I'm planning a deck for my new house. I think I've got pretty much everything figured out, but I'm concerned about one thing. My county requires 18" round, 24" deep footings with 8" of concrete. If I only use 8" of concrete, the post bases will be 16" down in an 18" hole. There's no room to swing a hammer down there. How can I attach my (6x6) posts to the post bases?
I have a couple ideas. Obviously, I could just pour enough concrete to raise the post bases up to the surface. That's a LOT of concrete to mix by hand, but it's not impossible. Another possibility is to use screws instead of nails with a 90 degree drill attachment. Anybody have a better idea? I'd really appreciate it.
*I think that every deck that I have seen has the footings come above the surface so that the wood and hardware is not in direct contact with the earth. The only thought that comes to my mind is to make wider holes.
I suppose you could put a long bolt directly into the footing with a long protrusion. Then drill out the center of the post and have it slide over it. I don't know how you would make a solid connection though.
Dig your 18" diameter hole 24" deep. Pour 8" of concrete. Stick in a few vertical rebar near the center. Let that sit for a bit. Position an 8" (or 10") diameter sonotube over the center of the base. (Pro Tip: the rebar should be inside the sonotube :) Cut off sonotube, leaving at least a few inches above grade. Carefully backfill. Pour. Done.
Run this by your local building inspector before you do it, of course.
18" round, 24" deep footings with 8" of concrete. The 8" depth part is the footing as you indicated. The remaining part should be at least above soil level height and of concrete as well. These are the piers. The piers can be round or square in shape. The posts you are working with go on top of the piers. There's more in the detail, but that's the general gist of things.
Get with the county when you pour the footings, they may want to observe the pour and check the depth before concrete sets up. The piers are tied to the footings via rebar that juts from the footings during that pour. Some ways to tie the 6X6 post to top of the pier is rebar jutting about 6" from the pier, drill a hole on the bottom of each 6X6 for that. Another way is using flashing embedded into top the pier while its poured and nailing that flashing to the 6X6. Suggest you dig all the holes, setup and tie the rebar etc. first. Rent a machine to mix all the concrete and do it in one day for the footings. Setup the piers forms or sonobuoys, and rebar, pour the piers a day or 2 later.
I'm guessing you're in the southern part of the states. We have a frostline of 42", in the part of the Midwest I'm in.
I have no idea where the people which said the lumber has to be above ground, get their information. With the properly treated lumber such as ACQ
0.40 retention, it is made for ground contact. Here's a couple links, and the net is full of ground contact lumber. Pole barns are commonly built this way, along with decks.
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You don't need a strong tie attachment at all, unless this was specified by the inspector. I would ask the inspector to clarify the 18" round. That would take one mighty big auger bit.
Look at the bottom photo where you can actually see the supporting 4X4s and the soil in its vicinity. You will see that the treated lumber is not in the soil. Its embedded in concrete below the soil line. None of it is actually contacting soil. At least, not for now. That is common.
The smart, but most laborious way, is to build the piers entirely of concrete. The piers supporting the beams that hold the deck. All treated lumber eventually rots.
No one said the building method was undoable. Its not long term oriented though. Common when bulding deck attachments to a home.
My pier and beam home sits on 24" round footings. Its in central TX. They used the machine normally used for making holes for utility poles to drill/cut it out. They flared the bottom of each hole manually.
18" round footings are common for structures that don't bear as much weight.
No earth to wood contact. It is in the code. All plates, pier blocks, and post connections are above grade.....excuse me. Cross-Section: Provide true section through building showing structural elements, foundation through roof, fireplace section, other sections as needed, earth-to-wood clearances and floor-to-ceiling heights.
WOOD AND EARTH SEPARATION - Wood used in construction of
permanent structures and located nearer than 6" to earth shall be treated
wood or wood of natural resistance to decay. Where located on concrete
slabs placed on earth, wood shall be treated wood or wood of natural
resistance to decay. Where not subject to water splash or to exterior
moisture and located on concrete having a minimum thickness of 3" with
an impervious membrane installed between concrete and earth, the wood
may be untreated and of any species. [2306.8]
POST-BEAM CONNECTIONS - Positive connection shall be provided to
5.0 - CLEARANCES AND TREATMENT FOR WOOD FRAMING 5.1 Preservative-treated wood or naturally durable wood shall be used for (CBC 2304.11): A. wood placed against concrete or masonry which is in contact with soil. B. wood in contact with soil or water C. wood subfloor and framing with clearances less than 18" under joist or 12" under girders. D. wood with less than ½" airspace on top, sides & end of members entering concrete or masonry. E. isolated posts surrounded by soil with base less than 8" above soil. F. posts over concrete subject to moisture with base less than 1" above slab or
6" above exposed
Please do, the OP already stated what the building inspector told him. I suppose you know more about his local building codes than the inspector. Oh pullllllleeeeeezzeeeee!
Check out 2304.11.4 here
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Here's a MD code, which sounds similar to the OP's area, since the deck footers are similar.
I'm sure the inspector said 18", because it's common to go 3x the lumber size. Since the OP is using 6x6, which is really 5-1/2", the footer for 8" of concrete should be 16.5".
I have a deck which is 22 yr old, I've seen how long they can last. Exactly what have you seen over the years, which last?
I read these forums, and people always throw out this solution or this solution, and have no idea how long something lasts.
Here's a code from MD, which sounds similiar to the OP situation. MD has a
20" frostline, the OP has a 24". We have a 42", and can build like MD code.
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Now, if you want to argue with someone, I suggest contacting all the states which allow _properly_ treated wood, _meant_ for ground contact, and tell them they're wrong.
.40 is for "Non-critical components" (UC4A) Pole barns, permanent foundations, etc. require .60. (or better)
Depending on your location, code may allow burial of .40. Then again, code is a minimum, not optimal, standard.
When practical, I like to keep wood above ground. From the top of the footing to 2" above grade is 18". At 10" diameter, that's .8 ft^3 per post. At 8" diameter, it's .52 ft^3 That's not much, even when hand mixing.
Again, an 18" round hole is common for footings that support less weight bearing. Personally, I've seen treated lumber deck supports rot in the ground and eventually, the whole deck fall of the house as result. That's why I have so much concern in this specific case that the OP is talking about.
Even the super-duper treated lumber used for pier supports eventually rots. They're removed and replaced on a regular basis by DOD contractors at Navy piers.
Regarding contacting states that allow such ground contact lumber, they are not looking at long term life.
Water contact, and the organisms in that water are what causes wood to rot including treated lumber. If that can be avoided or appreciably reduced, treated lumber can be used. Concrete encased treated lumber has a problem though. Concrete is porous. Commonly observed when having to replace treated wooden fence posts encased in concrete below the soil line.
I am not arguing. I am stating facts and my observations. I'm not making an emmotional issue as you imply by "arguing".
I am in agreemant and rather not argue. When we get a plan that says the pier footing to be 18" deep, and the concrete to be at least 8" and the hole to be 24" that is what we follow. Also in the mix, the wood,(be it pressure treated or #1 rdwd sill grade) is to be "above grade"....thus the concrete will have to fill the entire hole. I really do not understand the issue. I have pulled out of the ground many a "pressure treated" wood post and boards that were in earth contact and that had wrotted.
Last time I put in some 6x6 posts I also painted the sides where they were in contact with the ground with some asphalt paint. Another thing to consider if you are filling the holes all the way up with concrete and putting the post on top is that you lose a lot of side to side strength. Make sure to brace the 6x6's with some diagonal 4x4s up to the deck frame.
As I asked Loomis, to what degree was the wood treated, he has not replied. It's not uncommon for unscruplous contractors to use a lessor degree than is required. I too have seen 4x4 treated post rot, but they were not for ground contact.
I work for our State, its not uncommon for government entities to replace what doesn't need replaced. If you're not familiar with them not spending money, in order to get more money, it would be an eye opener for you.
There are different treatments for water submerged lumber, this is a non issue for this case. A side note, treated lumber should never be placed in or encased in concrete. Lumber shrinks, long after the concrete cures. This is why fences get wobbly.
If the code & or contract calls for "piers", then of course you can't do it any other way. This isn't the issue here. Why even bring it into the subject?
I asked b/4, were they ground contact? I highly doubt it. You can't even compare ground contact lumber, to "regular" treated lumber, why do you keep referring to treated lumber, like it's all the same? Do you know there are different ratings?
Lumber shrinks long after concrete cures, that is the number 1 reason not to put lumber in concrete.
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