Does setting posts in foam give them some protection from dry rot?

[Stephen Tashiro]

Does setting treated wooden posts in foam (the kind that's designed for setting posts) give them some protection from rotting?
Is it easier to replace a post that's been set in foam that a post that's been set in concrete?

I want to build a pergola and I'm debating how to set the posts.

Options:
1. Bury in the ground
2.. Set in concrete
3. Set in foam
4. Pour a concrete pad and set the post on a post anchor on top of the pad

My experience with cedar and treated lumber in this climate is that it dry rots in about 10 years when buried. I think posts last longer when set in concrete, but when they must be replaced, it's a pain in the neck. Posts set in post anchors on top of a concrete pad hold up well, but they must be temporarily supported during construction.

[Jamie Buxton]

Last week I watched a crew replacing a wood utility pole. They bored a hole with a truck-mounted auger, dropped the creosoted wood pole in, and backfilled with gravel. They used a vibrator to compact the gravel as it was poured in. Done. No footing, no concrete, no foam. There's a lesson there.

[Mike Henderson]

When I built one, I poured a slab then used those Samson devices. It's been a while but I think I drilled into the concrete and then used bolts set in construction epoxy to attach the Samson thing to the slab. Then you put the post into the Samson, drill some holes and attach it. The problem is that you have to make some skirts to hide the Samson. These only have to be about 18 inches high.

The Samson device supports the post about an inch from the slab so water doesn't wick into the bottom.

I'm going from memory here. Of course this approach assumes you're going to use a slab.

Mike

[Frank Pratt]

Are you talking about Simpson post anchors? They make all manner of brackets for joining lumber.

[Bryan Lisowski]

Last week I watched a crew replacing a wood utility pole. They bored a hole with a truck-mounted auger, dropped the creosoted wood pole in, and backfilled with gravel. They used a vibrator to compact the gravel as it was poured in. Done. No footing, no concrete, no foam. There's a lesson there.

There is no lesson to be learned, the utility company sends its customers a bill each month, so since you and the others are paying for present and future replacements, they don't care how long they last.

[Rich Aldrich]

I built one for my daughter and did not sink the posts in the ground. We used the sonotubes from Menards. We were down to bedrock at 30" so we poured concrete in the tube and used a simpson post anchor like Mike did. Both the tubes and the post anchors are available at Menards and something similar if not the same at the other box stores. That was 5 years ago.

[Lee Schierer]

There is no lesson to be learned, the utility company sends its customers a bill each month, so since you and the others are paying for present and future replacements, they don't care how long they last.

Maybe there is something to learn. The utility pole in front of our house was several years old when we moved in 1977! It is still the same pole. That's at least 43 years. How many fence posts last that long?

[Eric Arnsdorff]

20 years ago I built my deck and poured concrete footers with piers and used the Simpson brackets.
The only issue I had with my posts are the Simpson brackets are rusting out.
I added onto my deck and resurfaced it this last year. I decided to try a different approach.
I left rebar and galvanized all thread sticking up out of the piers. I coated the ends of the posts with primer and then bed-liner. I crossed drilled the holes for the rods so I could epoxy them in place.
This was a lot of work but seems to have worked well. Hopefully they will last well beyond 20 years.
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[Andrew Seemann]

Maybe there is something to learn. The utility pole in front of our house was several years old when we moved in 1977! It is still the same pole. That's at least 43 years. How many fence posts last that long?

Plenty, if they have been doused in that much creosote

A post will rot if water gets trapped around it, like if a post is set in concrete and is completely surrounded, including the bottom. For a fence post you can set the post in the hole touching the ground (needs to be rated for ground contact) and then pour concrete around it.

For anything bearing a load or that needs to resist uplift, it is best to pour a footing in concrete, and use one of the concrete to post anchors. Ones that you set in wet concrete are easier, but you need to get them located right, since you can't adjust them.

[Mike Henderson]

Are you talking about Simpson post anchors? They make all manner of brackets for joining lumber.

Yeah, it's been a long time and I couldn't think of the exact name. I drilled holes in the concrete and epoxied in threaded rods. Used that to anchor the Simpson brackets with nuts on the threaded rods. The Simpson brackets set the post up about an inch.

Mike

[Bruce King]

I rent a two person auger, dig hole at least 30 inches, more up north. Put some bricks in the bottom to keep water away and set the post on it. Fill with concrete to a few inches above grade.

[Bill Dufour]

Modern ground contact lumber should be rated at 50 years or better. I assume it does not rain that much in new Mexico so they should last longer. The two telephone poles at the family home are at least 70 years old but they came by every 5-10 years and drilled a hole and poured in more creosote then pounded in a dowel to seal the hole. Utilities have a department of actuaries to determine when to replace a pole. Growing up our neighbor was one.
Bill D

[John Gornall]

Fence on 1 side neighbor insisted on concrete. The other 2 sides my way - compacted sand. Dug 30 in deep, put in and plumb pressure treated post, pack sand in 6 inch layers. Concrete posts lasted about 15 years - wind blew fence down, rotten posts. Posts in sand still good over 30 years

[roger wiegand]

I was always told that water was the enemy and that concrete was an efficient way to wick water into the wood. With untreated or above ground treated posts (the only kind they seem to sell at the Borg) posts set in concrete seem to last in the 7-10 year range. Posts set in gravel last several years longer; wood treated with the underground rating lasts near forever. I stopped using concrete decades ago and have only used gravel since.

It's also easier to jack out a post that's been set in gravel than concrete. I've never noticed any increased rigidity with concrete.

[Thomas Colson]

#4: Set on top of concrete using an anchor that keeps it 1" high. OZCO has an amazing interactive catalog with at least 20 different post anchors that IMHO will outlast and outperform the Simpson. At least in my county, inspector will not approve any wood in the ground, for any use, reason, type of wood/treatment, or method of construction. I think it was UVA that demonstrated that even posts set in concrete can rot, and most jurisdictions amended their code shortly after. With the set on top method, you can, with some difficulty and approval of an engineer and the inspector, use specialty concrete grouts and adhesives to remove a post/bracket, drill a hole, and get another one in there without having to replace the concrete. Be careful how you orient the brackets: They only resist movement in one direction so you have to get creative with a free standing structure and plan to resist movement in both directions with your posts. In my office building, lots of exterior posts 8 X 8 set on these giant 3/4 inch galvanized steel brackets with the mounting part kerfed up into the middle of the post all secured with 1" stainless bolts. On my list to ask our buildings guy where those were spec'ed because that's what I'm going to use on my deck.