deck foundation

[RustyShackleford]

I am building a small deck and not sure how I want to do the footings and supports. One side is attached to the house (with a ledger board bolted to foundation wall), but the other side is supported by a 12ft girder of twin 2x8s, supported in the middle and each end. Code (and approved permit) says the middle and end supports must be on 16" and 12" diameter footers, respectively (all 8" thick, with the bottom 12" below grade in our pretty warm climate). Also, the bottom of the girder is less than a foot above grade.

At first I thought I'd use those cardboard tubes and have 'em come up a few inches above grade (so about 16" tall in all), with anchors and post bases holding 6x6s that support the girder. But that's a good bit of Sakrete to mix. Inspector rec'd just making the holes 16" square and using solid block (two layers of two 4x8x16" cap blocks) as the footer, with the 6x6s buried and resting on the block. But I don't like the idea of burying the 6x6, even though it's "ground contact" - though I gather that backfilling with crushed stone helps a lot with rotting. Burying the posts IN concrete is nutzoid IMHO, because it's the worst of both worlds: need lots of concrete, but wood can still rot. So I'm thinking maybe to bury the posts, but make them with Sakrete using 8"-diameter form tubes, so concrete comes all the way from the footer to the bottom of the girder; but I wonder if it's kosher to have a poured post like that (that comes above grade), or if it's ok if there's some rebar. Anyone have other ideas that don't involve so much concrete (as my original plan) but don't involve burying any wood either ?

 

[gzecc]

I would pour the footing 16" deep.

 

[semipro]

Use solid cap blocks in hole with these sitting on top to bring it above grade.

Since you should also prevent uplift of your deck from wind per code I'd also attach the posts to the blocks above somehow.

 

[Butcher]

6x6 is over kill for your posts. I've built many decks and never used anything bigger than a treated 4x4. I wouldn't worry about burying them in the ground if you use rock as fill for drainage. Here in my area we have to dig holes to a minimum depth of 48inches for frost. If they are available in your area and you were worried about rot you could go with a laminated treated post like use. Glued and nailed together after the treatment process so more chemical is infused into the wood.
OOPS sideways but you get the idea.

 

[RustyShackleford]

Thanks guys. I already have the 6x6 (the posts are so short that one 8ft-er is enough), and that was what was in the approved plan (I'm sure you're right that 4x4 would pass, but it'd be a minor hassle). I like the idea of those shaped pyramidal blocks - I've seen ones that'll hold a 6x6 on the www, but I don't think the local Lowes/H'Depot have any but the 4x4 ones.

 

[GENECOP]

Thanks guys. I already have the 6x6 (the posts are so short that one 8ft-er is enough), and that was what was in the approved plan (I'm sure you're right that 4x4 would pass, but it'd be a minor hassle). I like the idea of those shaped pyramidal blocks - I've seen ones that'll hold a 6x6 on the www, but I don't think the local Lowes/H'Depot have any but the 4x4 ones.

You can use the 4x4 pyramid with the 6x6 post, just rabbid out the foot of the 6x6 to 3-1/2"x3-1/2"....it will lock in nicely...

 

[DAKSY]

If you've already got the 6x6s, use them. Buy one Sono tube ,cut it in two & bury each piece to the depth you need
Fill it with Sacrete & before it sets up, mount a 1/2" diameter x 6 - 8" long "J" bolt in the top center, extending 3 - 4"
out of the concrete mix. This will allow you to drill into the bottom of the 6x6 & position the hole over the J-bolt.
Notch the top of the 6x6 so that your bearing beam will sit ON the 6x6 & also can be bolted or lagged to the post.
I've built 50+ decks in this manner, but I have to go to 42" deep up here to get below the 36" frost line depth...

 

[gzecc]

You could use these to secure your 6x6's
http://www.homedepot.com/p/Simpson-...ndoff-Post-Base-ABA66Z/100375370?N=5yc1vZaqzs

 

[RustyShackleford]

If you've already got the 6x6s, use them. Buy one Sono tube ,cut it in two & bury each piece to the depth you need
Fill it with Sacrete & before it sets up, mount a 1/2" diameter x 6 - 8" long "J" bolt in the top center, extending 3 - 4"
out of the concrete mix. This will allow you to drill into the bottom of the 6x6 & position the hole over the J-bolt.

You're talking about burying the posts then. Yeah, if I go that route, I was planning to do what you say (a hole in the bottom of the post to hold it in position over some kind of stud coming out of the concrete).

Notch the top of the 6x6 so that your bearing beam will sit ON the 6x6 & also can be bolted or lagged to the post.

Yup, planning to do that too. Great minds think alike

Isn't there some chemical you can out on treated wood where you have exposed untreated material - be it your positioning holes, or rabbiting out the bottom of the 6x6s so they fit in 4x4 pyramids - so rot doesn't start there ? Anyone know what that is ?

 

[RustyShackleford]

You could use these to secure your 6x6's
http://www.homedepot.com/p/Simpson-...ndoff-Post-Base-ABA66Z/100375370?N=5yc1vZaqzs

Yes, used those in another deck I built, where I had the sonotube come out slightly above grade.

 

[ChipTam]

If you've already got the 6x6s, use them. Buy one Sono tube ,cut it in two & bury each piece to the depth you need
Fill it with Sacrete & before it sets up, mount a 1/2" diameter x 6 - 8" long "J" bolt in the top center, extending 3 - 4"
out of the concrete mix. This will allow you to drill into the bottom of the 6x6 & position the hole over the J-bolt.
Notch the top of the 6x6 so that your bearing beam will sit ON the 6x6 & also can be bolted or lagged to the post.
I've built 50+ decks in this manner, but I have to go to 42" deep up here to get below the 36" frost line depth...

Last September, I finished a new deck for our summer home in Newfoundland and basically used your Sono tube technique. We did use a 6x6 adjustable steel post bracket on top of the J-Bolt. Also, we used a bubble level and string to determine a level line 2-3" above grade. We then drove a finish nail into the Sono-tubes at that level line so that we could pour concrete just up to that line.......not perfectly level but close enough. I would also have had to go down 42" if that were possible but we always hit ledge well before that. I guess they don't call Nfld. "the rock" for nothing.

ChipTam

 

[RustyShackleford]

I'm thinking that for the two outer posts (at the ends of the girder), I'll just pour 8" of Sakrete in a sonotube at the bottom of the hole, and then bury the post sitting on top of that (using a stud in the concrete, and a drilled hole in the bottom of the post to keep it in position). Lots of folks here seem to be saying it'll be just fine, that the post will not rot out. BUT ... if it does, it'll be easy to replace, as those will be at the edge of the deck and only extending 4-6" below grade (since the hole only needs to be 12" deep here).

For the one in the center, I'm going to figure out how to keep from burying wood (the deck is SO low, that it'd be a bear to replace). Maybe the pyramidal block, notching the 6x6 so it'll sit in the 4x4 recess (jerks at HomeDepot list one for a 6x6, and are spamming my facebook with it, but I can't actually buy it). Or maybe pouring an 8" diameter post on top of the 8" thick footer at the bottom of the hole. Seems like I could just stick three pieces of rebar in the base, and the next day stick an 8" sonotube over that and fill it. Sounds kinda fun.

 

[Retired Guy]

There used to be an outfit around here that used these.
http://www.postech-foundations.com/

 

[RustyShackleford]

There used to be an outfit around here that used these.
http://www.postech-foundations.com/

Thanks. I'm already over-thinking it, as I'll have a tendency to do. But I draw the line at using anything I can't buy locally

 

[RustyShackleford]

Decided to go the easy route and pour 6-8" of concrete at the bottom of the 12-14" deep hole, then set the posts on top of that and backfill.

Wondering if it's ok to do it today: temp will be pushing 50 when I pour in the afternoon, low 20s overnight. I know the concrete mustn't freeze, but I'd put some old fiberglass insulation in the 6" or so gap between the top of the concrete and the top of the hole (and of course It's an exothermic reaction). I want to get this done - but don't want to screw up.

 

[gzecc]

Decided to go the easy route and pour 6-8" of concrete at the bottom of the 12-14" deep hole, then set the posts on top of that and backfill.

Wondering if it's ok to do it today: temp will be pushing 50 when I pour in the afternoon, low 20s overnight. I know the concrete mustn't freeze, but I'd put some old fiberglass insulation in the 6" or so gap between the top of the concrete and the top of the hole (and of course It's an exothermic reaction). I want to get this done - but don't want to screw up.

Cover with plastic and dirt, hopefully it will be ok.

 

[RustyShackleford]

Cover with plastic and dirt, hopefully it will be ok.

Finally found a use for those 6" x 4' x 8' blocks of styrofoam I bought from a neighbor last year. Temp stayed at 44 last night !