require pin on bottom but can be fastened to concrete with TapCons. I would also suggest coating the bottom of the post with a good penetrating waterproofing solution. If you don't use the Simpson device, coat the bottom and up the sides of the post with asphalt mastic.

 

[dik]

careful, some asphalt mastics are carcinogenic...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[canwesteng]

Ron - would be CPS6, but I'm concerned about how to coat the base of the post - would have to jack the deck up quite a bit. I was thinking something like this could slide in

https://www.tremcosealants.com/mark...tems/protection-courses/elastomeric-sheeting/

Or slide CPS with this base

https://www.strongtie.com/retrofitpostbases_postbases/rpbz_base/p/rpbz

 

[Ron]

@canwesteng....lift a little, squeeze asphalt mastic under the post, then fix with the Simpson RPBZ.