Post Holes

[rdevine16]

I live in Florida and I am in the process of building a patio cover coming off the side of the house. There are three posts. Two are buried three feet into the group and surrounded by 320 lbs of concrete each. Im sure this is over kill but wanted to ensure it was not going anywhere. I placed the pressure treated and weather proofed stained post in the hole as I placed concrete around the post.

Is this method OK? Or should have I filled a mold with concrete and then put a bracket inside the hardening concrete?

I have scanned the internet for codes and have yet to find anything saying what I did was incorrect.

[ChugiakTinkerer]

I went through this recently with pressure-treated fence posts.  A rule-of thumb that I discerned from my internet searches is to have one-third of the post in the hole, so if you had a 10' long 4x4 it should ideally have 40" in the hole.  I suspect your 36" or so is more than adequate, particularly if frost is not a concern.

The other concern is water and whether the soil allows adequate drainage.  The two ways of anchoring a post are to pour concrete or pack and tamp crushed gravel around the post.  I opted for gravel on my replacement fence posts because the old ones, which were set in concrete, were rotting away due to water infiltration.  If your posts are going to be exposed to rain, you may want to give them a concrete crown which slopes away from the wood.  Hopefully I can find an image or link which explains it.

See if this helps: http://www.familyhandyman.com/garden-structures/fences/how-to-set-fence-posts-that-won-t-rot/view-all

[NathanS]

Is the post sitting directly on the ground with just concrete surrounding it? For a deck, and depending on your soil, you're probably ok but you should have made sure the concrete (footing) was underneath the post.

The thing is, if the post isn't bearing down on the concrete then the concrete is not really serving any purpose. The purpose of the concrete is to disperse the point load from 6x6 to 12x12 (or however large) where it contacts the ground. If you have soft earth and a lot of weight on those posts they could start sinking. Again, probably not a big deal for a deck.. also don't think it's really a safety issue either since your close to the ground.

Code doesn't talk much about point loads or decks.

[rdevine16]

I basically leveled the post in the ground and put 4 80 lbs backs on concrete around the post. Since this will just have rafters holding the roof on it I just want to make sure it will last before I start to place the roof on it.

[ChugiakTinkerer]

I basically leveled the post in the ground and put 4 80 lbs backs on concrete around the post. Since this will just have rafters holding the roof on it I just want to make sure it will last before I start to place the roof on it.

If your soil is well drained you probably have nothing to worry about.  If you have clayey soil then you might be wishing there was some crushed gravel underneath the post.

[Don_P]

we ran through the numbers for the roof beams 3315 lbs on each beam. The posts carry half the beam load so the end posts carry about 1658 lbs and the center post carries half the weight of 2 beams, 3315 lbs.

Typically if the soil isn't mush we assume 1500-2000 lbs of bearing capacity per square foot. A 6x6 is 1/4 of a square foot, optimistically the post end can hold up 500 lbs, the design load is 1650 lbs, the concrete sleeve is worthless for bearing. The wood dries and shrinks away from the 'crete and is free to slip down. The wood gets wet and cracks the concrete, again letting the post slip down. It does hold moisture around the post and helps to rot it faster. I see this all too often. Lagging angle iron to the post and out onto the top of the concrete will help engage the concrete as a footing... but that is not the right way to set posts.

[rdevine16]

Thanks for the help Don. I'm going to get the posts back up and do it right. What is a more secure methodology, setting a putting and then add the beam into the column of concrete or set a base and use a tube with concrete and set a column fastener at the top then attach the post to the concrete?

[Don_P]

Generally for stuff like this I dig a 2' square hole, and place at least 8" of concrete with 4 18" pieces of rebar 3" off the bottom in a # pattern. For FL the bottom of the footing needs to be at least 12" down but you do pick up bracing the deeper you go. I prefer to put the post in the ground, on the footing and attached there, no unbraced hinge points.

for you anything deeper than 1' is fine, the deeper you go the more lateral stability and uplift resistance. The roof diaphragm is really providing the lateral from its rigid connection with the house. At this frost depth if  the weight of the structure and concrete are higher than the uplift load, then if you want to put the post above grade just pour up to grade, a 2'x2'x1' tall footing is not going to overturn.

[rdevine16]

With the footing that you describe I have a couple questions.

Do I let the footing cure before I put the post in?
Do I need to rebar the concrete around the post to the footing?
Looks like concrete is only at the base of the post. You are just backfilling with earth correct?

[Don_P]

I let the footing set overnight, it is tender for a month don't bang it.
#2.. I hate it when a good sentence goes bad  I think you are asking about the post bracket. I do them a few ways. The easiest is to hammer drill angle iron clips into the footing later and lag to the post. You can tune the final location easier. Be aware that has real limits, if you drift over towards the edge of a footing it tips under load later... it is eccentrically loaded rather than being concentrically loaded. Another way, for a concealed connection I'll cast a flat plate vertically into the top and kerf the middle of the post, drop the post over the vertical steel, drill through pin and plug. You can also mount a steel plate to the bottom of the post. Cast a larger flat plate horizontally on top of the concrete, weld hooks on the bottom to go into the "mud", drift post around on the flat plate to final location and weld. Just remember the roof is a big kite, design thinking about down, up and sideways.
Concrete around the post increases its diameter, if it is buried that increases the bracing laterally against the soil. That is overrated, soil is slow molasses, especially if disturbed. Design your lateral resistance elsewhwere but if you want to dig deeper and backfill with soil or concrete view that as the gravy rather than the main course bracing wise, don't rely on it. The flat plane of the roof above, well connected to a rigid building is actually what is bracing the posts sideways, so you are good for lateral IMO.

[rdevine16]

Don, I ripped the post back up. The 320 lbs of concrete on the post was difficult but I got it done. I rebuild the holes to be 2'x2'x2.5'. I put about 7'' of concrete with rebar and then put rebar to hold the sonic tub up. At the top Im going to put a 6x6 simpson tie that is going to be cemented part way up.The pic below is showing the rebar about 3 inches in the cement. Then put another 4 inches on top.

[NathanS]

Looks great.

Can't believe you got that concrete and post out.

[rdevine16]

Let me tell you, it wasnt easy. I was lucky enough that I could just cut the post right off at the point where the concrete was. I was still able to have 8 feet of post left to put on top of the sonic tube. I am very happy with the changes you and Don had me make. I think it will be a much improved post. Also i am happy to have the post above the ground. Being Tampa, FL we do get a lot of rain during the summer and have had some standing water at times due to tropical storms so this will make me much happier.

The next obstacle to tackle is how to best attach the rafters to the top plate! I believe you and Don are helping me there as well. This weekend I will provide some more pictures of exactly what I have to work with. I have a much better idea of what the end result should be now.

Thanks again for all the help!

[Don_P]

Yeah, I'm thinking I'm pretty glad I was not within arms reach while you were getting that out    Looks like grey marl or is that just concrete on the soil?