Thread: deck post in contact with ground

I wrote up a deck with the post in contact with ground , I wrote it up as not a recommend practice, should maintain clearance between ground and support post, the builder told the owners that he used treated wood and I was ok to sink post in ground. My expercience is even through its treated when it in the ground for a few years it still begins to rot.

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dmn,

I have a couple of questions.

First of all, what chemical was it treated with? If it is "ground contact" pressure treated lumber, my understanding is that it should last for decades without significant decay. Around here, ACZA (very dark green, almost black colored) treated lumber can be used in direct and prolonged contact with soil. However, if it is the lighter green or reddish, probably not.

Another question, is what is the post resting on? If there is no concrete footing or pier block, then what is holding up the deck? If the post is sunk into the soil, then it is more likely to sink/settle.

Maybe the the builder would like to put that in writing for the owners.

Originally Posted by daniel nantell

I wrote up a deck with the post in contact with ground , I wrote it up as not a recommend practice, should maintain clearance between ground and support post, the builder told the owners that he used treated wood and I was ok to sink post in ground. My expercience is even through its treated when it in the ground for a few years it still begins to rot.

DN: It seems that this is what the IRC thinks it should look like:

Wood posts CAN be in ground contact:

From the 2006 IRC. (underlining is mine)
- R319.1.2 Ground contact. All wood in contact with the ground, embedded in concrete in direct contact with the ground or embedded in concrete exposed to the weather that supports permanent structures intended for human occupancy shall be approved pressure-preservative-treated wood suitable for ground contact use, except untreated wood may be used where entirely below groundwater level or continuously submerged in fresh water.

That said, a post in ground contact STILL requires a proper footing and anchoring to the footing.

This is from the American Wood Council, their Design for Code Acceptance 6, Prescriptive Residential Deck Construction Guide: http://www.awc.org/Publications/DCA/DCA6/DCA6.pdf

Scroll down to the Figure 12 on the bottom of page 9.

Have the builder provide documentation that the treatment of the wood posts meets or exceeds that which is required for ground contact and burial.

Like these from this morning's inspection? .40 CCA pressure-treated is all that is required, and that is what they are. Labels were still stapled to the tops. These are just 12 years old.

Why do it?

When they are 4x4's I pay more attention to them. With 6x6's there is much more material so it is less of an issue.

I look at each situation on a case by case basis.

A.D.

I don't get the 3rd diagram that shows toe nailing the beam/post connection.

I don't think that toe nailing is recognized as a positive connection.

Originally Posted by Eric Barker

A.D.

I don't get the 3rd diagram that shows toe nailing the beam/post connection.

I don't think that toe nailing is recognized as a positive connection.

EB: You'll have to contact the ICC. It is directly from the 2006 IRC, which I did not write.

One of the above post showed x4 post rotten off in 12 years, that has been my expierence, they say its treated and will last 20 years but Ive had them completely destroyed in 10 years, mabe the treating manufacture did a poor job pressure treating the lumber, that why I think its better building practice to keep the wood off the ground, even pressure treated. thanks

Treated Wood Alert

The issue with treated lumber in contact with the ground doesn't have as much to do with the decay of the wood which is eventually an issue with any lumber product and cannot be avoided. The issue lies in the action between the house, the deck and the ground.
Depending on the area which you live, and the type of soil you have, there is movement.
Take for instance the area which I live, Kansas. We have a freeze/thaw cycle that is serious enough to cause upheaval at ground level. If our decks support columns were not secured to a footing, below frost level, the column would rise with the ground which would then translate that movement to the deck ledger board attached to the house. Do that repeatedly and you have recipe for disaster from the ledger bolts working away from the house rim joist.
The 2006 IRC has some additional requirements for deck support column footings depending on the span of the deck joists, soil composition and frost line depth.
Bottom line would be depending on the soil composition of your area, your freeze/thaw cycle, footing requirements and local jurisdiction. Here, footings are required to extend 36" below ground (our frost line requirement) for house footings, and deck footings.

Originally Posted by Michael Greenwalt

Take for instance the area which I live, Kansas. We have a freeze/thaw cycle that is serious enough to cause upheaval at ground level. If our decks support columns were not secured to a footing, below frost level, the column would rise with the ground which would then translate that movement to the deck ledger board attached to the house. Do that repeatedly and you have recipe for disaster from the ledger bolts working away from the house rim joist.
The 2006 IRC has some additional requirements for deck support column footings depending on the span of the deck joists, soil composition and frost line depth.
Bottom line would be depending on the soil composition of your area, your freeze/thaw cycle, footing requirements and local jurisdiction. Here, footings are required to extend 36" below ground (our frost line requirement) for house footings, and deck footings.

The IRC states that, *IF* the deck is attached to the house in any way, shape or form, the foundations for the deck must be below frost depth just like those of the house it is attached to, HOWEVER ... *IF* the deck is a free standing deck and not attached to the house in any way, shape or form, then the deck does not require footings to be below frost level, the deck is free to rise and fall on it own, not being tied to the house in any way.

except untreated wood may be used where entirely below groundwater level. I am confused, which is easy to do, but what does this mean

Originally Posted by mathew stouffer

except untreated wood may be used where entirely below groundwater level. I am confused, which is easy to do, but what does this mean

I believe bacteria need more oxygen than is in most water. I know that the stumps in the bottom of Lake Norman are very sound! I've tried to knock a few of them out with a lead keel and the stump never wiggled.

I saw this deck last week. Eight of the nine suport posts that were beneath grade level had varying degrees of rot and deterioration. The second pic here shows how much the deck was dropping at the outside edge.

Nick

Thats defeats all the talk that PT post don't decay now doesn't it?

rick

Originally Posted by Rick Hurst

Thats defeats all the talk that PT post don't decay now doesn't it?

Rick,

All depends on what it is treated with and what it is treated for.

6x6 from yesterday.

Good find John , I guess they thought that putting rocks at top of 6x6 would prevent rot. If its in the ground its going to rot eventually and usually before the 20 years warranty expires.

Originally Posted by John Dirks Jr

6x6 from yesterday.

.
Might want to consider leaving that Ring in the Truck.
* could be a safety Issue ( climbing around & getting snagged on an exposed nail head. )
.