Pour concrete footing for carport post

[the fixer]

I have a carport that's settling a bit on one side due to a combination of a drainage issue and a lack of proper footing. It used to have a footing, but someone moved the post a foot or so away and must have just stuck it in bare dirt. I can tackle the drainage issue, but I need to figure out how to install a proper concrete footing under the affected post.

I've got this much of a plan figured out, partially by watching https://www.youtube.com/watch?v=MCa_87Dkw1M

• Rent a screw jack to support the carport beam near the post, jack up to level
• Remove the post
• Dig a post hole, add gravel, insert form, mix & pour concrete, add bracket
• Wait 2-3 days
• If possible, reuse old post by cutting to fit and reinstalling after concrete has set
• Remove screw jack

My questions:

• How much help should I expect to need on this project? It doesn't sound too hard, but some aspects like removing and reinstalling the post sound like I'll need at least one helper.
• How do I figure out what building codes apply, especially for how deep the footing needs to go?
• Any considerations for keeping the carport safely supported by a screw jack for 3 days? This is a rental so there will be tenants around.
• Am I missing anything?

[zataks]

Sounds like a 1-2 man job.
Call your local code enforcement office[r]?  (Not really sure here, never had to deal with it)
Section off the area with cones, tape, something to keep people from possibly hitting the jack.  Or dig the new post hole far enough away that you only need a jack for the     time between pulling the old post and inserting it into the new hole.  By spreading the concrete pour over 2 days you could probably avoid sinking issues (pour once deep to rest the next pour and post on).
I don't really think you need a form for this.  Just dig deep enough and wide enough to get ample concrete in that hole, pour and set and walk away.  If you're really concerned about it, do some light finishing/hand forming on the top 1"-2" of concrete and make sure the rest is buried.

[Greg]

For our PNW, you want the bottom of the footing 18" below grade.  I prefer to use cylindrical "sonotube" forms for footing piers.  A square pier will also work.  The idea of the pier is to get the wood up out of the dirt at least 6".  2 lengths of #4 (1/2") rebar at 90º in the footing (4 total).  The footing should be about 16" x 16" or 18" dia. if round.  Doesn't need to be pretty.

You could use a slightly too-long 4x4 to wedge up the end of the beam to relieve the pressure on the post. Set a Simpson EPB44 in the new footing to accept the bottom of the post.

[the fixer]

Okay, thanks for the suggestions.

I'm starting to consider using my truck bottle jack + jack stands instead of renting a screw jack. I'd just need a steel plate and some 4x4s to act as an extension, which I can repurpose later for other projects. I could use the old post sitting on the old pier to hold everything up for the couple days while the concrete is drying.

I'm not sure I understand where the rebar goes or its orientation... is it like this?

[Greg]

Yes, that's the orientation.  I usually evenly space it out, keeping it 3" from the edges, but in reality you don't have to be too exact.  You can even fill the footing 1/2 way with concrete, place the rebar by hand, and continue filling.

Use single lengths instead of overlapping pieces.  The ones in your image that are spliced are not acceptable.  They also don't need to stick out of the footing.

Hope that helps.

[zataks]

The ones in your image that are spliced are not acceptable.

This is news to me.  Please explain?

[Exflyboy]

The size of the footing math works this way.

Typically in the PNW roofs are designed for a snow load of 20 pounds per sq foot. Ok so take the size of your roof in sq feet and multiply by 20.. = big number


So take the big number and divide by the number of posts you have... This gives the load on each post.

Then for the nasty clay soils around here you are allowed a load of 1500 pounds per square foot.

So take the load on each post, divide by 1500 = the number of square feet the area of you footing needs to be.

Using Greg's example of an 18" round footing, then this is capable of supporting 1500 * the area of the footing (1.8 sqft) = 2650 pounds.

If you had say 4 posts the 2650 * 4 = 10,600 pounds total snow load.. thus the area of your roof could be 10,600/20 = 530 sqft.. or about 23 ft by 23ft.

Of course you would probably not try to put a 23 ft square roof on just 4 post.. but 6 posts, 12foot on center would be well within the design limitations.

Make sure your footing is think enough.. the building code guy around here would want 6" thick for an 18" round footing.. thats without rebar.

Frank

[Milspecstache]

Yes, that's the orientation.  I usually evenly space it out, keeping it 3" from the edges, but in reality you don't have to be too exact.  You can even fill the footing 1/2 way with concrete, place the rebar by hand, and continue filling.

Use single lengths instead of overlapping pieces.  The ones in your image that are spliced are not acceptable.  They also don't need to stick out of the footing.

Hope that helps.

Make sure you keep the rebar 3" from the edges.  This is to keep the rebar from rusting from water wicking into the concrete which could cause the rebar to rust and then 'spall' which will break up the concrete (and speed up this cycle).  If you look at concrete bridges you will see this occuring.

[the fixer]

Ugh, so I did some exploratory digging this afternoon and realized there's an existing concrete pier under there. It's several inches below grade, much more than the amount that the carport roof has settled. Now it seems like I'll need to pull out the old one.

Also in the photo you can see there's an old tree stump nearby... fun! I'll have to remove it in order to get a big enough post hole for an 18" diameter pier. It's also in the way of installing drainage pipe for the downspout.

[Greg]

If the footing you found is in the right place and big enough, you can rotohammer some holes in it and use epoxy to anchor some rebar in it to tie into a pier you form on top of it.

[Greg]

The ones in your image that are spliced are not acceptable.

This is news to me.  Please explain?

The splice weakens the reinforcement qualities of the bar, and in any case the splice does not overlap enough.  You want a 12" overlap.

[the fixer]

The footing is definitely not 18" wide, it's significantly less than that. Might be why the beam it supports shows signs of about an inch of settling.

[zataks]

The splice weakens the reinforcement qualities of the bar, and in any case the splice does not overlap enough.  You want a 12" overlap.

Good stuff; thanks!

[paddedhat]

Rebar, splicing, Calling the code official, what................TF.   You guys are doing mosquito control with a shotgun here.  First, in a tiny little footing like this, rebar is not a code requirement, a need, or anything but a waste of time and money. Dig the area out to below frost. Keep the sides of the poured area sharp and clean as possible. Get all the loose material out of the bottom.  Tamp the bottom vigorously with a piece of 4x4, and use the bottom of the hole as a form. Grab 3-4 bags of sacrete concrete mix, mix up a fairly stiff mix, and dump in the hole. Take a flat shovel and use it to vigorously place the mix in position by stabbing straight down into the wet mix a few dozen times to get it settled in. Reach down and use a short block of wood as a trowel, make the top surface decently flat and level............ that's all folks.  Remember there are thousands of buildings (pole barns) that sit on posts that were placed in holes bored by tractor driven augers, with the post sitting on top of a single bag of sacrete, poured into the hole DRY and tamped a bit, before placing the post.

Now for those of you that have an itchy keyboard finger here, and disagree. I have done countless hundreds of these, in an area where we get 4-5' of frost, where code inspectors look at, and measure every hole, and have done so for decades. I have yet to hear of an issue with a single one of them.

As for lifting the existing beam. It takes a 4x4, a bottle jack, and a small scrap of steel to prevent the bottle jack ram from penetrating the bottom of the 4x4. If you lack a firm base for the jack, use wood blocking, like a scrap of a floor joist, or landscape timber. Take measurements from a fixed point, before, during and after. Go slow, lift in small increments. And keep your game face on, because occasionally a beam like this will make a noise like a shotgun blast as it's being forced upward. Screaming like a little girl and running is not in your best interest. LOL. Be careful, take it slow, and it will turn out great.

[Greg]

Here is seismic zone D1 rebar is very often required in an isolated footing.  Seattle is even stricter in most cases, due to it being Seattle (too much coffee?) and not unincorporated county.  While the building dept. prescriptive forms actually show footing specs without rebar, usually they will recommend or require rebar in a footing if you ask or submit plans.

the fixer can do what he wants of course, but it being a rental and in the city, overdoing it is what I would recommend.

In general I'm not a fan of the post-in-a-hole method, simply because it puts wood in the ground.  I prefer the wood up in the air and accessible for future replacement or repair.

[paddedhat]

Here is seismic zone D1 rebar is very often required in an isolated footing.  Seattle is even stricter in most cases, due to it being Seattle (too much coffee?) and not unincorporated county.  While the building dept. prescriptive forms actually show footing specs without rebar, usually they will recommend or require rebar in a footing if you ask or submit plans.

I used to submit it on plans, until my concrete contractor, who is ahead of me by a few decades, an a few million yards asked why I was wasting money? As for seismic requirements, well if it's required and inspected there is no real option, but lets get real here, a few scraps of rebar in a carport footing is doing absolutely nothing but wasting metal.

the fixer can do what he wants of course, but it being a rental and in the city, overdoing it is what I would recommend.

I'm done with overdoing. Do it right, do your best, but wasting money because it makes me feel better to overbuild, nope it's over. I live in an area that traditionally had a well deserved rep. for low quality construction. In a neighborhood full of 30-40 Y.O crappy homes, with little exception, they are valued the same as the ones I built, do 99% of what they need to do, and were far cheaper to build. Overdone is an interesting obsession. You care about your work, you take pride in it, I am part of a limited audience that can appreciate what you done, and respect you for it. 99% of the other's out there don't know, couldn't care, and will suffer zero effect from things not being done to your standards. Not bitter in the least, just a realist.

In general I'm not a fan of the post-in-a-hole method, simply because it puts wood in the ground.  I prefer the wood up in the air and accessible for future replacement or repair.
In most locations and ground condition, a ground contact rated, uncut, treated 4x4 will be doing just fine in a hole, decades from now. It's cheaper, easier for a DIYer, provides lateral stability to the structure, and adequately durable.

[Greg]

I know, I know, we disagree on this.  A few dollars' worth of rebar in the footing is cheap piece of mind though.  I look at it this way; if someone with authority asks about the repair, and you could show a pic of the rebar in the hole to show that you did "a good job", then it's worth it to me.